Co-regulation of intermediate binding and water activation in sulfur-doped bismuth nanosheets for electrocatalytic CO2 reduction to formate

Electrochemical reduction CO2 to formate is highly desirable but promoting the stability, selectivity and current density still remains demanding. Here, Bi-S catalysts were prepared through in-situ electrochemical topotactic transformation. The Bi-S2 catalyst displays peak formate faradaic efficiency of 96.7 % at -0.9 V, high formate faradaic efficiency (>93 %) from -0.7 V to -1.1 V and durable stability of 35 h. A better formate faradaic efficiency (-97.8 % at -0.9 V) and formate partial current density (-182.1 mA cm-2) are achieved in a flow cell. The electrochemical measurement, coupled with In-situ FTIR and sulfur blocking method, reveal that the sulfur doping achieves co-regulation of intermediate binding and water activation. The energetically favourable HCOO* pathway and facilitated water activation promote the proton-coupled electron transfer process toward formate production. This work offers new insight for rational design of high-performance electrodes for CO2RR.