Metastable Ni(I)-TiO<sub>2–<i>x</i></sub> Photocatalysts: Self-Amplifying H<sub>2</sub> Evolution from Plain Water without Noble Metal Co-Catalyst and Sacrificial Agent
Marco Altomare, Shanshan Qin, Viktoriia A. Saveleva, Zdeňěk Baďura, Ondřej Tomanec, Anca Mazare, Giorgio Zoppellaro, Alberto Vertova, Angelo Taglietti, Alessandro Minguzzi, Paolo Ghigna, Patrik Schmuki
Abstract
High Resolution Image Download MS PowerPoint Slide 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.