Influence of the Chemical Compositions of Bismuth Oxyiodides on the Electroreduction of Carbon Dioxide to Formate

Bismuth oxyiodides with varying chemical compositions were fabricated to effectively electrochemical reduce CO₂ to formate. Bi₅O₇I and Bi₇O₉I₃ nanosheets assemble irregularly, and BiOI nanosheets form a sphere-like structure. Compared with BiOI and Bi₇O₉I₃, Bi₅O₇I exhibits an excellent Faradaic efficiency of 89 % for formate production with the partial current density of 13.2 mA/cm² at −0.89 V vs. RHE owing to the elevated amounts of Bi metal sites reduced from Bi³⁺ during electrolysis. The partial current densities of formate on BiOI were higher than those on Bi₇O₉I₃ which is attributed to the higher iodine content. The synergistic effect of bismuth and iodine of bismuth oxyiodides is responsible for their electrocatalytic properties during CO₂ reduction in aqueous solutions.