Journal of Membrane Science 326 (2009) 721–726 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci A novel composite Nafion membrane for direct alcohol fuel cells Lepakshi Barbora a , Simadri Acharya b , Rupesh Singh b , Keith Scott c , Anil Verma b,∗ a Centre for Energy, Indian Institute of Technology Guwahati, Guwahati 781039, India b Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India c School of Chemical Engineering and Advanced Materials, Newcastle University, Newcastle Upon Tyne NE1 7RU, United Kingdom article info Article history: Received 11 July 2008 Received in revised form 27 October 2008 Accepted 7 November 2008 Available online 17 November 2008 Keywords: Alcohol permeability Direct alcohol fuel cell Erbium triflate Nafion composite Proton conductivity abstract Trifluoromethanesulfonic acid or triflate acid, chemical formula CF 3 SO 3 H, is regarded as one of the strongest acids and resembles Nafion ® in structure. Erbium triflate, a lanthanum salt of triflate, is ther- mally stable. This paper reports data on the formation of membranes by the fixation of erbium triflate salts (ErTfO) into the Nafion structure. Five different loadings of ErTfO were used to fabricate ErTfO/Nafion com- posite membranes and these were characterized, extensively for possible use in direct alcohol fuel cells. The membranes were characterized using XRD, TGA, FTIR, and for mechanical strength, water uptake, ion exchange capacity, alcohol uptake, swelling, proton conductivity, alcohol permeability and oxygen stability. The ErTfO/Nafion composite membranes reduced alcohol permeability by 77–80%. The proton conductivity of 3% ErTfO/Nafion composite membranes was 38% higher than that of a pure cast Nafion membrane. The oxygen stability of the ErTfO/Nafion composite membranes was higher than pure cast Nafion. However, the mechanical strength of 7% and 9% ErTfO/Nafion was lower than that of pure cast Nafion. The composite membrane was chemically stable and has potential for use in direct alcohol fuel cells. © 2008 Elsevier B.V. All rights reserved. 1. Introduction In recent years there have been increasing interests in rare- earth doped polymer systems following innovative discoveries in the chemistry of polymer solutions, which has been motivated by the wide range of potential applications [1]. Erbium triflate (ErTFO), more formally known as erbium trifluoromethanesulfonate, has tri- flate (CF 3 SO 3 - ) as a functional group. The triflate anion, CF 3 SO 3 - , is an extremely stable polyatomic ion, being the conjugate base of triflic acid (CF 3 SO 3 H), one of the strongest acids known [2]. Tri- flic acid is defined as a superacid, because it is more acidic than pure sulfuric acid [3]. Triflate has been applied as a ligand for groups 11 and 13 metals along with lanthanides [4–6]. Er(CF 3 SO 3 ) 3 is a lanthanide triflate salt and has application in optical devices with polyethylene oxide polymer [1]. Er 3+ -doped compounds with potential applications for optical amplification, in particular for the production of wave-guides, have been reported by Correia et al. [7]. They have also reported the contribution to ionic conductive property by erbium triflate. At moderate temperature the erbium- based polymer showed relatively low ionic conductivity. However, at 100 ◦ C, erbium rich salt samples exhibited ionic conductivity of approximately 2 × 10 -5 S cm -1 [7]. Erbium triflate is stable in water ∗ Corresponding author. Tel.: +91 361 2582255; fax: +91 361 2582291. E-mail address: anil.verma@iitg.ernet (A. Verma). and is thus used as a Lewis acid in organic chemistry [8]. Lithium triflate is used in some lithium ion batteries as a component of the electrolyte [9]. Triflates are immune to oxidation and reduction and may be used as good proton conductors. The structure of the triflate resembles Nafion ® , as shown in Fig. 1 [10,11]. These properties of triflate justify research activities towards fixation of erbium triflate in stable membrane structures. Therefore, erbium triflate may be used to enhance the properties of Nafion membrane. Although erbium triflate has excellent properties but it has not been considered for fuel cell applications. In this work, we report the synthesis and characterization of ErTfO/Nafion compos- ite membranes for application in direct alcohol fuel cells (methanol and ethanol based). Different loadings of ErTfO were used to pre- pare the composite Nafion membranes. The membranes were characterized for surface morphology, thermal stability, tensile strength, water uptake, ion exchange capacity, alcohol uptake, swelling, proton conductivity, alcohol permeability and oxygen sta- bility. 2. Experimental 2.1. Materials Nafion ® dispersion, 5 wt% solid, was procured from DuPont, USA. Dimethylformamide (DMF) was purchased from Merck, India. Erbium triflate was obtained from Sigma–Aldrich, USA. Methanol, 0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2008.11.009