Vol.4 No.1 2011

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Research paper : Challenge for the development of micro SOFC manufacturing technology (Y. Fujishiro et al.)−49−Synthesiology - English edition Vol.4 No.1 (2011) of 2 mm or less, the optimization of the cell form (thickness of electrolyte and electrode, optimal cell length, etc.) that affected the final module generation capacity was important. In the anode supported cell, because the electrode has the roles of reactive field in the three-phase boundary for the electrochemical reaction and of the collector of current generated in the reaction, its design greatly affected the generation performance of the cell and integrated module. Figure 5 shows the results of the different power collection methods and the cell form for achieving high performance in the Anode supported microtube SOFC and its integrated module. The results were used to design the length of the cell collector. The collection resistance increased when the long cell design was used to extend the electrode surface area of the single cell structure, and the power generation output decreased (current collection loss).The design technology needed to manufacture the microtube SOFC with exterior diameter 2 mm (interior diameter 1.6 mm, electrode film thickness of 0.2 mm) is explained. Assuming the generation performance to be 0.5 W/cm2 at 550 °C, the current collection loss in the equivalent circuit was calculated using the single-end and double-end current collection models. The relationship of the current collection loss arising from the current collection resistance factor and cell length is shown in Fig. 5. When the length whereby the current collection loss in power generation would be 3 % or less was calculated, it was found that the integrated module must be designed with cell length of 2.0 cm for double-end current collection and 1.0 cm for single-end current collection. This showed that it was necessary to increase the thickness of the double-end current collector and anode in order to increase the surface area of the generation electrode by increasing the cell length[10]. Conversely, since it was necessary to decrease the electrode thickness to increase the cell performance, the cell length optimization was important to improve the integrated module generation performance at low temperature. Under such design guidance, the integrated module manufacturing technology was developed by bottom-up design, and the mass-producible cell manufacturing was developed by improving the film coating technology and the forming precision in the extrusion technology[11]. As a result, the anode supported micro SOFC using the 2.0 mm ceria electrolyte achieved a high power density of 1.0 W/cm2 at 570 °C[11]. Moreover, this high-performance cell (microtube cell) was combined to fabricate the module structure integrated inside porous ceramics, and the optimal cell arrangement within the module was studied by similar equivalent circuit simulation design. As shown in Fig. 6, by calculating the current collection loss in the integrated module model, it was found that the conductivity over 100 S/cm was required at cell interval of 1.0 mm for the current collector members (between cells). The 2 W level generation unit was realized where several microtube SOFC with 2.0 mm diameter was integrated in a space the size of a sugar cube. In this investigation, the design and manufacturing technology for the integrated module (cube module) with generation performance over 2 W/cm3 at 550 °C was developed, and it became possible to fabricate various integrated module structures such as of the serial connection[12].ii) Cell structure control technology in the advanced coating processIn achieving high performance for the SOFC and integrated module, it was necessary to develop the manufacture process technology that could be applied to macro connections by creating the multilayer structure of different materials such as ceramics electrode and electrolytes based on the electrochemical structure design at nano to micro size. Moreover, it was necessary to develop a simple and mass-producible manufacturing technology such as wet coating that could effectively control the degree of cell integration without being influenced by the composition of base material on which the cells were arranged. For the manufacture of electrodes for the ceramics electrochemical device such as SOFC, new developments of the various cell forms, composition control, and layer structures were necessary, and both the coating technology with high degree of freedom to form functional ceramics and advanced 3D coating technology had to be established. The increased density and formation of the electrolyte film and the structural controllability in cell structure formation had to also be increased. To form the film structure necessary to increase performance, we embarked on the development of the manufacturing process technology that allowed even slurry coating in sub-millimeter 3D space, by advancing the new wet coating manufacturing process technology.Figure 7 shows the characteristics of the various wet ceramics coating processes. For the wet paste coating on Fig. 6 Cube module design and the developed integrated modulea: Design model of integrated module b: Result of current collection loss calculation at 650 °Cc: Example of developed module1.21.00.80.60.40.20110(c)(b)(a)5 %49 S/cm108 S/cm139 S/cmConductivity of porous current collection partsInterval between tubes Z (mm)Current collection loss (%)100Micro SOFCyxZ(Cube module, etc.)Porous current collection parts/cathode Porous current collection parts1 cmCurrentcollectingelectrode

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