Electroreduction of CO₂ with Tunable Selectivity on Au-Pd Bimetallic Catalyst: A First Principle Study

The electroreduction of CO₂ exhibits great promise in mitigating CO₂ from the atmosphere. However, it is quite challenging to produce C₁ products selectively on metal surfaces due to inefficient binding of CO with a metal surface. Here, using density functional theory, we studied an experimentally viable system of gold alloyed with a high CO-binding metal palladium. It is observed that the selectivity toward formic acid and methane can be tuned on Au-Pd bimetallic catalysts. Pd-rich alloy surfaces such as Pd deposited on the (211) surface of Au (Pd@Au) are found to be highly selective toward formic acid with an ultralow limiting potential of -0.23 V vs SHE. Interestingly, as the surface of the alloy become Au-rich, the selectivity toward methane increases. Among all the Au-Pd bimetallic systems, the Au-rich (211) surface of Au₃Pd alloy has a very low limiting potential of -0.9 V vs SHE for CO₂ electroreduction to methane. The selectivity toward methane on this surface is enhanced due to its optimum CO* binding and the ease of CO* protonation to CHO*. The higher feasibility of CO* protonation is a result of the stabilization of adsorbed CHO*. This stabilization is attributed to the interaction of both C and O of the CHO* molecule with the surface Au and Pd. It is found that the selectivity of a catalyst depends upon the stability of various intermediates, which can be regulated by modifying the composition of Au and Pd in the alloy. The results presented here demonstrate broad opportunities to tune the selectivity of the catalyst with varying alloy compositions, which will help to develop novel catalysts for CO₂ electroreduction.