Copper-Oxide-Coated Silver Nanodendrites for Photoelectrocatalytic CO2 Reduction to Acetate at Low Overpotential

The photoelectrocatalytic reduction of CO2 uses sunlight to reduce the external energy needed to convert this greenhouse gas into value-added products. We report the deposition of a thin film of copper oxide onto a large-surface-area plasmonic silver structure, which generates an efficient photoelectrocatalyst for CO2 reduction. Using incoherent visible light illumination and applying -0.4 V versus Ag/AgCl(KCl 1M), CO2 was reduced to acetate with a faradaic efficiency of 54%. Rather than adding plasmonic nanoparticles as sensitizers onto semiconductors, here we electrodeposit a thin uniform layer of Cu2O/CuO over a plasmonic silver structure. The formation of acetate at this low potential has not been reported before and appears to arise from synergistic effects in this hybrid plasmonic-semiconductor material. In this work, we investigate changes in the photophysics under different preparation conditions. Varying the deposition time of Cu2O/CuO deposited onto the Ag to form the Ag/Cu2O/CuO electrodes alters electron-hole recombination. The Ag/Cu2O/CuO electrodes show the highest photocurrent density when a minimal Cu2O/CuO film covers the Ag structure. Synergistic effects between the localized surface plasmon resonance of silver and semiconductor properties of Cu2O/CuO decrease the necessary overpotential required for CO2 reduction, reduce charge recombination processes, and stabilize the Cu2O/CuO semiconductor on the photoelectrode. The stabilization of Cu2O/CuO in the presence of energetic charge carriers is believed to be key to producing acetate with high efficiency. These properties suggest an interesting approach to photoelectrocatalytic materials.