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Technical Briefs

# Two-Step Water Splitting Process With Solid Solution of YSZ and Ni-Ferrite for Solar Hydrogen Production (ISEC 2005-76151)

[+] Author and Article Information
Hideyuki Ishihara, Hiroshi Kaneko, Noriko Hasegawa

Research Center for Carbon Recycling Energy, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552, Japan

Yutaka Tamaura

Research Center for Carbon Recycling Energy, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552, Japanytamaura@chem.titech.ac.jp

J. Sol. Energy Eng 130(4), 044501 (Sep 08, 2008) (3 pages) doi:10.1115/1.2969813 History: Received May 09, 2005; Revised November 28, 2007; Published September 08, 2008

## Abstract

Ni-ferrite $(NiFe2O4)$ is a promising reactive ceramics of the ferrite for the solar hydrogen production by a two-step water splitting process using concentrated solar energy. However, it should be pretreated before $H2$-generation reaction by grinding the Ni-ferrite sintered after the $O2$-releasing reaction to make a fine powder. If the Ni-ferrite and yttria stabilized zirconia (YSZ) form a solid solution between these oxides ($YSZ∕NiFe2O4$ solid $solution=YSZ(Ni,Fe)$), it is expected that the two-step water splitting process with the Ni-ferrite system can proceed without treatment of the reduced product because of the high thermal stability of the $YSZ∕NiFe2O4$ solid solution. The $YSZ∕NiFe2O4$ solid solution was prepared by calcination of the mixture of the YSZ balls and $NiFe2O4$ powder at $T=1823K$ for $1h$, and its reactivity and thermal stability were examined for the two-step water splitting process. During the ten times repetition of the two-step water splitting reaction ($T=1773K$ for $O2$-releasing, and $1473K$ for $H2$-generation) with the $YSZ∕NiFe2O4$ solid solution using infrared imaging furnace, the reactivity for $O2$-releasing and $H2$-generation was kept constant. The molar ratio of the released $O2$ gas volume (the average $O2$ gas, $1.9cm3∕g$) and the generated $H2$ gas volume (the average $H2$ gas, $3.8cm3∕g$) was nearly 1:2, indicating that the water decomposition process via two steps proceeds. The X-ray diffractometry (XRD) measurement showed that the YSZ(Ni,Fe) keeps the YSZ phase structure during the ten times repetition of the two-step water splitting process. The successive $H2$ gas production by the two-step water splitting process was performed (ten times repetition of the two-step water splitting process). From comparative study on the reactivity and the thermal stability for the two-step water splitting reaction among the $YSZ∕NiFe2O4$ solid solution, $NiFe2O4$ and $ZnFe2O4$, it is concluded that the $YSZ∕NiFe2O4$ solid solution is superior to the others.

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## Figures

Figure 2

The XRD patterns of the mixture of YSZ ball and Ni-ferrite (a), the YSZ(Ni,Fe) obtained by calcinations in air (b), the solid sample after the 10th H2-generation reaction in Ar gas and steam flow (c), and the solid sample after the 11th O2-relreasing reaction in Ar gas flow (d)

Figure 1

Direct gas mass spectrometer (DGMS) signal of the O2-releasing reaction (a) and the H2-generation reaction (b)

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