Controlled synthesis of hierarchical Bi nanostructures by electrodeposition for selective electroreduction of CO₂ to formate

The electrocatalytic conversion of CO₂ into formate represents a promising strategy for carbon-neutral energy cycles. Critical to this process is the controlled synthesis of highly active and selective catalysts, enabling sustained high energy efficiency under industrially relevant conditions. Herein, a facile electrodeposition method was developed to synthesize nanostructured Bi catalysts with a precisely controlled morphology directly on carbon fiber paper (CFP) substrates. Through the systematic modulation of depositing current density to regulate Bi electrodeposition kinetics, Bi hierarchical hexagonal nanosheets (HSs) were synthesized, demonstrating remarkable CO₂RR activity and selectivity with a FE_formate of 97.2% at -1.1 V <i>versus</i> reversible hydrogen electrode (RHE). Operando Fourier-transform infrared (FT-IR) spectroscopy analysis revealed that the abundant active sites of the Bi HSs significantly enhanced CO₂ adsorption and stabilized the HCOO* intermediate. To address the mass transfer limitations, a gas-diffusion electrode (GDE) architecture was constructed with Bi HSs to achieve sustained formate production with 90.6% faradaic efficiency at -150 mA cm^-2. This study establishes a morphology-controlled synthesis protocol for p-block metal catalysts, offering new insights into the rational design of efficient CO₂RR electrocatalysts for formate electrosynthesis.