Electrochemical noise diagnostics of PEM fuel cell stack for micro-cogeneration application
Résumé
Electrochemical noise (EN) generated by a 3500 W PEM fuel cell stack (50 cells) has been measured during micro-cogeneration durability tests. The experiments have been provided during long term campaign of measurements (more than 1200 h and 100 h have been analyzed) in well controlled operational conditions following The U.S. Department of Energy (DOE) recommendations. The micro-cogeneration operation mode involves two different regimes, one at 5 A (0.02 A.cm-²) and the other 99 A (0.45 A.cm-²). Thus, recorded signals are non-stationary, under dynamic load and specific data treatment procedure has been developed to overcome this difficulty. For both currents robust and stable statistical noise descriptors have been obtained based on Power Spectral Density (PSD) in the frequency range 0.01 Hz < f < 103 Hz. The noise signature of these currents involves two fractional noises (1 / f α) with different slopes α and pronounced peaks, at the characteristic frequency f = 1.6 Hz. The obtained noise signature is similar to the one obtained previously with the same type of the stack under stationary operation mode. It was demonstrated that noise signature varies slightly during stack operation. It seems that the observed evolution of the noise signature is related with reversible phenomena because after sudden interruption of the stack operation the PSD spectra return back to its initial shape. The proposed methodology of data treatment demonstrates that EN can be used as a tool for diagnostics of possible faults in long-term operation of electrochemical sources of energy under non-stationary conditions.