A Tin Oxide‐Coated Copper Foam Hybridized with a Gas Diffusion Electrode for Efficient CO2 Reduction to Formate with a Current Density Exceeding 1 A cm−2

Abstract The electrochemical CO 2 reduction reaction (CO 2 RR) is a promising strategy for closing the carbon cycle. Increasing the current density ( J ) for CO 2 RR products is a critical requirement for the social implementation of this technology. Herein, nanoscale tin–oxide‐modified copper–oxide foam is hybridized with a carbon‐based gas‐diffusion electrode (GDE). Using the resultant electrode, the J formate is increased to −1152 mA cm −2 at −1.2 V versus RHE in 1 m KOH, which is the highest value for CO 2 ‐to‐formate electrolysis. The formate faradaic efficiency (FE formate ) reaches ≈99% at −0.6 V versus RHE. The achievement of ultra‐high‐rate formate production is attributable to the following factors: i) homogeneously‐modified Sn atoms suppressing H 2 evolution and ii) the hydrophobic carbon nanoparticles on GDEs penetrating the macroporous structure of the foam causing the increase in the thickness of triple‐phase interface. Additionally, the FE formate remains at ≈70% under a high J of −1.0 A cm −2 for more than 20 h.