Enhanced solar-driven benzaldehyde oxidation with simultaneous hydrogen production on Pt single-atom catalyst

• Combining the oxidation of the biomass-derived benzaldehyde with simultaneous proton reduction in a closed redox cycle. • Both benzaldehyde oxidation and H 2 production follows the order of single atom > nanocluster > nanoparticle. • Pt single atom catalyst demonstrates a nearly 100% efficiency per atom in producing benzoic acid and clean H 2 fuel. Sustainable development requires the use of renewable and clean energy resources to manufacture end-user products with high efficiency. Herein, we report an artificial photocatalysis system that combines the oxidation of the biomass-derived benzaldehyde with simultaneous proton reduction in a closed redox cycle driven by supported nanocatalysts in an aqueous solution. Our results demonstrate a nearly 100 % reactant efficiency for water splitting on a per-atom basis, and generates two targeted end-user products: benzoic acid and clean H 2 fuel. Nanocatalysts can be conveniently categorized into three groups according to their size: single atom, nanocluster, and nanoparticle. Nanocatalysts smaller in size are generally outstanding for oxidation, while larger particles are more efficient in proton reduction. To elucidate the size effects for the overall reaction in both half-reactions, we prepared Pt single atom (0.2 nm), nanocluster (1 nm), and nanoparticle (4 and 7 nm diameter) catalysts supported on polymeric carbon nitride (g-C 3 N 4 ) for the artificial photocatalytic oxidation of benzaldehyde and hydrogen production. The reaction rate for both benzaldehyde oxidation and H 2 production on the Pt nanocatalysts follows the order of single atom > nanocluster > nanoparticle. Photon-induced charge carriers are more likely to be trapped by single Pt atoms, which guarantees the efficiency of charge splitting and limits the recombination. In addition, the outstanding oxidation performance of the single atom and nanocluster catalysts consumes large amount of holes, which otherwise contribute more electrons for proton reduction and enhance H 2 production. On the other hand, the large nanoparticles potentially provide a stage to trap both photo-induced electrons and holes, with the potential to reduce the photocatalysis rate of hydrogen production from the proton reduction via the excess electrons and the benzaldehyde oxidation and the excess holes.