Electrochemical promotion of catalysis over Pd nanoparticles for CO₂ reduction

Electrochemical promotion of catalysis (EPOC) has been shown to accelerate the rate of many heterogeneous catalytic reactions; however, it has rarely been reported in low-temperature aqueous electrochemical reactions. Herein, we report a significant EPOC effect for the CO₂ reduction to generate formate over Pd nanoparticles (NPs) in a 1 M KHCO₃ aqueous solution. By applying a negative potential over differently-sized Pd NPs, the rate of formate production is greatly improved as compared to that at an open-circuit voltage, with a rate enhancement ratio ranging from 10 to 143. The thermocatalytic and electrocatalytic reduction of CO₂ compete with each other and are promoted by the applied negative potential and H₂ in the feeds, respectively. Inspired by the EPOC effect, a composite electrode containing Pd/C and Pt/C catalysts on different sides of a carbon paper was constructed for catalyzing the CO₂ reduction without adding H₂ to the feeds. Water electrolysis over Pt NPs generates H₂, which then effectively promotes formate production over Pd NPs.