No abstract

The photoelectrocatalytic reduction of CO 2 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 CO 2 reduction. Using incoherent visible light illumination and applying −0.4 V versus Ag/AgCl(KCl 1M), CO 2 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 Cu 2 O/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 Cu 2 O/CuO deposited onto the Ag to form the Ag/ Cu 2 O/CuO electrodes alters electron−hole recombination. The Ag/Cu 2 O/CuO electrodes show the highest photocurrent density when a minimal Cu 2 O/CuO film covers the Ag structure. Synergistic effects between the localized surface plasmon resonance of silver and semiconductor properties of Cu 2 O/CuO decrease the necessary overpotential required for CO 2 reduction, reduce charge recombination processes, and stabilize the Cu 2 O/ CuO semiconductor on the photoelectrode. The stabilization of Cu 2 O/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.

Lignin is a residual product can be reused for stabilize Cu2O on modified electrodes in CO2 reduction.

Electrochemical and, more recently, photoelectrochemical CO2 reductions have been widely investigated to convert atmospheric CO2 into other useful chemicals. However, understanding the mechanism and selectivity of materials capable of reducing CO2 remains a challenge. Using plasmonic dendritic electrodes of silver and cuprous oxide (Ag/Cu2O) and employing Raman spectroelectrochemistry detection, we observe the selective photoelectroreduction mechanism from CO2 to acetate as a value-added compound instead of the more commonly reported products like methanol, ethylene, or ethane. The selectivity, efficiency, and low overpotential (−0.4 V vs Ag/AgCl) in the CO2 reduction is favored by the basic microenvironment, the semiconductor properties of the Cu2O, and the accumulation of hot electrons from the localized surface plasmon resonance of the Ag nanostructure. Lateral surface interactions between adsorbed CO species are the key to the formation of acetate. The rate-determining step of the reaction is the single transfer of an electron from the electrode to the CO2 molecule to reduce it to the *CO2 – radical anion and subsequently form adsorbed CO, which is a key intermediate in the formation of the carbon–carbon bond during the reduction process.