An Integrated CO2 Electrolyzer and Formate Fuel Cell Enabled by a Reversibly Restructuring Pb–Pd Bimetallic Catalyst

A single device combining the functions of a CO2 electrolyzer and a formate fuel cell is a new option for carbon‐neutral energy storage but entails rapid, reversible and stable interconversion between CO2 and formate over a single catalyst electrode. We report a new catalyst with such functionalities based on a Pb–Pd alloy system that reversibly restructures its phase, composition, and morphology and thus alters its catalytic properties under controlled electrochemical conditions. Under cathodic conditions, the catalyst is relatively Pb‐rich and is active for CO2‐to‐formate conversion over a wide potential range; under anodic conditions, it becomes relatively Pd‐rich and gains stable catalytic activity for formate‐to‐CO2 conversion. The bifunctional activity and superior durability of our Pb–Pd catalyst leads to the first proof‐of‐concept demonstration of an electrochemical cell that can switch between the CO2 electrolyzer/formate fuel cell modes and can stably operate for 12 days. A lead–palladium alloy catalyst that reversibly changes its composition and function under electrochemically reducing versus oxidizing conditions is reported. Its bifunctional activity and superior durability enable a proof‐of‐concept electrochemical device integrating the functions of a carbon dioxide electrolyzer and a formate fuel cell.