Development of Reactive Ceramics for Conversion of Concentrated Solar Heat Into Solar Hydrogen With Two-Step Water-Splitting Reaction

The reactive ceramics suitable for the rotary-type solar reactor (proposed by Tokyo Institute of Technology, Tokyo) with two-step water-splitting reaction were developed. It is confirmed that $O2$ gas is evolved in the two-step water-splitting reaction with the reactive ceramics vigorously by rapid heating (⁠$α-O2$-releasing reaction). The $α-O2$-releasing reaction is due to the formation of interstitial defect and the conversion of lattice oxygen into $O2$ gas at a nonequilibrium state. Reactive ceramics (⁠$NiFe2O4$ and yttria stabilized zirconia $(YSZ)-NiFe2O4$ solid solution) can absorb solar thermal energy and convert thermal energy into chemical energy under high $O2$ partial pressure atmosphere in the $α-O2$-releasing reaction. Repetitive evolutions of $O2$ gas were observed in the two-step water-splitting reaction with $YSZ-Fe3O4$ solid solution and cerium based metal oxides (⁠$CeO2–NiO$⁠, $CeO2–ZrO2$⁠, and $CeO2–Ta2O5$⁠) at high $O2$ partial pressure. The $CeO2–Ta2O5$$(Ce:Ta=90:10)$ released a large amount of $O2$ gas $(3.95cm3/g)$ in the $α-O2$ releasing reaction in the flow of air.