Interfacial engineering of bismuth sulfide/oxychloride heterostructure for boosting the conversion from CO2 to formate at large current densities

•Bi2S3-BiOCl heterojunctions for electrocatalytic CO2RR is in-depth studied through experimentally and theoretically.•The formate selectivity of heterojuction reaches to 97.2 % at a high current density of 300 mA cm−2.•The in situ Raman studies indicate that the BiOCl can be converted to metallic Bi during catalytic process. Electrochemical reduction of CO2 into green fuels is considered as a promising strategy to achieve carbon neutrality and has received increasing attentions. Herein, bismuth sulfide-bismuth oxychloride heterojunctions (Bi2S3-BiOCl) with abundant hetero-interface are rational synthesized and used as electrocatalysts for CO2 reduction reaction. The high formate selectivity of 97.2% at large current density of 300 mA cm−2 can be easily achieved. The in situ Raman spectroscopy and ex situ characterizations indicate that BiOCl converts to metallic Bi at negative potential to form a Bi2S3-Bi heterojunction. Based on the theoretical calculations, Bi2S3-Bi shows increasing density of states around the Fermi level and decreased energy barrier for CO2 conversion, and eventually promots electrocatalytic CO2 reduction reaction. This work not only provides an in-depth study of the application of Bi-involved heterojunctions for CO2 conversion, but also proposes a new strategy for the development of efficient catalysts for industrial-level CO2 conversion.