Reinforce the Co-O Covalency via Ce(4f)-O(2p)-Co(3d) Gradient Orbital Coupling for High-efficiency Oxygen Evolution.

Abstract

Rare-earth (RE)-based transition metal oxides (TMO) are emerging as a frontier towards oxygen evolution reaction (OER), yet the knowledge regarding their electrocatalytic mechanism and active sites is very limited. Herein, we successfully design and synthesize atomically dispersed Ce on CoO 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 261mV at 10mA cm-2 and robust electrochemical stability, superior to individual CoO. X-ray absorption spectroscopy and in-situ electrochemical Raman spectroscopy uncover that the Ce-induced electron redistribution inhibits Co-O bond breakage in the Co-O-Ce unit site. Theoretical analyses demonstrate that the gradient orbital coupling reinforces the Co-O covalency of 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. We believe the establishment of this Ce-CoO model can set a basis for the mechanistic understanding and structural design of high-performance RE-TMO catalysts. This article is protected by copyright. All rights reserved.