Partial sulfonation of PVdF-co-HFP: A preliminary study and characterization for application in direct methanol fuel cell Suparna Das, Piyush Kumar, Kingshuk Dutta, Patit Paban Kundu ⇑ Advanced Polymer Laboratory, Department of Polymer Science & Technology, University of Calcutta, 92 A.P.C. Road, Kolkata 700 009, India highlights  Synthesis of sulfonated PVdF-co-HFP by reacting with chlorosulfonic acid.  Maximum degree of sulfonation and best properties were obtained for 7 h reaction.  A maximum water uptake value of 20% was obtained.  A maximum IEC value of 0.42 meq g 1 was obtained.  A methanol permeability of 2.44  10 7 cm 2 s 1 was obtained. graphical abstract article info Article history: Received 20 March 2013 Received in revised form 8 July 2013 Accepted 12 July 2013 Keywords: PVdF-co-HFP Sulfonation Ion exchange capacity Polymer electrolyte membrane Direct methanol fuel cell abstract Sulfonation of PVdF-co-HFP was conducted by treating the copolymer with chlorosulfonic acid. The effi- ciency of this sulfonated copolymer towards application as a polymer electrolyte membrane in direct methanol fuel cell (DMFC) was evaluated. For this purpose, we determined the thermal stability, water uptake, ion exchange capacity (IEC), methanol crossover, and proton conductivity of the prepared mem- branes as functions of duration and degree of sulfonation. The characteristic aromatic peaks obtained in the FT-IR spectra confirmed the successful sulfonation of PVdF-co-HFP. The effect of sulfonation on the semi-crystalline nature of pure PVdF-co-HFP was determined from XRD analysis. Water uptake results indicated that a sulfonation time of 7 h produced maximum water uptake value of about 20%, with a cor- responding IEC and proton conductivity values of about 0.42 meq g 1 and 0.00375 S cm 1 respectively. The maximum current density was recorded to be 30 mA cm 2 at 0.2 V potential. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Majority of the research works based on development of poly- mer electrolyte membranes (PEMs) have been centered on modifi- cation and substitution of the conventional PEM material ‘Nafion’ [1–11]. Primarily due to the excessive cost and certain critical drawbacks associated with this otherwise excellent PEM material [12–19], a constant search for a suitable second component that can ably complement it has been in progress. In this respect, poly(vinylidene fluoride) (PVdF), its copolymers and blends have shown some promising results [20–27]. In particular, PEMs based on PVdF-co-hexafluoropropylene (PVdF-co-HFP) have shown excitingly reduced methanol crossover owing to their excellent 0306-2619/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2013.07.030 ⇑ Corresponding author. Tel.: +91 2350 1397; fax: +91 2352 5106. E-mail address: ppk923@yahoo.com (P.P. Kundu). Applied Energy 113 (2014) 169–177 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy