Evaluation of PEFC Membrane based on Cross-linked PTFE by EB Grafting: Effect of Thickness for FC Performance

Abstract

The performance of a polymer electrolyte fuel cell (PEFC) was affected by the thickness of the thin proton exchange membrane (PEM). The PEMs with the different thickness were prepared by radiation induced grafting of styrene into the radiation-cross-linked polytetrafluoroethylene (RX-PTFE) membrane prepared from PTFE dispersion, and then sulfonated. The wet thicknesses of the obtained thin PEMs were lower than 25 µm. A PEM based on a 50 µm PTFE film, with the wet thickness of 73 µm, was also prepared under the same procedure for the comparison. The obtained PEMs were characterized in term of gas cross-over. The surface of platinum / carbon electrodes was coated with Nafion ® dispersion, and then membrane electrode assembles (MEAs) were prepared by the hot-pressing. The polarization curves and electrochemical impedances of the thin PEMs in a single fuel cell were analyzed. As a result, the cell performance of the MEA based on thinner PEM tended to give higher power density and current density. On the other hand, the performance of the thinnest PEM (13 m) decreased, and the MEA based on the thinner PEM gave the lower open circuit voltage (OCV) due to the higher gas cross-over. Thus, the thin PEM based on RX-PTFE had shown a high performance at the suitable thickness.

Radiation-Grafted Membranes for Polymer Electrolyte Fuel Cells: Current Trends and Future Directions

“…To enhance the stability of PEMs based on RX-PTFE, the concept of double cross-linking with the use of thin films was introduced. Hiraiwa et al prepared a cross-linked PEM by the RIG of St/DVB onto RX-PTFE of different thicknesses followed by sulfonation. Gas permeation experiments showed that thinner membranes (13.6 ± 0.5 μm) have higher gas crossover values than their thicker counterparts (73.8 ± 2.7 μm).…”

“…Gas permeation experiments showed that thinner membranes (13.6 ± 0.5 μm) have higher gas crossover values than their thicker counterparts (73.8 ± 2.7 μm). A maximum power density of 469 mW cm –2 was obtained for a MEA based on a 18.6 ± 1.3 μm thick PEM with a DG of 38.3% at 60 °C and a relative humidity of 16% …”

“…The durability of radiation-grafted PEMs was found to vary significantly depending on the starting polymeric materials, the composition of the monomer system, the RIG technique employed, reaction parameters, and not least the method of assembling the membrane with the electrodes. ,,− A number of new preparative routes for introducing substantial improvements in the stability of the desired PEMs have been proposed. These include three main strategies: (i) the grafting of alternative monomers such as m , p -methylstyrene or vinyltoluene, , p - tert -butylstyrene, vinylbenzyl chloride, , p -styryltrimethoxysilane, , methyl acrylate, and 2-bromotetrafluoroethyl trifluorovinyl ether and monomer combinations such as styrene/α-methylstyrene, styrene/acrylonitrile, styrene/methylacrylnitrile, ,,, styrene/acrylic acid, ,, styrene/methyl methacrylic acid, α-methylstyrene/methylacrylnitrile, , styrene/glycidyl methacrylate, , styrene/trimethoxysilylpropyl methacrylate, and methyl acrylate/methyl methacrylate; (ii) the introduction of new or modified substrate films for grafting of styrene or its derivatives with or without cross-linkers such as cross-linked PTFE, ,,,,,,,− engineering plastics such as poly­(ether ether ketone), ,− polyimide, , polyether sulfone, alicyclic polybenzimidazole, polymer powder (e.g., UHMWPE or PVDF) followed by thermal treatment, − or solution casting, porous films, ,,,​ − and nanofibrous mats; and finally (iii) the application of n...…”

“…Of particular note is the double cross-linking approach that involves grafting the styrene/cross-linker onto radiation-cross-linked PTFE prior to sulfonation. This interesting route yields PEMs with excellent mechanical properties. ,,,,,,,− Moreover, this approach enables the preparation of very thin membranes with not only low ionic resistance, but also low gas crossover coupled with high swelling resistance (thus only small dimensional changes). The latter is highly desirable for the fabrication of MEAs with high resistance to delamination, which can be caused by variations in the level of swelling during fuel cell operations.…”