Ion‐Enhanced Conversion of CO2 into Formate on Porous Dendritic Bismuth Electrodes with High Efficiency and Durability

Abstract Facile synthesis of efficient electrocatalysts that can selectively convert CO2 to value‐added chemicals remains a challenge. Herein, the electrochemical synthesis of porous Bi dendrite electrodes and details of their activity toward CO2 conversion to formate in aqueous solutions of bicarbonate are presented. The as‐synthesized multilayered, porous, dendritic Bi electrodes exhibit a faradaic efficiency (FE) of approximately 100 % for formate production. Added halides and cations significantly influence the steady‐state partial current density for formate production JFM (Cl−>Br−≈I−; Cs+>K+>Li+). DFT calculations revealed that the reaction pathway involving the species *OCOH occurs predominantly and the presence of both Cs+ and Cl− makes the overall reaction more spontaneous. Photovoltaic‐cell‐assisted electrocatalysis produced formate with an FE of approximately 95 % (JFM≈10 mA cm−2) at an overall solar conversion efficiency of approximately 8.5 %. The Bi electrodes maintain their activity for 360 h without a change in the surface states.