Electrochimica Acta 45 (2000) 1409 – 1414 Poly(methyl methacrylate)-based protonic gel electrolytes: a spectroscopic study H. Ericson a, *, C. Svanberg a , A. Brodin a , A.M. Grillone b , S. Panero b , B. Scrosati b , P. Jacobsson a a Chalmers Uniersity of Technology, SE-412 96 Go ¨teborg, Sweden b Uniersity of Rome ‘La Sapienza’, Piazzale Aldo Moro 5 Box 34 Roma 62 00195 Rome, Italy Received 5 November 1998; received in revised form 26 March 1999 Abstract We present the first vibrational spectroscopic investigation of a novel non-aqeous proton conducting polymer gel electrolyte consisting of a PMMA matrix and a solvent mixture (ethylene carbonate (EC)/propylene carbonate (PC) or EC/PC/-N,Ndimethylformamide (DMF)) with a dissolved organic acid (benzoic or salicylic acid). The protonic conductivity of the gels is of the order 10 -4 –10 -5 S/cm at room temperature. We show that the conductivity is proportional to the degree of dissociation of the acid, the latter determined from Raman spectroscopic data, and that the degree of dissociation depends on the properties of the solvent mixture. Finally, we comment on the relation between the proton conductivity and the solvent diffussion dynamics as studied by PCS. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: Polymer gels; Proton conduction; Vibrational spectroscopy; Photon correlation spectroscopy www.elsevier.nl/locate/electacta 1. Introduction Despite the success in recent years in the develop- ment of polymer-based proton conductors, there is a growing interest in new types of low temperature pro- ton conducting materials with optimised properties [1,2]. Large scale fuel cell applications for instance, call for cheap electrolytes that are easy to manufacture, while small scale electrochemical applications, require fine tuning of electrolyte properties to meet the needs of a particular device. Classical commercially available proton-conducting materials such as Nafion ® , represent a class of hydrated systems containing sulphonic acid as proton donor. These materials exhibit high protonic conductivity, in excess of 10 -2 S/cm, with sufficient amounts of water in the system [1]. There are, however, a number of applications where a modest conductivity is sufficient, while the presence of water in combination with acid is detrimental. Anhydrous proton-conducting polymer electrolytes have been formed by complexing a strong acid e.g., H 3 PO 4 or H 2 SO 4 , with a polymer containing a basic function such as poly(ethylene oxide) or poly(ethylene imine) [3]. Non-aqueous proton con- ducting gels with H 3 PO 4 and organic solvents in a polymer matrix have also been reported [4]. In the present study, a new type of water-free proton- conducting polymer gel was prepared following a well- known concept for gel-type Li + electrolytes for battery applications. Li + -ion conducting gels typically consist of a high-molecular-weight polymer, a mixture of or- ganic solvents and a Li + -salt [5]. The proton conduct- ing gels presented here, consist of a high-molecular-weight poly(methyl methacrylate) (PMMA) matrix, a solvent mixture consisting of ethylene carbonate (EC)/propylene carbonate (PC) or * Corresponding author. 0013-4686/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(99)00352-7