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

A MSO4—NH3 cycle method for producing H2 and O2 from a continuous and closed system consisting essentially of the steps of:

• feeding a 1 M aqueous (NH3)4SO3 solution into a photoctalytic reactor or electrochemical reactor to oxidize the aqueous (NH3)4SO3 into aqueous (NH3)2SO4 and reduce water to hydrogen;
• mixing the resulting aqueous (NH3)2SO4 with metal oxide to form a slurry, wherein the ratio of metal oxide to ammonium sulfate is maintained at 1.5 to 1;
• heating the slurry of aqueous (NH4)2SO4 and metal oxide in the low temperature reactor to produce a gaseous mixture of NH3 and H2O and metal sulfate;
• heating solid ZnSO4 at a high temperature reactor to produce a gaseous mixture of SO2 and O2 and solid ZnO, wherein the heating rate is maintained at 5° C./min to 50° C./min;
• recycling ZnO back to mix with aqueous (NH4)2SO4 solution to a slurry that is be fed into a low temperature reactor;
• mixing the gaseous mixture of SO2 and O2 with NH3 and H2O in an absorber to separate O2 from aqueous (NH4)2SO3 solution to produce O2;
• recycling the ammonium sulfite back to the photoreactor to close the water splitting cycle to produce both gaseous H2 and gaseous O2 as the only products output from the continuous and closed ZnSO4—NH3 cycle;
• and
• wherein the method implements a closed water splitting cycle, and wherein only the water is consumed by the closed water splitting cycle.

A M2S2O7—NH3 hybrid continuous and closed photo and thermo-chemical water splitting cycle method consisting essentially of the steps of:

• receiving a solar radiation;
• using the solar radiation for the production of hydrogen in a photoreactor via photochemical oxidation of aqueous ammonium sulfite solution to produce hydrogen;
• using the solar radiation for the production of oxygen including introducing a metal sulfate (K2SO4, Rb2SO4 and Cs2SO4) to convert ammonium sulfate into metal pyrosulfate (K2S2O7, Rb2S2O7 and Cs2S2O7), wherein the ratio of metal oxide or metal sulfate to ammonium sulfate is maintained at 1.5 to 1;
• decomposing the metal pyrosulfate for the production of O2, wherein the heating rate is maintained at 5° C./min to 50° C./min;
• supplying the regenerated ammonium sulfite to the photoreactor, and
• wherein the method implements a closed water splitting cycle, and wherein only the water is consumed by the closed water splitting cycle.