Electrochemical study on hydrogen evolution and CO2 reduction on Pt electrode in acid solutions with different pH

Hydrogen evolution reaction (HER) is the major cathodic reaction which competes CO2 reduction reaction (CO2 RR) on Pt electrode. Molecular level understanding on how these two reactions interact with each other and what the key factors are of CO2 RR kinetics and selectivity will be of great help in optimizing electrolysers for CO2 reduction. In this work, we report our results of hydrogen evolution and CO2 reduction on Pt(111) and Pt film electrodes in CO2 saturated acid solution by cyclic voltammetry and infrared spectroscopy. In solution with pH>2, the major process is HER and the interfacial pH increases abruptly during HER; COad is the only adsorbed intermediate detected in CO2 reduction by infrared spectroscopy; the rate for COad formation increases with the coverage of UPD-H and reaches maximum at the onset potential for HER; the decrease of COad formation under HER is attributed to the available limited sites and the limited residence time for the reduction intermediate (Had), which is necessary for CO2 adsorption and reduction.