Performance and Durability of Membrane Electrode Assemblies Based on Radiation‐Grafted FEP‐g‐Polystyrene Membranes

Abstract

Membrane electrode assemblies (MEAs) based on radiation‐grafted proton exchange membranes developed at PSI have shown encouraging performance in the past in hydrogen and methanol fuelled polymer electrolyte fuel cells. In this study, the effect of the pre‐treatment of crosslinked radiation‐grafted FEP membranes prior to lamination with the electrodes on the performance of the MEAs was investigated. Two approaches were assessed separately and in combination: (1) the impregnation of the radiation‐grafted membranes with solubilised Nafion®, and (2) the use of a swollen vs. dry membrane. It is found that the combination of coating the membrane with Nafion® ionomer and hot‐pressing the MEA with the membrane in the wet state produce the best single cell performance. In the second part of the study, the durability of an MEA, based on a radiation‐grafted FEP membrane, was investigated. The performance was stable for 4,000 h at a cell temperature of 80 °C. Then, a notable degradation of the membrane, as well as the electrode material, started to occur as a consequence of either controlled or uncontrolled start‐stop cycles of the cell. It is assumed that particular conditions, to which the cell is subjected during such an event, strongly accelerate materials degradation, which leads to the premature failure of the MEA.

Characterisation of Fuel Cell Membranes as a Function of Drying by Means of Contact Angle Measurements

“…Our laboratory has recently described how the electrochemical interface of MEAs based on radiation-grafted membranes can be improved significantly by hot-pressing the MEA and also, to a lesser extent, by Nafion -impregnation of the radiationgrafted membrane prior to hot-pressing [3]. Our other contribution to this volume examines, in more detail, how the formation of optimised MEA interfaces characterised by low charge transfer resistances can be favourably influenced by hot-pressing of the MEA [4]. In particular, the effects of the Nafion -impregnation of membranes prior to hot-pressing and the water swelling of the membrane immediately prior to the hot-pressing process are investigated in that work.…”

Novel Options and Limitations of Methanol‐Based Production and Storage for Mobile Applications

“…This reduces the net electrical energy that is available for the vehicle to 33% of the energy content in the methanol feed. Both the DMFC and in particular the autothermal reformer combined with hydrogen PEM thus compare favorably with the 17% fuel cycle efficiency of current state-of-art internal combustion engines [24]. .…”

“…. W e f urt he r as s ume t ha t t he P EM is o pe rate d at 750 mV , corresponding to an efficiency of 50.6% and a current density of 250 mA cm -2 [24]. Based on these voltages, the overall efficiency is then 20.6% since slightly more than 1/3 of the fuel cell power is available for the vehicle.…”

Proton Conducting Sulphonated Fluorinated Poly(Styrene) Crosslinked Electrolyte Membranes

“…In order to provide evidence for the presence of azido end-groups, the resulting copolymer was characterised by FT-IR spectroscopy ( Figure 2, spectrum recorded at t 0 ). Besides the signals observed in the 1,000-1,600 cm -1 range attributed to C=C and C-F frequencies, and in the 2,800-3,000 cm -1 range attributed to C-C and C-H stretches, a doublet at 2,264 cm -1 was observed, characteristic of the asymmetric stretching frequency of terminal azidos group [28]. The presence of doublet could be explained on the basis of Fermi resonance interaction of the fundamentals with the overtones or combination tones of certain low frequencies [37].…”

“…The terminal chloride atoms were then substituted by azide groups, allowing membrane crosslinking under UV-light [26,27]. In addition, radiation grafted membranes were also achieved from poly(fluorinated ethylene propylene) membranes [28][29][30], poly(vinylidene fluoride) [31] or poly(tetrafluoroethylene-co-perfluorovinyl ether) [32] leading to fluoropolymer grafted polystyrene sulphonic acid (FPg-PSSA) after sulphonation of the PS grafts. However, for most of them, these membranes were obtained from complex syntheses of grafted (co)polymers.…”