Controlling H+ vs CO2 Reduction Selectivity on Pb Electrodes

Nanocrystalline Pb films prepared by reducing PbO2 precursors have up to 700-fold lower H+ reduction activity than polycrystalline Pb foil electrodes but maintain the ability to reduce CO2. As a result, these “oxide-derived” Pb (OD–Pb) electrodes have higher Faradaic efficiency for CO2 reduction to HCO2– in aqueous solutions with almost no competitive H+ reduction. Even with very low CO2 concentrations in N2-saturated NaHCO3 solution, OD–Pb converts CO2 derived from HCO3– decomposition to HCO2– with almost quantitative Faradaic efficiency while Pb foil has less than 10% efficiency. Electrokinetic data suggest that the difference in selectivity between the two electrodes is caused by a difference in the coverage of a surface layer—likely a metastable Pb oxide—that is passivating for H+ reduction but active for CO2 reduction.