Hydrogen Production by the Mg-S-1 Thermochemical Water-Splitting Cycle \

Abstract

As a result of an investigation for the effects of various kind of metal oxides on separation of the HI-H₂SO₄ mixed solution produced in the S-I scheme, the Mg-S-I thermochemical water-splitting cycle was proposed as follows.
Sufficient rate and yield were experimentally confirmed for each of the constituent reactions. By use of the pyrolysis temperature difference between MgSO₄ and MgI₂, a batch system demonstration of the whole cycle was performed by repetition of 38 times of cycle operation with roughly constant production of O.3 dm³ H₂ and O.15 dm³ O₂ per hour, where the solid reactants were unmoved. More detailed study revealed that MgI₂ and MgSO₄ can be separated by the common ion (Mg²⁺) effect under the highly concentrated conditions of the MgI² MgSO⁴ mixed solution.
By use of the MgI²-MgSO⁴ separated process, a continuous flow system of the whole cycle was demonstrated for 33 h with roughly constant production of 0.5 dm³ H₂ and O.25 dm³ O₂ per hour, where all the reactants including solid ones were smoothly circulated in the cycle apparatus. Thermal efficiency of the cycle was estimated to be 17-39% for 65-85% of the overall heat recovery.