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Olga A. Krysiak, João Ricardo Coelho Junqueira, Felipe Conzuelo, Tim Bobrowski, Justus Masa, Andrzej Wysmolek, Wolfgang Schuhmann

• Photoelectrochemical water splitting is mostly impeded by the slow kinetics of the oxygen evolution reaction. The construction of photoanodes that appreciably enhance the efficiency of this process is of vital technological importance towards solar fuel synthesis. In this work, Mo-modified \(BiVO_{4}\) (Mo:\(BiVO_{4}\)), a promising water splitting photoanode, was modified with various oxygen evolution catalysts in two distinct configurations, with the catalysts either deposited on the surface of Mo:\(BiVO_{4}\) or embedded inside a Mo:\(BiVO_{4}\) film. The investigated catalysts included monometallic, bimetallic, and trimetallic oxides with spinel and layered structures, and nickel boride (\(Ni_{x}B\)). In order to follow the influence of the incorporated catalysts and their respective properties, as well as the photoanode architecture on photoelectrochemical water oxidation, the fabricated photoanodes were characterised for their optical, morphological, and structural properties, photoelectrocatalytic activity with respect to evolved oxygen, and recombination rates of the photogenerated charge carriers. The architecture of the catalyst-modified Mo:\(BiVO_{4}\) photoanode was found to play a more decisive role than the nature of the catalyst on the performance of the photoanode in photoelectrocatalytic water oxidation. Differences in the photoelectrocatalytic activity of the various catalyst-modified Mo:\(BiVO_{4}\) photoanodes are attributed to the electronic structure of the materials revealed through differences in the Fermi energy levels. This work thus expands on the current knowledge towards the design of future practical photoanodes for photoelectrocatalytic water oxidation.