Degradation membrane-electrode interface

The presence of phosphoric acid makes the chemistry in the Fenton test far more complex [69]. Firstly, the presence of phosphoric acid was shown to suppress the formation of radicals due to the lowered pH. Secondly, it was suggested that the presence of phosphoric acid further suppressed the degradation rate, possibly due to the formation of iron phosphates or by the ionization of the polymer. It was concluded that the presence of ferrous ion in the membrane-electrode interface had a negative impact on the fuel cell durability. However, this effect was mainly connected to the deterioration of the catalyst activity [69]. 

A comparison of the long-term DMFC performance between MFAs with good and poor interfaces between the membrane and the electrode(s) is shown in Fig. 7. The cell with a good membrane-electrode interface shows lower unrecoverable performance loss than the cell with a poor interface, 42 versus 70 mA cm after 700h of operation. A greater performance loss of the cell with the poor interface is accompanied by an increase in the high-frequency resistance of the cell (Fig. 7). However, the increased cell resistance is only in part responsible for the total performance loss caused by interfacial degradation. /R-corrected H -air polarization... 

Based on our observation, a membrane degradation and failure mechanism under the RH cycling, a pure mechanical effect is theorized as the following sequence electrode-microcracking- - crazing initiation at the electrode/electrolyte interface - crack growth under stress cycling- -fast fracture/instability. 

Electrochemical impedance spectroscopy (EIS) has been used to characterize the ionic conductivity of conducting polymers in the electrode, separating this ionic resistance from the membrane and ohmic contact resistances at the interfaces [24— 31]. Such measurements are helpful in quantifying degradation of the ionomer in... 

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