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  • 1. Almeida, Cristiane G.
    et al.
    Araujo, Rafael B.
    Yoshimura, Rafael G.
    Mascarenhas, Artur J. S.
    da Silva, Antonio Ferreira
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Silva, Luciana A.
    Photocatalytic hydrogen production with visible light over Mo and Cr-doped BiNb(Ta)O-42014In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 39, no 3, p. 1220-1227Article in journal (Refereed)
    Abstract [en]

    In the present work, we prepared pure and Cr(III) and Mo(V)-doped BiNbO4 and BiTaO4 by the citrate method. Pure BiNbO4 and BiTaO4 were obtained in triclinic phase at 600 degrees C and 800 degrees C, respectively. The metal doping influenced strongly the crystal structure as well as the photocatalytic activity of the oxides. The XRD data could prove that the Mo(V) doping induces the orthorhombic phase, while the Cr(III) doping favors the triclinic phase for both oxides. Metal doping also modified the photosensitivity of the oxides, extending the absorption toward the visible light region. The photocatalytic activity in water splitting under visible light irradiation was evaluated by monitoring the H-2, CO2 and CO evolution. The results showed that Cr(III)-doped BiTaO4 and BiNbO4, in general, are more selective for hydrogen production, while Mo(V)-doped materials are more selective for CO2 generation. Comparing the photocatalytic activity of BiTaO4 and BiNbO4, the former shows higher activity for hydrogen production as well as for CO2 generation, specially when the concentration was 2% in Cr(III) and Mo(V), respectively. Those results are in agreement with the computational study to access the effect of doping on the electronic structure. For Mo(V)-doped materials a negligible change of conduction band minimum potential was found, indicating that there might be no improvement on the reduction power of the material following the substitutional doping. In Cr(III)-doped BiNbO4 there is a slight shift of the CBM potential increasing a little bit the reduction power. However, the effect is much stronger in the Cr(III)-doped BiTaO4.

  • 2.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Electronic and optical properties of pressure induced phases of MgH22005In: Journal of Alloys and Compounds, ISSN 0925-8388, Vol. 404, no 16, p. 220-Article in journal (Refereed)
    Abstract [en]

    The electronic and optical properties of pressure-induced phases of MgH2 are investigated using the full-potential linearized augmented plane wave method. The absorption features are investigated by means of the calculated complex dielectric function and the analysis are made based on the electronic structure. The phases as a whole exhibit a color neutral insulator behavior. The calculated band gap are in good agreement with earlier theoretical investigations. The absorption edges corrected by scissor operation matched quite well the experimental findings. The optical anisotropy has also been evaluated.

  • 3.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Osorio Guillén, J. M.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Jena, Puru
    Role of Titanium in Hydrogen Desorption in Crystalline Sodium Alanate2005In: Applied Physics Letters, ISSN 0003-6951, Vol. 86, no 25, p. 251913-Article in journal (Refereed)
    Abstract [en]

    The role of Ti in improving the thermodynamics of hydrogen desorption in crystalline sodium alanate (NaAlH4) has been investigated by using the density functional theory. The total energy calculations reveal that Ti prefers to occupy the Na site over that of the Al site when the atomic energies are used as the reference. However, the use of the cohesive energies of Al, Na, and Ti leads to the Al site being the least unfavourable site. Irrespective of whether Ti occupies the Na or the Al site, the energy necessary to remove a hydrogen atom from Ti substituted sodium alanate is significantly lowered from that of the pure alanate. The understanding gained here may help in designing hydrogen storage materials suitable for industrial applications.

  • 4.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Osorio Guillén, Jorge Mario
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Jena, P
    Role of titanium in hydrogen desorption in crystalline sodium alanate2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 25, article id 251913Article in journal (Refereed)
    Abstract [en]

    The role of Ti in improving the thermodynamics of hydrogen desorption in crystalline sodium alanate (NaAlH4) has been investigated by using the density functional theory. The total energy calculations reveal that Ti prefers to occupy the Na site over that of the Al site when the atomic energies are used as the reference. However, the use of the cohesive energies of Al, Na, and Ti leads to the Al site being the least unfavourable site. Irrespective of whether Ti occupies the Na or the Al site, the energy necessary to remove a hydrogen atom from Ti substituted sodium alanate is significantly lowered from that of the pure alanate. The understanding gained here may help in designing hydrogen storage materials suitable for industrial applications.

  • 5.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Talyzin, A. V.
    Sundqvist, B.
    Pressure-induced structural phase transition in NaBH42005In: Physical Review B, ISSN 1198-0121, Vol. 72, no 5, p. 054125-Article in journal (Refereed)
    Abstract [en]

    We present a combined experimental and theoretical study of the technologically important NaBH4 compound under high pressure. Using Raman spectroscopy at room temperature, we have found that NaBH4 undergoes a structural phase transformation starting at 10.0 GPa with the pure high pressure phase being established above 15.0 GPa. In order to compare the Raman data recorded under high pressure with the low temperature tetragonal phase of NaBH4, we have also performed a cooling experiment. The known order-disorder transition from the fcc to the tetragonal structure was then observed. However, the new high pressure phase does not correspond to this low temperature structure. Using first principle calculations based on the density functional theory, we show that the new high pressure phase corresponds to the α-LiAlH4 type structure. We have found a good agreement between the measured and calculated transition pressures. Additionally, we present the electronic structure of both the fcc and the high pressure phases.

  • 6.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Lebègue, Sebastien
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Arnaud, B.
    Alouani, M.
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Electronic and optical properties of MgH2: a first-principle GW investigation2005In: Journal of Applied Physics, ISSN 0021-8979, Vol. 98, no 9, p. 096106-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of MgH2 is studied using the state of the art all-electron projector-augmented-wave GW approximation. Both the ground-state and the high-pressure transformations are considered in this investigation. We have found an indirect (direct) band-gap of 5.58 eV (6.52 eV) for α-MgH2, which has a good agreement with the experimental findings. For the γ- and β-phases, we have found indirect (direct) band-gap values of 5.24 eV (5.33 eV) and 3.90 eV (4.72 eV), respectively. The optical properties are investigated by means of the complex dielectric function, which is calculated within the framework of a full-potential linearized augmented plane wave method and corrected by scissor operators. All phases are found to be color neutral insulators.

  • 7.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Li, Sa
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
    Jena, Puru
    Vacancy Mediated Hydrogen Desorption in NaAlH42005In: Physical Review B, ISSN 1098-0121, Vol. 72, no 16, p. 165101-Article in journal (Refereed)
    Abstract [en]

    First principles calculations based on density functional theory are carried out to understand the mechanisms responsible for hydrogen desorption from Ti doped sodium-alanate (NaAlH4). While the energy needed to remove a hydrogen atom from NaAlH4 with Ti substituted either at the Na site or at Al site is found to be significantly lower than that from the pristine NaAlH4, the presence of Na-vacancies is shown to play an even larger role: It is not only an order of magnitude smaller than that from Ti doped sodium alanate, but the removal of hydrogen associated with a Na-vacancy is exothermic with respect to formation of H2 molecule. Furthermore, we show that the unusual stabilization of the magic AlH3 cluster in the vacancy containing sodium-alanate is responsible for this diminished value of hydrogen removal energy. It is suggested that this role of vacancy can be exploited in the design and synthesis of complex light metal hydrides suitable for hydrogen storage.

  • 8.
    Araujo, Carlos Moyses
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nagar, Sandeep
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Shukla, R.
    Jayakumar, O. D.
    Tyagi, A. K.
    Liu, Yi-Sheng
    Chen, Jeng-Lung
    Glans, Per-Anders
    Chang, Chinglin
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Lizárraga, Raquel
    Holmstrom, Erik
    Belova, Lyubov
    Guo, Jinghua
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
    Rao, K. V.
    Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites2014In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 4686-Article in journal (Refereed)
    Abstract [en]

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  • 9.
    Araujo, Rafael B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panigrahi, Puspamitra
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Hindustan Univ, Ctr Clean Energy & Nanoconvergence, Madras, Tamil Nadu, India.
    Yang, Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Sjödin, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Araujo, C. Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat, Appl Mat Phys, S-10044 Stockholm, Sweden.; Royal Inst Technol KTH, Dept Engn, S-10044 Stockholm, Sweden.
    Assessing Electrochemical Properties of Polypyridine and Polythiophene for Prospective Application in Sustainable Organic Batteries2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 4, p. 3307-3314Article in journal (Refereed)
    Abstract [en]

    Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties.

  • 10.
    Araujo, Rafael B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panigrahi, Puspamitra
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Hindustan Univ, Ctr Clean Energy & Nanoconvergence, Chennai, Tamil Nadu, India.
    Yang, Li
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Sjödin, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Araujo, C. Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden.
    Designing strategies to tune reduction potential of organic molecules for sustainable high capacity batteries application2017In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 9, p. 4430-4454Article in journal (Refereed)
    Abstract [en]

    Organic compounds evolve as a promising alternative to the currently used inorganic materials in rechargeable batteries due to their low-cost, environmentally friendliness and flexibility. One of the strategies to reach acceptable energy densities and to deal with the high solubility of known organic compounds is to combine small redox active molecules, acting as capacity carrying centres, with conducting polymers. Following this strategy, it is important to achieve redox matching between the chosen molecule and the polymer backbone. Here, a synergetic approach combining theory and experiment has been employed to investigate this strategy. The framework of density functional theory connected with the reaction field method has been applied to predict the formal potential of 137 molecules and identify promising candidates for the referent application. The effects of including different ring types, e.g. fused rings or bonded rings, heteroatoms, [small pi] bonds, as well as carboxyl groups on the formal potential, has been rationalized. Finally, we have identified a number of molecules with acceptable theoretical capacities that show redox matching with thiophene-based conducting polymers which, hence, are suggested as pendent groups for the development of conducting redox polymer based electrode materials.

  • 11.
    Damas, Giane B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Miranda, Caetano
    Institute of Physics, University of São Paulo, São Paulo 05508-090, Brazil.
    Sgarbi, Ricardo
    Institute of Chemistry, University of São Paulo, São Carlos 13560-970, Brazil.
    Portela, James
    Institute of Chemistry, University of São Paulo, São Carlos 13560-970, Brazil.
    Camilo, Mariana R.
    Institute of Chemistry, University of São Paulo, São Carlos 13560-970, Brazil.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    On the Mechanism of Carbon Dioxide Reduction on Sn-Based Electrodes: Insights into the Role of Oxide Surfaces2019In: Catalysts, E-ISSN 2073-4344, Vol. 9, no 8, article id 636Article in journal (Refereed)
    Abstract [en]

    The electrochemical reduction of carbon dioxide into carbon monoxide, hydrocarbons and formic acid has offered an interesting alternative for a sustainable energy scenario. In this context, Sn-based electrodes have attracted a great deal of attention because they present low price and toxicity, as well as high faradaic efficiency (FE) for formic acid (or formate) production at relatively low overpotentials. In this work, we investigate the role of tin oxide surfaces on Sn-based electrodes for carbon dioxide reduction into formate by means of experimental and theoretical methods. Cyclic voltammetry measurements of Sn-based electrodes, with different initial degree of oxidation, result in similar onset potentials for the CO2 reduction to formate, ca. −0.8 to −0.9 V vs. reversible hydrogen electrode (RHE), with faradaic efficiencies of about 90–92% at −1.25 V (vs. RHE). These results indicate that under in-situ conditions, the electrode surfaces might converge to very similar structures, with partially reduced or metastable Sn oxides, which serve as active sites for the CO2 reduction. The high faradaic efficiencies of the Sn electrodes brought by the etching/air exposition procedure is ascribed to the formation of a Sn oxide layer with optimized thickness, which is persistent under in situ conditions. Such oxide layer enables the CO2 “activation”, also favoring the electron transfer during the CO2 reduction reaction due to its better electric conductivity. In order to elucidate the reaction mechanism, we have performed density functional theory calculations on different slab models starting from the bulk SnO and Sn6O4(OH)4 compounds with focus on the formation of -OH groups at the water-oxide interface. We have found that the insertion of CO2 into the Sn-OH bond is thermodynamically favorable, leading to the stabilization of the tin-carbonate species, which is subsequently reduced to produce formic acid through a proton-coupled electron transfer process. The calculated potential for CO2 reduction (E = −1.09 V vs. RHE) displays good agreement with the experimental findings and, therefore, support the CO2 insertion onto Sn-oxide as a plausible mechanism for the CO2 reduction in the potential domain where metastable oxides are still present on the Sn surface. These results not only rationalize a number of literature divergent reports but also provide a guideline for the design of efficient CO2 reduction electrocatalysts.

  • 12.
    Damas, Giane
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Marchiori, Cleber F. N.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    On the Design of Donor Acceptor Conjugated Polymers for Photocatalytic Hydrogen Evolution Reaction: First-Principles Theory-Based Assessment2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 47, p. 26876-26888Article in journal (Refereed)
    Abstract [en]

    A set of fluorene-based polymers with a donor acceptor architecture has been investigated as a potential candidate for photocatalytic hydrogen evolution reaction. A design protocol has been employed based on first -principles theory and focusing on the following properties: (i) broad absorption spectrum to promote a higher number of photogenerated electron hole pairs, (ii) suitable redox potentials, and (iii) appropriate reaction thermodynamics using the hydrogen -binding energy as a descriptor. We have found that the polymers containing a fused -ring acceptor formed by benzo(triazole-thiadiazole) or benzo(triazole-selenodiazole) units display a suitable combination of such properties and stand out as potential candidates. In particular, PFO-DSeBTrT (poly (9,9'-dioctylfluorene)-2,7-diyl-alt-(4,7-bis(thien-2y1)-2-dodecyl-benzo-(1,2c:4,5c')-1,2,3-triazole-2,1,3-selenodiazole)) has an absorption maximum at around 950 nm for the highest occupied molecular orbital lowest unoccupied molecular orbital transition, covering a wider range of solar emission spectrum, and a reduction catalytic power of 0.78 eV. It also displays a calculated hydrogen -binding free energy of Delta G(H) = 0.02 eV, which is lower in absolute value than Furthermore, the results and trends analysis provide guidance for the rational design of novel photo-electrocatalysts. that of Pt (Delta G(H) approximate to -0.10 eV).

  • 13.
    Ebadi, Mahsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electrolyte decomposition on Li-metal surfaces from first-principles theory2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 20, article id 204701Article in journal (Refereed)
    Abstract [en]

    Animportant feature in Li batteries is the formation of a solid electrolyte interphase (SEI) on the surface of the anode. This film can have a profound effect on the stability and the performance of the device. In this work, we have employed density functional theory combined with implicit solvation models to study the inner layer of SEI formation from the reduction of common organic carbonate electrolyte solvents (ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate) on a Li metal anode surface. Their stability and electronic structure on the Li surface have been investigated. It is found that the CO producing route is energetically more favorable for ethylene and propylene carbonate decomposition. For the two linear solvents, dimethyl and diethyl carbonates, no significant differences are observed between the two considered reduction pathways. Bader charge analyses indicate that 2 e(-) reductions take place in the decomposition of all studied solvents. The density of states calculations demonstrate correlations between the degrees of hybridization between the oxygen of adsorbed solvents and the upper Li atoms on the surface with the trend of the solvent adsorption energies.

  • 14.
    Ebadi, Mahsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Costa, Luciano T.
    Univ Fed Fluminense, Dept Fis Quim, Inst Quim, Outeiro Sao Joao Batista S-N, BR-24020150 Niteroi, RJ, Brazil..
    Araujo, C. Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Modelling the Polymer Electrolyte/Li-Metal Interface by Molecular Dynamics simulations2017In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 234, p. 43-51Article in journal (Refereed)
    Abstract [en]

    Solid polymer electrolytes are considered promising candidates for application in Li-metal batteries due to their comparatively high mechanical strength, which can prevent dendrite formation. In this study, we have performed Molecular Dynamics simulations to investigate structural and dynamical properties of a common polymer electrolyte, poly(ethylene oxide) (PEO) doped with LiTFSI salt in the presence of a Li metal surface. Both a physical (solid wall) and a chemical (slab) model of the Li (100) surface have been applied, and the results are also compared with a model of the bulk electrolyte. The average coordination numbers for oxygen atoms around the Li ions are ca. 6 for all investigated systems. However, the calculated Radial Distribution Functions (RDFs) for Li+-(OPEO) and Li+-(OTFSI) show sharper peaks for the Li slab model, indicating a more well-defined coordination sphere for Li+ in this system. This is clearly a surface effect, since the RDF for Li+ in the interface region exhibits sharper peaks than in the bulk region of the same system. The simulations also display a high accumulation of TFSI anions and Li+ cations close to interface regions. This also leads to slower dynamics of the ionic transport in the systems, which have a Li-metal surface present, as seen from the calculated mean-square-displacement functions. The accumulation of ions close to the surface is thus likely to induce a polarization close to the electrode.

  • 15.
    Ebadi, Mahsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Lacey, Matthew
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Density Functional Theory Modeling the Interfacial Chemistry of the LiNO3 Additive for Lithium-Sulfur Batteries by Means of Simulated Photoelectron Spectroscopy2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 42, p. 23324-23332Article in journal (Refereed)
    Abstract [en]

    Lithium-sulfur (Li-S) batteries are considered candidates for next-generation energy storage systems due to their high theoretical specific energy. There exist, however, some shortcomings of these batteries, not least the solubility of intermediate polysulfides into the electrolyte generating a so-called "redox shuttle", which gives rise to self-discharge. LiNO3 is therefore frequently used as an electrolyte additive to help suppress this mechanism, but the exact nature of the LiNO3 functionality is still unclear. Here, density functional theory calculations are used to investigate the electronic structure of LiNO3 and a number of likely species (N-2, N2O, LiNO2, Li3N, and Li2N2O2) resulting from the reduction of this additive on the surface of Li metal anode. The N is X-ray photoelectron spectroscopy core level binding energies of these molecules on the surface are calculated in order to compare the results with experimentally reported values. The core level shifts (CLS) of the binding energies are studied to identify possible factors responsible for the position of the peaks. Moreover, solid phases of (cubic) c-Li3N and (hexagonal) alpha-Li3N on the surface of Li metal are considered. The N is binding energies for the bulk phases of Li3N and at the Li3N/Li interfaces display higher values as compared to the Li3N molecule, indicating a clear correlation between the coordination number and the CLS of the solid phases of Li3N.

  • 16.
    Ebadi, Mahsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Marchiori, Cleber
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mindemark, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Assessing structure and stability of polymer/lithium-metal interfaces from first-principles calculations2019In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 14, p. 8394-8404Article in journal (Refereed)
    Abstract [en]

    Solid polymer electrolytes (SPEs) are promising candidates for Li metal battery applications, but the interface between these two categories of materials has so far been studied only to a limited degree. A better understanding of interfacial phenomena, primarily polymer degradation, is essential for improving battery performance. The aim of this study is to get insights into atomistic surface interaction and the early stages of solid electrolyte interphase formation between ionically conductive SPE host polymers and the Li metal electrode. A range of SPE candidates are studied, representative of major host material classes: polyethers, polyalcohols, polyesters, polycarbonates, polyamines and polynitriles. Density functional theory (DFT) calculations are carried out to study the stability and the electronic structure of such polymer/Li interfaces. The adsorption energies indicated a stronger adhesion to Li metal of polymers with ester/carbonate and nitrile functional groups. Together with a higher charge redistribution, a higher reactivity of these polymers is predicted as compared to the other electrolyte hosts. Products such as alkoxides and CO are obtained from the degradation of ester- and carbonate-based polymers by AIMD simulations, in agreement with experimental studies. Analogous to low-molecular-weight organic carbonates, decomposition pathways through C-carbonyl-O-ethereal and C-ethereal-O-ethereal bond cleavage can be assumed, with carbonate-containing fragments being thermodynamically favorable.

  • 17.
    Ebadi, Mahsa
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Nasser, Antoine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. ENSTA ParisTech, 828 Blvd Marechaux, F-91120 Palaiseau, France.
    Carboni, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Younesi, Reza
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Marchiori, Cleber
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Insights into the Li-Metal/Organic Carbonate Interfacial Chemistry by Combined First-Principles Theory and X-ray Photoelectron Spectroscopy2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 1, p. 347-355Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) is a widely used technique to study surfaces and interfaces. In complex chemical systems, however, interpretation of the XPS results and peak assignments is not straightforward. This is not least true for Li-batteries, where XPS yet remains a standard technique for interface characterization. In this work, a combined density functional theory (DFT) and experimental XPS study is carried out to obtain the C 1s and O 1s core-level binding energies of organic carbonate molecules on the surface of Li metal. Decomposition of organic carbonates is frequently encountered in electrochemical cells employing this electrode, contributing to the build up of a complex solid electrolyte interphase (SEI). The goal in this current study is to identify the XPS fingerprints of the formed compounds, degradation pathways, and thereby the early formation stages of the SEI. The contribution of partial atomic charges on the core-ionized atoms and the electrostatic potential due to the surrounding atoms on the core-level binding energies, which is decisive for interpretation of the XPS spectra, are addressed based on the DFT calculations. The results display strong correlations between these two terms and the binding energies, whereas electrostatic potential is found to be the dominating factor. The organic carbonate molecules, decomposed at the surface of the Li metal, are considered based on two different decomposition pathways. The trends of calculated binding energies for products from ethereal carbon-ethereal oxygen bond cleavage in the organic carbonates are better supported when compared to the experimental XPS results.

  • 18.
    Espinosa-Garcia, W. F.
    et al.
    Universidad de San Buenaventura-Medellín, Facultad de Ingenierías, Grupo de Investigación en Modelamiento y Simulación Computacional; Universidad de Antioquia UdeA, Instituto de Física.
    Osorio-Guillen, J. M.
    Universidad de Antioquia UdeA, Instituto de Física.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dimension-dependent band alignment and excitonic effects in graphitic carbon nitride: a many-body perturbation and time-dependent density functional theory study2017In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 71, p. 44997-45002Article in journal (Refereed)
    Abstract [en]

    First-principles many-body theory and time-dependent density functional theory were used to study the dimension effects on the band alignment and optical properties of s-triazine and graphitic C3N4. The inclusion of quasiparticle corrections is very important to describe the quantum confinement and the enhancement of the electron-electron (e-e) interaction. The calculated quasiparticle gaps range from 4.0 eV (monolayer) to 3.21 eV (tetralayer). The position of the valence band maxima is found to be almost constant, whereas the conduction band minima show a strong quantum confinement effect with a variation of similar to 0.7 eV respective to the bulk structure. The calculated frequency-dependent imaginary part of the dielectric function using the Bethe-Salpeter equation shows prominent excitonic effects, where there is a strong redistribution of the spectral weight to lower photon energies in the ultraviolet frequencies where the major part of the absorption occurs. On the other hand, a less intense excitonic absorption in the visible region is due to light polarization perpendicular to the surface plane. In contrast, time-dependent density functional theory also shows a redistribution of the spectral weight in the ultraviolet but it fails to describe the excitonic features in the visible region.

  • 19.
    Espinosa-Garcia, W. F.
    et al.
    Univ San Buenaventura Medellin, Grp Invest Modelamiento & Simulac Computac, Fac Ingn, Carrera 56C 51-110, Medellin, Colombia.;Univ Antioquia UdeA, Inst Fis, Calle 70 52-21, Medellin, Colombia..
    Perez-Walton, S.
    ITM, Fac Ingn, Dept Elect, Calle 73 76A-354 Via Volador, Medellin, Colombia..
    Osorio-Guillen, J. M.
    Univ Antioquia UdeA, Inst Fis, Calle 70 52-21, Medellin, Colombia..
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    The electronic and optical properties of the sulvanite compounds: a many-body perturbation and time-dependent density functional theory study2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 3, article id 035502Article in journal (Refereed)
    Abstract [en]

    We have studied, by means of first-principles calculations, the electronic and optical properties of the sulvanite family: Cu3MX4 (M = V, Nb, Ta and X = S, Se), which, due to its broad range of gaps and chemical stability, have emerged as promising materials for technological applications such as photovoltaics and transparent conductivity. To address the reliability of those properties we have used semi-local and hybrid functionals (PBEsol, HSE06), many-body perturbation theory (G(0)W(0) approximation and Bethe-Salpeter equation), and time-dependent density functional theory (revised bootstrap kernel) to calculate the quasi-particle dispersion relation, band gaps, the imaginary part of the macroscopic dielectric function and the absorption coefficient. The calculated valence band maximum and the conduction band minimum are located at the R and X-points, respectively. The calculated gaps using PBEsol are between 0.81 and 1.88 eV, with HSE06 into 1.73 and 2.94 eV, whereas the G(0)W(0) values fall into the 1.91-3.19 eV range. The calculated dielectric functions and absorption coefficients show that all these compounds present continuous excitonic features when the Bethe-Salpeter equation is used. Contrarily, the revised bootstrap kernel is incapable of describing the excitonic spectra. The calculated optical spectra show that Cu3VS4 and Cu3MSe4 have good absorption in the visible, whereas Cu3NbS4 and Cu3TaS4 have it on the near ultraviolet.

  • 20.
    Gonzalez-Moya, Johan R.
    et al.
    Univ Fed Pernambuco UFPE, Recife, PE, Brazil.;Ctr Tecnol Estrateg Nordeste CETENE, Recife, PE, Brazil..
    Garcia-Basabe, Yunier
    Univ Fed Rio de Janeiro, Rio De Janeiro, RJ, Brazil.;Univ Fed Integracao Latino Amer, UNILA, Foz Do Iguacu, PR, Brazil..
    Rocco, Maria Luiza M.
    Univ Fed Rio de Janeiro, Rio De Janeiro, RJ, Brazil..
    Pereira, Marcelo B.
    Univ Fed Rio Grande do Sul, Inst Fis, Porto Alegre, RS, Brazil..
    Princival, Jefferson L.
    Univ Fed Pernambuco UFPE, Recife, PE, Brazil..
    Almeida, Luciano C.
    Univ Fed Pernambuco UFPE, Recife, PE, Brazil..
    Araujo, Carlos M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    David, Denis G. F.
    Univ Fed Bahia UFBA, Inst Fis, Salvador, BA, Brazil..
    da Silva, Antonio Ferreira
    Univ Fed Bahia UFBA, Inst Fis, Salvador, BA, Brazil..
    Machado, Giovanna
    Univ Fed Pernambuco UFPE, Recife, PE, Brazil.;Ctr Tecnol Estrateg Nordeste CETENE, Recife, PE, Brazil..
    Effects of the large distribution of CdS quantum dot sizes on the charge transfer interactions into TiO2 nanotubes for photocatalytic hydrogen generation2016In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 27, no 28, article id 285401Article in journal (Refereed)
    Abstract [en]

    Hydrogen fuels generated by water splitting using a photocatalyst and solar irradiation are currently gaining the strength to diversify the world energy matrix in a green way. CdS quantum dots have revealed a hydrogen generation improvement when added to TiO2 materials under visible-light irradiation. In the present paper, we investigated the performance of TiO2 nanotubes coupled with CdS quantum dots, by a molecular bifunctional linker, on photocatalytic hydrogen generation. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into the anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogeneous), while the concentration relative to the sulfate anion decreases by more than 80% with respect to the initial value after similar to 100 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix seemingly protected the CdS for photocorrosion in sacrificial solution leading to good stability properties proved by long duration, stable photocurrent measurements. The effect of the size and the distribution of sizes of CdS quantum dots attached to TiO2 nanotubes on the photocatalytic hydrogen generation were investigated. The experimental results showed three different behaviors when the reaction time of CdS synthesis was increased in the sensitized samples, i.e. similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related to two populations of sizes of CdS, where the population with a shorter band gap acts as a trap for the electrons photogenerated by the population with a larger band gap. Electron transfer from CdS quantum dots to TiO2 semiconductor nanotubes was proven by the results of UPS measurements combined with optical band gap measurements. This property facilitates an improvement of the visible-light hydrogen evolution rate from zero, for TiO2 nanotubes, to approximately 0.3 mu mol cm(-2) h(-1) for TiO2 nanotubes sensitized with CdS quantum dots.

  • 21.
    Hussain, Tanveer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maark, Tuhina Adit
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab initio study of lithium-doped graphane for hydrogen storage2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 96, no 2, p. 27013-Article in journal (Refereed)
    Abstract [en]

    Based on the first-principle density functional calculations we predict that Li-doped graphane (prehydrogenated graphene) can be a potential candidate for hydrogen storage. The calculated Li-binding energy on graphane is significantly higher than the Li bulk's cohesive energy ruling out any possibility of cluster formations in the Li-doped graphane. Our study shows that even with very low concentration (5.56%) of Li doping, the Li-graphane sheet can achieve a reasonable hydrogen storage capacity of 3.23 wt.%. The van der Waals corrected H(2) binding energies fall within the range of 0.12-0.29 eV, suitable for practical H(2) storage applications. 

  • 22.
    Kaewmaraya, Thanayut
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos M
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rosa, A. L.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Water adsorption on ZnO(10(1)over-bar0): The role of intrinsic defects2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 1, p. 17014-Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) calculations have been performed to investigate the interaction of water molecules with bare and defective ZnO(10 (1) over bar0) surfaces. We show that at high coverages water molecules avoid adsorption close to defect sites, whereas at low coverages adsorption on defective surfaces show a similar adsorption pattern to those adsorbed on the defect-free surface, adsorbing in a molecular fashion. Finally we show that the electronic structure of the defective non-polar surface is not much affected by the adsorption of water, with exception of the O-defect surfaces.

  • 23.
    Lanzilotto, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Silva, Jose Luis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhang, Teng
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Stredansky, Matus
    Univ Trieste, Dept Phys, Via A Valerio 2, I-34127 Trieste, Italy;CNR, IOM, Lab TASC, Basovizza SS-14,Km 163-5, I-34149 Trieste, Italy.
    Grazioli, Cesare
    CNR, ISM, Unit LD2, Basovizza SS-14,Km 163-5, I-34149 Trieste, Italy.
    Simonov, Konstantin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Giangrisostomi, Erika
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany.
    Ovsyannikov, Ruslan
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany.
    De Simone, Monica
    CNR, IOM, Lab TASC, Basovizza SS-14,Km 163-5, I-34149 Trieste, Italy.
    Coreno, Marcello
    CNR, ISM, Unit LD2, Basovizza SS-14,Km 163-5, I-34149 Trieste, Italy.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Spectroscopic Fingerprints of Intermolecular H-Bonding Interactions in Carbon Nitride Model Compounds2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 53, p. 14198-14206Article in journal (Refereed)
    Abstract [en]

    The effect of intermolecular H-bonding interactions on the local electronic structure of N-containing functional groups (amino group and pyridine-like N) that are characteristic of polymeric carbon nitride materials p-CN(H), a new class of metal-free organophotocatalysts, was investigated. Specifically, the melamine molecule, a building block of p-CN(H), was characterized by X-ray photoelectron (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The molecule was studied as a noninteracting system in the gas phase and in the solid state within a H-bonded network. With the support of DFT simulations of the spectra, it was found that the H-bonds mainly affect the N1s level of the amino group, leaving the N1s level of the pyridine-like N mostly unperturbed. This is responsible for a reduction of the chemical shift between the two XPS N1s levels relative to free melamine. Consequently, N K-edge NEXAFS resonances involving the amino N1s level also shift to lower photon energies. Moreover, the solid-state absorption spectra showed significant modification/quenching of resonances related to transitions from the amino N1s level to sigma* orbitals involving the NH2 termini.

  • 24.
    Lanzilotto, Valeria
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Silva, Jose Luis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhang, Teng
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Stredansky, Matuš
    Department of Physics University of Trieste.
    Grazioli, Cesare
    CNR-ISM, Istituto di Struttura della Materia (LD2 Unit).
    Simonov, Konstantin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Giangrisostomi, Erika
    Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin GmbH.
    Ovsyannikov, Ruslan
    Institute Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin GmbH.
    de Simone, Monica
    CNR-IOM, Istituto Officina dei Materiali (Laboratorio TASC).
    Coreno, Marcello
    CNR-ISM, Istituto di Struttura della Materia (LD2 Unit).
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Puglia, Carla
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Spectroscopic Fingerprints of Carbon Nitride Functional Groups Locked-up in Intermolecular H-bonding InteractionsIn: Chemistry: A European Journal, ISSN 0947-6539Article in journal (Refereed)
    Abstract [en]

    We have investigated the effect of intermolecular H- bonding interactions on the local electronic structure of N- functionalities, amino group and pyridine-like N, which are characteristic of a new class of metal-free polymeric photo-catalysts named graphitic carbon nitrides, g-C3N4. Specifically, we have performed a characterization of the melamine molecule, a building block of g-C3N4, combining X-ray photoemission (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The molecule has been studied in the gas phase, as non-interacting system, and in the solid state within a hydrogen bonded network. With the support of density functional theory (DFT) simulations of the spectra, we have found that the H-bonds mainly affect the N 1s level of the amino group, leaving the N 1s level of the pyridine-like N mostly unperturbed. This fact is responsible for a reduction of the chemical shift between the two XPS N 1s levels, compared to the free melamine. Consequently, N K-edge NEXAFS resonances involving the amino N 1s level also shift to lower photon energies. Moreover, the solid state absorption spectra have shown strong modification/quenching of resonances related with transitions from the amino N 1s level towards σ*orbitals involving the -NH2 terminations. 

  • 25. Lebegue, Sebastien
    et al.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kim, Duck Young
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mao, Ho-kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Semimetallic dense hydrogen above 260 GPa2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 25, p. 9766-9769Article in journal (Refereed)
    Abstract [en]

    Being the lightest and the most abundant element in the universe, hydrogen is fascinating to physicists. In particular, the conditions of its metallization associated with a possible superconducting state at high temperature have been a matter of much debate in the scientific community, and progress in this field is strongly correlated with the advancements in theoretical methods and experimental techniques. Recently, the existence of hydrogen in a metallic state was reported experimentally at room temperature under a pressure of 260-270 GPa, but was shortly after that disputed in the light of more experiments, finding either a semimetal or a transition to an other phase. With the aim to reconcile the different interpretations proposed, we propose by combining several computational techniques, such as density functional theory and the GW approximation, that phase III at ambient temperature of hydrogen is the Cmca-12 phase, which becomes a semimetal at 260 GPa. From phonon calculations, we demonstrate it to be dynamically stable; calculated electron-phonon coupling is rather weak and therefore this phase is not expected to be a high-temperature superconductor.

  • 26. Li, Wen
    et al.
    Miao, Ling
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Xiong, Zhitao
    Wu, Guotao
    Araújo, C. Moysés
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Feng, Yuanping
    Chen, Ping
    Li-Na ternary amidoborane for hydrogen storage: experimental and first-principles study2012In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 41, no 16, p. 4754-4764Article in journal (Refereed)
    Abstract [en]

    Li-Na ternary amidoborane, Na[Li(NH2BH3)(2)], was recently synthesized by reacting LiH and NaH with NH3BH3. This mixed-cation amidoborane shows improved dehydrogenation performance compared to that of single-cation amidoboranes, i.e., LiNH2BH3 and NaNH2BH3. In this paper, we synthesized the Li-Na ternary amidoborane by blending and re-crystallizing equivalent LiNH2BH3 and NaNH2BH3 in tetrahydrofuran (THF), and employed first-principles calculations and the special quasirandom structure (SQS) method to theoretically explore the likelihood for the existence of Li1-xNax(NH2BH3) for various Li/Na ratios. The thermodynamic, electronic and phononic properties were investigated to understand the possible dehydrogenation mechanisms of Na[Li(NH2BH3)(2)].

  • 27.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yan-Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Single-layer MoS2 as an efficient photocatalyst2013In: Catalysis Science & Technology, ISSN 2044-4753, Vol. 3, no 9, p. 2214-2220Article in journal (Refereed)
    Abstract [en]

    The potential application of the single-layer MoS2 as a photocatalyst was revealed based on first-principles calculations. It is found that the pristine single-layer MoS2 is a good candidate for hydrogen production, and its catalysing ability can be tuned by the applied mechanical strain. Furthermore, the p-type doping could make the single layer a good photocatalyst for the overall water splitting.

  • 28. Lizarraga, Raquel
    et al.
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Holmström, Erik
    Structural characterization of amorphous YCrO3 from first principles2012In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 99, no 5, p. 57010-Article in journal (Refereed)
    Abstract [en]

    We perform a theoretical prediction of the structure of amorphous YCrO3. We obtained equivalent amorphous structures by means of two independent first principles density functional theory based methods: molecular dynamics and stochastic quenching. In our structural analysis we include radial and angle distribution functions as well as calculations of bond lengths and average coordination numbers. We find Cr+3 atoms situated in slightly distorted oxygen octahedra throughout the amorphous structures and that the distribution of these octahedra is disordered. The presence of the same Cr+3 local environments that give rise to ferroelectricity in the orthorhombic perovskite structure suggests that the amorphous phase of YCrO3 may also exhibit ferroelectric properties. Copyright (c) EPLA, 2012

  • 29.
    Marchiori, Cleber F.N.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Predicting Structure and Electrochemistry of Dilithium Thiophene-2,5-Dicarboxylate Electrodes by Density Functional Theory and Evolutionary Algorithms2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 8, p. 4691-4700Article in journal (Refereed)
    Abstract [en]

    Organic electroactive materials are promising candidates to be TUC used as lithium insertion electrodes in the next generation of environmentally friendly battery technologies. In this work, evolutionary algorithms at interplay with density functional theory calculations have been employed to predict the crystal structure for both delithiated and lithiated phases of dilithium thiophene dicarboxylate (Li2TDC). On the basis of the resulting crystals, electronic structure modifications and voltage profiles for the lithiation process have been calculated. The obtained structure for the delithiated phase showed a well-defined salt layer intercalating the organic components, forming a so-called lithium organic framework (LOF). Upon lithiation, new structures appear which deviate from the LOF as a consequence of the reduction of the S atoms, which coordinate with the additional Li ions. The calculated average potential of similar to 1.00 V vs Li/Li+ is found to be in good agreement with experimental findings. An additional study at the molecular level has also been conducted aiming at gaining insight into the importance of the crystallographic environment on the structural and thermodynamics properties. This strategy is suitable for an initial assessment of the electrochemical process that underlies the lithiation mechanism of electrode materials. Moreover, the employed evolutionary algorithm emerges as a promising tool to predict crystal structures during lithiation, which are otherwise difficult to resolve experimentally.

  • 30.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Silva, Luciana Almeida
    Instituto de Quimica, Universidade Federal da Bahia.
    Almeida, Cristiane Gomes
    Instituto de Quimica, Universidade Federal da Bahia.
    Mascarenhas, Artur José Santos
    Instituto de Quimica, Universidade Federal da Bahia.
    Wang, Baochang
    Department of Materials and Engineering, Royal Institute of Technology (KTH).
    Araújo, Carlos Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pepe, Iuri
    Instituto de Física, Universidade Federal da Bahia.
    Almeida, Jailton Souza de
    Instituto de Física, Universidade Federal da Bahia.
    Silva, Antonio Ferreira da
    Instituto de Física, Universidade Federal da Bahia.
    Study of electronic and optical properties of BiTaO4 for photocatalysis2012In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, p. 1593-1596Article in journal (Refereed)
    Abstract [en]

    We present the optical absorption spectrum of BiTaO4 using the photo acoustic spectroscopy (PAS) technique and first principle approach. Band gap have been estimated 2.65 and 2.45 eV using PAS method and DFT calculations, respectively. Position of reduction and oxidation level with respect to vacuum level are identified, which shows that BiTaO4 can be used as photocatalyst for hydrogen production. Electronic structure is explained by plotting total density of states (TDOS).

  • 31.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wang, Baochang
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    da Silva, Antonio Ferreira
    Kang, Tae Won
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Band gap engineering by anion doping in the photocatalyst BiTaO4: First principle calculations2012In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 37, no 4, p. 3014-3018Article in journal (Refereed)
    Abstract [en]

    We have shown the effect of mono and co-doping of non-metallic anion atoms on the electronic structure in BiTaO4 using the first-principles method. It can improve the photocatalytic efficiency for hydrogen production in the presence of visible sunlight. It is found that the band gap of BiTaO4 has been reduced significantly up to 54% with different nonmetallic doping. Electronic structure analysis shows that the doping of nitrogen is able to reduce the band gap of BiTaO4 due to the impurity N 2p state at the upper edge of the valence band. In case of C or C-S doped BiTaO4, double occupied (filled) states have been observed deep inside the band gap of BiTaO4. The large reduction of band gap has been achieved, which increases the visible light absorption. These results indicate that the doping of non-metallic element in BiTaO4 is a promising candidate for the photocatalyst due to its reasonable band gap.

  • 32.
    Panigrahi, Puspamitra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses Graca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Crafting ferromagnetism in Mn-doped MgO surfaces with p-type defects2014In: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514, Vol. 15, no 3, p. 035008-Article in journal (Refereed)
    Abstract [en]

    We have employed first-principles calculations based on density functional theory (DFT) to investigate the underlying physics of unusual magnetism in Mn-doped MgO surface. We have studied two distinct scenarios. In the first one, two Mn atoms are substitutionally added to the surface, occupying the Mg sites. Both are stabilized in the Mn3+ valence state carrying a local moment of 4.3 mu(B) having a high-spin configuration. The magnetic interaction between the local moments display a very short-ranged characteristic, decaying very quickly with distance, and having antiferromagnetic ordering lower in energy. The energetics analysis also indicates that the Mn ions prefer to stay close to each other with an oxygen atom bridging the local interaction. In the second scenario, we started exploring the effect of native defects on the magnetism by crafting both Mg and O vacancies, which are p-and n-type defects, respectively. It is found that the electrons and holes affect the magnetic interaction between Mn ions in a totally different manner. The n-type defect leads to very similar magnetism, with the AFM configuration being energetically preferred. However, in the presence of Mg vacancy, the situation is quite different. The Mn atoms are further oxidized, giving rise to mixed Mn(d) ionic states. As a consequence, the Mn atoms couple ferromagnetically, when placed in the close configuration, and the obtained electronic structure is coherent with the double-exchange type of magnetic interaction. To guarantee the robustness of our results, we have benchmarked our calculations with three distinct theory levels, namely DFT-GGA, DFT-GGA+U and DFT-hybrid functionals. On the surface, the Mg vacancy displays lower formation energy occurring at higher concentrations. Therefore, our model systems can be the basis to explain a number of controversial results regarding transition metal doped oxides.

  • 33.
    Panigrahi, Puspamitra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses Graca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hole induced Jahn Teller distortion ensuing ferromagnetism in Mn-MgO: bulk, surface and one dimensional structures2014In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 26, p. 265801-Article in journal (Refereed)
    Abstract [en]

    Using density functional theory, we investigate the magnetic properties of Mn doped MgO in its bulk (3D), surface (2D) and one dimensional (1D) structures. At a low dilute limit (1.5 %), the Mn impurity behaves indifferent to its position in 3D but energetically prefers to be on one of the surfaces of 2D and 1D structures. At a higher dilute limit (3.1 %), the Mn impurities stabilizing at Mn-d((3+)) ionic states prefer to be in a close configuration (4.2 angstrom compared to 5.95 angstrom) and the antiferromagnetic ordering (AFM) between them is preferred over the ferromagnetic ordering. The n-type extrinsic defects (O vacancy), when introduced to Mn doped MgO structures, also result in similar AFM exchanges as between the Mn impurities. However, the p-type defects (Mg vacancy) in the Mn doped MgO structures result in a reduced magnetic moment for the Mn atoms and bring a significant Jahn Teller (JT)-type of distortion to the e(g) and t(2)g degenerate states of Mn-d((3+)) ions. The strong hybridization between distorted Mnd states and O-2p states results in a FM exchange coupling between the Mn ions, in all the three mentioned Mn doped MgO structures. As we move from 3D to 2D, to 1D structures, the influence of JT distortion decreases, reflecting a decreasing trend for the strength of the FM exchange coupling between the Mn atoms.

  • 34.
    Pati, Palas Baran
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Damas, Giane
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tian, Lei
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Fernandes, Daniel L. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Zhang, Lei
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Bayrak Pehlivan, Ilknur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tian, Haining
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    An experimental and theoretical study of an efficient polymer nano-photocatalyst for hydrogen evolution2017In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 10, no 6, p. 1372-1376Article in journal (Refereed)
    Abstract [en]

    In this work, we report a highly efficient organic polymer nano-photocatalyst for light driven proton reduction. The system renders an initial rate of hydrogen evolution up to 50 +/- 0.5 mmol g(-1) h(-1), which is the fastest rate among all other reported organic photocatalysts. We also experimentally and theoretically prove that the nitrogen centre of the benzothiadiazole unit plays a crucial role in the photocatalysis and that the Pdots structure holds a close to ideal geometry to enhance the photocatalysis.

  • 35.
    Pavliuk, Mariia V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Alvarez, Sol Gutierrez
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hattori, Yocefu
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Messing, Maria E.
    Lund Univ, Solid State Phys & NanoLund, Box 118, S-22100 Lund, Sweden.
    Czapla-Masztafiak, Joanna
    Polish Acad Sci, Inst Nucl Phys, PL-31342 Krakow, Poland.
    Szlachetko, Jakub
    Polish Acad Sci, Inst Nucl Phys, PL-31342 Krakow, Poland;Polish Acad Sci, Inst Phys Chem, PL-01224 Warsaw, Poland.
    Silva, Jose Luis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Fernandes, Daniel L. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Lu, Li
    Kiely, Christopher J.
    Lehigh Univ, Dept Mat Sci & Engn, 5 East Packer Ave, Bethlehem, PA 18015 USA.
    Abdellah, Mohamed
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. South Valley Univ, Qena Fac Sci, Dept Chem, Qena 83523, Egypt.
    Nordlander, Peter
    Rice Univ, Dept Phys, 6100 South Main St, Houston, TX 77251 USA.
    Sá, Jacinto
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Polish Acad Sci, Inst Phys Chem, PL-01224 Warsaw, Poland.
    Hydrated Electron Generation by Excitation of Copper Localized Surface Plasmon Resonance2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 8, p. 1743-1749Article in journal (Refereed)
    Abstract [en]

    Hydrated electrons are important in radiation chemistry and charge transfer reactions, with applications that include chemical damage of DNA, catalysis, and signaling. Conventionally, hydrated electrons are produced by pulsed radiolysis, sonolysis, two-ultraviolet-photon laser excitation of liquid water, or photodetachment of suitable electron donors. Here we report a method for the generation of hydrated electrons via single-visible-photon excitation of localized surface plasmon resonances (LSPRs) of supported sub-3 nm copper nanoparticles in contact with water. Only excitations at the LSPR maximum resulted in the formation of hydrated electrons, suggesting that plasmon excitation plays a crucial role in promoting electron transfer from the nanoparticle into the solution. The reactivity of the hydrated electrons was confirmed via proton reduction and concomitant H-2 evolution in the presence of a Ru/TiO2 catalyst.

  • 36.
    Pavliuk, Mariia V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Gutiérrez Álvarez, Sol
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hattori, Yocefu
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Messing, Maria E.
    Czapla-Masztafiak, J.
    Szlachetko, J.
    Silva, Jose Luis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Fernandes, Daniel L. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Lu, L.
    Kiely, C.J.
    Abdellah, Mohamed
    Nordlander, Peter
    Sá, Jacinto
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Hydrated Electron Generation by Excitation of Localized Surface Plasmons in Copper NanoparticlesIn: Science Advances, E-ISSN 2375-2548Article in journal (Refereed)
  • 37.
    Qian, Zhao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Sa
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses Graca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Puru
    C-60-mediated hydrogen desorption in Li-N-H systems2012In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 48, p. 485406-Article in journal (Refereed)
    Abstract [en]

    Hydrogen desorption from a LiH + NH3 mixture is very difficult due to the formation of the stable LiNH4 compound. Using cluster models and first-principles theory, we demonstrate that the C-60 molecule can in fact significantly improve the thermodynamics of ammonia-mediated hydrogen desorption from LiH due to the stabilization of the intermediate state, LiNH4. The hydrogen desorption following the path of LiNH4-C-60 -> LiNH3-C-60 + 1/2H(2) is exothermic. Molecular dynamic simulations show that this reaction can take place even at room temperature (300 K). In contrast, the stable LiNH4 compound cannot desorb hydrogen at room temperature in the absence of C-60. The introduction of C-60 also helps to restrain the NH3 gas which is poisonous in proton exchange membrane fuel cell applications.

  • 38.
    Renault, Stéven
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Oltean, Viorica Alina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Araujo, C. Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Edström, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Superlithiation of Organic Electrode Materials: The Case of Dilithium Benzenedipropiolate2016In: Chemistry of Materials, Vol. 28, no 6, p. 1920-1926Article in journal (Refereed)
    Abstract [en]

    Dilithium benzenedipropiolate was prepared and investigated as a potential negative electrode material for secondary lithium-ion batteries. In addition to the expected reduction of its carbonyls, this material can reduce and reversibly oxidize its unsaturated carbon–carbon bonds leading to a Li/C ratio of 1/1 and a specific capacity as high as 1363 mAh g–1: the highest ever reported for a lithium carboxylate. Density functional theory calculations suggest that the lithiation is preferential on the propiolate carbons.

  • 39.
    Rudisch, Katharina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Espinosa-Garcia, William F.
    Univ San Buenaventura Medellin, Fac Ingn, Grp Invest Modelamiento & Simulac Computac, Carrera 56C 51-110, Medellin, Colombia.
    Osorio-Guillen, Jorge M.
    Univ Antioquia UdeA, Inst Fis, Calle 70 52-21,Carrera 56C 51-110, Medellin, Colombia.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Platzer Björkman, Charlotte
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Scragg, Jonathan J.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Structural and Electronic Properties of Cu2MnSnS4 from Experiment and First-Principles Calculations2019In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 256, no 7, article id 1800743Article in journal (Refereed)
    Abstract [en]

    Cu2MnSnS4 shares several promising properties with the widely investigated Cu2ZnSnS4 for photovoltaic applications such as containing only earth abundant and non-toxic elements, and suitable absorption characteristics for absorber materials. Thin film Cu2MnSnS4 samples with various cation compositions are co-sputtered reactively followed by a high temperature anneal. Formation of Cu2MnSnS4 and co-existence of several secondary phases is verified by XRD and Raman. Our investigation of the crystal structure based on first-principles DFT confirms that stannite crystal structure is preferred over kesterite, although, further verification considering cation disorder is needed. The direct band gap of Cu2MnSnS4 is calculated as 1.52 eV (1.62 eV) for stannite (kesterite), which coincides with the range of the measured band gaps from spectrophotometry of 1.42-1.59 eV. After further annealing treatments below 240 degrees C, the absorption shows reversible changes: the band gap blue-shifts and the Urbach tail energy is reduced. It is concluded that, just like Cu2ZnSnS4, disorder also occurs in Cu2MnSnS4. The implications of our findings are discussed and related to the current understanding of cation disorder in Cu2ZnSnS4 and related compounds. Furthermore, for the first time first-principles DFT investigations are presented for the thiospinel Cu2MnSn3S8 which is observed experimentally as a secondary phase in Sn-rich Cu2MnSnS4 thin films.

  • 40.
    Sanchez-de-Armas, Rocio
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rivalta, Ivan
    Ecole Normale Super Lyon, Lab Chim, CNRS, UMR 5182, F-69364 Lyon 07, France..
    Araujo, Carlos Moyses Graca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Soft X-ray Spectroscopic Properties of Ruthenium Complex Catalyst under CO2 Electrochemical Reduction Conditions: A First-Principles Study2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 40, p. 22899-22907Article in journal (Refereed)
    Abstract [en]

    Solar fuel production through photoelectrochemical reduction of CO2 is a promising route to popularize the use of solar energy. However, the underlying mechanisms of these complex reactions are not yet fully resolved, hindering the rational design of novel photoelectrocatalysts. To shed light on this challenging problem, the X-ray photoelectron spectroscopy (XPS) and the near edge X-ray absorption fine structure (NEXAFS) of a number of molecular systems have been calculated using first-principles theory. First, it was found that both XPS and NEXAFS display specific features that correlate with the complex charge state and the coordination number of Ru atom. Furthermore, through the analysis of C 1s and N 1s XPS and NEXAFS spectra of key intermediates, we have identified clear fingerprints for metal-hydride and Ru-CO2 chemical bonding formation, two alternative pathways for catalytic CO, reduction. These results indicate that the understanding of the electrochemical properties of the electrocatalyst, as well as the reaction pathways, could be significantly advanced through operando X-ray spectroscopy experiments based on synchrotron radiation. We expect that these theoretical findings will be the basis of and motivate future experimental initiatives.

  • 41. Tang, Shi
    et al.
    Mindemark, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Araujo, Carlos Moyses Graca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Brandell, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
    Edman, Ludvig
    Identifying Key Properties of Electrolytes for Light-Emitting Electrochemical Cells2014In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 26, no 17, p. 5083-5088Article in journal (Refereed)
    Abstract [en]

    The electrolyte is a key component in light-emitting electrochemical cells (LECs), as it facilitates in situ electrochemical doping and associated attractive device features. LiCF3SO3 dissolved in hydroxyl-capped trimethylolpropane ethoxylate (TMPE-OH) constitutes an electrolyte with which we have attained high stability and efficiency for polymer LECs, but the turn-on time of such devices is unfortunately slow. By replacing hydroxyl with methoxy as the TMPE end-group, we produced LECs with a desired combination of high efficiency, good stability, and fast turn-on time. Specifically, we showed that the turn-on time to high luminance (300 cd/m(2)) at a current density of 7.7 mA/cm(2) is lowered from 1740 to 16 s, that the efficiency is improved by similar to 20%, and that the other device properties are either maintained or improved. In a parallel modeling and experimental effort, we demonstrated that the faster kinetics following the shift in the TMPE end-group is attributed to a marked decrease in the level of both inter- and intramolecular interactions of the electrolyte, as manifested in a lowered electrolyte viscosity, faster ion transport, and more facile ion release during doping.

  • 42.
    Triana, Carlos A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Disentangling the intricate atomic short-range order and electronic properties in amorphous transition metal oxides2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 2044Article in journal (Refereed)
    Abstract [en]

    Solid state materials with crystalline order have been well-known and characterized for almost a century while the description of disordered materials still bears significant challenges. Among these are the atomic short-range order and electronic properties of amorphous transition metal oxides [aTMOs], that have emerged as novel multifunctional materials due to their optical switching properties and high-capacity to intercalate alkali metal ions at low voltages. For decades, research on aTMOs has dealt with technological optimization. However, it remains challenging to unveil their intricate atomic short-range order. Currently, no systematic and broadly applicable methods exist to assess atomic-size structure, and since electronic localization is structure-dependent, still there are not well-established optical and electronic mechanisms for modelling the properties of aTMOs. We present state-of-the-art systematic procedures involving theory and experiment in a self-consistent computational framework to unveil the atomic short-range order and its role for the electronic properties. The scheme is applied to amorphous tungsten trioxide aWO(3), which is the most studied electrochromic aTMO in spite of its unidentified atomic-size structure. Our approach provides a one-to-one matching of experimental data and corresponding model structure from which electronic properties can be directly calculated in agreement with the electronic transitions observed in the XANES spectra.

  • 43.
    Triana, Carlos A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Edvinsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Modeling of Electronic Properties of Amorphous Oxides2018In: Encyclopedia of Interfacial Chemistry:: Surface Science and Electrochemistry / [ed] Wandelt, K., Elsevier, 2018, p. 319-331Chapter in book (Refereed)
    Abstract [en]

    Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry summarizes current, fundamental knowledge of interfacial chemistry, bringing readers the latest developments in the field. As the chemical and physical properties and processes at solid and liquid interfaces are the scientific basis of so many technologies which enhance our lives and create new opportunities, its important to highlight how these technologies enable the design and optimization of functional materials for heterogeneous and electro-catalysts in food production, pollution control, energy conversion and storage, medical applications requiring biocompatibility, drug delivery, and more. This book provides an interdisciplinary view that lies at the intersection of these fields.

  • 44.
    Walbruhl, Martin
    et al.
    Royal Institute of Technology, Department of Materials Science and Engineering, Stockholm.
    Blomqvist, Andreas
    Sandvik Coromant R & D.
    Korzhavyi, Pavel A.
    Royal Institute of Technology, Department of Materials Science and Engineering, Stockholm.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Surface gradients in cemented carbides from first-principles-based multiscale modeling: Atomic diffusion in liquid Co2017In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 66, p. 174-179Article in journal (Refereed)
    Abstract [en]

    The kinetic modeling of cemented carbides, where Co is used as binder element, requires a detailed diffusion description. Up to now, no experimental self- or impurity diffusion data for the liquid Co system have been available. Here we use the fundamental approach based on ab initio molecular dynamics simulations to assess diffusion coefficients for the liquid Co system, including six solute elements. Our calculated Co self-diffusion coefficients show good agreement with the estimates that have been obtained using scaling laws from the available literature data. To validate the modeling method, we performed one set of calculations for liquid Ni self-diffusion, where experimental data are available, showing good agreement between theory and experiments. The computed diffusion data were used in subsequent DICTRA simulations to model the gradient formation in cemented carbide systems. The results based on the new diffusion data allows for correct predictions of the gradient thickness.

  • 45. Wang, Baochang
    et al.
    Arhammar, Cecilia
    Jiang, Xue
    Araujo, Carlos Moyses Graca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A Comparison Between Hybrid Functional, GW Approach and the Bethe Salpether Equation: Optical Properties of High Pressure Phases of TiO22014In: Science of Advanced Materials, ISSN 1947-2935, Vol. 6, no 6, p. 1170-1178Article in journal (Refereed)
    Abstract [en]

    Titanium dioxide has good corrosion resistance in aqueous solutions and is a good candidate for photoelectrodes. The limitation of the anatase phase of TiO2 is its large band gap. High pressure phases of TiO2 like fluorite, pyrite and cotunnite may possess a more suitable band gap than the well known atmospheric phases. In this paper, the electronic properties of high pressure phases of TuO(2), fluorite, pyrite and cotunnite, have been investigated by hybrid functional and GW methods. Our calculations suggest that the band gap of fluorite and pyrite phases have optimal band gaps to absorb visible light for photocatalysis to decompose water. The imaginary part of the dielectric function has also been calculated for fluorite, pyrite, cotunnite and anatase phases using the Bethe-Salpether (BSE) method. The dielectric function calculated by BSE for the anatase phase agrees well with experiment and with previous studies, using the same level of theory. Therefore we expect that we are also able to predict the optical properties of the high pressure phases of TiO2 by the BSE method. The spatial properties and the localization character of excitons in these high pressure phases were investigated and discussed in terms of photoconversion efficiency.

  • 46. Wang, Baochang
    et al.
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Almeida, Cristiane Gomes
    Santos Mascarenhas, Artur Jose
    Silva, Luciana Almeida
    Francis David, Denis Gilbert
    Bargiela, Pascal
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    da Silva, Antonio Ferreira
    Optical and electronic properties of nanosized BiTaO4 and BiNbO4 photocatalysts: Experiment and theory2014In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 251, no 5, p. 1034-1039Article in journal (Refereed)
    Abstract [en]

    Nanosized BiTaO4 and BiNbO4 were prepared by the citrate method. The electronic and optical properties of BiTaO4 and BiNbO4 have been investigated by means of photo-acoustic spectroscopy (PAS), X-ray photo-electron spectroscopy (XPS), and first-principles calculations based on density functional theory. The measured valence band (from XPS) of both materials agreed well with the theoretical findings. It was also found that the calculated optical properties such as dynamical dielectric function and optical absorption spectra are in good agreement with the experimental findings. According to the absorption spectra, the absorption edges of BiNbO4 and BiTaO4 are located at 370 and 330nm, respectively. Both phases have the ability to harvest UV light and relatively high surface area to volume ratio and can be used as UV/visible light-driven photocatalysts.

  • 47.
    Zhou, Yu
    et al.
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Pondick, Joshua, V
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Silva, Jose Luis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Woods, John M.
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Hynek, David J.
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Matthews, Grace
    North Carolina State Univ, Dept Mat Sci & Engn, Raleigh, NC 27695 USA.
    Shen, Xin
    Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA;Yale Univ, Dept Chem & Environm Engn, New Haven, CT 06511 USA.
    Feng, Qingliang
    Northwestern Polytech Univ, Sch Sci, Shaanxi Key Lab Opt Informat Technol, Xian 710072, Shaanxi, Peoples R China.
    Liu, Wen
    Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Lu, Zhixing
    Yale Univ, Dept Chem, 225 Prospect St, New Haven, CT 06511 USA;Tsinghua Univ, Dept Chem, Beijing 10084, Peoples R China.
    Liang, Zhixiu
    Brookhaven Natl Lab, Dept Chem, Upton, NY 11973 USA.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cai, Zhao
    Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA;Yale Univ, Dept Chem, 225 Prospect St, New Haven, CT 06511 USA.
    Wu, Min
    Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA;Yale Univ, Dept Chem, 225 Prospect St, New Haven, CT 06511 USA.
    Jiao, Liying
    Tsinghua Univ, Dept Chem, Beijing 10084, Peoples R China.
    Hu, Shu
    Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA;Yale Univ, Dept Chem & Environm Engn, New Haven, CT 06511 USA.
    Wang, Hailiang
    Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA;Yale Univ, Dept Chem, 225 Prospect St, New Haven, CT 06511 USA.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cha, Judy J.
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Unveiling the Interfacial Effects for Enhanced Hydrogen Evolution Reaction on MoS2/WTe2 Hybrid Structures2019In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 15, no 19, article id 1900078Article in journal (Refereed)
    Abstract [en]

    Using the MoS2-WTe2 heterostructure as a model system combined with electrochemical microreactors and density function theory calculations, it is shown that heterostructured contacts enhance the hydrogen evolution reaction (HER) activity of monolayer MoS2. Two possible mechanisms are suggested to explain this enhancement: efficient charge injection through large-area heterojunctions between MoS2 and WTe2 and effective screening of mirror charges due to the semimetallic nature of WTe2. The dielectric screening effect is proven minor, probed by measuring the HER activity of monolayer MoS2 on various support substrates with dielectric constants ranging from 4 to 300. Thus, the enhanced HER is attributed to the increased charge injection into MoS2 through large-area heterojunctions. Based on this understanding, a MoS2/WTe2 hybrid catalyst is fabricated with an HER overpotential of -140 mV at 10 mA cm(-2), a Tafel slope of 40 mV dec(-1), and long stability. These results demonstrate the importance of interfacial design in transition metal dichalcogenide HER catalysts. The microreactor platform presents an unambiguous approach to probe interfacial effects in various electrocatalytic reactions.

  • 48.
    Zhou, Yu
    et al.
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Silva, Jose Luis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Woods, John M.
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Pondick, Joshua V.
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Feng, Qingliang
    Northwestern Polytech Univ, Shaanxi Key Lab Opt Informat Technol, Xian 710072, Shaanxi, Peoples R China.
    Liang, Zhixiu
    Brookhaven Natl Lab, Chem Dept, Upton, NY 11973 USA.
    Liu, Wen
    Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA;Yale Univ, Dept Chem, 225 Prospect St, New Haven, CT 06511 USA.
    Lin, Li
    Peking Univ, Coll Chem & Mol Engn, Beijing 100871, Peoples R China.
    Deng, Bingchen
    Yale Univ, Dept Elect Engn, New Haven, CT 06511 USA.
    Brena, Barbara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Xia, Fengnian
    Yale Univ, Dept Elect Engn, New Haven, CT 06511 USA.
    Peng, Hailin
    Peking Univ, Coll Chem & Mol Engn, Beijing 100871, Peoples R China.
    Liu, Zhongfan
    Peking Univ, Coll Chem & Mol Engn, Beijing 100871, Peoples R China.
    Wang, Hailiang
    Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA;Yale Univ, Dept Chem, 225 Prospect St, New Haven, CT 06511 USA.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cha, Judy J.
    Yale Univ, Dept Mech Engn & Mat Sci, New Haven, CT 06511 USA;Energy Sci Inst, Yale West Campus, West Haven, CT 06525 USA.
    Revealing the Contribution of Individual Factors to Hydrogen Evolution Reaction Catalytic Activity2018In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 30, no 18, article id 1706076Article in journal (Refereed)
    Abstract [en]

    For the electrochemical hydrogen evolution reaction (HER), the electrical properties of catalysts can play an important role in influencing the overall catalytic activity. This is particularly important for semiconducting HER catalysts such as MoS2, which has been extensively studied over the last decade. Herein, on-chip microreactors on two model catalysts, semiconducting MoS2 and semimetallic WTe2, are employed to extract the effects of individual factors and study their relations with the HER catalytic activity. It is shown that electron injection at the catalyst/current collector interface and intralayer and interlayer charge transport within the catalyst can be more important than thermodynamic energy considerations. For WTe2, the site-dependent activities and the relations of the pure thermodynamics to the overall activity are measured and established, as the microreactors allow precise measurements of the type and area of the catalytic sites. The approach presents opportunities to study electrochemical reactions systematically to help establish rational design principles for future electrocatalysts.

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