Abstract
Decoration of semiconductor photocatalysts with cocatalysts is generally done by a step-by-step assembly process. Here, we describe the self-assembling and self-activating nature of a photocatalytic system that forms under illumination of reduced anatase TiO(2) nanoparticles in an aqueous Ni(2+) solution. UV illumination creates in situ a Ni(+)/TiO(2)/Ti(3+) photocatalyst that self-activates and, over time, produces H(2) at a higher rate. In situ X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy show that key to self-assembly and self-activation is the light-induced formation of defects in the semiconductor, which enables the formation of monovalent nickel (Ni(+)) surface states. Metallic nickel states, i.e., Ni(0), do not form under the dark (resting state) or under illumination (active state). Once the catalyst is assembled, the Ni(+) surface states act as electron relay for electron transfer to form H(2) from water, in the absence of sacrificial species or noble metal cocatalysts.