Effect of Ni Metals on the [PTiW<sub>11</sub>O<sub>40</sub>]<sup>5–</sup> POM-Stabilized Self-Doped TiO<sub>2</sub> NPs toward Visible Light-Induced Hydrogen Evolution Reactions
Shweta Gomey, Rinki Aggarwal, Mohd Fazil, Laxmikanta Mallick, Sayan Halder, Sucheta Sengupta, Biswarup Chakraborty, Tokeer Ahmad, Chanchal Chakraborty, Manoj Raula
Abstract
[PTiW 11 O 40 ] 5–, a Ti = O derivative of [PW 11 O 39 ] 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 TiO 2 NPs to provide a well-dispersed TiO 2 -[PTiW 11 O 40 ] 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 TiO 2 -[PTiW 11 O 40 ] 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 H 2 production during catalytic turnover.