Photoinduced self-stability mechanism of CdS photocatalyst: The dependence of photocorrosion and H2-evolution performance

Abstract

• The lattice Cd 2+ reduction during CdS photocorrosion was carefully investigated. • The isolated Cd nanoparticles were produced on CdS surface in Na 2 S-Na 2 SO 3 system. • A metallic Cd layer is uniformly coated on CdS surface in the lactic acid system. • A photoinduced self-stability mechanism of CdS photocatalyst has been proposed. CdS photocorrosion is one of the most important factors that greatly affect the photocatalytic H 2 -production rate and long-time stability. However, the reported works about CdS photocorrosion are mainly focused on the surface oxidation by photogenerated holes, while the possible reduction of lattice Cd 2+ by photogenerated electrons is usually ignored. In this work, the lattice Cd 2+ reduction by photogenerated electrons during CdS photocorrosion were carefully investigated to reveal its potential effect on the microstructure change and photocatalytic H 2 -production performance of CdS photocatalyst based on the two typical Na 2 S-Na 2 SO 3 and lactic acid H 2 -evolution systems. It was found that many isolated metallic Cd nanoparticles (5–50 nm) were produced on the CdS surface in the Na 2 S-Na 2 SO 3 system, causing its serious destroy of CdS surface and a gradually decreased photocatalytic activity, while only a metallic Cd layer (2-3 nm) is homogeneously coated on the CdS surface in the lactic acid system, leading to an increased H 2 -evolution rate. In fact, once a certain amount of metallic Cd was produced on the CdS surface, the resulting CdS-Cd composites can present a stable photocatalytic H 2 -production activity and excellent stability for the final CdS-Cd photocatalysts. Hence, a photoinduced self-stability mechanism of CdS photocatalyst has been proposed, namely, the spontaneously produced metallic Cd contributes to the transformation of unstable CdS into stable CdS-Cd structure, with the simultaneous realization of final stable H 2 -evolution performance.