Vol.5 No.1 2012

Research paper : Durable polymer electrolyte fuel cells (PEFC) for residential co-generation application (K. Tanimoto et al.)−58−Synthesiology - English edition Vol.5 No.1 (2012) system with the gas engine was commercialized and became wide spread in 2003. The generation efficiency of the gas engine was over 20 %, and it was heat-main electricity-sub supply where the main supply would be heat rather than electricity. As the energy utility form at home, the percentage of electric appliances increased, and considering the hot and humid climate in Japan, it was thought that electricity-main heat-sub supply where the percentage of electricity supply was higher would have higher demand. Therefore, high electric power generation efficiency was required in the cogeneration devices. As the generation efficiency of PEFC was expected to surpass 30 %, the potential for the marketability of residential fuel cell cogeneration system was expected to be high. In fact, accompanying the continuous progress in the R&D for PEFC after the 1990s, the generation efficiency was in the 30 % level performance and the conditions for commercialization were being fulfilled. However, the durability of the product was insufficient compared to the competing technologies, and the technological development to maintain the durability for withstanding practical use was necessary. In this situation, in 2004, the government policy was set to introduce the residential fuel cell cogeneration to expand the use of fuel cells by 2008. The demonstration of PEFC residential cogeneration system started in 2005, and at the same time, R&Ds were conducted for increasing the durability that was necessary for commercialization. The goal for durability of the PEFC in its initial commercialization stage was set at 40,000 hours considering the social acceptability and system cost. Figure 2 shows the thinking of the development in the background of the social shift to low carbon energy society, where the downsized fuel cells would lower the hurdle of technological issues against the competing technologies, and the focus on durability as the development issue for residential cogeneration would enhance commercialization.The technological development of improved durability was also essential for the automotive and mobile power system uses in which the PEFC technology could be used. In automotive use, the severe usage environment, rapid output shift for the power source device, start-up in a short time, and others were expected, and in practical use, the actual operating time would be shorter than the idle time. Such difference in operating conditions may require different measures when making technological estimates for obtaining durability. However, there is no major difference in the PEFC material configuration, and the findings on degradation phenomenon and mechanism obtained in the investigation for residential cogeneration system can be applied.3 Objective and necessity of accelerated aging method of PEFCThe development of PEFC technology in Japan was started as the national project and by fuel cell system manufacturers in the early 1990s. Therefore, the system manufacturers accumulated unique technologies for the PEFC material, configuration, and system. As mentioned earlier, around 2004 the direction for the commercialization in 2008 of the fuel cell residential cogeneration was given to promote energy savings and as a measure against global warning. While the companies were aware of the common technological issues for obtaining the 40,000-hour durability, the exchange of technological information did not occur. Particularly, the degradation phenomenon that was the issue in practical use was unclear, although it was expected that the operating condition of PEFC would affect the material, performance, and cell structure.As part of the establishment of technology pertaining to the durability for the commercialization of PEFC in 2008, the 3.5 year NEDO Project “Fundamental Research of Degradation of PEFC Stacks” was started in October 2004, in the industry-academia-government collaborative consortium consisting of the system maker, energy supplier, universities, and AIST. While 40,000-hours-operation were required as the durability of the fuel cell that would be the main body of the fuel cell residential cogeneration system, the lifetime of PEFC stack in 2005 was about 10,000 hours, and the technology to dramatically increase the durability was necessary. To clarify the common degradation issue for which the fuel cell system makers possessed unique technological information, the makers set the goal of developing the accelerated test protocol for the fuel cells. The project was executed under the scheme of clarifying the degradation phenomenon and mechanism. Since 40,000 hours was about 4.6 years in actual time, the development of the accelerated test to predict the 40,000-hour durability in a year was meaningful to the companies. At the same time, since the accelerated test protocol would be explained by the degradation mechanism, the investigation of degradation Fig. 2 Past processes of the fuel cell development and the development toward commercializationPower source of residential cogeneration systemMachine power source, engine, turbine, secondary batteryPerformance, reliability, cost, safetyCommercialization of productMismatch of design as a productMismatch of design as a productCommercialization is difficultCostCostDurabilityDurabilityPerformancePerformanceFuel cellRecent social background:Sustainable economic development, low carbon energy technologyScenario-driven commercializationLower technological hurdle through small power generation sourceIncreased performance of device, increased requirements for performance(generation system, automobile, cogeneration system, electric appliances)CommercializationIssue for commercialization: technology to increase lifetimeSteady advance from basic technology


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