Rare-earth (RE)-based transition metal oxides (TMO) are emerging as a frontier toward the oxygen evolution reaction (OER), yet the knowledge regarding their electrocatalytic mechanism and active sites is very limited. In this work, atomically dispersed Ce on CoO is successfully designed and synthesized by an effective plasma (P)-assisted strategy as a model (P-Ce SAs@CoO) to investigate the origin of OER performance in RE-TMO systems. The P-Ce SAs@CoO exhibits favorable performance with an overpotential of only 261 mV at 10 mA cm-2 and robust electrochemical stability, superior to individual CoO. X-ray absorption spectroscopy and in situ electrochemical Raman spectroscopy reveal that the Ce-induced electron redistribution inhibits CoO bond breakage in the CoOCe unit site. Theoretical analysis demonstrates that the gradient orbital coupling reinforces the CoO covalency of the Ce(4f)─O(2p)─Co(3d) unit active site with an optimized Co-3d-eg occupancy, which can balance the adsorption strength of intermediates and in turn reach the apex of the theoretical OER maximum, in excellent agreement with experimental observations. It is believed that the establishment of this Ce-CoO model can set a basis for the mechanistic understanding and structural design of high-performance RE-TMO catalysts.
Keywords: 4f buffer bands; Ce─O─Co unit site; Co─O covalency; gradient orbital coupling; oxygen evolution.
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