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: 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: 2023-02-19

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: http://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