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.
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© 2014 American Chemical Society.