Reinforcing CoO Covalency via Ce(4f)─O(2p)─Co(3d) Gradient Orbital Coupling for High‐Efficiency Oxygen Evolution

• Published in: Advanced materials (Weinheim) Vol. 35; no. 30; pp. e2302462 - n/a
• Main Authors: Li, Meng, Wang, Xuan, Liu, Kun, Sun, Huamei, Sun, Dongmei, Huang, Kai, Tang, Yawen, Xing, Wei, Li, Hao, Fu, Gengtao
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.07.2023
• Subjects: 4f buffer bands; Absorption spectroscopy; Ce─O─Co unit site; Coupling; Co─O covalency; gradient orbital coupling; oxygen evolution; Oxygen evolution reactions; Raman spectroscopy; Spectrum analysis; Structural design; Transition metal oxides; Ce─O─Co unit site; gradient orbital coupling; Co─O covalency; 4f buffer bands; oxygen evolution
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202302462

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 CoO bond breakage in the CoOCe unit site. Theoretical analysis demonstrates that the gradient orbital coupling reinforces the CoO 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. Atomically dispersed Ce on CoO is prepared as a model to identify the active sites of rare‐earth‐based transition metal oxides toward oxygen evolution reaction (OER) and the corresponding catalytic mechanism is elucidated. The CeOCo unit site is identified as the active center. The enhanced OER performance is ascribed to reinforce CoO covalency through Ce(4f)─O(2p)─Co(3d) gradient orbital coupling.