Selective CO production from aqueous CO2 using a Cu96In4 catalyst and its integration into a bias-free solar perovskite–BiVO4 tandem device

Abstract

Sunlight-driven production of fuels is attracting attention for the generation of storable renewable energy, but the design of selective catalysts for CO₂ utilization and the assembly of unassisted devices for selective and efficient CO₂-to-fuel conversion remains challenging. In this study, we report a bimetallic Cu₉₆In₄ alloy with a dendritic foam morphology for the reduction of aqueous CO₂ to CO at an onset potential of −0.3 V vs. the reversible hydrogen electrode (RHE) and with >70% selectivity. Operando Raman spectroscopy reveals weaker *CO adsorption on the Cu₉₆In₄ alloy surface compared to bare Cu and supports the immediate release of CO(g) as the product from the electrocatalyst surface. The Cu₉₆In₄ catalyst is subsequently employed in an overall bias-free tandem device for CO₂ conversion using water as an electron donor. The buried photovoltaic-biased photoelectrochemical cell relies on state-of-the-art triple-cation mixed halide perovskite and BiVO₄ photoabsorbers that can also be assembled in an artificial leaf configuration. The device reaches a solar-to-CO energy conversion efficiency of 0.19% with a selectivity of 75% for CO after 10 h simulated sunlight irradiation using bias-free conditions. The buried perovskite|Cu₉₆In₄ cathode shows robust, unaltered PEC activity at different solar intensities, which also allows it to function under low and diffuse sunlight. This study highlights the potential of alloying to improve catalytic performance and strategies to integrate such catalysts into solar-driven PEC devices.