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Reference Electrodes for Solid-Electrolyte Devices Vladislav V. Kharton and Ekaterina V. Tsipis

9.1

Introduction

Solid electrolytes are a class of solids where electrical conduction occurs predominantly via migration of ions and the overall level of ionic transport is high enough for practical applications, whilst electronic contribution to the total electrical conductivity is negligible. This term is commonly used for the materials with ion transport numbers (tion) equal to or higher than 0.99 under given external conditions. The range of conditions (temperature, pressure, and thermodynamic activities of components) where tion
0.99 is often called the electrolytic domain. A large number of solid electrolytes (SEs) with mono-, bi-, and trivalent ion charge carriers are known. The groups important from the practical point of view include [1–5]: (i) Solids with fast diffusion of monovalent cations (Li+, Na+, K+, Ag+, Cu+, etc.), which find their applications in many types of batteries, sensors, fuel cells, accumulators, alkali-metal thermal to electric converters (AMTECs), and electrochromic and ionic memory devices. Examples are the families of βalumina and NASICON (Na1+xZr2SixP3xO12), their analogues and derivatives where almost all alkaline-metal cations and protons may have high mobility, numerous alkaline-metal salts, and also oxide, halide, sulfide, and nitride compounds such as Li4SiO4, Li2SO4, Li3N, KMO2 (M ¼ Al, Ga, Fe), KAlSi2O6, AgI, CuI, RbAg4I5, and Rb4Cu16I7Cl13.

V.V. Kharton (*) Department of Materials and Ceramic Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal e-mail: [email protected] E.V. Tsipis UCQR, IST/ITN, Instituto Superior Te´cnico, Universidade Te´cnica de Lisboa, CFMC-UL, Estrada Nacional 10, 2686-953 Sacave´m, Portugal e-mail: [email protected] G. Inzelt et al. (eds.), Handbook of Reference Electrodes, DOI 10.1007/978-3-642-36188-3_9, # Springer-Verlag Berlin Heidelberg 2013

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(ii) Oxygen-anion conductors, which are used for solid oxide fuel cells (SOFCs), high-temperature electrolyzers of carbon dioxide and water vapor, electrochemical oxygen pumps and compressors, gas dosage, various electrochemical reactors where oxygen is involved in catalytic and/or electrocatalytic processes over an anion-conducting membranes or electrodes, gas sensors, and a variety of other appliances for thermodynamic and analytical measurements. Key families of the oxygen ion-conducting solid electrolytes include stabilized hightemperature polymorphs of ZrO2, Bi2O3, Bi4V2O11, La2Mo2O9 and Ba2In2O5, apatite-type La10x(MO4)6O2δ (M ¼ Si, Ge), acceptor-doped CeO2 with fluorite structure, perovskite-type LaMO3 (M ¼ Ga, Al), and pyrochloretype titanates and zirconates such as (Gd, Ca)2Ti2O7δ. (iii) Protonic conductors have numerous potential and current applications in hydrogen-separation membranes, hydrogen pumps and dosing devices, catalytic processes, steam electrolysis, SOFCs with proton-conducting oxide electrolyte membranes, and sensors of H-containing