Structure and Valency of a Cobalt−Phosphate Water Oxidation Catalyst Determined by in Situ X-ray Spectroscopy
A water oxidation catalyst generated via electrodeposition from aqueous solutions containing phosphate and Co2+ (Co−Pi) has been studied by in situ X-ray absorption spectroscopy. Spectra were obtained for Co−Pi films of two different thicknesses at an applied potential supporting water oxidation cat...
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Veröffentlicht in: | Journal of the American Chemical Society 2010-10, Vol.132 (39), p.13692-13701 |
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creator | Kanan, Matthew W. Yano, Junko Surendranath, Yogesh Dincă, Mircea Yachandra, Vittal K. Nocera, Daniel G. |
description | A water oxidation catalyst generated via electrodeposition from aqueous solutions containing phosphate and Co2+ (Co−Pi) has been studied by in situ X-ray absorption spectroscopy. Spectra were obtained for Co−Pi films of two different thicknesses at an applied potential supporting water oxidation catalysis and at open circuit. Extended X-ray absorption fine structure (EXAFS) spectra indicate the presence of bis-oxo/hydroxo-bridged Co subunits incorporated into higher nuclearity clusters in Co−Pi. The average cluster nuclearity is greater in a relatively thick film (∼40−50 nmol Co ions/cm2) deposited at 1.25 V vs NHE than in an extremely thin film (∼3 nmol Co ions/cm2) deposited at 1.1 V. X-ray absorption near edge structure (XANES) spectra and electrochemical data support a Co valency greater than 3 for both Co−Pi samples when catalyzing water oxidation at 1.25 V. Upon switching to open circuit, Co−Pi undergoes a continuous reduction due to residual water oxidation catalysis, as indicated by the negative shift of the edge energy. The rate of reduction depends on the average cluster size. On the basis of structural parameters extracted from fits to the EXAFS data of Co−Pi with two different thicknesses and comparisons with EXAFS spectra of Co oxide compounds, a model is proposed wherein the Co oxo/hydroxo clusters of Co−Pi are composed of edge-sharing CoO6 octahedra, the structural motif found in cobaltates. Whereas cobaltates contain extended planes of CoO6 octahedra, the Co−Pi clusters are of molecular dimensions. |
doi_str_mv | 10.1021/ja1023767 |
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Spectra were obtained for Co−Pi films of two different thicknesses at an applied potential supporting water oxidation catalysis and at open circuit. Extended X-ray absorption fine structure (EXAFS) spectra indicate the presence of bis-oxo/hydroxo-bridged Co subunits incorporated into higher nuclearity clusters in Co−Pi. The average cluster nuclearity is greater in a relatively thick film (∼40−50 nmol Co ions/cm2) deposited at 1.25 V vs NHE than in an extremely thin film (∼3 nmol Co ions/cm2) deposited at 1.1 V. X-ray absorption near edge structure (XANES) spectra and electrochemical data support a Co valency greater than 3 for both Co−Pi samples when catalyzing water oxidation at 1.25 V. Upon switching to open circuit, Co−Pi undergoes a continuous reduction due to residual water oxidation catalysis, as indicated by the negative shift of the edge energy. The rate of reduction depends on the average cluster size. On the basis of structural parameters extracted from fits to the EXAFS data of Co−Pi with two different thicknesses and comparisons with EXAFS spectra of Co oxide compounds, a model is proposed wherein the Co oxo/hydroxo clusters of Co−Pi are composed of edge-sharing CoO6 octahedra, the structural motif found in cobaltates. Whereas cobaltates contain extended planes of CoO6 octahedra, the Co−Pi clusters are of molecular dimensions.</description><identifier>ISSN: 0002-7863</identifier><identifier>EISSN: 1520-5126</identifier><identifier>DOI: 10.1021/ja1023767</identifier><identifier>PMID: 20839862</identifier><language>eng</language><publisher>United States: American Chemical Society</publisher><subject>Catalysis ; Cobalt - chemistry ; Electrochemistry ; Membranes, Artificial ; Molecular Structure ; Oxidation-Reduction ; Phosphates - chemistry ; Surface Properties ; Water - chemistry ; X-Ray Absorption Spectroscopy</subject><ispartof>Journal of the American Chemical Society, 2010-10, Vol.132 (39), p.13692-13701</ispartof><rights>Copyright © 2010 American Chemical Society</rights><lds50>peer_reviewed</lds50><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-a380t-c6eba04dfc06563e92d4375e5dcf111637b9a550885e97333a9087e92d33742a3</citedby><cites>FETCH-LOGICAL-a380t-c6eba04dfc06563e92d4375e5dcf111637b9a550885e97333a9087e92d33742a3</cites></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><linktopdf>$$Uhttps://pubs.acs.org/doi/pdf/10.1021/ja1023767$$EPDF$$P50$$Gacs$$H</linktopdf><linktohtml>$$Uhttps://pubs.acs.org/doi/10.1021/ja1023767$$EHTML$$P50$$Gacs$$H</linktohtml><link.rule.ids>314,780,784,2765,27076,27924,27925,56738,56788</link.rule.ids><backlink>$$Uhttps://www.ncbi.nlm.nih.gov/pubmed/20839862$$D View this record in MEDLINE/PubMed$$Hfree_for_read</backlink></links><search><creatorcontrib>Kanan, Matthew W.</creatorcontrib><creatorcontrib>Yano, Junko</creatorcontrib><creatorcontrib>Surendranath, Yogesh</creatorcontrib><creatorcontrib>Dincă, Mircea</creatorcontrib><creatorcontrib>Yachandra, Vittal K.</creatorcontrib><creatorcontrib>Nocera, Daniel G.</creatorcontrib><title>Structure and Valency of a Cobalt−Phosphate Water Oxidation Catalyst Determined by in Situ X-ray Spectroscopy</title><title>Journal of the American Chemical Society</title><addtitle>J. Am. Chem. Soc</addtitle><description>A water oxidation catalyst generated via electrodeposition from aqueous solutions containing phosphate and Co2+ (Co−Pi) has been studied by in situ X-ray absorption spectroscopy. Spectra were obtained for Co−Pi films of two different thicknesses at an applied potential supporting water oxidation catalysis and at open circuit. Extended X-ray absorption fine structure (EXAFS) spectra indicate the presence of bis-oxo/hydroxo-bridged Co subunits incorporated into higher nuclearity clusters in Co−Pi. The average cluster nuclearity is greater in a relatively thick film (∼40−50 nmol Co ions/cm2) deposited at 1.25 V vs NHE than in an extremely thin film (∼3 nmol Co ions/cm2) deposited at 1.1 V. X-ray absorption near edge structure (XANES) spectra and electrochemical data support a Co valency greater than 3 for both Co−Pi samples when catalyzing water oxidation at 1.25 V. Upon switching to open circuit, Co−Pi undergoes a continuous reduction due to residual water oxidation catalysis, as indicated by the negative shift of the edge energy. The rate of reduction depends on the average cluster size. On the basis of structural parameters extracted from fits to the EXAFS data of Co−Pi with two different thicknesses and comparisons with EXAFS spectra of Co oxide compounds, a model is proposed wherein the Co oxo/hydroxo clusters of Co−Pi are composed of edge-sharing CoO6 octahedra, the structural motif found in cobaltates. Whereas cobaltates contain extended planes of CoO6 octahedra, the Co−Pi clusters are of molecular dimensions.</description><subject>Catalysis</subject><subject>Cobalt - chemistry</subject><subject>Electrochemistry</subject><subject>Membranes, Artificial</subject><subject>Molecular Structure</subject><subject>Oxidation-Reduction</subject><subject>Phosphates - chemistry</subject><subject>Surface Properties</subject><subject>Water - chemistry</subject><subject>X-Ray Absorption Spectroscopy</subject><issn>0002-7863</issn><issn>1520-5126</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2010</creationdate><recordtype>article</recordtype><sourceid>EIF</sourceid><recordid>eNptkMtKxDAUhoMoOl4WvoBkI-KimsskaZcyXkFQGG-7cpqmTIdOU5MU7Bu49hF9EjOMzsrNORzOx885H0KHlJxRwuj5HGLjSqoNNKKCkURQJjfRiBDCEpVKvoN2vZ_HccxSuo12GEl5lko2QnYaXK9D7wyGtsQv0JhWD9hWGPDEFtCE78-vx5n13QyCwa-xOPzwUZcQatviCQRoBh_wpYmLRd2aEhcDrls8rUOP3xIHA552RgdnvbbdsI-2Kmi8Ofjte-j5-uppcpvcP9zcTS7uE-ApCYmWpgAyLitNpJDcZKwccyWMKHVFKZVcFRkIQdJUmExxziEjqVpinKsxA76HTla5nbPvvfEhX9Rem6aB1tje50pIlkU1KpKnK1LHE70zVd65egFuyCnJl3rztd7IHv2m9sXClGvyz2cEjlcAaJ_Pbe_a-OQ_QT_cJYFv</recordid><startdate>20101006</startdate><enddate>20101006</enddate><creator>Kanan, Matthew W.</creator><creator>Yano, Junko</creator><creator>Surendranath, Yogesh</creator><creator>Dincă, Mircea</creator><creator>Yachandra, Vittal K.</creator><creator>Nocera, Daniel G.</creator><general>American Chemical Society</general><scope>CGR</scope><scope>CUY</scope><scope>CVF</scope><scope>ECM</scope><scope>EIF</scope><scope>NPM</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7X8</scope></search><sort><creationdate>20101006</creationdate><title>Structure and Valency of a Cobalt−Phosphate Water Oxidation Catalyst Determined by in Situ X-ray Spectroscopy</title><author>Kanan, Matthew W. ; Yano, Junko ; Surendranath, Yogesh ; Dincă, Mircea ; Yachandra, Vittal K. ; Nocera, Daniel G.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-a380t-c6eba04dfc06563e92d4375e5dcf111637b9a550885e97333a9087e92d33742a3</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2010</creationdate><topic>Catalysis</topic><topic>Cobalt - chemistry</topic><topic>Electrochemistry</topic><topic>Membranes, Artificial</topic><topic>Molecular Structure</topic><topic>Oxidation-Reduction</topic><topic>Phosphates - chemistry</topic><topic>Surface Properties</topic><topic>Water - chemistry</topic><topic>X-Ray Absorption Spectroscopy</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Kanan, Matthew W.</creatorcontrib><creatorcontrib>Yano, Junko</creatorcontrib><creatorcontrib>Surendranath, Yogesh</creatorcontrib><creatorcontrib>Dincă, Mircea</creatorcontrib><creatorcontrib>Yachandra, Vittal K.</creatorcontrib><creatorcontrib>Nocera, Daniel G.</creatorcontrib><collection>Medline</collection><collection>MEDLINE</collection><collection>MEDLINE (Ovid)</collection><collection>MEDLINE</collection><collection>MEDLINE</collection><collection>PubMed</collection><collection>CrossRef</collection><collection>MEDLINE - Academic</collection><jtitle>Journal of the American Chemical Society</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Kanan, Matthew W.</au><au>Yano, Junko</au><au>Surendranath, Yogesh</au><au>Dincă, Mircea</au><au>Yachandra, Vittal K.</au><au>Nocera, Daniel G.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Structure and Valency of a Cobalt−Phosphate Water Oxidation Catalyst Determined by in Situ X-ray Spectroscopy</atitle><jtitle>Journal of the American Chemical Society</jtitle><addtitle>J. Am. Chem. Soc</addtitle><date>2010-10-06</date><risdate>2010</risdate><volume>132</volume><issue>39</issue><spage>13692</spage><epage>13701</epage><pages>13692-13701</pages><issn>0002-7863</issn><eissn>1520-5126</eissn><abstract>A water oxidation catalyst generated via electrodeposition from aqueous solutions containing phosphate and Co2+ (Co−Pi) has been studied by in situ X-ray absorption spectroscopy. Spectra were obtained for Co−Pi films of two different thicknesses at an applied potential supporting water oxidation catalysis and at open circuit. Extended X-ray absorption fine structure (EXAFS) spectra indicate the presence of bis-oxo/hydroxo-bridged Co subunits incorporated into higher nuclearity clusters in Co−Pi. The average cluster nuclearity is greater in a relatively thick film (∼40−50 nmol Co ions/cm2) deposited at 1.25 V vs NHE than in an extremely thin film (∼3 nmol Co ions/cm2) deposited at 1.1 V. X-ray absorption near edge structure (XANES) spectra and electrochemical data support a Co valency greater than 3 for both Co−Pi samples when catalyzing water oxidation at 1.25 V. Upon switching to open circuit, Co−Pi undergoes a continuous reduction due to residual water oxidation catalysis, as indicated by the negative shift of the edge energy. The rate of reduction depends on the average cluster size. On the basis of structural parameters extracted from fits to the EXAFS data of Co−Pi with two different thicknesses and comparisons with EXAFS spectra of Co oxide compounds, a model is proposed wherein the Co oxo/hydroxo clusters of Co−Pi are composed of edge-sharing CoO6 octahedra, the structural motif found in cobaltates. Whereas cobaltates contain extended planes of CoO6 octahedra, the Co−Pi clusters are of molecular dimensions.</abstract><cop>United States</cop><pub>American Chemical Society</pub><pmid>20839862</pmid><doi>10.1021/ja1023767</doi><tpages>10</tpages></addata></record> |
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subjects | Catalysis Cobalt - chemistry Electrochemistry Membranes, Artificial Molecular Structure Oxidation-Reduction Phosphates - chemistry Surface Properties Water - chemistry X-Ray Absorption Spectroscopy |
title | Structure and Valency of a Cobalt−Phosphate Water Oxidation Catalyst Determined by in Situ X-ray Spectroscopy |
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