Electrodeposition of bismuth nanoclusters using deep eutectic solvent for electroreduction of carbon dioxide to formic acid

Electrochemical carbon dioxide reduction reaction (eCO₂RR) to value-added chemicals has been widely considered as a promising route to achieve carbon neutrality. However, its efficiency and selectivity are strongly governed by catalyst structure and surface chemistry. In this work, bismuth (Bi) nanoclusters were electrodeposited using choline chloride–glycerol deep eutectic solvents (DES) with different molar ratios to regulate nucleation behavior and tailor electrocatalytic performance. Here, it was found that variations in DES composition markedly influenced deposition kinetics, estimated Bi loading, crystallographic orientation, and surface morphology. While electrode deposited with DES at a 1:1 ratio promoted higher conductivity, faster nucleation, and improved activity, as evidenced by more positive onset potentials and lower overpotentials, electrode deposited with glycerol-rich DES (1:4 M ratio) favored enhanced selectivity toward formic acid, with a Faradaic efficiency (FE) of 70.11%. Density functional theory (DFT) calculations revealed that slowly formed low-density Bi nanoclusters exhibited more favorable adsorption energetics and reaction pathways for formic acid formation than larger clusters generated under rapid nucleation conditions.