Synergetic effects of multiple junction and surface hydroxyl in Cu/CuO/Cu2O/TiO2 heterostructures towards highly efficient photocatalysts for hydrogen generation

Abstract

The implementation of titanium dioxide (TiO₂) as a photocatalyst material in hydrogen (H₂) evolution reaction (HER) has embarked renewed interest in the past decade. Rapid electron-hole pairs recombination and wide band gap of a photo-sensitive material of TiO₂ are detrimental toward the targeted catalytical reaction. In this study, we present the rational design, fabrication, photocatalytic performance of TiO₂-Cu/CuO/Cu₂O heterostructures (CuTi) using viable chemical reduction method. The Z-scheme and S-scheme are succesfully generated across the TiO₂/CuO/Cu₂O interfaces, while the Schottky junction arises on the Cu perimeters. This is evidenced from the blue shifted about 0.3 eV of Cu 2p core level determined by using X-ray photoemission spectroscopy (XPS), in combination with the formation of inverse V-shape of the Mott-Schottky plots. In addition, we find that Cu/CuO/Cu₂O facilitates photon absorption range up to the visible region. The multiple heterojunction and the large number of OH_surface enhanced charge carrier transfer are associated to the suppression of photoluminescence (PL) intensity, high surface hydroxyl (OH_surface) density in CuTi probed by XPS, and fast electron transfer based on the electrochemical measurements. The presence of OH_surface inhibits the recombination of electron. A significant H₂ photogeneration rate enhancement is achieved when an optimized 5 wt% Cu/CuO/Cu₂O concentration is used on TiO₂ to achieve 7,157.19 μmol·g⁻¹ (1,789.30 μmol·g⁻¹·h⁻¹). Based on this finding, zero emission energy innitiative could be materialized under multiple heterojunctions in photocatalytic process is beneficial for enhancing the H₂ production.