Aim of this proposal is to perform operando XAS measurements on an aqueous reduced-TiO2 photocatalyst slurry in the presence of Ni(II) ions under light illumination. Such experimental conditions were recently found to trigger the formation of monovalent Ni species (Ni(I)), as observed by in-situ EPR results, which can catalyze H2 production without the need of a sacrificial agent or noble metal co-catalyst. Ni(I) formation is likely dependent on the presence in the reduced-TiO2 nanoparticles ('grey' titania) of surface Ti(III) sites, thus creating an artificial redox chain based on a monovalent nickel (Ni(I)) electron transfer relay. To corroborate the mechanism, we propose the use of High Energy Resolution Fluorescence Detected (HERFD) X-ray Absorption Spectroscopy and Resonant Inelastic X-ray Scattering (RIXS) at the Ni and Ti K-edges, to study in operando the local electronic and atomic structure of Ti and Ni under photocatalytic H2 evolution conditions.