Electrochemical noise analysis of a PEM fuel cell stack under long-time operation: noise signature in the frequency domain
Résumé
Electrochemical noise (EN) generated by a PEM fuel cell stack (600 W, 8 cells with surface area 220 cm2) has been measured in well-controlled operational conditions following DOE recommendations for 100 h. For the first time, robust and stable statistical noise descriptors of a PEM fuel cell stack have been obtained based on PSD (power spectral density) spectra in the frequency range of 0.1 Hz < f < 103 Hz. The reference noise signature of the stack involves white noise at the low-frequency range (f < 0.1 Hz), two fractional noises (1/fα) with different slopes, and a pronounced peak at the characteristic frequency f = 1.6 Hz. In the intermediate frequency range (0.1 Hz < f < 1 Hz), the slope α1 = 1.49 and in the high-frequency range (f > 10 Hz), the slop α2 = 3.23. Qualitative interpretations of the obtained noise signature have been proposed. The influence of interruption of stack operation on noise signature has been studied. It was shown that, just after a few hours, other peaks are visible in noise signature at f = 0.004 Hz and f = 0.06 Hz. These peaks disappear after about 20 h; this time can be considered as a characteristic time of relaxation of the slowest processes. It can be also noted that during stack relaxation, the slope in the intermediate frequency range increases and the slope at the high-frequency domain remains constant. It seems that fractional noise at high-frequency range reflects charge transfer processes in catalytic layers with smaller time constants. On the other hand, low and intermediate frequency ranges are related to mass transport and water management processes with higher time constants.
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