Surface Modification of Nickel Titanate Nanocubes with Ultra-small Palladium and Platinum Nanocrystals to Promote Solar Hydrogen Generation under Visible Light

Abstract

Modification of nickel titanate nanocubes with metal nanocrystals is a viable approach to build a Schottky heterojunction for efficient hydrogen generation. The deconvoluted XPS spectrum of Pt 4 f (peaks at 72.0 and 75.5 eV corresponding to Pt-degrees and Pt2+) and Pd 3d3/2 (335.4 and 336.7 eV corresponding to Pt-degrees and Pt2+) and presence of lattice fringes in HRTEM at 2.19 angstrom of Pd-degrees, reveal the formation of heterojunction in Pd-NiTiO3 and Pt-NiTiO3 nanocubes. The solar hydrogen generation investigation exhibits 2-fold enhancement in HER (130 and 165 mu mol g(-1) h(-1) while using Pt-NiTiO3 and Pd-NiTiO3, respectively) than that of bare NiTiO3 (88 mu mol g(-1) h(-1)). The creation of heterojunctions between titanates and metal nanoparticles, facilitating efficient transport of photo-generated electron to empty or partially filled d or f orbitals of metals, thereby lowering electron-hole recombination rate, as revealed by shorter average lifetime 29 ns (Pd-NiTiO3) than 64 ns (NiTiO3). Further, the unison of faster charge transfer kinetics as revealed by the Nyquist plot, more negative flatband potential (E-fb -0.3 vs. RHE) leading to appropriate band bending, reduced overpotential requirement, higher oxygen vacancies (19.46 %) and uniform dispersion of metal atoms on NiTiO3 surfaces that are acting as trapping centers etc. are enabling improved hydrogen generation in the case of Pd-NiTiO3.