J. Schubert, J. Popovic, G.M. Haselmann, S. Nandan, J. Wang, A. Giesriegl, A. Cherevan, D. Eder:
"Immobilization of Co, Mn, Ni and Fe oxide co-catalysts on TiO2 for photocatalytic water splitting reactions";
Journal of Materials Chemistry A, 7 (2019), 12 S.

Kurzfassung englisch:
Here we report a systematic study of a series of non-noble-metal co-catalysts based on Co, Mn, Ni and Fe oxides that were prepared by wet impregnation of the corresponding acetylacetonate precursors onto a model TiO2 substrate, followed by their oxidative decomposition. We analyze thermal evolution of the impregnated M(acac)x-TiO2 composites with a combination of analytical methods and reveal strong differences in the precursor decomposition onsets and the resulting product composition, compared to the case of pure M(acac)x precursors. Consequent electron microscopy analyses of the resulting MOx-TiO2 composites indicate the presence of small (1-5 nm) amorphous MOx nanoparticles that are homogeneously distributed on the surface of the substrate TiO2. Complementing Raman and photoluminescence (PL) spectra confirm pronounced effects of MOx deposition on the state of TiO2 substrate and suggest strong electronic communication between the components. The composites obtained at 350 °C were further tested towards sacrificial hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) demonstrating the dynamic nature of the NiOx-TiO2 photocatalyst whose Ni0 active HER sites were generated in situ upon light exposure. In contrast, FeOx-TiO2, CoOx-TiO2, and NiOx-TiO2 were all active towards OER, featuring water oxidation ability in descending order, while XPS data of the samples after reaction indicate that partial oxidation of M species takes place during the course of the photocatalytic experiment. This work provides detailed insights on the wet chemistry-based preparation of MOx co-catalysts decorating oxide nanopowders including optimization of the thermal treatment, potential substrate effects and synergy as well as further prospects in photocatalysis.

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