Electronic Microenvironment Regulation of Bismuth-salophen Single-site Catalysts for Enhanced Selectivity in CO2 Electrolysis to Formic Acid

Electrocatalytic CO₂ reduction reactions (CO₂RR) hold significant industrial potential, with Bi-based catalysts demonstrating notable advantages in promoting the formation of formic acid (HCOOH). Despite progress, developing selective and efficient catalysts for CO₂RR remains challenging. In this study, Bi single-site catalysts (SSCs) is designed modified with various electronegative groups (─F, ─H, and ─OMe (─OCH₃)) to improve the CO₂RR selectivity of Bi through atomic-level microenvironment tuning. Among these, ─F group-modulated Bi-Sal-F catalyst exhibited a high Faradaic efficiency (FE) of 95% for HCOOH within the current density range of −0.1 to −0.5 A cm⁻². In contrast, the microenvironment modification with the neutral ─H group and the electron-donating ─OMe group both led to decreased HCOOH selectivity and promoted HER. Combined with theoretical calculations, this is revealed that the microenvironment regulated by the ─F group strongly correlates with the catalytic activity of the metal center. By reducing the band gap and electron density of Bi, this microenvironment enhances the Bi center's ability to adsorb CO₂ via oxygen-coordinated, while effectively lowering the activation barrier for intermediate formation during CO₂RR, thus promoting high selectivity for HCOOH production. This finding provides valuable theoretical insights and holds great potential for the design of highly efficient SSCs with microenvironment control.