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In polymer electrolyte membrane fuel cell (PEMFC), the cost and durability are main challenges to commercialization. To achieve the long-term durability target, the durability of PEMFC materials should be further improved. In this paper, we investigated the chemical and electrochemical degradation of the expanded polytetrafluoroethylene (e-PTFE) support and examined how it influences the mechanical properties of the e-PTFE support. We conducted the Fenton test and open circuit voltage (OCV) holding and analyzed the chemical and physical structural changes of the e-PTFE support by utilizing Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and tensile test. After the chemical and electrochemical degradations, the molecular bonds of e-PTFE were broken, and the microstructures of e-PTFE were deformed. As the result the mechanical properties of e-PTFE showed significant decrease. Consequently, our results show that the e-PTFE support is deteriorated chemically during PEMFC operation, and this chemical degradation lead reduction of mechanical strength. [ABSTRACT FROM AUTHOR]

During the durability tests for PEMFC membranes, performance characterization is conducted to determine the degree of degradation, the interval for which is different for each durability test protocol. Before performance characterization, activation is carried out to determine the reliability. Most activations are accompanied by voltage changes, which can lead to electrode degradation. However, this has largely been neglected because the activation time is shorter than the durability test time. In this study, activation was conducted at 24, 48, and 144 h intervals, during the membrane durability test of a PEMFC, and the effect of activation on the degradation of the membrane and electrode was investigated. For a shorter activation interval during the durability test, the lifetime of the membrane was reduced by up to 35%. For the same durability test time, more activations led to greater electrode and membrane degradation. Through scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDS) analysis, it was found that for a shorter activation interval, more Pt was deposited into the membrane and then the membrane was thinner. During the durability test, frequent activation accelerated membrane and electrode degradation. [ABSTRACT FROM AUTHOR]

During the operation of a PEMFC, the polymer membrane is degraded by electrochemical reactions and mechanical stresses. We investigated the effects of repeated electrochemical and mechanical degradations in a membrane. For mechanical degradation, the membrane and MEA were repeatedly subjected to wet/dry cycles; for electrochemical degradation, the cell was operated under open-circuit voltage (OCV)/low-humidity conditions. The repeated wet/dry cycles led to a decrease in the mechanical strength of the membrane. When the MEA was degraded electrochemically, repeated wet/dry cycling resulted in the formation of pinholes in the membrane. In the case of different MEAs that were first degraded electrochemically, the extents of their hydrogen crossover currents increased due to repeated wet/dry cycling being different. Therefore, these results indicated that the membrane durability could be evaluated by these methods of repeated electrochemical degradation and wet/dry cycles. [ABSTRACT FROM AUTHOR]

An accelerated single cell test and single electrode cell test were carried out to investigate membrane degradation by Pt dissolved/deposited on the membrane. For a cell operating under accelerated conditions (OCV, 90°C, anode RH 0%, cathode O2 supply), MEA analyses revealed that Pt particles were deposited in the membrane at the anode side, with a decrease in F, O, and C content near the anode side of the membrane. Dissolved Pt from the cathode showed that Pt existed mainly in the form of Pt2+ ionic species. Oxygen and hydrogen helped Pt dissolution from the cathode and Pt deposition in the membrane, respectively. Radical formation on deposited Pt in the membrane was detected by electron spin resonance (ESR). Fluoride emission rate (FER, an indicator of membrane degradation rate) increased with an increase in the amount of Pt in the membrane. [ABSTRACT FROM AUTHOR]