Ionomer-Modulated Electrochemical Interface Leading to Improved Selectivity and Stability of Cu₂O-Derived Catalysts for CO₂ Electroreduction

Copper is an attractive catalyst for the electrochemical reduction of CO₂ to high value C₂₊ products such as ethylene and ethanol. However, the activity, selectivity and stability of Cu-based catalysts must be improved for industrial applications. In this work, we investigate the effects of ionomers on the microenvironment and consequently the catalytic performance of Cu₂O particles with a well-defined cubic shape. Cu₂O particles without an ionomer coating were compared to those with a Nafion-based cation-exchange layer (CEL) and a Sustainion-based anion-exchange layer (AEL), as well as electrodes with two successive layers of Nafion and Sustainion in either order. Using these model electrodes, we found that the selectivity to C₂₊ products is significantly improved with a Nafion coating, regardless of whether it is in direct contact with the copper surface or present as an overlayer on top of chloride-exchanged Sustainion. The selectivity improvement by Nafion is ascribed to the exclusion of proton-donating bicarbonate ions, which limits the competing hydrogen evolution reaction. Interestingly, introducing a second layer of Sustainion causes a selectivity shift from ethylene to ethanol. In addition, improved catalyst stability is observed for the Nafion-containing electrodes due to a mitigation of potassium bicarbonate precipitation and copper agglomeration. These results demonstrate that regulating the catalyst microenvironment via ionomer coatings is a promising approach to designing electrodes with superior and tunable catalytic performance.