Coupling In nanoclusters and Bi nanoparticles in nitrogen-doped carbon for enhanced CO2 electroreduction to HCOOH

CO₂ electrochemical reduction reaction (CO₂RR) to formic acid (HCOOH) is beneficial for the recycling of carbon resources, which needs the highly selective catalysts with long-term stability for HCOOH production. In this study, the coupling of In nanoclusters (In_clus) and Bi nanoparticles (Bi_nps) in nitrogen-doped carbon was designed by the thermal decomposition of the mixture of bimetallic MOFs and dicyanamide. When the In/Bi molar ratio was 1:2 (In_clus/Bi_nps-1:2), the hybrid catalyst achieved a HCOOH Faradaic efficiency (FE_HCOOH) of 94.5 % at −1.1 V vs reversible hydrogen electrode (RHE) in an H-type electrolysis cell, superior to that of single metal counterparts. Moreover, the In_clus/Bi_nps-1:2 can maintain high stability of structures during the catalytic process, leading to no significant decay of FE_HCOOH over 32 h. The enhanced performance of In_clus/Bi_nps-1:2 is attributed to the strong electron interactions induced by the charge transfer between the In and Bi sites in In_clus/Bi_nps-1:2 catalyst. The tuned electronic structure results in an offset effect that optimizes the binding energy to HCOO* intermediate, thus accelerating the CO₂ to HCOOH conversion, as proven by the in-situ ATR-SEIRAS and density functional theory (DFT) calculations.