ZnO/CdS/PbS nanotube arrays with multi-heterojunctions for efficient visible-light-driven photoelectrochemical hydrogen evolution

High performance, low cost and sustainable photocatalytic evolution of hydrogen is a promising energy supply alternative for modern society to resolve the depletion crisis of fossil fuel. The design of multi-heterojunction visible-light photocatalysts combined with electrochemical means is considered one of the most attractive options in recent years. In this work, a photoanode composed of top-opened ZnO/CdS/PbS nanotube arrays (ZnO/CdS/PbS ONTs) with multi-heterojunctions was synthesized via a three-step process, i.e. hydrothermal treatment, chemical bath deposition and successive ionic layer adsorption reaction (SILAR). This as-prepared photoanode exhibited remarkable photoelectrochemical activity under visible light irradiation. The photocurrent density and photoelectrochemical hydrogen evolution efficiency of the optimized ZnO/CdS/PbS ONTs reached up to 14.2 mA cm⁻² and 5.5 mL cm⁻² h⁻¹ at 0.0 V vs. Ag/AgCl, respectively. The efficiency was 3.1 times that of top-closed ZnO/CdS nanotubes (1.8 mL cm⁻² h⁻¹). The experimental results suggest that the high photoelectrochemical activity can be ascribed to the inherent advantages of the structural and successive energy level relays design: on the one hand, the top-opened nanotube structure significantly enlarges surface area of the nanostructure, which facilitates efficient light absorption and rapid mass transport; on the other hand, the well-matched band energy edge of the multi-heterojunction interfaces literally build efficient electron highways to deliver electrons to reaction sites and reduce the recombination of photogenerated charge carriers.