pH dependent CO adsorption and roughness-induced selectivity of CO 2 electroreduction on gold surfaces

Gold belongs to the category of metal electrocatalysts for CO2 reduction reaction (CO2RR) producing CO as a major product due to its inability to bind CO. In this work, we found that when the interfacial pH becomes alkaline, CO, the major product of CO2RR, interacts with gold surfaces to produce minor products like formate and methanol. The course of product formation and CO adsorption on gold was explored by their oxidative voltammetric responses obtained immediately after CO2RR in the forward cathodic scan and SECM studies provided more insights into the effect of interfacial pH on product selectivity. The electrode roughness was found to change the interfacial pH gradients as a result of microheterogeneity of surfaces. The roughness of gold surface was systematically changed from smoothened surface to nanoporous (highly rough) surface. NMR spectroscopic analysis pointed to the presence of methanol and formate being formed on nanoporous Au (np- Au) in significant amounts. Formate production was found increasing as a result of changes in the interfacial pH.