关键词: CO₂电化学还原, Pd/C催化剂, 载量, 电解质, 选择性

Abstract: Nanostructured heterogeneous catalysts have been widely used in the electrochemical carbon dioxide (CO₂) reduction reaction (CO₂RR), which can simultaneously achieve the electrocatalytic conversion of CO₂ to fuels and the storage of renewable energy sources. Carbon supported palladium nanoparticles (Pd/C) catalysts have been previously reported to show excellent CO₂RR performance. However, the crucial role of the metal loading in supported electrocatalysts has been rarely reported. In this work, we study the Pd loading effect on the structure of Pd/C catalysts as well as their activity and selectivity of CO₂RR to CO. The Pd loadings in Pd/C catalysts were well controlled by an effective liquid synthesis method. The Pd nanoparticles were homogeneously dispersed on the carbon support, and the Pd loading played a minor role in the particle size. The as-prepared Pd/C catalysts were studied in an optimized electrolyte, 0.1 mmol·L^-1 KHCO₃. It shows a volcano relationship between CO Faradaic efficiency (FE) and the Pd loading, with the highest CO FE of 91.2% over the 20wt% Pd/C catalyst at -0.89 V versus the reversible hydrogen electrode (vs. RHE). The geometric CO partial current density had a positive correlation with the Pd loading, while the highest turnover frequency for CO production was observed over the 2.5wt% Pd/C catalyst (~ 918 h^-1 at -0.89 V vs. RHE). The Pd loading effects on the activity and selectivity of CO₂RR to CO could be attributed to the number of active sites, reaction kinetics, and the stabilization of key intermediates, as well as the mass transport of reactants, intermediates and products. This work provides new insight into the loading effect, an important reactivity descriptor determining the CO₂RR performance.

Key words: electrochemical carbon dioxide reduction reaction, Pd/C catalysts, loading, electrolyte, selectivity