Solid-state Cd/Cd 2+ reference electrode based on PMMA gel electrolytes Jakub Reiter a, ⁎ , Jiří Vondrák a , Zdeněk Mička b a Institute of Inorganic Chemistry, Academy of Sciences, 250 68 Řež near Prague, Czech Republic b Faculty of Science, Charles University, 128 40 Prague, Czech Republic Received 31 March 2006; received in revised form 8 October 2006; accepted 10 October 2006 Abstract All solid-state reference electrode based on Cd/Cd 2+ system was developed for the electrochemical measurements in aprotic organic carbonates ( propylene PC, ethylene EC and dimethyl carbonate DMC). The electrode was designed by using poly(methyl methacrylate) – propylene carbonate polymer electrolyte with immobilised Cd(ClO 4 ) 2 solution and a cadmium wire. The electrode performance in various solvents was studied including potential determination and its dependence on the solution ionic strength. Cyclic voltammetry of ferrocene in particular solvents showed good reproducibility of the electrode potential within the set of 18 electrodes: E(PMMA-Cd-Cd 2+ )= - 0.439 ± 0.013 vs. SCE in propylene carbonate. Also long-term chronopotentiometric measurements showed good potential stability and no potential drift within 3-week continuous experiment. Three versions of electrode material filling were studied (glass frit, ceramic separator and graphite rod) with the aim to reduce unwelcome penetration of chemicals into the electrode material and leakage of cadmium ions into solution. Reliable electrochemical data were obtained during the 5-year employment of the PMMA-Cd-Cd 2+ electrode. © 2006 Elsevier B.V. All rights reserved. Keywords: Polymer gel electrolyte; Cadmium; Poly(methyl methacrylate); Carbonate; Reference electrode 1. Introduction The electrochemical measurements in the solid state require specific conditions, especially utilisation of a reference electrode containing no liquid phase. This electrode is useful especially in the electrochemical gas sensors, “lab on chip” devices, and micro-multisensors, where miniaturization and mechanical robustness is required [1]. All solid-state electrodes can be exposed to higher temperatures and pressures than the liquid filled electrode, and they do not need to be used in vertical position. Due to absence of liquid filling solution, the contribution of the liquid junction is minimised [2]. Solid-state reference electrode can be also widely used in electrochemistry of solid and gel polymer electrolytes (GPEs), where the measurements can be performed in the aprotic liquid systems as well as in the polymer media with one reference system within the whole experiment. Polymer gel electrolytes, composite materials combining polymer with an aprotic solvent, are widely used in electrochemical devices such as electrochromic units [3], lithium-ion batteries [4], supercapacitors [5], and solid-state gas sensors [6]. Since the introduction of poly(ethylene oxide)-LiClO 4 binary electrolyte in late 1970′s by M. B. Armand [7], miscellaneous aprotic systems were prepared and studied [8–11]. Ternary systems polymer- aprotic solvent–salt based on various methacrylates were studied in our laboratory. Solutions of inorganic perchlorates and tetrafluor- oborates in propylene carbonate were combined with poly(methyl methacrylate), poly(ethyl methacrylate) or poly(2-ethoxyethyl methacrylate) [12–15]. Prepared composites exhibit high ionic conductivity (up to 0.6 mS cm - 1 ) (cit. [13,14]) together with wide accessible potential window over 4 V. Generally, for the electrochemical measurements in the solid- state and for the electrochemical sensors, various reference or pseudoreference systems were described. Pt-air electrode was used for many thermodynamic measurements [16] and in electrochem- ical gas sensors [17,18]. Rosini and Siebert used quinhydrone-poly (benzimidazole) electrode for hydrogen sensor [19]. Also for hydrogen detection in air, Maffei and Kuriakose developed Ag/ Solid State Ionics 177 (2007) 3501 – 3506 www.elsevier.com/locate/ssi ⁎ Corresponding author. Tel.: +420 266172198; fax: +420 220941502. E-mail address: reiter@iic.cas.cz (J. Reiter). 0167-2738/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2006.10.011