Hydrogen Produced from Hydrohalic Acid Solutions by a Two-Electron Mixed-Valence Photocatalyst

Abstract

Energy conversion cycles are aimed at driving unfavorable, small-molecule activation reactions with a photon harnessed by a transition metal complex. A challenge that has occupied researchers for several decades is to create molecular photocatalysts to promote the production of hydrogen from homogeneous solution. We now report the use of a two-electron mixed-valence dirhodium compound to photocatalyze the reduction of hydrohalic acid to hydrogen. In this cycle, photons break two Rh^II–X bonds of a LRh⁰–Rh^IIX₂ core in the presence of a halogen trap to regenerate the active LRh⁰–Rh⁰ catalyst, which reacts with hydrohalic acid to produce hydrogen.