A solar thermochemical water-splitting cycle which utilizes the electrolytic oxidation of aqueous ammonium sulfite as the hydrogen production half cycle, and an all-liquid potassium sulfate/potassium pyrosulfate salt solution for the oxygen production half cycle was modeled using Aspen Plus. The thermochemistry of various molten salt mixtures for the oxygen production half cycle was studied. A robust Aspen Plus chemical plant model represents the thermodynamic characteristics of the cycle, as

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... rified by experiment. The laboratory experiments showed that the melting point of the salt may be lowered by 100°C with the addition of sodium sulfate/pyrosulfate to the potassium sulfate/pyrosulfate and that the viscosities of the mixtures are low enough for pumping. There is a temperature separation of ~25°C between evolution of ammonia and SO 3 gases during molten salt decomposition.