Two-step water-splitting at 1273–1623 K using yttria-stabilized zirconia-iron oxide solid solution via co-precipitation and solid-state reaction

Reactive ceramics are investigated for potential use in a rotary-type solar reactor. The two-step water-splitting process, which consists of O2-releasing (MOoxidized=MOreduced+1/2O2) and H2-generation (MOreduced+H2O(g)=MOoxidized+H2) reactions with yttria-stabilized zirconia (YSZ)-iron oxide solid solutions prepared by co-precipitation and solid-state reaction, is examined at temperatures of 1623 K for O2 release and 1273 K for H2 generation. The YSZ-iron oxide solid solutions with a single phase are obtained at mole ratios lower than 15% and 20% of iron ions to total cations (Fe3+, Zr4+, Y3+) by co-precipitation and the solid-state reaction, respectively. The two-step water-splitting process using YSZ-iron oxide solid solutions prepared by both preparation methods are repeated successfully. The amount of O2 gas evolved per weight of the sample (ml/g) is observed to increase with the iron content of the YSZ-iron oxide solid solution because of the high reactivity of iron ions in the solid solution. The maximum amounts of H2 and O2 gases evolved in the two-step water-splitting process with the YSZ-iron oxide solid solution were 0.89 and 1.2 ml/g, respectively.