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.