PdAg bimetallic electrocatalyst for highly selective reduction of CO2 with low COOH^* formation energy and facile CO desorption

For electrocatalytic reduction of CO2 to CO,the stabilization of intermediate COOH^* and the desorption of CO^* are two key steps.Pd can easily stabilize COOH^*,whereas the strong CO^* binding to Pd surface results in severe poisoning,thus lowering catalytic activity and stability for CO2 reduction.On Ag surface,CO^* desorbs readily,while COOH^* requires a relatively high formation energy,leading to a high overpotential.In light of the above issues,we successfully designed the PdAg bimetallic catalyst to circumvent the drawbacks of sole Pd and Ag.The PdAg catalyst with Ag-terminated surface not only shows a much lower overpotential(-0.55 V with CO current density of 1 mA/cm^2)than Ag(−0.76 V),but also delivers a CO/H2 ratio 18 times as high as that for Pd at the potential of-0.75 V vs.RHE.The issue of CO poisoning is significantly alleviated on Ag-terminated PdAg surface,with the stability well retained after 4h electrolysis at-0.75 V vs.RHE.Density functional theory(DFT)calculations reveal that the Ag-terminated PdAg surface features a lowered formation energy for COOH^* and weakened adsorption for CO^*,which both contribute to the enhanced performance for CO2 reduction.