Electroreduction of carbon dioxide to hydrocarbons using bimetallic Cu-Pd catalysts with different mixing patterns

Electrochemical conversion of CO₂ holds promise for utilization of CO₂ as a carbon feedstock and for storage of intermittent renewable energy. Presently Cu is the only metallic electrocatalyst known to reduce CO₂ to appreciable amounts of hydrocarbons, but often a wide range of products such as CO, HCOO^-, and H₂ are formed as well. Better catalysts that exhibit high activity and especially high selectivity for specific products are needed. Here a range of bimetallic Cu-Pd catalysts with ordered, disordered, and phase-separated atomic arrangements (Cu_at:Pd_at = 1:1), as well as two additional disordered arrangements (Cu3Pd and CuPd3 with Cu_at:Pd_at = 3:1 and 1:3), are studied to determine key factors needed to achieve high selectivity for Cl or C2 chemicals in CO₂ reduction. When compared with the disordered and phase-separated CuPd catalysts, the ordered CuPd catalyst exhibits the highest selectivity for Cl products (>80%). The phase-separated CuPd and Cu3Pd achieve higher selectivity (>60%) for C2 chemicals than CuPd3 and ordered CuPd, which suggests that the probability of dimerization of Cl intermediates is higher on surfaces with neighboring Cu atoms. Based on surface valence band spectra, geometric effects rather than electronic effects seem to be key in determining the selectivity of bimetallic Cu-Pd catalysts. These results imply that selectivities to different products can be tuned by geometric arrangements. This insight may benefit the design of catalytic surfaces that further improve activity and selectivity for CO₂ reduction.