Electroreduction of Carbon Dioxide to Methane on Copper, Copper–Silver, and Copper–Gold Catalysts: A DFT Study

The electrochemical reduction of CO₂ is a promising process capable of efficiently recycling CO₂ waste and converting it into hydrocarbon fuel. To date, copper is the best metal catalyst; however the overpotential to achieve this reaction on Cu is excessively high. It follows that the development of a catalyst to efficiently catalyze the conversion with a low overpotential at a reasonable current density is needed. Many aspects of the molecular details of the reaction are still unclear. In this work, DFT calculations are applied to investigate CO₂ electroreduction to CH₄ over Cu₃Ag and Cu₃Au stepped surfaces (211) compared to that over Cu(211). In the resulting analysis, the Cu₃Ag surface shows a slightly lower overpotential and suppresses OH poisoning compared to the Cu surface, yet the selectivity toward H₂ increases. The Cu₃Au is not a good candidate due to higher overpotential and a relatively weak CO adsorption resulting in CO desorption rather than further reduction. The CO desorption can also be problematic on Cu₃Ag as well. The thermodynamics and kinetics of the nonelectrochemical hydrogenations are also examined to explore alternative paths which might result in an absence of formaldehyde intermediate production during CO₂ reduction on Cu.