In-situ diagnosis on performance degradation of high temperature polymer electrolyte membrane fuel cell by examining its electrochemical properties under operation

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Ex-situ electrochemical characterization techniques could significantly alter or misrepresent the materials of high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) to the point where they are not reflective of their conditions during operation, resulting in difficulties in obtaining realistic fuel cell durability. To minimize this disturbance, we proposed an in-situ low-invasive technique of electrochemical impedance spectroscopy (EIS), combining with polarization curve and Tafel slope analysis, to investigate the performance degradation of HT-PEMFC. The membrane electrode assemblies (MEAs) used in the HT-PEMFC were lab-made but with commercial catalyst and poly(2,5-benzimidazole) (ABPBI) membrane. Two common test modes, i.e. steady-state operation and dynamic-state operation, were employed to mimic practical HT-PEMFC operation. By examining the changes of electrochemical properties of the HT-PEMFC under steady- or dynamic-state operation, the main mechanism for the performance degradation can be determined. The results from the study suggests that a high cell performance decay rate cannot be directly attributed to materials degradation, especially in a short-term steady-state operation. In contrast, the change of Tafel slope can be seen as a clear indicator to determine the extent of catalyst degradation of HT-PEMFC, no matter which test protocol was applied. Post-analysis of TEM on the catalysts before and after tests further confirmed the main mechanism for the performance losses of the HT-PEMFCs underwent two test protocols, while acid loss and membrane degradation were considered to be negligible during the short-term tests.