Aerosol spray pyrolysis synthesis of water-splitting ferrites for solar hydrogen production

Aerosol spray pyrolysis (ASP) was employed for the synthesis of oxygen-deficient doped ferrite systems to be used as redox materials for the production of solar Hydrogen from water via a two-step thermochemical water-splitting cycle. In the first step (water splitting) the reduced state of a metal oxide is oxidized by taking oxygen from water and producing hydrogen; in the second step (regeneration) it is reduced again by delivering some of its lattice oxygen. Redox materials of the iron spinel family doped with other bivalent metals (Zn, Ni, Mn) were synthesized via ASP, characterized and evaluated with respect to their water-splitting activity. Organic additives, like citric acid, in the precursor solutions were found to result in products with finer particle size and to enhance the water-splitting activity of the synthesized materials. Material performance (water splitting activity, hydrogen yield, regeneration capability) was found to depend on the dopants' kind and stoichiometry; in particular high percentages of Zn dopant seem to enhance the overall materials' performance. ASP synthesized materials have demonstrated higher water conversion and hydrogen yields than materials of the same composition synthesized through solid-state routes. The ASP synthesis process was scaled-up successfully maintaining the favorable characteristics of the synthesized materials.