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Correlations among Structure, Electronic Properties, and Photochemical Water Oxidation: A Case Study on Lithium Cobalt Oxides


Liu, Hongfei; Zhou, Ying; Moré, René; Müller, Rafael; Fox, Thomas; Patzke, Greta R (2015). Correlations among Structure, Electronic Properties, and Photochemical Water Oxidation: A Case Study on Lithium Cobalt Oxides. ACS Catalysis, 5(6):3791-3800.

Abstract

Construction of {M4O4} motifs is an effective design paradigm for molecular polyoxometalate- and oxide-based water oxidation catalysts (WOCs). However, the mechanisms beneath this bioinspired design strategy remain a topic of intense debate. The two modifications of LiCoO2 with spinel-type and layer structures are exceptionally versatile model systems to explore the correlations among structure, electronic properties, and photochemical water oxidation. The electronic properties of both LiCoO2 modifications are tunable through delithiation while the basic structural frameworks are maintained. This provides a unique opportunity to assign the respective influence of structures and electronic properties on the water oxidation properties. While spinel-type LiCoO2 with {Co4O4} cubane motifs is active for photochemical water oxidation, the layered modification without cuboidal structural elements is nearly inactive. Here, we demonstrate that the water oxidation performance of both modifications can be significantly improved through chemical delithiation. A wide range of analytical methods were applied to investigate the transition of electronic properties upon delithiation, and a direct correlation between enhanced hole mobility and improved water oxidation activity was established. The difference in water oxidation activities between the two structural modifications was further linked to the role of {Co4O4} cubane motifs in constructing 3D Co–O–Co networks with expanded hole transfer paths. Thus, the promoting effects of both delithiation and {Co4O4} cubane motifs on water oxidation can be consistently explained by enhanced hole mobility.

Abstract

Construction of {M4O4} motifs is an effective design paradigm for molecular polyoxometalate- and oxide-based water oxidation catalysts (WOCs). However, the mechanisms beneath this bioinspired design strategy remain a topic of intense debate. The two modifications of LiCoO2 with spinel-type and layer structures are exceptionally versatile model systems to explore the correlations among structure, electronic properties, and photochemical water oxidation. The electronic properties of both LiCoO2 modifications are tunable through delithiation while the basic structural frameworks are maintained. This provides a unique opportunity to assign the respective influence of structures and electronic properties on the water oxidation properties. While spinel-type LiCoO2 with {Co4O4} cubane motifs is active for photochemical water oxidation, the layered modification without cuboidal structural elements is nearly inactive. Here, we demonstrate that the water oxidation performance of both modifications can be significantly improved through chemical delithiation. A wide range of analytical methods were applied to investigate the transition of electronic properties upon delithiation, and a direct correlation between enhanced hole mobility and improved water oxidation activity was established. The difference in water oxidation activities between the two structural modifications was further linked to the role of {Co4O4} cubane motifs in constructing 3D Co–O–Co networks with expanded hole transfer paths. Thus, the promoting effects of both delithiation and {Co4O4} cubane motifs on water oxidation can be consistently explained by enhanced hole mobility.

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Additional indexing

Item Type:Journal Article, not refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:5 June 2015
Deposited On:18 Jan 2016 15:57
Last Modified:27 May 2017 07:21
Publisher:American Chemical Society (ACS)
ISSN:2155-5435
Publisher DOI:https://doi.org/10.1021/acscatal.5b00078

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