Optimizing d-Orbital Electronic Configuration via Metal-Metal Oxide Core-Shell Charge Donation for Boosting Reversible Oxygen Electrocatalysis.

Tuning the d-orbital electronic configuration of active sites to achieve well-optimized adsorption strength of oxygen-containing intermediates toward reversible oxygen electrocatalysis is desirable for efficient rechargeable Zn-Air batteries but extremely challenging. Herein, this work proposes to construct a Co@Co 3 O 4 core-shell structure to regulate the d-orbital electronic configuration of Co 3 O 4 for the enhanced bifunctional oxygen electrocatalysis. Theoretical calculations first evidence that electron donation from Co core to Co 3 O 4 shell could downshift the d-band center and simultaneously weak spin state of Co 3 O 4 , result in the well-optimized adsorption strength of oxygen-containing intermediates on Co 3 O 4 , thus contributing a favor way for oxygen reduction/evolution reaction (ORR/OER) bifunctional catalysis. As a proof-of-concept, the Co@Co 3 O 4 embedded in Co, N co-doped porous carbon derived from thickness controlled 2D metal-organic-framework is designed to realize the structure of computational prediction and further improve the performance. The optimized 15Co@Co 3 O 4 /PNC catalyst exhibits the superior bifunctional oxygen electrocatalytic activity with a small potential gap of 0.69 V and a peak power density of 158.5 mW cm -2 in ZABs. Moreover, DFT calculations shows that the more oxygen vacancies on Co 3 O 4 contribute too strong adsorption of oxygen intermediates which limit the bifunctional electrocatalysis, while electron donation in the core-shell structure can alleviate the negative effect and maintain superior bifunctional overpotential.