Essential Concept Of The Experimental Approach

In a time course of the practical operation of PAFCs, all of the factors mentioned above may change simultaneously, even in the small model cell used in the project as the standard (10X10 cm2), attributable to the degradation of the cell performance and the life-time. Therefore, it is very difficult to separate the degree of their contribution to the degradation just by post-analysis of changes of the constructing materials or by the performance measurements such as cell voltage, 02 gain, internal resistance or polarization curves. In order to clarify which factor may be attributed predominantly to the degradation and which factor may require further improvement through fulure R&D, we have been challenged to evaluate the independent contribution of each factor (i) to the degradation of cell performance (¿1 £), typically the cell voltage (E), at the cells which have had alloy catalysts at different corrosion-levels prepared under various corrosion conditions and had gas-diffusion electrodes at well-defined filling-levels with phosphoric acid electrolyte. We tried to change each factor independently within a short time by applying a more severe experimental condition or using specially designed experimental cells. The results can be combined with each other and can serve to isolate the dominant factor to the degradation and in the principle to evaluate the overall degradation rate of the model cell performance (dE/dt) as in the following:

4E = Z(dEldi)di (1), dEldt=2(dEldi)l(dildt) (2), where the practical degradation rate of each factor ( d M d t) can be obtained from post-analysis for the model cell operated under a fixed condition of temperature, pressure and current density. Details of (he experimental or the experimental results are described in the other pages of the proceedings for our poster papers.

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