Solar metal sulfate-ammonia based thermochemical water splitting cycle for hydrogen production.

Two classes of hybrid/thermochemical water splitting processes for the production of hydrogen and oxygen have been proposed based on (1) metal sulfate - ammonia cycles (2)metal pyrosulfate - ammonia cycles. Methods and systems for a metal sulfate MS04 - NH3 cycle for producing H2 and 0 2 from a closed system including feeding an aqueous (NH3)4SO3 solution into a photocatalytic reactor to oxidize the aqueous (NH3)4SO3 into aqueous(NH3)2S04 and reduce water to hydrogen, mixing the resulting aqueous (NH3)2S04 with metal oxide (e.g. ZnO) to form a slurry, heating the slurry of aqueous (NH4)2S04 and ZnO(s)in the low temperature reactor to produce a gaseous mixture of NHs and H20 and solid 10 ZnS04(s), heating solid ZnS04 at a high temperature reactor to produce a gaseous mixture of SO2 and 0 2 and solid product ZnO, mixing the gaseous mixture of SO2 and 02 with an NH3 and H20 stream in an absorber to form aqueous (NH4)2SO3 solution and separate O2 for aqueous solution, recycling the result