S-Scheme Heterojunction/Single-Atom Dual-Driven Charge Transport for Photocatalytic Hydrogen Production

Abstract

The rational design and modification of heterojunction photocatalysts aimed at achieving fast charge transport and efficient photocatalytic performance is a central goal of solar-light-driven water splitting and hydrogen evolution, yet this remains a challenge. Herein, we prepare a hierarchical photocatalyst composed of a few-layer violet phosphorene (VP), cadmium sulfide (CdS) nanoparticles (NPs), and Pd single atoms (SAs) by a facile one-step ball-milling strategy. The underlying VP/CdS p–n heterojunctions are verified to adopt S-scheme directional charge transfer by combining in situ irradiated X-ray photoelectron spectroscopy and electron paramagnetic resonance. The atomically dispersed Pd sites of the low-valence state coupled with the VP/CdS S-scheme heterojunctions synergistically achieve ultrafast electron transport (2.2 ps), in which the interfacial Pd–S and Pd–P bonds serve as electron transfer channels. In addition, density-functional theory calculations reveal the key role of Pd atoms in the enhancement of light-harvesting capacity and optimization of proton adsorption thermodynamics. A visible-light hydrogen production rate of 82.5 mmol h–1 g–1 is attained by an optimal 1 wt % Pd–5 wt % VP/CdS photocatalyst, which manifests a 54-fold increase with respect to that of CdS NPs, in addition to an apparent quantum efficiency (AQE) of 25.7% at 420 nm. This work showcases a valid combination of S-scheme heterojunctions and SAs for efficient charge separation promoting photocatalytic hydrogen evolution, and others.