The Cu-Cl cycle
Step I: Hydrogen production step (endothermic)
2CuCl(aq) + 2HCl(aq) ? 2CuCl2(aq) + H2(g), in aqueous solution of HCl, 80~100°C (I)
Step II: Drying step (endothermic)
CuCl2(aq) + nfH2O(l) ? CuCl2.nhH2O(s) + (nf – nh)H2O, nf >7.5, nh = 0~4, at 30~80°C (crystallization) or 100~260°C (spray drying) (II)
Step III: Hydrolysis step (endothermic)
2CuCl2.nhH2O(s) + H2O(g) ? CuOCuCl2(s) + 2HCl(g) + nhH2O(g), nh is 0~4, at 375°C (III)
Step IV: Oxygen production step (endothermic)
CuOCuCl2(s) ? 2CuCl(molten) + 1/2O2(g), 500~530°C (IV)
The S-I cycle
Step 1: Hydrolysis of iodine and sulfur dioxide (exothermic)
I2(l+g) + SO2(g) + 2H2O(g) ? 2HI(g) + H2SO4(l), 120°C (1)
Step 2: Oxygen production (endothermic)
H2SO4(g) ? SO2(g) + H2O(g) + 1/2O2(g), 850°C (2)
Step 3: Hydrogen production (endothermic)
2HI(g) ? I2(g)+ H2(g), 450°C (3)