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  • 1.
    Damas, Giane B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Atomic Scale Modelling in Photoelectrocatalysis: Towards the Development of Efficient Materials for Solar Fuel Production2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Using sunlight to produce valuable chemicals has been pointed out as an interesting alternative to deal with the well-known environmental problem related to the use of fossil fuels for energy generation. Thus, it is crucial for this field the development of novel photocatalysts that could drive the uphill reactions with high efficiency while presenting low price and toxicity. In this context, conjugated polymers with a donor-acceptor architecture have shown good photoactivity for the hydrogen evolution reaction (HER) due to their advantageous properties, including a broad UV-Vis absorption spectrum and thermodynamic driving force to carry out the charge transfer processes. In this thesis, a series of fluorene- and benzothiadiazole-based polymers are evaluated by means of ab initio methods as potential candidates for photocatalytic HER. A set of small-molecules with well-defined molecular weight have also been considered for this application. In general, tailoring a chemical unit has enabled an improvement of the absorption capacity in benzo(triazole-thiadiazole)-based polymers and cyclopentadithiophene-based polymers, with a higher impact exhibited upon acceptor tailoring. On the other hand, all systems under investigation present favorable thermodynamics for proton reduction or hole removal by an appropriate sacrificial agent. In particular, it is demonstrated the active role played by nitrogen atoms from the acceptor units in the hydrogenation process, whose binding strength is significantly decreased in benzo(triazole-thiadiazole)-based polymers. Furthermore, the extension of the electron-hole separation has been assessed through the calculation of the exciton binding energies, which are diminished with an improvement in the donating ability on cyclopentadithiophene-based materials.

    In another approach to deal with the aforementioned problem, it has been considered the direct conversion of carbon dioxide into formic acid, an important chemical that finds applications in fuel cells, medicine and food industries. In this thesis, such electrocatalytic process has been investigated by using Sn-based electrodes and Ru-complexes. In the former case, a solid-state modelling approach based on slab geometries to model surface states has been employed to explore the reaction thermochemistry. The outcomes support the reaction mechanism where the carbon dioxide insertion into the Sn-OH bond is a thermodynamically favorable step prior to reduction, which has a redox potential in fair agreement with the measurements carried out by our collaborators. In a Ru-complex, the reaction mechanism is likely to follow the route with natural production of CO due to ligand release after the first reduction process, which is further protonated to originate the active species. In this case, the insertion occurs at the Ru-H bond to generate a carbon-bound species that is the intermediate in the formic acid production after the second protonation step. Finally, it has been studied the physical adsorption of carbon dioxide in metal-organic frameworks with a varying metallic center in a theoretical point of view.

    List of papers
    1. An experimental and theoretical study of an efficient polymer nano-photocatalyst for hydrogen evolution
    Open this publication in new window or tab >>An experimental and theoretical study of an efficient polymer nano-photocatalyst for hydrogen evolution
    Show others...
    2017 (English)In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 10, no 6, p. 1372-1376Article in journal (Refereed) Published
    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.

    Keywords
    CATALYSTS; H-2; SYSTEM; ENVIRONMENTAL SCIENCES; CELLS; CONJUGATED POLYMERS; ENERGY & FUELS; ARTIFICIAL PHOTOSYNTHESIS; WATER; ENGINEERING, CHEMICAL; GENERATION; CHEMISTRY, MULTIDISCIPLINARY; VISIBLE-LIGHT
    National Category
    Polymer Chemistry Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-332949 (URN)10.1039/c7ee00751e (DOI)000403320300009 ()
    Funder
    Knut and Alice Wallenberg FoundationSwedish Energy AgencyÅForsk (Ångpanneföreningen's Foundation for Research and Development)Stiftelsen Olle Engkvist ByggmästareStandUp
    Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2019-12-03Bibliographically approved
    2. On the Design of Donor Acceptor Conjugated Polymers for Photocatalytic Hydrogen Evolution Reaction: First-Principles Theory-Based Assessment
    Open this publication in new window or tab >>On the Design of Donor Acceptor Conjugated Polymers for Photocatalytic Hydrogen Evolution Reaction: First-Principles Theory-Based Assessment
    2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 47, p. 26876-26888Article in journal (Refereed) Published
    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).

    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-372709 (URN)10.1021/acs.jpcc.8b09408 (DOI)000451933400012 ()
    Funder
    Swedish Research CouncilCarl Tryggers foundation StandUp
    Available from: 2019-01-09 Created: 2019-01-09 Last updated: 2019-12-03Bibliographically approved
    3. Tailoring the Electron-Rich Moiety in Benzothiadiazole-Based Polymers for an Efficient Photocatalytic Hydrogen Evolution Reaction
    Open this publication in new window or tab >>Tailoring the Electron-Rich Moiety in Benzothiadiazole-Based Polymers for an Efficient Photocatalytic Hydrogen Evolution Reaction
    2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 42, p. 25531-25542Article in journal (Refereed) Published
    Abstract [en]

    Polymeric materials containing an extended π-conjugated backbone have shown a wide range of applicability including photocatalytic activity for the hydrogen evolution reaction (HER). The latter requires highly efficient materials with optimal light absorption and thermodynamic driving force for charge transfer processes, properties that are tailored by linking chemical units with distinct electron affinity to form a donor−acceptor architecture. Here, this concept is explored by means of ab initio theory in benzothiadiazole-based polymers with varying electron-rich moieties, viz., fluorene (PFO), cyclopentadithiophene (CPT), methoxybenzodithiophene (O-BzT), thiophenebenzodithiophene (T-BzT), and thiophene (T, VT)and thienethiophene (TT, VTT)-based units. All materials exhibit a red-shifted absorption spectrum with respect to the reference polymer (PFO-DT-BT) while keeping the catalytic power for hydrogen production almost unchanged. In particular, a displacement ofΔλ = 167 nm in the first absorption maximum has been achieved upon combination of chemical units with high donating character in CPT-VTT-BT. Furthermore, the exciton binding energies (Eb) have been systematically investigated to unveil the effects of geometry relaxation, environment polarity, and finite temperature contributions to the free energy. For instance, we show a significant change in Eb when going from the gas phase (Eb = 1.43−1.85 eV) to the solvent environment (Eb = 0.29−0.54 eV in 1-bromooctane with ε = 5.02). Furthermore, we have found a linear correlation between the lowering of exciton binding energies and the increasing of the ratio between donor and acceptor contributions to the HOMO orbital. This is a consequence of increased donating ability and enhanced spatial separation of electron−hole pairs, which weakens their interaction. Finally, our findings reveal that the donor unit plays a crucial role in key properties that govern the photocatalytic activity of donor−acceptor polymers contributing to the development of a practical guideline to design more efficient photocatalysts for the HER. This goes through a proper combination of electron-rich moieties to tune the optical gap, favor thermodynamic driving force for charge transfer, and lower exciton binding energies.

    National Category
    Atom and Molecular Physics and Optics
    Research subject
    Physics with specialization in Quantum Chemistry
    Identifiers
    urn:nbn:se:uu:diva-395873 (URN)10.1021/acs.jpcc.9b06057 (DOI)000492803300001 ()
    Funder
    Swedish Research CouncilCarl Tryggers foundation
    Available from: 2019-10-24 Created: 2019-10-24 Last updated: 2019-12-03Bibliographically approved
    4. Symmetric Small-Molecules With Acceptor-Donor-Acceptor Architecture for Efficient Visible-Light Driven Hydrogen Production: Optical and Thermodynamic Aspects
    Open this publication in new window or tab >>Symmetric Small-Molecules With Acceptor-Donor-Acceptor Architecture for Efficient Visible-Light Driven Hydrogen Production: Optical and Thermodynamic Aspects
    Show others...
    2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 51, p. 30799-30808Article in journal (Refereed) Published
    Abstract [en]

    Small-molecules (SM) have attracted a great deal of attention in the field of solar energy conversion due to their unique propertiescompared to polymers, such as well-defined molecular weight and lack of regio-isomeric impurities. Furthermore, these materials can be synthesized in a variety of configurational architectures, representing an opportunity for tailoring chemical and optical properties that could lead to a better photocatalytic efficiency for hydrogen generation. Here, we evaluate by means of density functional theory (DFT) and time-dependent DFT methods a set of small-molecules with A-D-A architecture (A-acceptor; D- donor) based on well-known building blocks like thiophene (T), cyclopentadithiophene (CPT) and benzothiadiazole (BT) as potential candidates for photocatalytic hydrogen evolution reaction (HER). We also propose i) the replacement of the thiophene unit by 3,4-ethylenedioxythiophene (EDOT) to form with CPT unit an extended donor core ii) an additional acceptor unit, the 1,3,4-thiadiazole (Tz), in the extremities and iii) insertion of the difluoromethoxy (DFM) as substituent in the BT unit. Our outcomes reveal that these materials have a broad absorption spectrum with λ= 318-719 nm, being the most intense absorption peak originated from an electronic transition with charge-transfer nature, as the spatial distribution of LUMO is concentrated on the acceptor units for all materials. Moreover, these small-molecules not only present catalytic power or thermodynamic driving force to carry out the chemical reactions involved in the process of hydrogen production, but can be coupled in cooperative photocatalytic systems to promote intramolecular charge transfer that is expected to boost the overall photocatalytic efficiency of these materials.

    Keywords
    Small Molecules, Photocatalysis, Hydrogen Production, Density Functional Theory
    National Category
    Other Chemistry Topics
    Research subject
    Chemistry
    Identifiers
    urn:nbn:se:uu:diva-398119 (URN)10.1021/acs.jpcc.9b07721 (DOI)000505632900005 ()
    Funder
    Swedish Research CouncilStandUp
    Available from: 2019-12-02 Created: 2019-12-02 Last updated: 2020-01-28Bibliographically approved
    5. On the Mechanism of Carbon Dioxide Reduction on Sn-Based Electrodes: Insights into the Role of Oxide Surfaces
    Open this publication in new window or tab >>On the Mechanism of Carbon Dioxide Reduction on Sn-Based Electrodes: Insights into the Role of Oxide Surfaces
    Show others...
    2019 (English)In: Catalysts, E-ISSN 2073-4344, Vol. 9, no 8, article id 636Article in journal (Refereed) Published
    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.

    Keywords
    electrocatalysis, carbon dioxide conversion, formic acid, tin-based electrodes, tin oxide, tin-carbonate, reaction mechanism
    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-390068 (URN)10.3390/catal9080636 (DOI)000482799100047 ()
    Funder
    StandUpSwedish Research CouncilSwedish National Infrastructure for Computing (SNIC)
    Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-12-03Bibliographically approved
    6. X‑ray Photoelectron Fingerprints of High-Valence Ruthenium−Oxo Complexes along the Oxidation Reaction Pathway in an Aqueous Environment
    Open this publication in new window or tab >>X‑ray Photoelectron Fingerprints of High-Valence Ruthenium−Oxo Complexes along the Oxidation Reaction Pathway in an Aqueous Environment
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    2019 (English)In: The Journal of Physical Chemistry Letters, Vol. 10, no 24, p. 7636-7643Article in journal (Refereed) Published
    Abstract [en]

    Recent advances in operando-synchrotron-based X-ray techniques are making it possible to address fundamental questions related to complex proton-coupled electron transfer reactions, for instance, the electrocatalytic water splitting process. However, it is still a grand challenge to assess the ability of the different techniques to characterize the relevant intermediates, with minimal interference on the reaction mechanism. To this end, we have developed a novel methodology employing X-ray photoelectron spectroscopy (XPS) in connection with the liquid-jet approach to probe the electrochemical properties of a model electrocatalyst, [RuII(bpy)2(py)-(OH2)]2+, in an aqueous environment. There is a unique fingerprint of the extremely important higher-valence ruthenium−oxo species in the XPS spectra along the oxidation reaction pathway. Furthermore, a sequential method combining quantum mechanics and molecular mechanics is used to illuminate the underlying physical chemistry of such systems. This study provides the basis for the future development of in-operando XPS techniques for water oxidation reactions.

    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-398067 (URN)10.1021/acs.jpclett.9b02756 (DOI)000503919300014 ()31747290 (PubMedID)
    Available from: 2019-12-01 Created: 2019-12-01 Last updated: 2020-01-22Bibliographically approved
    7. Carbon Dioxide  Reduction Mechanism on Ru-based Electrocatalysts: Insights from First-principles Theory
    Open this publication in new window or tab >>Carbon Dioxide  Reduction Mechanism on Ru-based Electrocatalysts: Insights from First-principles Theory
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Solar fuel production through the so-called artificial photosynthesis has attracted a great deal of attention to the development of a new world energy matrix that is renewable and environmentally friendly. This process basically comprises the absorption of sunlight energy by an appropriate photocatalyst that is active for carbon dioxide conversion into organic fuels. Commonly, an electrocatalyst can be coupled to the system for later improvement of the photocatalytic efficiency and selectivity. In this work, we have undertaken a thorough investigation of the redox reaction mechanism of Ru-based electrocatalysts by means of density functional theory (DFT) methods under the experimental conditions that have been previously reported. More specifically, we have studied the electrochemistry and catalytic activity of the coordination complex [Ru(bpy)2(CO)2]2+. Our theoretical assessment support the following catalytic cycle: (i) [Ru(bpy)2(CO)2]2+ is transformed into [Ru(bpy)2(CO)]0 upon the two-electron reduction and CO release; (ii) [Ru(bpy)2(CO)]0 is protonated to form the hydride complex [Ru(bpy)2(CO)H]+; (iii) CO2 is activated by the hydride complex through an electrophilic addition to form the intermediate [Ru(bpy)2(CO)(OCHO)]+, with the formation of C-H bond; (iv) the resulting formate ligand ion is then released in solution; and, finally, (iv) CO ligand is reattached to the complex to recover the initial complex [Ru(bpy)2(CO)2]2+.  

    Keywords
    Ru-complex, Carbon dioxide conversion, Electrocatalysis, formic acid production, Density Functional Theory
    National Category
    Other Chemistry Topics
    Identifiers
    urn:nbn:se:uu:diva-398121 (URN)
    Available from: 2019-12-02 Created: 2019-12-02 Last updated: 2019-12-19Bibliographically approved
    8. Understanding Carbon Dioxide Capture on Metal-Organic Frameworks from First-Principles Theory: The Case of MIL-53(X), with X=Fe, Al and Cu
    Open this publication in new window or tab >>Understanding Carbon Dioxide Capture on Metal-Organic Frameworks from First-Principles Theory: The Case of MIL-53(X), with X=Fe, Al and Cu
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Metal-organic frameworks (MOFs) constitute a class of three-dimensional porous materials that have shown applicability for carbon dioxide capture at low pressures, which is particularly advantageous to deal with the well-known environmental problem related to the carbon dioxide emissions into the atmosphere. In this work, the effect of changing the metallic center in the inorganic counterpart in MIL-53 (X), where X= Fe3+, Al3+, Cu3+ has been evaluated over the ability of the porous material to adsorb carbon dioxide by means of ab initio methodology. More specifically, we have employed a solid-state approach to study the thermochemistry of this process also considering the effects of spin-polarization. By using GGA+U methods with U= 7 eV on Fe 3d and Cu 3d states and GGA with Al-based MOF, it has been verified a preferential stabilization of the guest molecule at the pore center, which exhibits long-range interaction via oxygen atoms with the axial hydroxyl groups. In this sense, MIL-53 (Cu3+) shows potential absorption capacity for carbon dioxide, with a binding energy higher than that verified for the Al-based MOF within the same of level. Furthermore, applying Hubbard corrections on atoms exhibiting an open shell configuration (Cu, Fe) has been demonstrated to be essential for a proper assessment of the electronic structure and atomic magnetic moment, which affect the final binding energy values through an unequal influence on the electronic energies in the pure system and after carbon dioxide adsorption.

    Keywords
    Metal Organic Frameworks, Carbon Dioxide Capture, DFT methods
    National Category
    Chemical Sciences
    Identifiers
    urn:nbn:se:uu:diva-398174 (URN)
    Available from: 2019-12-03 Created: 2019-12-03 Last updated: 2019-12-12
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  • 2.
    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.

    Download full text (pdf)
    catalysts-09-00636
  • 3.
    Damas, Giane
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Costa, Luciano T.
    Ahuja, Rajeev
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Understanding Carbon Dioxide Capture on Metal-Organic Frameworks from First-Principles Theory: The Case of MIL-53(X), with X=Fe, Al and CuManuscript (preprint) (Other academic)
    Abstract [en]

    Metal-organic frameworks (MOFs) constitute a class of three-dimensional porous materials that have shown applicability for carbon dioxide capture at low pressures, which is particularly advantageous to deal with the well-known environmental problem related to the carbon dioxide emissions into the atmosphere. In this work, the effect of changing the metallic center in the inorganic counterpart in MIL-53 (X), where X= Fe3+, Al3+, Cu3+ has been evaluated over the ability of the porous material to adsorb carbon dioxide by means of ab initio methodology. More specifically, we have employed a solid-state approach to study the thermochemistry of this process also considering the effects of spin-polarization. By using GGA+U methods with U= 7 eV on Fe 3d and Cu 3d states and GGA with Al-based MOF, it has been verified a preferential stabilization of the guest molecule at the pore center, which exhibits long-range interaction via oxygen atoms with the axial hydroxyl groups. In this sense, MIL-53 (Cu3+) shows potential absorption capacity for carbon dioxide, with a binding energy higher than that verified for the Al-based MOF within the same of level. Furthermore, applying Hubbard corrections on atoms exhibiting an open shell configuration (Cu, Fe) has been demonstrated to be essential for a proper assessment of the electronic structure and atomic magnetic moment, which affect the final binding energy values through an unequal influence on the electronic energies in the pure system and after carbon dioxide adsorption.

  • 4.
    Damas, Giane
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ivashchenko, Dmitri
    Rivalta, Ivan
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Carbon Dioxide  Reduction Mechanism on Ru-based Electrocatalysts: Insights from First-principles TheoryManuscript (preprint) (Other academic)
    Abstract [en]

    Solar fuel production through the so-called artificial photosynthesis has attracted a great deal of attention to the development of a new world energy matrix that is renewable and environmentally friendly. This process basically comprises the absorption of sunlight energy by an appropriate photocatalyst that is active for carbon dioxide conversion into organic fuels. Commonly, an electrocatalyst can be coupled to the system for later improvement of the photocatalytic efficiency and selectivity. In this work, we have undertaken a thorough investigation of the redox reaction mechanism of Ru-based electrocatalysts by means of density functional theory (DFT) methods under the experimental conditions that have been previously reported. More specifically, we have studied the electrochemistry and catalytic activity of the coordination complex [Ru(bpy)2(CO)2]2+. Our theoretical assessment support the following catalytic cycle: (i) [Ru(bpy)2(CO)2]2+ is transformed into [Ru(bpy)2(CO)]0 upon the two-electron reduction and CO release; (ii) [Ru(bpy)2(CO)]0 is protonated to form the hydride complex [Ru(bpy)2(CO)H]+; (iii) CO2 is activated by the hydride complex through an electrophilic addition to form the intermediate [Ru(bpy)2(CO)(OCHO)]+, with the formation of C-H bond; (iv) the resulting formate ligand ion is then released in solution; and, finally, (iv) CO ligand is reattached to the complex to recover the initial complex [Ru(bpy)2(CO)2]2+.  

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    Carbon Dioxide Reduction Mechanism on Ru-based Electrocatalysts
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    Supporting Information
  • 5.
    Damas, Giane
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Marchiori, Cleber
    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.
    Tailoring the Electron-Rich Moiety in Benzothiadiazole-Based Polymers for an Efficient Photocatalytic Hydrogen Evolution Reaction2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 42, p. 25531-25542Article in journal (Refereed)
    Abstract [en]

    Polymeric materials containing an extended π-conjugated backbone have shown a wide range of applicability including photocatalytic activity for the hydrogen evolution reaction (HER). The latter requires highly efficient materials with optimal light absorption and thermodynamic driving force for charge transfer processes, properties that are tailored by linking chemical units with distinct electron affinity to form a donor−acceptor architecture. Here, this concept is explored by means of ab initio theory in benzothiadiazole-based polymers with varying electron-rich moieties, viz., fluorene (PFO), cyclopentadithiophene (CPT), methoxybenzodithiophene (O-BzT), thiophenebenzodithiophene (T-BzT), and thiophene (T, VT)and thienethiophene (TT, VTT)-based units. All materials exhibit a red-shifted absorption spectrum with respect to the reference polymer (PFO-DT-BT) while keeping the catalytic power for hydrogen production almost unchanged. In particular, a displacement ofΔλ = 167 nm in the first absorption maximum has been achieved upon combination of chemical units with high donating character in CPT-VTT-BT. Furthermore, the exciton binding energies (Eb) have been systematically investigated to unveil the effects of geometry relaxation, environment polarity, and finite temperature contributions to the free energy. For instance, we show a significant change in Eb when going from the gas phase (Eb = 1.43−1.85 eV) to the solvent environment (Eb = 0.29−0.54 eV in 1-bromooctane with ε = 5.02). Furthermore, we have found a linear correlation between the lowering of exciton binding energies and the increasing of the ratio between donor and acceptor contributions to the HOMO orbital. This is a consequence of increased donating ability and enhanced spatial separation of electron−hole pairs, which weakens their interaction. Finally, our findings reveal that the donor unit plays a crucial role in key properties that govern the photocatalytic activity of donor−acceptor polymers contributing to the development of a practical guideline to design more efficient photocatalysts for the HER. This goes through a proper combination of electron-rich moieties to tune the optical gap, favor thermodynamic driving force for charge transfer, and lower exciton binding energies.

  • 6.
    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).

  • 7.
    Damas, Giane
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    von Kieseritzky, Fredrik
    Arubedo AB.
    Hellberg, Jonas
    Arubedo AB.
    Marchiori, Cleber
    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.
    Symmetric Small-Molecules With Acceptor-Donor-Acceptor Architecture for Efficient Visible-Light Driven Hydrogen Production: Optical and Thermodynamic Aspects2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 51, p. 30799-30808Article in journal (Refereed)
    Abstract [en]

    Small-molecules (SM) have attracted a great deal of attention in the field of solar energy conversion due to their unique propertiescompared to polymers, such as well-defined molecular weight and lack of regio-isomeric impurities. Furthermore, these materials can be synthesized in a variety of configurational architectures, representing an opportunity for tailoring chemical and optical properties that could lead to a better photocatalytic efficiency for hydrogen generation. Here, we evaluate by means of density functional theory (DFT) and time-dependent DFT methods a set of small-molecules with A-D-A architecture (A-acceptor; D- donor) based on well-known building blocks like thiophene (T), cyclopentadithiophene (CPT) and benzothiadiazole (BT) as potential candidates for photocatalytic hydrogen evolution reaction (HER). We also propose i) the replacement of the thiophene unit by 3,4-ethylenedioxythiophene (EDOT) to form with CPT unit an extended donor core ii) an additional acceptor unit, the 1,3,4-thiadiazole (Tz), in the extremities and iii) insertion of the difluoromethoxy (DFM) as substituent in the BT unit. Our outcomes reveal that these materials have a broad absorption spectrum with λ= 318-719 nm, being the most intense absorption peak originated from an electronic transition with charge-transfer nature, as the spatial distribution of LUMO is concentrated on the acceptor units for all materials. Moreover, these small-molecules not only present catalytic power or thermodynamic driving force to carry out the chemical reactions involved in the process of hydrogen production, but can be coupled in cooperative photocatalytic systems to promote intramolecular charge transfer that is expected to boost the overall photocatalytic efficiency of these materials.

  • 8.
    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.

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  • 9.
    Silva, Jose Luis
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Unger, Isaak
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Matias, Tiago A.
    Franco, Leandro R.
    Damas, Giane
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Costa, Luciano T.
    Toledo, Kalil C. F
    Rocha, Tulio C. R.
    de Brito, Arnaldo N.
    Saak, Clara-Magdalena
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Coutinho, Kaline
    Araki, Koiti
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Brena, Barbara
    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.
    X‑ray Photoelectron Fingerprints of High-Valence Ruthenium−Oxo Complexes along the Oxidation Reaction Pathway in an Aqueous Environment2019In: The Journal of Physical Chemistry Letters, Vol. 10, no 24, p. 7636-7643Article in journal (Refereed)
    Abstract [en]

    Recent advances in operando-synchrotron-based X-ray techniques are making it possible to address fundamental questions related to complex proton-coupled electron transfer reactions, for instance, the electrocatalytic water splitting process. However, it is still a grand challenge to assess the ability of the different techniques to characterize the relevant intermediates, with minimal interference on the reaction mechanism. To this end, we have developed a novel methodology employing X-ray photoelectron spectroscopy (XPS) in connection with the liquid-jet approach to probe the electrochemical properties of a model electrocatalyst, [RuII(bpy)2(py)-(OH2)]2+, in an aqueous environment. There is a unique fingerprint of the extremely important higher-valence ruthenium−oxo species in the XPS spectra along the oxidation reaction pathway. Furthermore, a sequential method combining quantum mechanics and molecular mechanics is used to illuminate the underlying physical chemistry of such systems. This study provides the basis for the future development of in-operando XPS techniques for water oxidation reactions.

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