Effect of Ni Metals on the [PTiW₁₁O₄₀]^5– POM-Stabilized Self-Doped TiO₂ NPs toward Visible Light-Induced Hydrogen Evolution Reactions

[PTiW11O40]5–, a Ti = O derivative of [PW11O39]7– lacunary Keggin polyoxometalates (POMs), is employed as an excited state electron reservoir for the hydrogen evolution reaction (HER) via water-splitting in the presence of sacrificial agents. This POM also stabilizes the surface of crystalline anatase TiO2 NPs to provide a well-dispersed TiO2-[PTiW11O40]5– hybrid material. Modifications of the bandgap through self-doping on the anatase surfaces, along with impregnation of ultrasmall Ni NPs, were executed, resulting in self-doped TiO2-[PTiW11O40]5–-Ni ternary hybrid materials with improved absorbance in the visible regions. Various analytical techniques, such as Tauc plots, powder XRD, HAADF-STEM, and XPS, were used to characterize these synthesized ternary hybrid materials. These hybrid materials showed very high photocatalytic activity under UV–vis and visible-light irradiation. These hybrids also display a very low Tafel slope of 62 mV dec–1 toward electrocatalytic HER activity. A comprehensive mechanistic investigation elucidating the electron transfer dynamics during hydrogen evolution is shown here. Under photo- and electrocatalytic conditions, Ni NPs act as active sites for hydrogen evolution, whereas POMs act as excited-state electron scavengers and storage. According to a molecular-level calculation, the ternary hybrid’s Ni NPs active-site-dependent HER effectiveness exhibits a “dose-response” relationship in comparable experimental conditions. The Hill slope coefficient highlights the cooperative mechanisms between the Ni active sites for H2 production during catalytic turnover.