Photocatalytic Uphill Reactions with Apparent Quantum Efficiency over 10%

Despite the massive research effort in photocatalysis for solar fuels production, the efficiencies reached are still much lower than required for practical application. The present work proposes that to reach high apparent quantum yields in photocatalytic solar-to-chemicals conversions, mechanistically simple reactions should be used. Thus, instead of H2 generation or photocatalytic CO2 reduction, the present work reports data on the photocatalytic conversion of redox mediators that upon a single electron transfer convert the most stable form of a reversible redox pair into the highest energy species of the redox coupling. Specifically, by using two metal-organic frameworks as photocatalysts, the reduction of three bipyridinium dications and the oxidation of ferrocyanide and NADH was studied. Very high apparent quantum efficiencies were measured in most of the cases, the apparent quantum yields being particularly high for the conversion of methyl viologen to the corresponding radical cation and the photooxidation of ferrocyanide to ferricyanide. These findings outline a new strategy for solar energy conversion that emphasizes efficiency and mechanistic simplicity, shifting the focus from complex multi-step transformations such as water splitting or CO2 reduction to more straightforward reactions capable of storing highly efficiently sunlight in high-energy chemical states.