Promoting the interfacial H^sub 2^-evolution reaction of metallic Ag by Ag^sub 2^S cocatalyst: A case study of TiO^sub 2^/Ag-Ag^sub 2^S photocatalyst

Metallic Ag has been widely demonstrated to be an excellent oxygen-reduction cocatalyst to significantly improve the photocatalytic decomposition performance of various organic substances. However, as a H2-evolution cocatalyst, the improved photocatalytic performance by metallic Ag is quite limited due to its low H2-evolution rate. In this study, for the well-known TiO2/Ag photocatalyst, Ag2S as the efficient H2-evolution active sites was selectively loaded on the metallic Ag surface to greatly promote the interfacial H2-evolution reaction rate. In this case, the TiO2/Ag-Ag2S sample was synthesized by a two-step process including the simple photoinduced deposition of metallic Ag on the TiO2 surface and the following in situ sulfidation of partial Ag into Ag2S. Photocatalytic experimental results indicated that the TiO2/Ag-Ag2S(40uL) photocatalysts clearly exhibited a significantly higher UV-light photocatalytic H2-evolution activity (119.11 µmol h-1) than the pure TiO2, TiO2/Ag and TiO2/Ag2S photocatalysts by a factor of 51.8, 3.9 and 3.6 times, respectively. On the basis of the present results, a synergistic effect of dual electron-cocatalyst (metallic Ag and Ag2S) is proposed for the improved photocatalytic H2-evolution activity, namely, the Ag-nanoparticle cocatalyst can steadily capture and transfer the photogenerated electrons from TiO2 surface, while the Ag2S cocatalyst is considered to be the interfacial active sites to promote the rapid H2-evolution reaction. This research may provide new strategies for the development of highly efficient photocatalytic materials used in various fields.