A Tin Oxide-Coated Copper Foam Hybridized with a Gas Diffusion Electrode for Efficient CO 2 Reduction to Formate with a Current Density Exceeding 1 A cm -2 .

The electrochemical CO reduction reaction (CO RR) is a promising strategy for closing the carbon cycle. Increasing the current density (  J) for CO 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 is increased to -1152 mA cm at -1.2 V versus RHE in 1 m KOH, which is the highest value for CO -to-formate electrolysis. The formate faradaic efficiency (FE ) 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 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 remains at ≈70% under a high J of -1.0 A cm for more than 20 h.