Photochemical production of hydrogen from alkaline solution containing polysulfide dyes

Efficient hydrogen production was achieved by irradiating solutions containing polysulfide dyes as a photoabsorber. In the presence of polysulfide only, considerable amount of hydrogen was initially evolved and followed by the rapid decrease of the evolution rate. On the contrary, in the co-presence of NiOx(x<1)/TiO2 and polysulfide, steady evolution of hydrogen was observed even after long period of illumination. The photocatalytic evolution of hydrogen was divided into two stages: i) in the first stage within 1 hour irradiation, the hydrogen evolution rate was abruptly increased due to the conversion of polysulfide to partially oxidized sulfur, S2Ox2-; ii) in the secondary stage after 1 hour irradiation, steady evolution of hydrogen was observed due to the conversion of partially oxidized sulfur to fully oxidized sulfur. The oxidation/reduction of sulfur occurred more favorably over SiC catalyst where more steady evolution of hydrogen was achieved.