The study of thermochemical hydrogen preparation, (2)

Thermochemical water splitting processes by use of sulfur compounds are presented. These processes are partly based on the thermal decomposition of sulfuric acid for the step evolving oxygen. Three hydrogen evolving steps were investigated; (1) C//SO2,H2SO4sub(aq), H2//Pt, electrolysis (2) C//SP2, H2SO4sub(aq)/I2, HIsub(aq)/Pt, electrolysis (3) C//SO2, H2SO4sub(aq)/I2, HIsub(aq)//Pt, electrolysis without external electric power. Activated charcoal was found to be favorable material for the anodic reaction. In the case (1), the cycle is completed with two reaction steps but still it needs some electric power. In the cases (2) and (3), a cation exchange membrane is used and an additional step (2HI → H2+I2) is necessary to produce hydrogen. The electric power required can be reduced compared with the case (1), and especially in the case (3), no electric power is required. On the basis of the present study, some future problems are proposed. (auth.)