Soluble-Salt-Induced Embedding of Metal Catalysts into Gas Diffusion Electrodes for Electrochemical CO ₂ Reduction to Formate

Electrochemical CO2 reduction to formic acid (HCOOH) has great potential for reducing the carbon footprint and producing liquid fuel. Although several p-block metals have been recognized to be formate-selective, the flooding of catholytes into the catalyst layer at high current densities significantly promotes the competing hydrogen evolution reaction (HER), compromising the efficiency. Here, we report a soluble-salt-inducing fabrication method to disperse formate-selective metals into the carbon matrix of gas diffusion electrodes, in contrast to the conventional surface-supported architectures. This deep metal infiltration effectively suppresses HER under flooding conditions, enabling high formate Faradaic efficiencies of 93% across a broad current density ranging from −50 to −900 mA cm–2, using chloride-derived indium (CD-In) as a model catalyst. An unexpected compressive strain of 2–4% is also identified as the origin of the faster kinetics over CD-In. Furthermore, we demonstrate the generality of this method with other formate-selective metals, highlighting its potential for scalable CO2 electroreduction.