Fig. 1-13 Concept of hydrogen and electric power co-generation system using HTGR This system provides co-generation of hydrogen and electric power from high temperature energy and methane.

Fig. 1-14 Electrolyte materials that show high ion conductivity at high temperatures The solid electrolyte BiO2 system has the highest ion conductivity presently known.

Fig. 1-15 Nano thin film formed on a sapphire single crystal base Nano thin film of about 250 nm thickness that consists of sintered nano particles of CeSmO2. These particles form this thin film on a sapphire base.

At a high temperature, near 1000 degree Celsius, hydrogen and carbon monoxide can be produced, using the following partial oxidation reaction of methane, CH4 + 1/2 O2 CO + 2H2 (1) This reaction will also result in a flow of electrons between solid electrolyte films by electron exchange between oxygen ions and ionized methane as shown in Fig. 1-13. Moreover, hydrogen can also be obtained by reaction (1) simultaneously with the production of electricity (co-generation). On the other hand, to generate electric power and hydrogen simultaneously by this method, a solid electrolyte material that exhibits high ion conductivity near 1000 degree Celsius is required. Various solid electrolyte materials that show high ion conductivity near 1000 degree Celsius are shown in Fig.1-14. As typical materials, the solid electrolyte BiO2 system, the LaGaO2 system, and the CeO2 system are well known for high temperature use. The solid electrolyte BiO2 system is the material with the highest ion conductivity presently known, although this material has a low melting point and is unstable at high temperatures. The chemical composition of the CeSmO2 solid electrolyte was formed by sol gel process using an organic solvent, doping Sm into CeO2 that shows the second highest known ion conductivity. Furthermore, it is doped on a sapphire single crystal base that is rotated at a fixed speed in the solution. The composition begins to gel as the viscosity increases. The gelled film of CeSmO2 forms on the base, and this single crystal is then heated to a high temperature. The process that creates the gelled film sinter is shown in Fig. 1-15. The nano thin film, about 250 nm in thickness, consists of sintered nano particles of CeSmO2 on a sapphire base (lower part of figure). When the ion conductivity of this nano thin film was measured at 1000 degree Celsius, the ion conductivity of this film has the highest value of any conventional material, as shown in Fig. 1-14. When this nano thin film is applied for use in the future, the electric power system shown in Fig. 1-13 and the new energy system that can produce hydrogen will simultaneously become viable.

Reference S. Ishiyama, Electricity and Hydrogen Multi Production Process with New Solid Electrolyte for HTGR (I), Nippon Genshiryoku Gakkai Wabun Ronbunshi, 2(1), 14 (2003) (in Japanese).

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