10.17169\/refubium-4900<\/a><\/p>\nAuthors:<\/h4>\n
Marcel Risch<\/p>\n
Abstract:<\/h4>\n
The sustainable, large-scale extraction of protons from water for dihydrogen as a fuel requires utilization of efficient catalysts for (i) water oxidation and (ii) hydrogen formation that are based on inexpensive and abundant materials. The water oxidation reaction may be the bottleneck for dihydrogen production because it requires an intricate managing of its four-electron \/four-proton chemistry by the catalyst. At the atomic level, electrochemical water oxidation is only insufficiently understood. In particular, the knowledge about water oxidation is very limited for amorphous transition metal oxides. A cobalt-based catalyst for electrochemical water oxidation (CoCat) has attracted much interest because of its efficiency at neutral pH and oxidative self-assembly from low-cost materials. A CoCat is formed by electrodepositing a thin film consisting of cobalt, potassium and phosphate on inert anodes. It electrochemically catalyzes water oxidation at moderate overpotentials. The CoCat exhibits similarities to the photosynthetic water- oxidizing manganese complex with respect to self-assembly and self-repair, as well as in its metal-oxido structure. The CoCat consists of cobalt octahedra which exclusively share edges and thereby form clusters of molecular dimensions. The macroscopic film could consist of interconnected molecular clusters in an extended but overall disordered network with water molecules as well as cations and anions from the electrolyte between cobalt oxido clusters. The basic CoCat structure is retained when the catalyst is formed in different electrolytes, but the size (or order) of its cobalt-oxido clusters depends on the type of the co-deposited anion. Various oxidation states of the CoCat can be obtained by variation of either the electric potential or the electrolyte pH, which suggests a coupled proton\u2014electron transfer in the redox reaction. The formal cobalt oxidation of the CoCat varies between +2.6 and +3.2. The transition from five-coordinated Co(II) to six-coordinated Co(III) is coupled to formation of an additional \u00b5-O(H) bridge. Furthermore, the Co\u2014Co distance spread increases at potentials fostering water oxidation, which is likely associated with deprotonation of \u00b5-OH bridges. A mechanistic scheme describing the mode of catalysis is proposed based on the structural and functional results in this work. The bulk of the hydrated cobalt oxide is assumed to be catalytically active. The scheme comprises four steps: (i) equilibrium between three distinct structural motifs; (ii) formation of a local active site by two Co(IV) ions; (iii) O\u2014O bond formation and cobalt reduction at the active site; and (iv) reoxidation of cobalt at the active site and return to equilibrium conditions. The involvement of bridging type changes is a unique aspect of the proposed mechanistic scheme. Structural changes analogous to those in the bulk of the CoCat have not been described before for any heterogeneous catalyst for water-oxidation.<\/p>\n","protected":false},"excerpt":{"rendered":"
DOI: 10.17169\/refubium-4900 Authors: Marcel Risch Abstract: The sustainable, large-scale extraction of protons from water for dihydrogen as a fuel requires utilization of efficient catalysts for (i) water oxidation and (ii) hydrogen formation that are based on inexpensive and abundant materials. The water oxidation reaction may be the bottleneck for dihydrogen production because it requires an […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-716","post","type-post","status-publish","format-standard","hentry","category-freeze-quench"],"_links":{"self":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts\/716","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=716"}],"version-history":[{"count":0,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=\/wp\/v2\/posts\/716\/revisions"}],"wp:attachment":[{"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=716"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=716"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/citations.tools.bio-logic.fr\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=716"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}