Preparation of Various Pd-Based Alloys for Electrocatalytic CO₂ Reduction Reaction—Selectivity Depending on Secondary Elements

The electrochemical conversion of CO2 to fuels such as CO and HCOO– is a highly attractive approach for decreasing the amount of greenhouse gases in the atmosphere and sustainable generation of valuable resources. Herein, electrocatalytic selectivities toward CO2 reduction reaction over nanosized Pd–M (M = Zn, Cu, Sn, and Ag) bimetallic alloys were investigated. It was found that the selectivity for the products in the CO2 reduction reaction depends on the effects of secondary elements, with Pd–Zn and Pd–Cu alloys showing formate selectivity and Pd–Ag3 and Pd–Sn alloys showing CO selectivity. The faradic efficiency (FE) of HCOO– for PdZn NPs/CB was found to be significantly higher than that of the conventional Pd nanoparticles catalyst for the CO2 reduction reaction at −0.1 V, and a record high FE of 99.4% at −0.1 V was also found. On the other hand, bimetallic PdAg3 exhibits CO selectivity with a low overpotential and a much high FE (96.2% at −0.8 V) compared to Pd. The analysis of the center of the Pd d-band (i.e., d-band center) allowed us to rationalize the obtained high FE toward the CO2 reduction reaction. We believe that this systematic effort will accelerate the development of novel highly selective and active electrocatalysts.