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When the voltage drops because the degradation accelerates with time, it is possible for a sudden voltage drop to occur after a certain time. For this reason, it is not possible to precisely estimate the durability on the basis of early-stage changes in the voltage under normal operation.
It is therefore necessary to develop a technique that allows accelerating degradation to occur for the major degradation factors.
In the NEDO project, made up of Japan’s leading manufacturers and experienced academics, Osaka Gas fully exploited its know-how on the cell evaluation method and was responsible for long-term durability tests on cell stacks and for verification of the accelerated degradation evaluation technique, establishing an accelerated degradation evaluation technique that takes about one month to forecast a 10-year durability.
An example of accelerated degradation evaluation methods developed under the NEDO project. When oxygen (O2) exists locally in the fuel electrode, the potential of the air electrode on the opposite side becomes higher, and as a result, the catalyst carrier carbon in the air electrode is oxidized and flooding is accelerated. By alternately supplying hydrogen (H2) and air to the fuel electrode, a reverse current is generated and degradation is accelerated.
A comparison of the degradation rate in the accelerated test and the continuous operation test showed an acceleration factor of 300.
On cell stack to be installed on ENE・FARM also, operating life forecasting was conducted using the fuel electrode gas switching method, confirming the 40,000-hour durability that was necessary for the early stages of commercialization.