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 CO2 reduction reaction (CO2RR) is a promising strategy for closing the carbon cycle. Increasing the current density (J) for CO2RR 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 Jformate is increased to −1152 mA cm−2 at −1.2 V versus RHE in 1 m KOH, which is the highest value for CO2-to-formate electrolysis. The formate faradaic efficiency (FEformate) 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 H2 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 FEformate remains at ≈70% under a high J of −1.0 A cm−2 for more than 20 h.