Visible-Light-Driven Photoproduction of Hydrogen Using Rhodium Catalysts and Platinum Nanoparticles with Formate

Photochemical hydrogen production is carried out using molecular Rh complexes and sodium formate in the presence of platinum nanoparticles (PtNPs) in aqueous buffer solution. Visible-light-driven photocatalytic reactions for hydrogen production with and without nicotinamide adenine dinucleotide (NAD+) follow two different pathways. Complex [Cp*Rh(bpy)(OH2)]2+ selectively reduces NAD+ to generate NADH using formate as a proton and electron donor and the chemically generated NADH is sequentially used by PtNPs upon photoactivation of eosin Y to produce hydrogen. However, hydrogen is also produced in photoreactions of the Rh catalyst and PtNPs with formate in the absence of NAD+ and eosin Y. The second pathway for hydrogen production was performed under the conditions without NAD+ and eosin Y and derived from a direct electron transfer from in situ generated rhodium(III)-hydride species to photoexcited PtNPs. The direct electron transfer from the rhodium-hydride species to visible-light-driven PtNPs was first observed in this study. These two pathways for hydrogen production showed different rate-limiting steps based on a Hammett plot using Rh catalysts containing electron-donating and electron-withdrawing groups. Kinetic isotope effects as well as Hammett plot supported the rate-limiting step of the NADH generation for the first pathway of hydrogen production and the Rh–H formation for the second pathway.