Perfect Photon-to-Hydrogen Conversion Efficiency.

We report a record 100% photon-to-hydrogen production efficiency, under visible light illumination, for the photocatalytic water-splitting reduction half-reaction. This result was accomplished by utilization of nanoparticle-based photocatalysts, composed of Pt-tipped CdSe@CdS rods, with a hydroxyl anion-radical redox couple operating as a shuttle to relay the holes. The implications of such record efficiency for the prospects of realizing practical over all water splitting and solar-to-fuel energy conversion are discussed.