Visible light induced hydrogen evolution over the heterosystem Bi2S3/TiO2

A new photochemical heterosystem Bi2S3/TiO2 immersed in solutions of X2− (=S2− or S2O32−) as reducing agents for generated minorities is proposed. Bi2S3, synthesized via solvent thermal process, has a good crystallinity and exhibits n-type conduction as evidenced from photocurrent-potential characteristics. The flat band potential of Bi2S3 (−0.83VSCE) is pH-insensitive and shifts negatively with increasing S2− concentration by ∼53 mV/pS. The heterosystem shows a much higher activity than Bi2S3 alone where efficient H2-photoevolution can be realized with concomitant oxidation of X2−. The optimal value of the mass ratio (Bi2S3/TiO2) was equal to unity. In S2O32− electrolyte, the photoactivity peaks at pH ∼13.7 with an evolution rate of 2.9 μmol mg−1 h−1 and decreases gradually to zero near pH 7. The competitive back reduction of end products S4O62− and S22− slows down the H2-evolution. The regression of the photoactivity over time is also due to the decrease of band bending at the interface TiO2/electrolyte.