CO₂ Electrochemical Reduction Catalyzed by Graphene Supported Palladium Cluster: A Computational Guideline

By means of periodic density functional theory calculations, we investigated the heterogeneous catalytic reduction of CO2 to formic acid, including electrocatalytic and thermocatalytic reduction on graphene-supported Pd10 and hydride Pd10 materials. The hydrogen proportion of palladium hydride, nH-Pd10-graphene (n = 1–10), is considered to mimic the various hydrogen ratios caused by the changed applied potential. We predicted the limiting potentials (UL) for CO2 reduction on the nH*-Pd10-graphene models and found the UL for the formation of formate intermediate (HCOO*) changed with the hydrogen ratio of nH*-Pd10-graphene models. In addition, the HCOO* adsorption strength was found to play an important role for CO2 reduction reaction (CO2RR) on the nH*-Pd10-graphene. The saturated H* metal hydride in our calculation is 10H*Pd10-graphene, but the CO2RR preferably takes place under the negative potential of −0.17 V on the 8H*-Pd10-graphene. The hydrogen evolution reaction (HER) occurs to compete with the CO2RR when the external negative potential is applied. For n = 9–10, the HER is more comparable than the CO2RR due to the lower UL of the HER. Over the UL of −0.41 V, the hydride Pd10-graphene would be refreshed to bare Pd10-graphene, and the electrochemical adsorption of CO2 to form HCOO* becomes an endergonic process.