CO2 Reduction at Low Overpotential on Cu Electrodes Resulting from the Reduction of Thick Cu2O Films

Abstract

Modified Cu electrodes were prepared by annealing Cu foil in air and electrochemically reducing the resulting Cu2O layers. The CO2 reduction activities of these electrodes exhibited a strong dependence on the initial thickness of the Cu2O layer. Thin Cu2O layers formed by annealing at 130 °C resulted in electrodes whose activities were indistinguishable from those of polycrystalline Cu. In contrast, Cu2O layers formed at 500 °C that were ≥ ∼3 μm thick resulted in electrodes that exhibited large roughness factors and required 0.5 V less overpotential than polycrystalline Cu to reduce CO2 at a higher rate than H2O. The combination of these features resulted in CO2 reduction geometric current densities >1 mA/cm2 at overpotentials <0.4 V, a higher level of activity than all previously reported metal electrodes evaluated under comparable conditions. Moreover, the activity of the modified electrodes was stable over the course of several hours, whereas a polycrystalline Cu electrode exhibited deactivation within 1 h under identical conditions. The electrodes described here may be particularly useful for elucidating the structural properties of Cu that determine the distribution between CO2 and H2O reduction and provide a promising lead for the development of practical catalysts for electrolytic fuel synthesis.