With the U.S. DOE funding, Florida Solar Energy Center (FSEC) of the University of Central Florida (UCF) and Science Applications International Corporation (SAIC) are jointly developing advanced solar-powered thermochemical water splitting cycles for the production of hydrogen. At FSEC, we have developed a new class of hybrid photo/thermochemical water splitting cycles represented by the following reactions:

SO2(g) + 2NH3(g) + H2O(l) → (NH4)2SO3(aq) (chemical absorption)
(NH4)2SO3(aq) + H2O → (NH4)2 SO4(aq) + H2(g) (solar photocatalytic)
x(NH4)2SO4 + M2Ox → 2xNH3 + M2(SO4)x + xH2O (solar thermocatalytic)
M2(SO4)x(s) → xSO2(g) + 2MO(s) + (x-1)O2(g) (solar thermocatalytic)

Where, M = Zn, Mg, Ca, Ba, Fe, Co, Ni, Mn, Cu.

In these cycles, the photonic portion of solar irradiance drives the hydrogen production step, while the solar thermal portion (i.e. IR) is used in the reactions that generate oxygen. The photocatalytic hydrogen production step employs aqueous ammonium sulfite solution that is oxidized to ammonium sulfate in the presence of visible light sensitive photocatalysts. The overall efficiency of these water splitting cycles depends, in part, on the efficiency of the photocatalytic step. A novel method for the preparation of cadmium sulfide based visible light activated photocatalysts using chemical precipitation and hydrothermal technique is reported. Experimental results show that the purity and degree of crystallinity of the nanosized photocatalyst particles are key factors affecting the efficiency of the prepared photocatalysts. Results obtained, to date, are presented and their ramifications discussed.