Nanoporous bismuth for the electrocatalytic reduction of CO₂ to formate

Bi is an attractive catalyst towards the electrochemical reduction of CO₂ to formate. In this work, nanoporous bismuth was prepared by dealloying Mg₃Bi₂ with tartaric acid (TA) solution, and the size of the primary Bi nanoparticles was adjusted according to the concentration of TA. When the concentration of TA increased from 2 wt% to 20 wt%, the particle size of Bi increased from about 70 nm to 400 nm. The synthesized nanoporous Bi samples were investigated as electrocatalysts for the reduction of CO₂ in KHCO₃ electrolyte, and it was found that the smaller the particle size, the higher the catalytic activity. However, nanoporous Bi comprising 70 nm particles suffered from mass transfer difficulty and sintering during the reaction, whereas the 100 nm nanoporous Bi delivered both a high formate formation current and faradaic efficiency (FE) (16 mA cm^-2, FE > 90% at -0.88 V vs. RHE) and showed excellent durability.