Robust Photogeneration of H 2 in Water Using Semiconductor Nanocrystals and a Nickel Catalyst

Robust Reduction A major challenge in the design of artificial photosynthesis catalysts has been their instability under the reaction conditions—a problem that plants and other autotrophs address by perpetually reproducing their biochemical machinery. Han et al. (p. 1321, published online 8 November) now demonstrate a system for photoreductive hydrogen generation in water that manifests undiminished activity for weeks at a time. Semiconductor nanoparticles for light absorption were combined with a soluble nickel complex for the catalytic chemistry. The system currently requires a sacrificial electron donor, but its robustness shows promise for future pairing with an integrated oxidation catalyst. A photoreduction system combining nanoparticulate light absorbers with a soluble molecular catalyst proves stable for weeks. Homogeneous systems for light-driven reduction of protons to H2 typically suffer from short lifetimes because of decomposition of the light-absorbing molecule. We report a robust and highly active system for solar hydrogen generation in water that uses CdSe nanocrystals capped with dihydrolipoic acid (DHLA) as the light absorber and a soluble Ni2+-DHLA catalyst for proton reduction with ascorbic acid as an electron donor at pH = 4.5, which gives >600,000 turnovers. Under appropriate conditions, the precious-metal–free system has undiminished activity for at least 360 hours under illumination at 520 nanometers and achieves quantum yields in water of over 36%.