Cyclodextrin-Enhanced Photocatalytic Hydrogen Evolution Based on Formate Decomposition With Bio/Metal Catalysts

Formic acid is an attractive hydrogen carrier in terms of hydrogen capacity and safety. Focusing on hydrogen release from formic acid, the developments of catalysts with easy controllability in mild conditions have been desirable. Previous study reported a hybrid catalytic system of enzymes, photosensitizers, and metal nanoparticles for controllable hydrogen production with visible light. However, methyl viologen, which is a toxic compound, was utilized as an electron mediator from photosensitizers to metal nanoparticles. 9-Mesityl-10-methyl acridinium (Mes-Acr⁺) is one of the promising candidates which hold a long-lived charge-separated state for the removal of methyl viologen from the hybrid system to enhance the safety and the catalytic activity. In this work, cyclodextrins (CDs) were employed to form a complex with Mes-Acr⁺ using supramolecular interactions such as ionic and hydrophobic interactions, which improved photocatalytic activity in aqueous solution. This supramolecular photocatalyst was finally applied to photocatalytic hydrogen production with a system of formate dehydrogenase, NAD⁺, Mes-Acr⁺, CD, and colloidal platinum nanoparticles dispersed by polyvinylpyrrolidone. An ultimate yield from formate to hydrogen reached 24% at pH 6.0, indicating a rate-determining step would be electron transfer from Mes-Acr radical to Pt-PVP to reduce protons.