Selective Photocatalytic CO<sub>2</sub> Reduction in Water through Anchoring of a Molecular Ni Catalyst on CdS Nanocrystals

Photocatalytic conversion of CO<sub>2</sub> into carbonaceous feedstock chemicals is a promising strategy to mitigate greenhouse gas emissions and simultaneously store solar energy in chemical form. Photocatalysts for this transformation are typically based on precious metals and operate in nonaqueous solvents to suppress competing H<sub>2</sub> generation. In this work, we demonstrate selective visible-light-driven CO<sub>2</sub> reduction in water using a synthetic photocatalyst system that is entirely free of precious metals. We present a series of self-assembled nickel terpyridine complexes as electrocatalysts for the reduction of CO<sub>2</sub> to CO in organic media. Immobilization on CdS quantum dots allows these catalysts to be active in purely aqueous solution and photocatalytically reduce CO<sub>2</sub> with >90% selectivity under UV-filtered simulated solar light irradiation (AM 1.5G, 100 mW cm<sup>–2</sup>, λ > 400 nm, pH 6.7, 25 °C). Correlation between catalyst immobilization efficiency and product selectivity shows that anchoring the molecular catalyst on the semiconductor surface is key in controlling the selectivity for CO<sub>2</sub> reduction over H<sub>2</sub> evolution in aqueous solution.