Bulk Layering Effects of Ag and Cu for Tandem CO₂ Electrolysis

The electrochemical reduction of carbon dioxide (CO₂) presents an opportunity to close the carbon cycle and obtain sustainably sourced carbon compounds. In recent years, copper has received widespread attention as the only catalyst capable of meaningfully producing multi-carbon (C₂₊) species. Notably carbon monoxide (CO) can also be reduced to C₂₊ compounds on copper, motivating tandem systems that combine copper and CO-producing species, like silver, to enhance overall C₂₊ selectivities. In this work, we examine the impact of layered-combinations of bulk Cu and Ag by varying the location and proportion of the CO-producing Ag layer. We report an effective increase in the C₂₊ oxygenate selectivity from 23 % with a 100 nm Cu to 38 % for a 100 : 15 nm Cu : Ag layer. Notably, however, for all co-catalyst cases there is an overproduction of CO vs Cu alone, even for 5 nm Ag layers. Lastly, due to restructuring and interlayer mobility of the copper layer it is clear that the stability of copper limits the locational advantages of such tandem solutions.