ETFE-based membranes

Saarinen V, Kallio T, Paronen M, Tikkanen P, Rauhala E, Kontturi K (2005) New ETFE-based membrane for direct methanol fuel cell. Electrochim Acta 50 3453-3460... 

ETFE)-based membrane showed better chemical stability than a styrene sulfonic acid-grafted PTFE membrane, due to the poor oxidative stabihty of the styrene group. 

Saarinen et al. [95] prepared new PCMs for DMFC by direct introduction of sulfonic acid groups to ETFE films. This was carried out by irradiation of ETFE films by means of protons followed by sulfonation. These membranes have exceptionally low water uptake, excellent dimensional stability, and 10% methanol permeability lower than Nafion 115. The performance of these membranes was tested in DMFC at 30-85°C, with a maximum power densities of 40-65% lower than the corresponding values of the Nafion 115. Chemical and mechanical stabihties of new ETFE-based membranes appeared to be promising since it was tested over 2,000 h in the DMFC without obvious performance loss. 

V. Saarinen, T. KaUio, M. Pttfonen, P. Tikkanen, E. Rauheila and K. Kontturi, New ETFE-based membrane for direct methemol fuel cell, Electrochem. Acta 50, 3453 (2005). 

Recently, Arico et al. investigated durability of ETFE-based membranes during DMFC operation. They performed DMFC operation at temperatures of 90-130°C [55], Their MEA showed an initial performance of 92 mW cm at 110°C, with 1 M methanol and 2 atm air as anode and cathode fuel, respectively. After 20 days the performance still remained the same as the initial value, and the authors confirmed a good adhesion of electrodes to the membrane by observation of MEA cross-section using optical microscopy. 

For ETFE- -PSSA membranes with the same lEC, water uptake is higher than MeOH uptake of the membrane, but for Nation and S-SEBS membranes, MeOH uptake of membrane is always higher than water uptake. Chemical structure and morphology of membranes affect the solvent absorption. Nafion is considered to consist of ionic clusters that are separated from the polymer phase. For grafted polymers, heterogeneity exists to some extent due to the hydrophobic base polymer however, a regular clustered structure, as in the case of Nafion, has not been proposed for these materials. 

Sulfonation of PEP- and ETFE-based grafted films at PSI was performed by using 30% chlorosulfonic acid in dichloromethane (at 95 C, 5 h) and membranes with reasonably good sulfonic acid content have been observed. Sulfonation conditions almost identical to those used at PSI have been used by others for the sulfonation of PFA-g-polystyrene films, i.e., a mixture of chlorosulfonic acid and 1,1,2,2-tetrachloroethane (30 70 v/v, 90 °C, 5h) [133]. Phadnis et al. [83] performed the sulfonation of styrene-acrylic acid grafted FEP films in concentrated sulfuric acid (at room temperature). Concentrated... 

Arico, A.S., Baglio, V., Creti, P, Di Blasi, A., Antonucci, V., Biunea, J., Chapotot, A., Bozzi, A. and Schoemans, J. 2003a. Investigation of grafted ETFE-based polymer membranes as alternative electrolyte for direct methanol fuel ceUs. J. Power Sour. 123 107-115. 

T. Tran Duy, S.I. Sawada, S. Hasegawa, Y. Katsumura, Y. Maekawa, Poly(ethylene-co-tetrafluoroethylene)(ETFE)-based graft-type polymer electrolyte membranes with different ion exchange capacities relative humidity dependence for fuel cell applications, J. Membr. Sci. 447 (2013) 19-25. 

Chen, J., M. Asano, T. Yamaki et al. 2006. Effect of crosslinkers on the preparation and properties of ETFE-based radiation-grafted polymer electrolyte membranes. Journal of Applied Polymer Science 100 4565-4574. 

In their efforts to use various fluoropolymer films to develop PCMs, Scherer and co-workers [51] prepared PVDF-g-PSSA membranes in comparison with their counterparts based on ETFE films. PVDF films were activated from y-radiation (dose of 20 kGy at dose rate of 5.9 kGy h ) at room temperature in air and grafting of styrene with peroxidation method interestingly occurred at 60°C. The influence of the base polymer properties on the grafting behavior was addressed [52], Sulfonation of the grafted films conducted with chlorosulfonic acid/dichloromethane mixture at room temperature. The PEMFC performance of PVDF-based membranes was found to be inferior to their ETFE-based counterparts [52],... 

Reactant permeability is an important quantity in the context of durability, since interdiffusing and in the PEFC will lead to the formation of aggressive radical species in the catalyst layers. In styrene grafted ETFE (50 jm) based membranes,... 

Gubler, L., Ben youcef, H., Alkan Giirsel, S., Wokaun, A. and Scherer, G.G. (2007a) Crosslinker effect on fuel cell performance characteristics of ETFE based radiation grafted membranes. Electrochem. Soc. Trans. 11, 27-34. 

Chen, J., Asano, M., Maekawa, Y., Sakamura, T., Kubota, H., Yoshida, M. (2006) Preparation of ETFE-based fuel ceU membranes using UV-induced photografting and electron beam-induced crosslinking techniques. Journal of Membrane Science, 283, 373-379. 

The PVDF-based membrane [104,116-119] obtained after amination and the alkaline exchange process is a very brittle material due to a physical degradation of the backbone. Moreover, these materials exhibited low lECs (0.7 x 10 equiv./g) and would be unsuitable for use in any kind of fuel cell or electrochemical device. However, membranes based on FEP, ETFE-co-FEP, and ETFE obtained high enough conductivities to be tested for AFC application. FEP-based AEMs showed conductivities on the order of 10-20 X10 S/cm at room temperature [104,116,124]. Fuel cell test data obtained with FEP-based MEAs (with 0.5 x 10 g/cm Pt/C (20wt%) electrodes) show a peak power density of 55 x 10 W/cm at 0.5 V at 50 °C and 100% relative humidity [104,126]. AEM based on FEP exhibited a conductivity of 30 X 10 S/cm when fully hydrated [127]. This result represents a high level of conductivity for a solid alkaline polymer without incorporation of metal hydroxide species. Unfortunately, at lower humidity, the conductivity of these membranes drops considerably and even if they are operational with low-humidity gases, they exhibit low efficiency. 

Values of proton conductivity of ETEE-g-PSSA, Nafion , PTFSSA, and BPSH membranes are strongly dependent on EW (Fig. 14a). The conductivity of Nafion and PTFSSA membranes maximizes at intermediate EWs, while the conductivity of ETFE-g-PSSA and BPSH membranes increases with decreasing EW. ETFE-g-PSSA membranes possess an exceptionally high conductivity. Compared to ETFE-g-PSSA membranes, a moderate conductivity can be achieved for Nafion , PTFSSA, and BPSH membranes by adjusting the EW of the membrane. However, based on the conductivity-EW relationship for SSEBS membranes, the maximum conductivity obtained is only 0.05 S cm and this is much lower than that of other membranes. 

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