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 H-2 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.