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Damas, G. B. (2020). Atomic Scale Modelling in Photoelectrocatalysis: Towards the Development of Efficient Materials for Solar Fuel Production. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Atomic Scale Modelling in Photoelectrocatalysis: Towards the Development of Efficient Materials for Solar Fuel Production
2020 (English)Doctoral 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.

Abstract [sv]

Solenergi är en naturlig kandidat för att tillfredsställa den globala efterfrågan på energi som för närvarande är satt till 14 TWh/år, eftersom dess förekomst når 100 000 TWh på årsbasis med ett belopp per dag (274 TWh) som är tillräckligt för att uppfylla de mänskliga behoven. Faktum är att den huvudsakliga användningen av fossila bränslen för att uppnå ett sådant energibehov har intensifierat den globala uppvärmningen alltigenom åren, ett välkänt miljöproblem som vårt samhälle står inför sedan den industriella revolutionen. I detta sammanhang öppnar solenerginäringen genom att använda en fotokatalysator för att producera el, vattenvärme eller solbränslen inklusive väte, alkoholer och även kortkedjiga kolväten ett nytt område för utveckling av ren energi som förväntas leda marknaden på energi produktion inom en nära framtid.

Tekniker som involverar elektrokemiska anordningar som använder solljusenergi är mycket bättre utvecklade för väteproduktion än för koldioxidomvandling till organiska bränslen för närvarande. Just nu bör det betonas att denna viktiga gas inte kan utvinnas från en naturlig källa trots dess överflöd på jordskorpan, men den erhålls genom reformering av naturgas eller förnybar biomassa och vattenelektrolys, som är dyra och miljömässigt kostsamma. I denna mening är intresset som ligger på detta bränsle relaterat till dess höga duglighet som energibärare, eftersom det uppvisar högre gravimetrisk energitäthet än bensin för bränslerelaterade tillämpningar vid omgivningsförhållanden, förutom den kolfria återstoden som genereras efter förbränningsprocessen. Däremot används molekylärt väte mycket inom andra områden, varav 61% av den totala produktionen under det senaste decenniet avsett för ammoniak-härledda gödselmedel, 23% till petroleum-raffinering och 9% till metanolproduktion. Tillämpningar i bränsleceller, kraftproduktion i turbiner och rymdrelaterad teknik beaktas också.

För att vara en potentiell kandidat i solstyrd vätegenerering är det ett grundläggande krav att fotokatalysatorn har ett inre energigap, som definieras som energiförskjutningen mellan det sista besatta tillståndet av en elektron och det första tillståndet som är tillgänglig att besättas, det ska vara mindre eller jämförbart med den infallande fotonenergin. Med andra ord bör solljusenergin vara tillräcklig för att ta bort elektroner från materialet som vidare överförs till protonen för att bilda en vätefotokatalysatorbindning. Detta är faktiskt den grundläggande mekanismen från solceller, men de fotoexciterade elektronerna används för att producera elektricitet i detta fall. Som ett ytterligare steg bör de bundna väteatomerna kombineras ihop för att frigöra det molekylära bränslet. Tidigare studier vid universitetet i Tokyo har visat titandioxid(TiO2) som ett pionjärmaterial för att fotokatalysera den så kallade vattendelningen utan att tillämpa en extern potential, men kolbaserade material har representerat ett ytterligare framsteg på området för att kombinera lågt pris med jordens överflöd av dess utgörande element. Som ett viktigt exempel har polymert kolnitrid (g-C3N4) intensivt undersökts för väteproduktion och koldioxidomvandling. Dessutom har en överlägsen prestanda funnits för bensotiadiazolbaserade polymerer med en givar-acceptorarkitektur som har en nyckelroll för förbättring av laddningsöverföring och separationsprocesser i dessa material. I allmänhet kännetecknas dessa material av ordning på nanonivå även om själva materialet är amorft.

I denna avhandling har en serie fluoren- och bensotiadiazolbaserade polymerer med givar-acceptorarkitektur utvärderats med hjälp av täthetsfunktionalteori-(DFT) och tidsberoende täthetsfunktionalteori-(TD-DFT) metoder som potentiella kandidater för fotokatalytisk väteproduktion. En uppsättning små molekyler med väl definierad molekylvikt har också beaktats för denna tillämpning. DFT/TD-DFT är ett beräkningsverktyg som har använts allmänt av forskare för att reproducera/förutsäga experimentella resultat för optiska och termodynamiska egenskaper, men också den fotokatalytiska effektiviteten i fast tillstånd eller molekylära material genom att använda de så kallade deskriptorerna. Här har intensiteten av den kemiska bindningen mellan väteatomen och fotokatalysatorn, såväl som excitonbindande energier, som bestämmer om den fotoexciterade elektronen kommer att utföra den kemiska reaktionen eller helt enkelt återgå till det ursprungliga tillståndet, använts som deskriptor för att bestämma tillämpningen av de nämnda materialen i fotokatalytisk väteproduktion. I allmänhet har kemiska modifieringar av dessa material möjliggjort en förbättring av absorptionsområdet i benso(triazol-tiadiazol)baserade polymerer och cyklopentaditio-fenbaserade polymerer, med en högre påverkan uppvisad genom modifiering av acceptorenheten. Däremot presenterar alla undersökta system katalytisk effekt för protonreduktion eller borttagning av ett lämpligt kandidat. I synnerhet visades den aktiva roll som kväveatomer spelade från acceptorenheterna i hydreringsprocessen, som fungerar som de katalytiska platser för vätebindning. Dessutom ses en bättre laddningsseparation för cyklopentaditiofenbaserade polymerer  en innehållande bensotiadiazolenhet som förväntas leda till en högre fotokatalytisk effektivitet för dessa material.

I ett annat tillvägagångssätt för att hantera det ovannämnda miljöproblemet har det betraktats som direkt omvandling av koldioxid till myrsyra, en viktig kemikalie som hittar tillämpningar i bränsleceller, medicin och matindustrier. Detta är en process med flera steg som också kräver användning av en lämplig foto- eller elektrokatalysator för att minska de kinetiska barriärerna för reaktion. I denna avhandling har Sn-baserade material och Ru-komplex använts som elektrokatalysatorer för att genomföra koldioxid-omvandlingen till myrsyra genom att lägga på en extern potential. I det tidigare fallet stöder resultaten reaktionsmekanismen där koldioxid införs i Sn-OH-bindningen innan reduktionsprocessen som leder till myrsyraproduktion. I detta steg uppvisar den beräknade reduktions-potentialen (ϕ=-1,09 V mot RHE) ett gott överensstämmande med de mätningar som utförs av våra medarbetare, vilket bekräftar giltigheten för de teoretiska metoder som vi har använt. I ett Ru-komplex kommer reaktionsmekanismen sannolikt att följa vägen med naturlig produktion av kolmonoxid på grund av ligandfrisättning efter den första reduktionsprocessen, som ytterligare protoneras för att originera den aktiva arten. I detta fall kommer koldioxidinsättningen att ske vid Ru-H-bindningen för att generera en kolbunden mellanprodukt som är ytterligare protonerad för att frisätta myrsyra. Slutligen har det studerats den fysiska adsorptionen av koldioxid i metallorganiska ramverk med ett varierande metalliskt centrum i en teoretisk synvinkel.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. p. 86
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1884
Keywords
Photocatalytic hydrogen production, polymeric materials, donor-acceptor architecture, small molecules, density functional theory, hydrogen binding free energies, exciton binding energies, electrocatalysis, carbon dioxide conversion, formic acid production, Sn-based electrodes, Tin oxides, Ru-complexes, Metal Organic Frameworks, carbon dioxide capture.
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-398175 (URN)978-91-513-0827-2 (ISBN)
Public defence
2020-01-31, Å80101, Uppsala, 13:30 (English)
Opponent
Supervisors
Available from: 2020-01-10 Created: 2019-12-03 Last updated: 2020-03-05
Damas, G. B., Miranda, C., Sgarbi, R., Portela, J., Camilo, M. R. & Araujo, C. M. (2019). On the Mechanism of Carbon Dioxide Reduction on Sn-Based Electrodes: Insights into the Role of Oxide Surfaces. Catalysts, 9(8), Article ID 636.
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
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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
Damas, G., von Kieseritzky, F., Hellberg, J., Marchiori, C. & Araujo, C. M. (2019). Symmetric Small-Molecules With Acceptor-Donor-Acceptor Architecture for Efficient Visible-Light Driven Hydrogen Production: Optical and Thermodynamic Aspects. The Journal of Physical Chemistry C, 123(51), 30799-30808
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
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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
Damas, G., Marchiori, C. & Araujo, C. M. (2019). Tailoring the Electron-Rich Moiety in Benzothiadiazole-Based Polymers for an Efficient Photocatalytic Hydrogen Evolution Reaction. The Journal of Physical Chemistry C, 123(42), 25531-25542
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
Silva, J. L., Unger, I., Matias, T. A., Franco, L. ., Damas, G., Costa, L. T., . . . Araujo, C. M. (2019). X‑ray Photoelectron Fingerprints of High-Valence Ruthenium−Oxo Complexes along the Oxidation Reaction Pathway in an Aqueous Environment. The Journal of Physical Chemistry Letters, 10(24), 7636-7643
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
Damas, G., Marchiori, C. F. N. & Araujo, C. M. (2018). On the Design of Donor Acceptor Conjugated Polymers for Photocatalytic Hydrogen Evolution Reaction: First-Principles Theory-Based Assessment. The Journal of Physical Chemistry C, 122(47), 26876-26888
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
Pati, P. B., Damas, G., Tian, L., Fernandes, D. L. A., Zhang, L., Bayrak Pehlivan, I., . . . Tian, H. (2017). An experimental and theoretical study of an efficient polymer nano-photocatalyst for hydrogen evolution. Energy & Environmental Science, 10(6), 1372-1376
Open this publication in new window or tab >>An experimental and theoretical study of an efficient polymer nano-photocatalyst for hydrogen evolution
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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
Damas, G., Ivashchenko, D., Rivalta, I. & Araujo, C. M. 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
Damas, G., Costa, L. T., Ahuja, R. & Araujo, C. M.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
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5853-0819

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