Structural features of p-type semiconducting NiO as a co-catalyst for photocatalytic water splitting

Perovskite-like NaTaO3 photocatalysts, synthesized by sol–gel and solid-state methods, were loaded with NiO co-catalyst to enhance water splitting activity under UV illumination. Activity increased significantly with NiO loading and reached a maximum at 3 and 0.7 wt%, respectively, for the sol–gel and solid-state synthesized NaTaO3. Beyond this point, photocatalytic activity decreased with further loading. Analysis using X-ray diffraction, high-resolution transmission electron microscopy, and diffuse reflectance spectroscopy shows that the interdiffusion of Na+ and Ni2+ cations created a solid–solution transition zone on the outer sphere of NaTaO3. For NiO contents less than 3 wt%, no NiO clusters appeared on the NaTaO3 surface, and the reduction/oxidation pretreatment did not enhance photocatalytic activity. The high activity resulting from a low NiO loading suggests that the interdiffusion of cations heavily doped the p-type NiO and n-type NaTaO3, reducing the depletion widths and facilitating charge transfers through the interface barrier.

Graphical abstractThe interdiffusion of Ni2+ and Na+ can form p-doped NiO (i.e. NaxNi1-2x2+Nix3+O) and n-doped NaTaO3 (i.e. NixNa1−xTaO3) at the interface and facilitate charge transport for splitting water.Figure optionsDownload full-size imageDownload high-quality image (73 K)Download as PowerPoint slide