Vol.4 No.1 2011

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Research paper : Challenge for the development of micro SOFC manufacturing technology (Y. Fujishiro et al.)−51−Synthesiology - English edition Vol.4 No.1 (2011) process, and the co-sintering of laminated material. We succeeded in forming a flawless solid electrolyte film with thickness of single m in the cycle of the R&D model shown in Fig. 3. Also, the electrochemical reaction resistance and the reaction dispersal were confirmed in detail through the original evaluation and analysis of the micro SOFC prototype using the zirconia electrolyte (ScSZ: Scandia stabilized zirconia) at temperature lower than 650 °C for which there were few precedents. In the low temperature range, it was newly found that the resistance factors of the fuel cell changed according to the operation condition and contributed greatly to the increased generation performance. As shown in Fig. 8, by the optimization of the ceramics manufacturing process, high porosity surpassing 50 % was realized for the anode, and it was found that this greatly reduced the reaction resistance of generation at low temperature range. Figure 8b shows the relationship of the porosity of anode and the cell impedance resistance value at 600 °C. As shown in Fig. 8b, it was confirmed that the reduction resistance values represented as arcs decreased in relation to the increase of porosity of the anode. As a result, the output power performance surpassing 1 W/cm2 was realized in the low temperature range of 600 °C, as shown in Fig. 8c. From the post-reaction observation of the electrode structure, it was thought that the reduced nickel became nano particles in the electrode structure with high porosity, a high dispersal structure was formed, and this led to the increased number of three-phase boundaries that provided the active sites[15]. For the realization of this technology, the major factor was that the ceramics companies and others were able to achieve high properties at the cell manufacture level through the extrusion and wet coating processes that enabled mass-production and cost reduction. By considering the manufacturing process technology that incorporated the PDCA cycle in the R&D model in Fig. 3, we were able to achieve the micro SOFC manufacturing technology at low temperature range of 600 °C with the same performance as the zirconia electrolyte SOFC with power density 1 W/cm2 at 700−800 °C[16].Attentions were drawn in Japan and from abroad to this highly integrated module of fingertip or palm size that was distinctly different from the conventional energy module. Through the manufacture and evaluation in collaboration with user companies, it was demonstrated that these cells could be used to manufacture integrated modules of several hundred W level and were capable of realizing efficiency surpassing 40 % as fuel cells[17]. The future issues will be the development of kW class modules using the integrated modules composed of the developed microtube SOFC, as well as the development of the low-cost manufacturing technology.In the honeycomb micro SOFC development shown in Fig. 9a, it is necessary to create the electrochemical module of the integrated cell and to ensure the gas seal between the honeycomb SOFCs. As shown in Fig. 9b, a new integrated module technology was developed to handle rapid thermal history utilizing the thermomechanical property that was the stronghold of the honeycomb structure by forming the joint structure using the silver-silica paste as the interconnect. It became possible to manufacture an arbitrary serial structure unit by combining the highly integrated structure of several hundred cell/cm3 using this SOFC module technology. Also, by utilizing the easily warming property of the micro SOFC structure that has high relative surface area and low relative heat capacity and by confirming the electromotive force and current value, as shown in Fig. 9c and 9d, we proposed the micro SOFC module manufacturing technology that could handle 3-5 minute rapid startup, which was one of the required technical issues[18]. Also, the output power performance per unit volume at 650 °C was 2.8 W/cm3 or equivalent to the tubular integrated module, and high conversion efficiency could be expected for the SOFC. The (b)(e)(d)(c)(a)Cell CCell BCell AVoltage (V)Power density(W/cm2)Current density (A/cm2)Z’ (Ω cm2)Z’ (Ω cm2)0.00.51.03.02.01.00.00.20.40.60.81.01.2200 Wmodule1 W cellAfter reduction10 µm10 µmElectrolyte film formationScSZ cellIntermediate layerAnodeCathode~3 µmElectrolyte 1 µm37 %54 %47 %Fuel electrode porosityCell CCell CCell BCell BCell ACell A0.0-0.2-0.1-0.30.10.00.30.51.01.52.02.53.0-0.2-0.4-0.6-0.8-1.0-1.2Z’’ (Ω cm2)Z’’ (Ω cm2)Cell AFig. 8 Realization of zirconia low-temperature micro SOFC modulea: Photograph of cell cross sectionb: Relationship of electrode porosity and electrode resistance (600 °C)c: Generation performance (600 °C, humidified hydrogen)d: Structure of developed porous fuel electrode e: Example of developed cell and integrated module

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