Making Hydrogen from Water Using a Homogeneous System Without Noble Metals

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Abstract
A photocatalytic noble metal-free system for the generation of hydrogen has been constructed using Eosin Y (1) as a photosensitizer, the complex [Co(dmgH)2pyCl]2+ (5, dmgH = dimethylglyoximate, py = pyridine) as a molecular catalyst, and triethanolamine (TEOA) as a sacrificial reducing agent. The system produces H2 with an initial rate of ∼100 turnovers per hour upon irradiation with visible light (λ > 450 nm). Addition of free dmgH2 greatly increases the durability of the system addition of 12 equiv of dmgH2 (vs cobalt) to the system produces ∼900 turnovers of H2 after 14 h of irradiation. The rate of H2 evolution is maximum at pH = 7 and decreases sharply at more acidic or basic pH. Spectroscopic study of photolysis solutions suggests that hydrogen production occurs through protonation of a CoI species to give a CoIII hydride, which then reacts further by reduction and protolysis to give CoII and molecular hydrogen.
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