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  Intermediate temperature proton conductors for PEM fuel cells based on phosphonic acid as protogenic group: A progress report

Steininger, H., Schuster, M., Kreuer, K. D., Kaltbeitzel, A., Bingöl, B., Meyer, W. H., et al. (2007). Intermediate temperature proton conductors for PEM fuel cells based on phosphonic acid as protogenic group: A progress report. Physical Chemistry Chemical Physics, 9(15), 1764-1773.

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Steininger, H.1, Author           
Schuster, M.1, Author           
Kreuer, K. D.1, Author           
Kaltbeitzel, A., Author
Bingöl, B., Author
Meyer, W. H., Author
Schauff, S., Author
Brunklaus, G., Author
Maier, J.1, Author           
Spiess, H. W., Author
1Department Physical Chemistry of Solids (Joachim Maier), Max Planck Institute for Solid State Research, Max Planck Society, ou_3370483              


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 Abstract: The melting behaviour and transport properties of straight chain alkanes mono- and difunctionalized with phosphonic acid groups have been investigated as a function of their length. The increase of melting temperature and decrease of proton conductivity with increasing chain length is suggested to be the consequence of an increasing ordering of the alkane segments which constrains the free aggregation of the phosphonic acid groups. However, the proton mobility is reduced to a greater extent than the proton diffusion coefficient indicating an increasing cooperativity of proton transport with increasing length of the alkane segment. The results clearly indicate that the "spacer concept'', which had been proven successful in the optimization of the proton conductivity of heterocycle based systems, fails in the case of phosphonic acid functionalized polymers. Instead, a very high concentration of phosphonic acid functional groups forming "bulky'' hydrogen bonded aggregates is suggested to be essential for obtaining very high proton conductivity. Aggregation is also suggested to reduce condensation reactions generally observed in phosphonic acid containing systems. On the basis of this understanding, the proton conductivities of poly( vinyl phosphonic acid) and poly(meta-phenylene phosphonic acid) are discussed. Though both polymers exhibit a substantial concentration of phosphonic acid groups, aggregation seems to be constrained to such an extent that intrinsic proton conductivity is limited to values below sigma = 10(-3) S cm(-1) at T = 150 degrees C. The results suggest that different immobilization concepts have to be developed in order to minimize the conductivity reduction compared to the very high intrinsic proton conductivity of neat phosphonic acid under quasi dry conditions. In the presence of high water activities, however, (as usually present in PEM fuel cells) the very high ion exchange capacities (IEC) possible for phosphonic acid functionalized ionomers (IEC > 10 meq g(-1)) may allow for high proton conductivities in the intermediate temperature range (T similar to 120 - 160 degrees C).


Language(s): eng - English
 Dates: 2007
 Publication Status: Issued
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: eDoc: 338570
ISI: 000245472600002
 Degree: -



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Title: Physical Chemistry Chemical Physics
Source Genre: Journal
Publ. Info: -
Pages: - Volume / Issue: 9 (15) Sequence Number: - Start / End Page: 1764 - 1773 Identifier: ISSN: 1463-9076