Abstract:

CdS photocorrosion is one of the most important factors that greatly affect the photocatalytic H₂-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 Cd²⁺ by photogenerated electrons is usually ignored. In this work, the lattice Cd²⁺ reduction by photogenerated electrons during CdS photocorrosion were carefully investigated to reveal its potential effect on the microstructure change and photocatalytic H₂-production performance of CdS photocatalyst based on the two typical Na₂S-Na₂SO₃ and lactic acid H₂-evolution systems. It was found that many isolated metallic Cd nanoparticles (5-50 nm) were produced on the CdS surface in the Na₂S-Na₂SO₃ 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 H₂-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 H₂-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 H₂-evolution performance.

Key words: Photocatalysis, H₂ evolution, CdS, Photocorrosion, Self-stability