Thermodynamic investigation on new thermochemical water-decomposition cycles

New thermochemical water-decomposition cycles to produce hydrogen have been devised by a stepwise selection of the component reactions. First, various hydrogen-and oxygen-generating reactions are classified into several groups, and the candidate reactions are then selected from them by using such requirements as follows. (1) ΔG0 of the reaction is less than 10 kcal/mol-H2 for the reaction to take place. (2) When a one-step reactant-regenerating reaction is supposed, the ΔG0 of this reaction is less than ΔG0(250C) of direct water-decomposition (= 56 kcal/mol-H2O). Then, in order to close the cycle, possible reactant-regenerating reactions are selected from known chemical reactions. As a result, two types of new cycles which have thermodynamic feasibility are proposed by using I2Na2CO3 and Cu-Cl as the main cyclic reactants. (author)