A Hierarchical 3D TiO2/Ni Nanostructure as an Efficient Hole‐Extraction and Protection Layer for GaAs Photoanodes

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Photoelectrochemical (PEC) water splitting is a promising clean route to hydrogen fuel. The best‐performing materials (III/V semiconductors) require surface passivation, as they are liable to corrosion, and a surface co‐catalyst to facilitate water splitting. At present, optimal design combining photoelectrodes with oxygen evolution catalysts remains a significant materials challenge. Here, we demonstrate that nickel‐coated amorphous three‐dimensional (3D) TiO2 core‐shell nanorods on a TiO2 thin film function as an efficient hole‐extraction layer and serve as a protection layer for the GaAs photoanode. Transient‐absorption spectroscopy (TAS) demonstrated the role of nickel‐coated (3D) TiO2 core‐shell nanorods in prolonging photogenerated charge lifetimes in GaAs, resulting in a higher catalytic activity. This strategy may open the potential of utilizing this low‐cost (3D) nanostructured catalyst for decorating narrow‐band‐gap semiconductor photoanodes for PEC water splitting devices.