pH and Anion Effects on Cu-Phosphate Interfaces for CO Electroreduction

Cu electrodes are promising materials to catalyze the conversion of CO2 and CO into renewable fuels and valuable chemicals. However, a detailed description of the properties of the Cu-electrolyte interface is still crucial to reach a complete understanding of the CO reduction mechanism. Herein, we have investigated the interfacial properties of Cu(111) and Cu(100) in phosphate buffer solutions at different pH conditions and in the presence of CO. Ab initio molecular simulations of the Cu-electrolyte interface were combined with voltammetric experiments carried out on Cu(100) and Cu(111) single-crystalline electrodes. Combining multiple cyclic voltammograms on Cu single crystals across the whole pH scale with simulations allows for an in-depth insight into the stability of specifically adsorbed protonated (H2PO4* or HPO4*) or non-protonated (PO4*) phosphate species from the electrolyte. We show that the adsorption strength of phosphate species on the different Cu facets affects the potential range at which CO poisons the surface, thus evidencing that the properties of the Cu-electrolyte interface control the potential range for CO reduction on Cu. This combination of systematic experimental and theoretical analysis across the pH scale is a robust method to gain fundamental structural insight into electrochemical interfaces.