Electrochimica Acta 52 (2007) 5046–5052 Electrochemical modification of cation exchange membrane with polyaniline for improvement in permselectivity P. Sivaraman, J.G. Chavan, A.P. Thakur, V.R. Hande, A.B. Samui ∗ Naval Materials Research Laboratory (DRDO), Anand Nagar, Ambernath 421 506, Maharashtra, India Received 22 December 2006; received in revised form 31 January 2007; accepted 1 February 2007 Available online 13 February 2007 Abstract A novel method of modification of cation exchange membrane for improved permselectivity is reported in this paper. Acrylic acid grafted fluori- nated ethylene propylene copolymer membrane after sulphonation (FEP-g-AA-SO 3 H) was used as the cation exchange membrane for modification. Polyaniline is deposited electrochemically on to the membrane. The deposition of polyaniline starts from the surface of the membrane and growth proceeds inside the membrane. The amount of polyaniline deposited depends upon the polymerization time. The presence of polyaniline is con- firmed by FTIR, scanning electron microscopy, X-ray mapping, cyclic voltammetry and ion exchange capacity measurements. The electrodialysis experiments show improved permselectivity for divalent cations. © 2007 Elsevier Ltd. All rights reserved. Keywords: Cation exchange membrane; Electrochemical modification; Polyaniline 1. Introduction Polymer electrolyte membranes, also called as ion exchange membranes, are interesting materials which have been used in various application like fuel cells [1], supercapacitors [2], sen- sors [3], chloro-alkali [4], electrodialysis [5–12], etc. In recent years, considerable amount of research have been carried out on the modification of ion exchange membranes, due to their requirement with increased permselectivity for efficient removal of valuable ions from waste solution, removal of monovalent cation from mixed salt solution, removal of nitrate ions from ground water [5,6]. It is reported that when ion exchange membrane is coated with conducting polymers like polyaniline (PANI) or polypyr- role (PPY) their barrier properties or permselectivity improves several times compared to bare membrane [7–10]. Sata et al. [7] modified an ion exchange membrane by polymerizing a thin layer of PANI. The modified composite membrane showed sodium ion permselectivity in electrodialysis compared with divalent cations. The permeability coefficient of the neutral molecules through the ion exchange membrane considerably ∗ Corresponding author. Tel.: +91 251 2621836; fax: +91 251 2620604. E-mail address: absamui@rediffmail.com (A.B. Samui). decreased by the formation of a thin PPY layer on the mem- brane [8–10]. Tan et al. [11] demonstrated that the presence of thin PANI layer on to the surface of an ion exchange mem- brane enhanced the permselectivity properties. They showed that the leakage of Zn 2+ and Cu 2+ through the membrane is reduced at least by 20 times compared to the bare membrane. Tan et al. [12] also reported that the optimum permselectiv- ity for proton against divalent cations depends on the optimum time of polymerization of PANI on the surface of ion exchange membrane. Similarly, improvement on permselectivity of pro- ton compared to divalent ions, when Nafion was coated with polyethyleneimine was reported [13]. Composite membrane based on high impact polystyrene and PANI prepared by melt extrusion has been reported for higher permselectivity properties [14]. Recently Gohil et al. studied the composite anion exchange membrane modified by PPY. It is reported that the modified membrane shown efficient separation of monovalent ions from bivalent electrolyte [15]. PANI can be synthesized both by chemical and electrochem- ical methods. Electrochemical method of preparation of PANI has been reported by many researchers [16–19]. Comparison of PANI prepared by both chemical and electrochemical methods also been reported. It was reported that properties of the electro- chemically prepared PANI was better than chemically prepared one [19]. In all the methods reported so far, conventional chem- 0013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2007.02.016