Journal Article

Precise composition modulation for optimizing NiWO 4 /Pt/CdS Z‐scheme system

Tohji, Kazuyuki, Li, Mingjie, Takahashi, Hideyuki, Yokoyama, Shun, Yan, Keyou

2021

Overview

A reasonable structure is crucial for the solar‐to‐chemical conversion process of the integrated Z‐scheme system. Composition modulation provides a new dimension for the optimization of Z‐scheme system. Herein, a composition modulated NiWO 4 /Pt/CdS Z‐scheme system is demonstrated for photocatalytic hydrogen generation. Proportions of Ni, W, Cd, and S in NiWO 4 /Pt/CdS are precisely tuned through the ion‐exchange reaction between NiWO 4 and CdS. Important features of the Z‐scheme system in terms of light harvesting, charge separation and charge transfer are optimized accordingly. Bandgap of CdS is tuned continuously from 2.22 to 1.52 eV through controlling the Cd and S contents in NiWO 4 /Pt/CdS. The results of photoluminescence spectrometry and photoelectrochemical analyses demonstrate that the NiS generated from ion‐exchange reaction increase the charge separation and transfer rates. Furthermore, the molar ratio of NiWO 4 to CdS is regulated to a balance state, leading to the decrease of charge recombination. The optimized NiWO 4 /Pt/CdS Z‐scheme system delivers the comprehensive performance of excellent light harvesting and charge separation abilities, low charge recombination rate, and suitable energy band structure for water reduction. The hydrogen generation rate is increased to 14.39 mmol h ‐1 g ‐1 after the optimization. The optimized method brings a new insight into the rational design of Z‐scheme system.