Enhancing bifunctional oxygen electrocatalysis with in-situ etching of oxide overlayers on sulfur-vacancy enriched CuCo2O4/CuCo2S4

Transition metal sulfide (TMS) are considered promising alternatives to noble metals for high-efficiency oxygen reduction and oxygen evolution (ORR/OER). However, traditional preparation methods or post-treatment processes can lead to the formation of oxide overlayers on the TMS catalysts, which can hinder their electrochemical performance. Herein, a sulfur-vacancy enriched CuCo 2 O 4 /CuCo 2 S 4 heterostructure was prepared using cold plasma. Plasma also achieved the in-situ etching of oxide overlayers on the surface of catalysts. There is a strong correlation between the oxide overlayers and ORR/OER activity. Specifically, the number of ORR electrons transferred increased (n: from 2.8 to 3.7), while the OER overpotential decreased ( η : from 417 to 330 mV) in 0.1 M KOH with the decrease of the oxide overlayer concentration ( SO 4 2 − / S M − S ${\mathrm{SO}}_4^{2-}/{\mathrm{S}}_{\mathrm{M}-\mathrm{S}}$ : from 1.795 to 0.798). The theoretical calculation reveals the influence of oxide overlayers and S vacancy on the binding energy of the intermediate. The findings suggest that this work provides a new idea for designing metal sulfide electrochemical catalyst.