Polyimide ionomer membranes

Several reviews on membranes for DMFC fuel cells have been published in the last decade [1-9], starting with that by Kreuer [1], discussing the differences between Nafion and sulfonated polyether ketone membranes. According to Fig. 6.1, reviews published till 2006 [1 ] cover only one third of the ionomeric membranes currently developed for DAFC. More recent reviews deal with polyimide ionomer membranes [5], composite membranes for high temperature DMFC [6], non-perfluorated sulfonic acid membranes [7], modified Nafion membranes [8], and hybrid membranes [9-11]. 

Miyatake K, Watanabe M (2008) Polyimide ionomer membranes for PEFCs and DMFCs. In Peinemann KV, Pereira Nunes S (eds) Membranes for energy conversion. Wiley VCH, Weinheim, pp 47-59, Chap. 2... 

G. Gehel, Study of the casting of suhbnated polyimide ionomer membranes structural evolution and influence on transport properties, J. Phys. Chem. B 109 (22) (2005) 11332-11339. 

Rollet, Ai., Diat, O., Gebel, G. (2004) Transport anisotropy of ions in sulfonated polyimide ionomer membranes. The Journal of Physical Chemistry B, 108, 1130-1136. Perrin, J.C., Lyonnard, S., Guillermo, A., Levitz, P. (2006) Water dynamics in ionomer membranes by field-cycling NMR relaxometry. The Journal of Physical Chemistry B, 110, 5439 5444. 

Miyatake, K., Asano, N., Tombe, T., Watanabe, M., Effect of cross-linking on polyimide ionomer membranes, Electrochemistry, 2007, 75,122-125. 

Asano, N., Aoki, M., Suzuki, S., Miyatake, K., Uchida, H. and Watanabe, M. 2006. Aliphatic/aromatic polyimide ionomers as a proton conductive membrane for fuel cell applications. Journal of the American Chemical Society 128 1762-1769. 

Results from a long-term durabihty test of a hydrocarbon membrane show behavior opposite to that predicted. The sulfonated polyimide (SPI) membrane demonstrated 5,000-h lifetime when tested at 0.2 A cm, 80°C, and ambient pressure (Aoki et al. 2006a). Even if there is Nafion PFSA ionomer in the electrode, the SPI cell does not show any fluoride release, indicating that ionomer degradation in the catalyst layer is minimal. It must be stressed that SPI is 40 times less permeable to... 

More recently, another intermediate timescale was explored by NMR relaxom-etry [102]. The spin-lattice relaxation times of water molecules were determined in the range of 20 ns to 20 ps by varying the magnetic field frequency from 10 kHz to 20 MHz and depending on the water content. This technique is well suited for the study of ionomer membranes because of its extreme sensitivity to water-polymer interactions, but it requires a structural and dynamic model to extract characteristic features. The effect of confinement is predominant in polyimides even at high water content (algebraic law with a slope of —0.5 characteristic of porous materials), whereas the diffusion quickly reaches a bulk behavior in Nafion (a plateau is observed at low magnetic fields). 

Several non-fluorinated alternative polymers have been proposed for DAFC, mainly based on sulfonated ionomers with an aromatic or aliphatic hydrocarbon skeleton [7], Kim and Pivovar [4] have reported the number of DMFC alternative membranes papers appearing in open hterature for years 1994—2004, showing that polyarylenes, polyvinyl alcohols, grafted and block polystyrenes copolymers, and polyimides were among the most studies polymer electrolytes. In view of the dramatic increase in the number of publications since 2005 (see Fig. 6.1), the trends have changed, as shown in Table 6.1, which sununaiized the publications in open literature for the period 2005-2012, as compared to the previous period. 

Linkov VM, Bobrova LP, Timofeev SV, Sanderson RD (1995) Composites membranes from perfluoro-sulfonated ionomer on carbon and ceramic supports. Mater Lett 24 (1-3) 147-151 David LIB, Ismail AF (2003) Influence of the thermostabilization process and soak time during pyrolysis process on the polyacrylonitrile carbon membranes for OyN separation. J Membr Sci 213 (1-2) 285-291 Geiszler VC (1997) Polyimide precursors for carbon membranes. PhD Thesis, University of Texas at Austin, TX, USA... 

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