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Understanding polyoxometalates as water oxidation catalysts through iron vs. cobalt reactivity

  • Identification data

    Identifier: imarina:9216836
    Authors:
    Azmani, KhalidBesora, MariaSoriano-Lopez, JoaquinLandolsi, MeriemTeillout, Anne-Luciede Oliveira, PedroMbomekalle, Israel-MartyrPoblet, Josep M.Galan-Mascaros, Jose-Ramon
    Abstract:
    Cobalt polyoxometalates (Co-POMs) have emerged as promising water oxidation catalysts (WOCs), with the added advantage of their molecular nature despite being metal oxide fragments. In comparison with metal oxides, that do not offer well-defined active surfaces, POMs have a controlled, discrete structure that allows for precise correlations between experiment and computational analyses. Thus, beyond highly active WOCs, POMs are also model systems to gain deeper mechanistic understanding on the oxygen evolution reaction (OER). The tetracobalt Weakley sandwich [Co-4(II)(H2O)(2)(B-alpha-PW9O34)(2)](10-) (Co-4-WS) has been one of the most extensively studied. We have compared its activity with that of the iron analog [Fe-4(III)(H2O)(2)(B-alpha-PW9O34)(2)](6-) (Fe-4-WS) looking for the electronic effects determining their activity. Furthermore, the effect of POM nuclearity was also investigated by comparison with the iron- and cobalt-monosubstituted Keggin clusters. Electrocatalytic experiments employing solid state electrodes containing the POMs and the corresponding computational calculations demonstrate that Co-II-POMs display better WOC activity than the Fe-III derivatives. Moreover, the activity of POMs is less influenced by their nuclearity, thus Weakley sandwich moieties show slightly improved WOC characteristics than Keggin clusters. In good agreement with the experimental data, computational methods, including pK(a) values, confirm that the resting state for Fe-POMs in neutral media corresponds to the S-1 (Fe-III-OH) species. Overall, the proposed reaction mechanism for Fe-4-WS is analogous to that found for Co-4-WS, despite their electronic differences. The potential limiting step is a proton-coupled electron transfer event yielding the active S-2 (Fe-IV=O) species
  • Others:

    Author, as appears in the article.: Azmani, Khalid; Besora, Maria; Soriano-Lopez, Joaquin; Landolsi, Meriem; Teillout, Anne-Lucie; de Oliveira, Pedro; Mbomekalle, Israel-Martyr; Poblet, Josep M.; Galan-Mascaros, Jose-Ramon;
    Department: Química Física i Inorgànica
    URV's Author/s: Azmani, Khalid / Besora Bonet, Maria / Poblet Rius, Josep Maria
    Keywords: Water oxidation catalysts Structure-reactivity relationships Solid-state electrodes Proton coupled electron transfers Polyoxometalates Phosphate Oxygen-evolution Oxygen evolution reaction (oer) Oxidation Molecular-orbital methods Iron compounds Hydrogen Homogeneous catalyst Exchange Energy Electronic differences Electron transport properties Electrocatalysts Computational calculations Computational analysis Cobalt Catalysts Activation energy Abundant transition-metal Ab-initio
    Abstract: Cobalt polyoxometalates (Co-POMs) have emerged as promising water oxidation catalysts (WOCs), with the added advantage of their molecular nature despite being metal oxide fragments. In comparison with metal oxides, that do not offer well-defined active surfaces, POMs have a controlled, discrete structure that allows for precise correlations between experiment and computational analyses. Thus, beyond highly active WOCs, POMs are also model systems to gain deeper mechanistic understanding on the oxygen evolution reaction (OER). The tetracobalt Weakley sandwich [Co-4(II)(H2O)(2)(B-alpha-PW9O34)(2)](10-) (Co-4-WS) has been one of the most extensively studied. We have compared its activity with that of the iron analog [Fe-4(III)(H2O)(2)(B-alpha-PW9O34)(2)](6-) (Fe-4-WS) looking for the electronic effects determining their activity. Furthermore, the effect of POM nuclearity was also investigated by comparison with the iron- and cobalt-monosubstituted Keggin clusters. Electrocatalytic experiments employing solid state electrodes containing the POMs and the corresponding computational calculations demonstrate that Co-II-POMs display better WOC activity than the Fe-III derivatives. Moreover, the activity of POMs is less influenced by their nuclearity, thus Weakley sandwich moieties show slightly improved WOC characteristics than Keggin clusters. In good agreement with the experimental data, computational methods, including pK(a) values, confirm that the resting state for Fe-POMs in neutral media corresponds to the S-1 (Fe-III-OH) species. Overall, the proposed reaction mechanism for Fe-4-WS is analogous to that found for Co-4-WS, despite their electronic differences. The potential limiting step is a proton-coupled electron transfer event yielding the active S-2 (Fe-IV=O) species, which receives a water nucleophilic attack to form the O-O bond. The latter has activation energies slightly higher than those computed for the Co-POMs, in good agreement with experimental observations. These results provide new insights for the accurate understanding of the structure-reactivity relationships of polyoxometalates in particular, and or metal oxides in general, which are of utmost importance for the development of new bottom-up synthetic approaches to design efficient, robust and non-expensive earth-abundant water oxidation catalysts.
    Thematic Areas: Química Materiais Interdisciplinar General chemistry Farmacia Ciências biológicas iii Ciências biológicas i Chemistry, multidisciplinary Chemistry (miscellaneous) Chemistry (all) Astronomia / física
    licence for use: https://creativecommons.org/licenses/by/3.0/es/
    Author's mail: maria.besora@urv.cat josepmaria.poblet@urv.cat
    Author identifier: 0000-0002-6656-5827 0000-0002-4533-0623
    Record's date: 2024-07-27
    Journal volume: 12
    Papper version: info:eu-repo/semantics/publishedVersion
    Link to the original source: https://pubs.rsc.org/en/content/articlelanding/2021/SC/D1SC01016F#!divAbstract
    Licence document URL: https://repositori.urv.cat/ca/proteccio-de-dades/
    Papper original source: Chemical Science. 12 (25): 8755-8766
    APA: Azmani, Khalid; Besora, Maria; Soriano-Lopez, Joaquin; Landolsi, Meriem; Teillout, Anne-Lucie; de Oliveira, Pedro; Mbomekalle, Israel-Martyr; Poblet, (2021). Understanding polyoxometalates as water oxidation catalysts through iron vs. cobalt reactivity. Chemical Science, 12(25), 8755-8766. DOI: 10.1039/d1sc01016f
    Article's DOI: 10.1039/d1sc01016f
    Entity: Universitat Rovira i Virgili
    Journal publication year: 2021
    Publication Type: Journal Publications
  • Keywords:

    Chemistry (Miscellaneous),Chemistry, Multidisciplinary
    Water oxidation catalysts
    Structure-reactivity relationships
    Solid-state electrodes
    Proton coupled electron transfers
    Polyoxometalates
    Phosphate
    Oxygen-evolution
    Oxygen evolution reaction (oer)
    Oxidation
    Molecular-orbital methods
    Iron compounds
    Hydrogen
    Homogeneous catalyst
    Exchange
    Energy
    Electronic differences
    Electron transport properties
    Electrocatalysts
    Computational calculations
    Computational analysis
    Cobalt
    Catalysts
    Activation energy
    Abundant transition-metal
    Ab-initio
    Química
    Materiais
    Interdisciplinar
    General chemistry
    Farmacia
    Ciências biológicas iii
    Ciências biológicas i
    Chemistry, multidisciplinary
    Chemistry (miscellaneous)
    Chemistry (all)
    Astronomia / física
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