Enhancement of Catalytic Activity and Selectivity for the Gaseous Electroreduction of CO₂ to CO: Guidelines for the Selection of Carbon Supports

To secure the economic feasibility of electrochemical carbon dioxide reduction reaction (CO₂RR), a method of using support materials to reduce the amount of catalyst loading and increase catalytic activity for CO₂RR can be a solution. Herein, guidelines for selecting carbon support materials suitable for CO₂RR are reported. In a gaseous CO₂-fed CO₂RR electrolyzer, an Ag nanoparticle-composited carbon nanocage (denoted as Ag/CNC) electrode exhibits an optimal performance for CO₂RR with a partial current density of ≈400 mA cm⁻². Ag/CNC showcases a uniformly dispersed morphology with Ag nanoparticles and sufficient hydrophobicity after the reaction to prevent flooding, which is known to inhibit the mass transfer of CO₂. Furthermore, the CNCs possess small amounts of carbon defects; this suppresses the catalytic activity for the hydrogen evolution reaction (HER), which is a side reaction of CO₂RR. Results of a three-stack cell experiment with the Ag/CNC electrode reveal the possibility of a support-based strategy for achieving an industrial-level scaling of CO₂RR. This study suggests that the support material for CO₂RR should be considered not only on the basis of the morphology of carbon, uniform dispersion of Ag nanoparticles, and hydrophobicity of the electrode but also factors influencing the HER, such as carbon defects.