Vol.5 No.1 2012
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Research paper : Durable polymer electrolyte fuel cells (PEFC) for residential co-generation application (K. Tanimoto et al.)−57−Synthesiology - English edition Vol.5 No.1 (2012) three-phase interface composed of gas as the fuel (hydrogen gas) or oxidant, liquid as the electrolyte, and a solid electrode, respectively. The Bacon cell, which achieved the basic design of the practical fuel cell, was put to actual use, although in a special circumstance, as the power generating device for the spacecraft in the American space program. Later, the alkaline fuel cell was installed as the power source of the space shuttle.On the other hand, the fuel cell used in the actual spacecraft Gemini 5 in 1965 was the type in which the cation exchange membrane was used as the electrolyte, rather than the alkaline type. This fuel cell used pure hydrogen and pure oxygen that were the propellant of the spacecraft. Later, as mentioned earlier, the alkaline type became the mainstream for space use. On the other hand, DuPont developed Nafion, the fluorocarbon cation exchange membrane, and the performance increased greatly. In the 1970s, the development of the fuel cell power system was started as the next generation power generation technology. As the power generation technology, it was preferable to use air as the oxidizing gas due to its simplicity as a system. However, air contains carbon dioxide, and in the fuel cell that uses alkaline solution as the electrolyte, there was the issue of decreased performance due to the production and accumulation of unsolved carbonate salt in the electrolyte. Moreover, the fuel gas of the fuel cell power technology contains carbon dioxide because the hydrogen gas as fuel is produced from hydrocarbon. Therefore, in the development of the fuel cell power technology, it was necessary to add a device for removing the carbon dioxide or to use acid electrolyte. Therefore, both the developments of the fuel cell using alkaline and the one using acid, for example, phosphoric acid were conducted in parallel. Later, from the standpoint of long-term performance stability, the development of phosphoric acid fuel cell progressed. Today, it is developed as the distributed generation system of about 100 kW with lifespan of about 60,000 hours. In terms of system cost, it is competitive as the distributed power generation technology. During the Great East Japan Earthquake, it was used as the alternative power generation system during the blackouts,Note 1) and its durability and cost are the issues for practical application.After the development of the Nafion membrane, the nanotechnology to reduce the amount of platinum in the catalyst to a few fractions was developed in the late 1980s, by utilizing the platinum surface efficiently as a catalyst, by mixing the platinum supported carbon and the cation exchange resin electrolytes. This kicked off the development of the polymer electrolyte fuel cell (PEFC) for power generation in Japan as well as the United States and Europe in the 1990s. The developments were planned for distributed cogeneration and automobile application. Although there is a long history of development of the fuel cell, the cases of its practical application are limited. For its product realization, there are research efforts necessary in the phases from basic research, development, and commercialization. AIST engages in Full Research that engages systematically from basic research to product realization. Here, we present the efforts in Full Research using the example of the fuel cell. 2 For the practical application of fuel cellsThe fuel cell is a power generation device that produces electricity by the electrochemical reaction of hydrogen and oxygen. It is a component of the product used by the end user. Therefore, the fuel cell itself is not the product. For example, considering the product such as the fuel cell automobile, the fuel cell is the engine that propels the automobile, and whether the end user buys this product depends on his/her thinking on the value of the fuel cell automobile. While the fact that the automobile has an efficient power generation system that is clean and environment friendly, which are the characteristics of the fuel cell, as the engine may enhance the value of the fuel cell automobile, the value of an automobile is determined by the combination of driving performance, fuel-savings, and price. In conducting the fuel cell technology development for practical application, the issues of performance, cost, and durability were handled one by one. This arose from the fact that the fuel cell technology was in the technological budding stage where the three issues could not be solved at once. Therefore, it could not get out of the R&D stage. At the same time, this indicated that the fuel cell technology was always the technology of the future against the competing technologies such as the internal combustion engine and secondary batteries. This was not just a problem of fuel cell technology. In the basic research phase of many next-generation technologies, the simultaneous achievement of the solutions that must be solved for practical application is difficult, and the research must concentrate on one issue at a time. Therefore, as the development of the solution to one issue is sought, other technological issues are left behind in terms of practical application. This is a difficulty that faces the researchers conducting the R&D.In the fuel cell technology, attempt was made to overcome this issue by downsizing the fuel cell in the product to lower the hurdle of technological issues, yet not detracting from the value as a product. While this method may not be effective for all products, there seemed to be opportunities for trials due to the demand of the social situation or due to the marketability of the product. The residential cogeneration system that incorporated PEFC as the generation device could be used in the residential cogeneration where the exhaust water used for cooling the heat produced along with the electricity generated by PEFC at around 70 °C could be used as hot water. This was expected to be the product with the role in global warming countermeasure through energy saving and reduction of CO2 emission at home. In fact, there was a preceding case where the residential cogeneration

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