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

Abstract

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.

Innovative solar thermochemical water splitting.

“…An important consequence is that high porosity may not be needed and sintering of the porous zirconia may not be an issue. These observations appear to be in good agreement with those obtained by Ishihara et al, [16] and may be a key to the CR5 concept viability. They suggest a new type of redox material with high internal oxygen mobility for transport of oxygen to and from dispersed redox sites.…”

“…It is slightly exothermic and is spontaneous at ambient temperature to about 1200 K. In recent years, research has focused on mixedmetal oxides called ferrites that have a spinel crystal structure involving Fe and a second metal A (where A = Mn, Mg, Co, Zn, and/or Ni) as a way to lower the temperatures required to reduce the oxide. [9][10][11][12][13] Recently, Kodama et al, [14,15] and Ishihara et al, [16] have demonstrated that dispersing the ferrite in zirconia enhances reactivity and improves reduction and hydrolysis kinetics. They have also shown that the supported materials maintain reactivity when repeatedly cycled between TR and WO reactions.…”

A review and perspective of efficient hydrogen generation via solar thermal water splitting

“…The oxidization of the dissolved cations has an activation energy of 53.9 kJ/mol, while the solid solution of CoOFeO has an activation energy of 141 kJ/mol. Like CoFe 2 O 4 , NiFe 2 O 4 splits water repeatedly with a high H 2 production capacity, producing roughly 179 µmol H 2 /g when deposited on YSZ and reduced at <1500°C . Similar to the cases of CoFe 2 O 4 and Fe 3 O 4 deposited on YSZ, Fe 2+ ions from the reduction of NiFe 2 O 4 dissolve into the YSZ support and NiFe 2 O 4 is stable over multiple cycles.…”

Reactive ceramics of CeO2–MOx (M=Mn, Fe, Ni, Cu) for H2 generation by two-step water splitting using concentrated solar thermal energy

“…YSZFe 3 O 4 was synthesized for the cyclic two-step watersplitting reaction as a reactive ceramic, which has the stability at the temperature of the O 2 -releasing reaction and high conductivities of O 2À . The amount of H 2 evolved in the H 2 -generation reaction with YSZ-Fe 3 O 4 after the O 2 -releasing reaction at 1773 K was 1.77 cm 3 /g [13]. The temperature of the O 2 -releasing reaction with CeO 2 -Ce 2 O 3 (CeO 2 ¼ cerium dioxide) system was evaluated above 2500 K from the thermodynamic data calculated by MALT2 software [14].…”