Various Scales of Aging Heterogeneities upon PEMFC Operation – A Link between Local MEA Materials Degradation and the Cell Performance

It is no secret that PEMFC performances decay upon operation, owing to the degradation of their core materials ¹. Refining the data obtained from several experimental campaigns made in close collaboration between Axane and academic laboratories, it soon appeared that the materials degradations were not homogeneous within a PEMFC, whatever its operating conditions (stationary on the field or accelerated stress test at the laboratory scale) and their constitutive materials.

If one limits to the cathode active layer, there are three distinct levels of degradation heterogeneities. (i) At the scale of the MEA, the degradations are neither homogeneous along the gas channels of the bipolar plates (BP, from the inlet to the outlet, Figure 1) ², nor along the active layer thickness (from the membrane interface to the diffusion layer interface) ^2,3. (ii) The BP geometry also matters, since in the particular case of repeated start/stop and associated fuel-starvation events, harsher degradation was observed for the cathode regions facing the anode regions located under the land of the BP (Figure 2) ⁴. (iii) Finally, not all the cells operate and age in the same manner at the stack level (Figure 3) ⁵.

In any case, the degradations are strongly linked to the materials composing the MEA, but also depend on the fluidics of the cell (e.g. design of the bipolar plates and stack), which renders difficult any generalization of the conclusions obtained for a particular test.

References

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