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 CO 2 electrolyzer and a formate fuel cell is a new option for carbon‐neutral energy storage but entails rapid, reversible and stable interconversion between CO 2 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 CO 2 ‐to‐formate conversion over a wide potential range; under anodic conditions, it becomes relatively Pd‐rich and gains stable catalytic activity for formate‐to‐CO 2 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 CO 2 electrolyzer/formate fuel cell modes and can stably operate for 12 days.