Hydrogen Production Through Two-Step Water Splitting Using YSZ (Ni,Fe) System for Solar Hydrogen Production

The two-step water splitting with the solid solution of YSZ (Yttrium stabilized Zirconia) and Ni-ferrite (NiFe₂O₄) was studied for solar hydrogen production. The sample of YSZ/Ni-ferrite solid solution was prepared by calcination of the mixture of the YSZ balls and Ni-ferrite (NiFe₂O₄) powder. The two-step water splitting process composed of O₂-releasing reaction (T = 1773K) in Ar gas flow and H₂-generation reaction (T = 1473K) in Ar gas and steam flow with the YSZ/Ni-ferrite solid solution were repeated ten times, and the molar ratio of the released O₂ gas and the generated H₂ gas was nearly equal to 1:2 in each cycle, indicating that the two-step water splitting process proceeded stoichiometrically. The lattice constants of the YSZ/Ni-ferrite solid solution products after each step of the water splitting process were varied, therefore it was assumed that the oxidation and reduction of the iron ions proceeded in the YSZ phase. It is confirmed that the YSZ/Ni-ferrite was the solid solution and reactive ceramics of high thermal stability. The contents of iron ions determined by the atomic absorption spectroscopy indicated that the YSZ/Ni-ferrite solid solution heated at 1773K contained the only 36% of iron loaded initially. The generated O₂ gas was 42% of the theoretical yield. These suggest that YSZ/Ni-ferrite solid solution is more effective reactive ceramics which has the ability to split water with concentrated solar heat than Ni-ferrite.