Abstract
In this paper, the main faults in a commercial proton exchange membrane fuel cell (PEMFC) stack for micro-combined heat and power ( μ -CHP) application are investigated, with the scope of experimentally identifying fault indicators for diagnosis purposes. The tested faults were reactant starvation (both fuel and oxidant), flooding, drying, CO poisoning, and H2S poisoning. Galvanostatic electrochemical impedance spectroscopy (EIS) measurements were recorded between 2 kHz and 0.1 Hz on a commercial stack of 46 cells of a 100- cm 2 active area each. The results, obtained through distribution of relaxation time (DRT) analysis of the EIS data, show that characteristic peaks of the DRT and their changes with the different fault intensity levels can be used to extract the features of the tested faults. It was shown that flooding and drying present features on the opposite ends of the frequency spectrum due the effect of drying on the membrane conductivity and the blocking effect of flooding that constricts the reactants’ flow. Moreover, it was seen that while the effect of CO poisoning is limited to high frequency processes, above 100 Hz, the effects of H2S extend to below 10 Hz. Finally, the performance degradation due to all the tested faults, including H2S poisoning, is recoverable to a great extent, implying that condition correction after fault detection can contribute to prolonged lifetime of the fuel cell.
Highlights
Proton exchange membrane (PEM) fuel cells have been extensively characterized under various operating conditions in the literature [1,2,3]
The peaks of distribution of relaxation time (DRT) analysis are indicative of the different processes that occur in the fuel cell, and their size, the characteristic frequencies at which they occur, and their response to changes in operating conditions are considered as features and discussed below for all the tests
There were at least four DRT peaks for each impedance spectrum, with the exception of anode starvation and H2 S poisoning at higher fault intensity levels, which showed an extra peak in the low frequency region
Summary
Proton exchange membrane (PEM) fuel cells have been extensively characterized under various operating conditions in the literature [1,2,3]. Despite the improvements made in understanding their behavior, fuel cells are yet to meet the durability and reliability requirements to replace traditional technologies, both for automotive and stationary applications. To reduce maintenance cost and improve reliability and durability, it is crucial that sudden system failures due to prolonged operation under faulty conditions are avoided. This can be achieved through prognostics that include health-monitoring, online diagnostics, and remaining useful lifetime prediction [5,6,7]. A robust diagnostics system starts with thorough characterization and identification of fault features and, with proper integration with the system control, can alleviate the faults before system failure happens
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