pH-Universal Electrocatalytic CO2 Reduction with Ampere-Level Current Density on Doping-Engineered Bismuth Sulfide

Abstract

The practical application of the electrocatalytic CO₂ reduction reaction (CO₂RR) to form formic acid fuel is hindered by the limited activation of CO₂ molecules and the lack of universal feasibility across different pH levels. Herein, we report a doping-engineered bismuth sulfide pre-catalyst (BiS-1) that S is partially retained after electrochemical reconstruction into metallic Bi for CO₂RR to formate/formic acid with ultrahigh performance across a wide pH range. The best BiS-1 maintains a Faraday efficiency (FE) of ~95 % at 2000 mA cm⁻² in a flow cell under neutral and alkaline solutions. Furthermore, the BiS-1 catalyst shows unprecedentedly high FE (~95 %) with current densities from 100 to 1300 mA cm⁻² under acidic solutions. Notably, the current density can reach 700 mA cm⁻² while maintaining a FE of above 90 % in a membrane electrode assembly electrolyzer and operate stably for 150 h at 200 mA cm⁻². In situ spectra and density functional theory calculations reveals that the S doping modulates the electronic structure of Bi and effectively promotes the formation of the HCOO* intermediate for formate/formic acid generation. This work develops the efficient and stable electrocatalysts for sustainable formate/formic acid production.