Electrocatalytic carbon dioxide conversion to formate using gas-diffusion electrodes with group 12–15 metals

The group 12−15 metals of the periodic table are considered promising catalysts for the electrochemical conversion of CO₂ to formate. The activities of these metals are estimated and compared using bulk metals (i.e., metal plates) in conventional aqueous CO₂ electrolysis systems. Herein, five group 12–15 metals (Cd, In, Sn, Pb, and Bi) in the particulate form are hydrothermally synthesized, and their catalytic activities in formate production are examined in the gas-diffusion electrode device with continuous CO₂ supply, with catalyst mass loading and applied current density as independent variables. The faradic efficiency values lower than 80% are obtained for Pb and Cd regardless of the experimental conditions. By contrast, In, Sn, and Bi show the relatively reliable faradaic efficiency values of >80% and cathodic energy efficiency values of >45% at cathodic J of 100−300 mA cm⁻² (hence partial current density for formate, J_FM ∼250 mA cm⁻²). Surface characterization reveals the crystalline structures of BiOCl, Cd(OH)₂, In(OH)₃, PbO, and SnO₂. Among the metals, Sn is further modified under a reductive atmosphere to increase its energy efficiency. The figures of merit (faradaic efficiency, current, and cathodic energy efficiency) for the modified Sn are marginally higher than those for the other Sn types.