Synergetic of Built-In Electric Field and Sulfur Defects in Co@Co 9 S 8 Mott-Schottky To Achieve High-Efficiency Zinc-Air Battery Performance.

The slow kinetics of the bifunctional (OER/ORR) oxygen electrocatalyst is the bottleneck problem restricting the performance of zinc-air batteries (ZABs). The design and synthesis of an efficient and stable electrocatalyst at the air cathode to improve the performance of ZABs is of great significance for the development of sustainable energy conversion devices. Herein, we have developed a sulfur vacancy-rich Mott-Schottky catalyst (Co@Co 9 S 8 -NCNT), which shows superior ORR/OER bifunctional electrochemical activity and stability. Specifically, the OER overpotential is only 210 mV at 10 mA cm -2 , and the half-wave potential ( E 1/2 ) of ORR is up to 0.88 V. Furthermore, a ZAB has been assembled using the Co@Co 9 S 8 -NCNT, which delivers a high power density (196.7 mW cm -2 ) and an open-circuit voltage (1.501 V), showing excellent battery performance. Density functional theory calculations demonstrate that the Co@Co 9 S 8 Mott-Schottky heterojunction and S vacancy defects are beneficial to elevate the d-band central energy level to the Fermi level, significantly enhancing the adsorption/desorption capacity of oxygen-containing intermediates, thereby effectively improving the OER activity. Moreover, the N-doped carbon nanotubes can promote the continuous electron transfer between the metal and semiconductor interface. This work proposes a valid method for the construction and structural regulation of Mott-Schottky catalysts and offers new insights into the development of catalytic materials for energy conversion equipment.