Electrosynthesis of Concentrated Formate as a Direct Liquid Fuel from a Bicarbonate Feedstock

Electrochemical CO 2 reduction into liquid fuels is promising for carbon recycling when integrated with carbon capture and fuel cell applications. Direct bicarbonate-to-formate conversion provides a seamless route to power direct formate fuel cells (DFFCs) as renewable energy storage systems. Here, we demonstrate proton exchange membrane (PEM) electrolyzers with 25 cm 2 electrodes that convert in situ-generated CO 2 ( i -CO 2 ) to potassium formate solution at 200 mA cm –2, achieving 83% Faradaic efficiency and 92% i -CO 2 utilization efficiency. Replacing the anodic reaction from oxygen evolution to hydrogen oxidation enabled the production of 3.0 M formate from a model capture solution (3.0 M KHCO 3 ) in ∼4 h owing to the suppression of the crossover dilution. The resulting liquid fuel delivered a peak power density of 90.3 mW cm –2 in a DFFC operated at 80 °C, highlighting its potential for long-term energy storage.