Highly phosphonated polypentafluorostyrene: Characterization and blends with polybenzimidazole Vladimir Atanasov a,⇑ , Dietrich Gudat b , Bastian Ruffmann c , Jochen Kerres a,d a Institute of Chemical Process Engineering, University of Stuttgart, Germany b Institute of Inorganic Chemistry, University of Stuttgart, Germany c Hydrogen and Informatics Institute for Applied Technology, Schwerin, Germany d Focus Area: Chemical Resource Beneficiation, North-West University, Potchefstroom 2520, South Africa article info Article history: Received 14 June 2013 Received in revised form 5 September 2013 Accepted 6 September 2013 Available online 15 September 2013 Keywords: Phosphonated polymer Polyelectrolyte Fuel cell Conductivity Blend membrane Doping with phosphoric acid abstract In this study we present results of the conductivity and resistance to thermooxidative and condensation reactions of a highly phosphonated poly(pentafluorostyrene) (PWN2010) and of its blends with poly(benzimidazole)s (PBI). This polymer, which combines both: (i) a high degree of phosphonation (above 90%) and (ii) a relatively high acidity (pK a (–PO 3- H 2 M –PO 3 H  )  0.5) due to the fluorine neighbors, is designed for low humidity operating fuel cell. This was confirmed by the conductivity measurements for PWN2010 reaching r =5  10 4 S cm 1 at 150 °C in dry N 2 and r =1  10 3 S cm 1 at 150 °C(k = 0.75). Fur- thermore, this polymer showed only 48% of anhydride formation when annealing it at T = 250 °C for 5 h and only 2% weight loss during a 96 h Fenton test. These properties com- bined with the ability of the PWN2010 to form homogeneous blends with polybenzimidaz- oles resulting in stable and flexible polymer films, makes PWN2010 a very promising candidate as a polymer electrolyte for intermediate- and high-temperature fuel cell applications. Ó 2013 Published by Elsevier Ltd. 1. Introduction The growing need of devices delivering electricity in different locations is essential in the modern world. A pro- ton – exchange membrane fuel cell (PEM FC) is one exam- ple of such a device using a polymer electrolyte as ion- conductor. The most commonly used polyelectrolytes are based on sulfonated polymers, e.g. Nafion Ò . Their proton conductivity is principally based on water bridging the sul- fonic acid function, where the water molecule’s diffusion serves as a vehicle for the proton transport, either as H 3 O + ,H 5 O þ 2 ions, etc. (vehicular proton-transport mecha- nism), or as a medium for proton tunneling via hydrogen bridges (Grotthus proton transport mechanism) [1]. There- fore, at temperatures above 100 °C, most of these polyelec- trolytes show a dramatic decrease of ion-conductivity due to water evaporation. The increase in FC operating temper- ature is, however, required for attenuating the activation enthalpy and overcoming the poisoning effect of CO on the Pt-catalyst by temperature-driven acceleration of the electrode kinetics. Thus, polyelectrolytes based on phos- phoric acid (PA) doped polybenzimidazole (PBI) currently attract considerable attention [2].The conductivity in this case is based on the excellent proton-carrier properties of PA [3]. Moreover, high doping levels of PA are required (commonly above 200%) to induce sufficient proton con- ductivity [4], which can lead to unsustainability and leak- age of PA from the polymer membrane especially at FC operation temperatures below 100 °C. One approach to overcome these drawbacks lies in the utilization of highly phosphonated polymers where the phosphonic acid group serves as an amphoteric proton conductor substituting the role of PA. In comparison to the sulfonated ionomers, there are currently only few examples of phosphonated polymers being used as proper electrolytes for FCs [5–7], which 0014-3057/$ - see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.eurpolymj.2013.09.002 ⇑ Corresponding author. Tel.: +49 711 68585163; fax: +49 711 68585242. E-mail address: vladimir.atanasov@icvt.uni-stuttgart.de (V. Atanasov). European Polymer Journal 49 (2013) 3977–3985 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj