In situ/operando soft x-ray spectroscopic identification of a Co4+ intermediate in the oxygen evolution reaction of defective Co3O4 nanosheets

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Title:	In situ/operando soft x-ray spectroscopic identification of a Co4+ intermediate in the oxygen evolution reaction of defective Co3O4 nanosheets
Authors:	Dong, Chung-li
Date:	2022-09
Issue Date:	2023-05-15 12:09:57 (UTC+8)
Abstract:	Defect engineering is an important means of improving the electrochemical performance of the Co3O4 electrocatalyst in the oxygen evolution reaction (OER). In this study, operando soft X-ray absorption spectroscopy (SXAS) is used to explore the electronic structure of Co3O4 under OER for the first time. The defect-rich Co3O4 (D-Co3O4) has a Co2.45+ state with Co2+ at both octahedral (Oh) and tetrahedral (Td) sites and Co3+ at Oh, whereas Co3O4 has Co2.6+ with Co2+ and Co3+ at Td and Oh sites, respectively. SXAS reveals that upon increasing the voltage, the Co2+ in D-Co3O4 is converted to low-spin Co3+, some of which is further converted to low-spin Co4+; most Co2+ in Co3O4 is converted to Co3+ but rarely to Co4+. When the voltage is switched off, Co4+ intermediates quickly disappear. These findings reveal Co(Oh) in D-Co3O4 can be rapidly converted to active low-spin Co4+ under operando conditions, which cannot be observed by ex situ XAS.
Relation:	Journal of Physical Chemistry Letters 13(35), p.8386–8396
DOI:	10.1021/acs.jpclett.2c01557
Appears in Collections:	[Graduate Institute & Department of Electrical Engineering] Journal Article

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