Proton Conducting Polymer Electrolytes for Electrochemical Capacitors H. Gao, Q.Tian and K. Lian Department of Materials Science and Engineering, University of Toronto, Toronto, Ont., Canada M5S 3E4 Solid polymer electrolytes containing phosphotungstic acid (PWA) and/or silicotungstic acid (SiWA) blended in polyvinyl alcohol (PVA) were investigated. The polymer electrolyte with a mixed PWA and SiWA had a synergistic effect on its proton conductivity over that of pure PVA-PWA or PVA-SiWA electrolytes. When adding a small amount of polyacrylic acid (PAA), a further increase in proton conductivity was obtained. Electrochemical and structural analyses were conducted on these electrolytes as well. Introduction Solid-polymer electrolytes are important enabling materials for energy storage devices, such as batteries and electrochemical capacitors (EC), which require high energy density, high power density, and thin and flexible form factors. However, the conductivities of polymer electrolytes are typically a few orders of magnitude lower than that of their liquid counterparts. Moreover, the ionic conductivities of many proton conducting polymer electrolytes such as Nafion and its derivatives depend strongly on the relative humidity (RH) and temperature [1,2], which is not desirable for electrochemical energy storage devices that operate in an ambient environment. Solid electrolytes using poly(vinyl alcohol) (PVA) and heteropoly acids (HPA) have been demonstrated for solid-state ECs and showed promising conductivities and stability [3]. In previous studies, we have demonstrated that PVA and silicotungstic acid (SiWA) can form a solid film with a conductivity of 0.01 S/cm which was implemented in an EC [3]. We further optimized the conductivities by adjusting the ratio of PWA and SiWA in PVA matrix and obtained a synergistic effect with a conductivity of ca. 0.013 S/cm, exceeding that of pure PVA-PWA or PVA-SiWA solid electrolytes [4]. The objectives of the current study are: a) to further optimize PVA-HPA polymer electrolytes through HPA loading and additives and, b) to develop an understanding of the mechanism of the proton conduction in the solid polymer electrolyte. Experimental Two precursors were prepared by mixing a PVA solution (PVA, Aldrich MW = 125,000) with a heteropoly acid solution, either H 4 SiW 12 O 40 ·xH 2 O (SiWA, alfa aesar) or H 3 PW 12 O 40 ·xH 2 O (PWA, alfa aesar). The precursor solutions were composed of 32.5% SiWA or PWA, 1.5% PVA, and 66% de-ionized water (all in wt. %). The PVA-PWA and PVA-SiWA precursors were combined in equal volumes for a mixed polymer electrolyte (we henceforth refer to this mixture as PVA-Mix). In addition, a 0.02 wt. % of polyacrylic acid (PAA) was added to PVA solution as additive in some cases. The matrix ECS Transactions, 28 (8) 77-82 (2010) 10.1149/1.3490684 © The Electrochemical Society 77 ecsdl.org/site/terms_use address. Redistribution subject to ECS license or copyright; see 142.150.190.39 Downloaded on 2013-08-16 to IP