Research outline of Nano-ionics Materials Group

To spread fuel cell devices and develop sustainable society, a development of new type fuel cell which operates at temperature ranging from 200° to 500°C is required. However it is too difficult to develop those fuel cells, it is because there are no high quality solid electrolytes and electrodes which can be used in aforementioned fuel cells. In nano-ionics materials group, we are going to develop high quality solid electrolytes and electrodes through the following 6 sub-projects.

Sub-project 1. A design of nano-structured solid electrolytes:
To develop high quality solid electrolytes (i.e. bulk and thin film solid electrolytes), micro-structural features that are under detectable level of X-ray diffraction analysis should be taken into account. To maximize the oxide ionic conductivity in the solid electrolytes, we are going to design the nano-structure in the solid electrolytes.
Sub-project 2. A design of organic-inorganic hybrid membrane:
To maximize proton conductivity in the membrane, we have been developed organic-inorganic hybrid membranes that can be used above 150°C. It is expected that high quality organic-inorganic hybrid membranes with high temperature stability at temperature from 200° to 300°C will be developed by a design of interface conduction pathway between acid and base sites in aforementioned membranes.
Sub-project 3. A design of new nano-pore and meso-pore materials with high conductivity:
We have been developed lots of new nano-pore and meso-pore materials in NIMS. To develop new high quality electrodes in fuel cells, we will design the nano-/ meso-pore materials with high temperature stability and high conductivity for industrial application.
Sub-project 4. Development of high quality Pt-oxide composite electrodes:
To use low purity hydrogen or methanol as a fuel, Pt-Ru anodes have been developed. But Pt and Ru are rare metals. The limited resources of Pt and Ru in ore bodies on the planet will make the cost of large scale production expensive and so it is imperative that the Pt and Ru content of any potential electrode be reduced to a minimum. As a consequence of this, we have been developed new composite anodes with small amount of Pt for fuel cell applications.

Research topics

A) Research topic of sub-project 1:
CeO₂ doped with oxides of di- or trivalent metals possess higher oxide ionic conductivity than any reported stabilized zirconia electrolytes. At high oxygen partial pressures, these CeO₂ based oxides show high oxide ionic conductivity. At low oxygen partial pressures associated with anodic conditions above 600°C, however, the Ce⁴⁺ ion can be partially reduced to Ce³⁺ ion. In this reduction of CeO₂ based oxides, quasi-free electrons are introduced into a fluorite lattice. CeO₂ based oxides exhibit high oxide ionic conductivity in oxidizing atmosphere, whereas they are partially reduced and develop electronic conductivity under anodic conditions in the fuel cell over aforementioned temperature region. As a consequence of this, these materials should be used under 500°C for fuel cell applications. But the oxide ionic conductivity of doped CeO₂ in both atmospheres is not satisfactory level below 500°C. In order to overcome this problem and improve the oxide ionic conductivity at temperature ranging from 300° to 500°C, a design of nano-structure in doped CeO₂ electrolytes is required. Moreover, true microstructures in prepared specimens should be observed at atomic scale for conclusion of conduction mechanism and development of high quality solid electrolytes.
In this study, the nano-structural features in M_xCe_1-xO_2-x/2 (M: Gd, Sm, Y, Yb, Dy, La, Ho, Tb, and so on, 0 To maximize the conductivity in those materials, micro-domain should be minimized. To minimize the influence of micro-domains on conductivity, we improved our processing routes and developed high quality electrolytes.
Project staffs: Toshiyuki MORI, Ding Rong Ou, Fei Ye, Richard Buchanan, and Hirokazu Suga
Please look at our publication data if you are interested in this project.

B) Research topic of sub-project 2:
To develop the organic-inorganic hybrid membranes which can be used above 150°C, some hybrid membranes were prepared and characterized as proton conductors. Our hybrid membrane has high conductivity at temperature between 100° and 200°C. Also we examined power density using our membrane electrolytes above 100°C. We observed high power density in this test. We are going to improve the conductivity and thermal stability of our membrane electrolytes at temperature ranging from 200° and 300°C.
Project staffs: Je-Deok Kim, (Toshiyuki Mori)
Please look at the publication data if you are interested in this project.

C) Research topic of sub-project 3:
In this project, we already fabricated new CN, BCN meso-porous compounds. Also quite new nano-cage and nano-coop type porous materials were invented in this project. All our porous materials are quite unique materials. It is because they have high selectivity as catalysts or separation membranes. Since we can fabricate pore-size tunable porous materials with high conductivity for fuel cell applications, it is expected that our unique technique for fabrication of porous materials and our novel porous materials will be promising functional materials for development of fuel cell devices, catalysis, separation membrane and nano-bio reactors.
Project staffs: Ajayan Vinu, Pavuluri Srinivasu, Srinivasan Anandan, Anand Chokkalingam
Please look at our publication data if you are interested in this project.

D) Research topic of sub-project 4:
We investigated the anode performance of Pt-CeO₂ for the development of high quality anode materials for use in fuel cells. The Pt-CeO₂ composite anode was synthesized using the combined process of precipitation and co-impregnation methods. The processing technique leads to well dispersed Pt particles (7-8nm) on the CeO₂ particles. The peak current density for methanol oxidation on Pt-CeO₂ composite anode was 1.9 times higher than that on commercially available Pt-Ru alloy anode. The onset potential of methanol oxidation on Pt-CeO₂ composite anode shifted to a lower potential and the activation energy of the Pt-CeO₂ composite anode for methanol oxidation reaction was lower than that of the Pt-Ru alloy anode. The current density for methanol oxidation on Pt-CeO₂ composite anode at temperature between 28°C to 60°C was much higher than that on the Pt-Ru alloy anode. These results suggest that the anode performance of the Pt-CeO₂ composite anode is superior to that of the commercially available Pt-Ru alloy anode at the operation temperature (80°C) of the fuel cells. It is concluded that the redox reaction on CeO₂ surface plays the key role in enhancing CO oxidation on the Pt surface. The high performance and low cost anode material could be obtained using nano size CeO₂ particles instead of Ru as rare metal. Also, it will be possible to reduce the Pt content in our anode. Therefore, it is expected that the Pt-CeO₂ composite anode in the present study will be one of promising anode materials for development of the direct methanol fuel cells or the polymer fuel cells using low purity hydrogen as a fuel.
Project staffs: Toshiyuki Mori, Motoi Takahashi
Please look at our publication data if you are interested in this project.

Members of Nano-ionics Materials Group

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