Solid Electrolyte Systems

From the point of view of lifetime, mechanical ruggedness, and, possibly, ease of manufacture, solid electrolyte systems are very attractive. Two main difficulties are, however, apparent. The first of these is the difficulty in making an intimate high-surface-area soiid-solid interface and maintaining it over a wide temperature range. Even if the electroiyte can be introduced into the pores as a liquid, it may prove difficult to maintain contact on solidification by cooiing or soivent evaporation. The second problem Is that most solid electrolytes are distinctly inferior to liquid electrolytes In terms of their resistivity and the temperature coefficient of that resistivity. 

Other inorganic solid electrolytes have also been employed in electrochemical capacitor applications, including hydrogen uranyl phosphate, (H3OUO2PO4) and Zr(HP04)2 xH20 (proton conductors) (65), Li and Na /9-alumina (66), LiNaSO (67). Clearly, these systems will only be satisfactory for relatively slow applications. 

---

Solid Electrolyte Systems. Whereas there has been considerable research into the development of soHd electrolyte batteries (18—21), development of practical batteries has been slow because of problems relating to the low conductivity of the soHd electrolyte. The development of an all sohd-state battery would offer significant advantages. Such a battery would overcome problems of electrolyte leakage, dendrite formation, and corrosion that can be encountered with Hquid electrolytes. 

I. The parameter 2Fr0/Io ( A ) must be larger than unity (Chapter 4). Catalysis at the metal/gas interface must be faster than electrocatalysis. This is easy to satisfy in solid electrolyte systems and more difficult to satisfy in aqueous electrolyte systems. 

Cairns EJ, Shimotake H (1969) High-temperature batteries. Science 164 1347-1355 Kennedy JH (1977) Thin film solid electrolyte systems. Thin Solid Films 43 41-92 Linford RG (1988) Apphcations of solid state ionics for batteries. Solid State Ionics 28-30 831-840... 

Figure 7. The differences of real potentials of the Ag ion in metal-solid electrolyte systems.

Except for some exotic surface-mount technology (SMT/SMD) aluminum electrolytic capacitor types with solid electrolyte systems, in general, an aluminum electrolytic capacitor contains a wound capacitor element (the coil), impregnated with liquid electrolyte, connected to terminals, and sealed in a can (with a rubber plug at the end). The aluminum in the name,... 

In most solid electrolyte systems, it is not possible to vary the composition sufficiently so as to have the complete spectrum of mobile ion concentrations, from n,. = 0 to n,. = 1. Instead, the properties are usually limited to one or other of the wings in the type of behaviour... 

It is important to appreciate that solid electrolyte systems are different from aqueous systems in one important way. In a solid electrolyte system the charge transfer takes place across the catalyst/electrolyte interface whereas the chemical reaction takes place on the gas-exposed surface of the catalyst. In aqueous systems the surface at which charge-transfer occurs is the same as the surface over which any catalysis occurs. As a result care must be exercised when making analogies between the two types of cell. 

It must be remembered that in aqueous systems the redox process occurs over the entire electrode area, whereas in solid electrolyte systems the redox process occurs only in the three-phase or charge-transfer region. The technique has been used with solid electrolyte systems for sometime to study the oxidation and reduction of metals and metal oxides in inert atmospheres,94,95 the behaviour of solid oxide fuel cell (SOFC) electrodes and has also been applied to the in-situ study of catalysts.31,32,95... 

Ionically conducting polymers and their relevance to lithium batteries were mentioned in a previous section. However, there are several developments which contain both ionically conducting materials and other supporting agents which improve both the bulk conductivity of these materials and the properties of the anode (Li)/electrolyte interface in terms of resistivity, passivity, reversibility, and corrosion protection. A typical example is a composite electrolyte system comprised of polyethylene oxide, lithium salt, and A1203 particles dispersed in the polymeric matrices, as demonstrated by Peled et al. [182], By adding alumina particles, a new conduction mechanism is available, which involved surface conductivity of ions on and among the particles. This enhances considerably the overall conductivity of the composite electrolyte system. There are also a number of other reports that demonstrate the potential of these solid electrolyte systems [183],... 

Both solid electrolyte systems have a transparent and elastomeric appearance, whose thickness is about 0.3 mm and whose ionic conductivities are of the... 

The technique of cyclic voltammetry or, more precisely, linear potential sweep chronoamperometry, is used routinely in aqueous electrochemistry to study the mechanisms of electrochemical reactions. Currently, cyclic voltammetry has become a very popular technique for initial electrochemical studies of new systems and has proven very useful in obtaining information about fairly complicated electrochemical reactions. There have been some reported applications of cyclic voltammetry for solid electrochemical systems. It is worth pointing out that, although the theory of cyclic voltammetry originally developed by Sevick, ° Randles, Delahay, ° and Srinivasan and Gileadi" and lucidly presented by Bard and Faulkner, is very well established and understood in aqueous electrochemistry, one must be cautious when applying this theory to solid electrolyte systems of the type described here, as some non-trivial refinements may be necessary. 

The existence of a current hump near Tc is confirmed by several additional facts. In the first place, these are deduced from the results of the quantitative treatment of the impedance spectra of the HTSC/solid electrolyte system [147]. This approach consists of calculating from the experimental complex-plane impedance diagrams the parameters characterizing the solid electrolyte, the polarization resistance of the reaction with the participation of silver, and the double-layer capacitance (Cdi) for each rvalue (measured with an accuracy of up to 0.05°). Temperature dependence of the conductance and capacitance of the solid electrolyte (considered as control parameters) were found to be monotonic, while the similar dependences of two other parameters exhibited anomalies near Tc- The existence of a weakly pronounced minimum of Cji near Tc, which is of great interest in itself, was interpreted by the authors as the result of sharp reconstruction of the interface in the course of superconducting transition [145]. 

The polycrystalline metal film/oxidic solid electrolyte system provides a reasonable approximation to nanocrystalline metal/metal oxide catalysts. 

Spillover-Backspillover in Metal—Solid Electrolyte Systems Thermodynamics We start from Eq. (13), which, under open-circuit conditions, is at equilibrium at the three-phase boundaries (tpb) metal (M)-gas-YSZ (Figure 5) ... 

The kinetics of ion backspillover in metal-solid electrolyte systems depends on two factors on the rate, IjnF, of overall neutral backspillover species formation at the tpb and on their surface diffusivity, D, on the metal surface. Experiment has shown that the rate of electrochemically controlled ion backspillover is normally limited by IjnF, i.e., the slow step is their creation at the tpb [13]. Surface diffusion is usually fast. For the case of Pt electrodes, reliable surface O diffusivity data exist for the Pt(lll) and Pt(llO) surfaces, obtained by Corner and Lewis several years ago [122], and thus a conservative estimate for the surface diffusivity of can be made ... 

The phenomenon of EPOC or NEMCA effect was first reported in solid electrolyte systems [23, 195-205], but several NEMCA studies already exist using aqueous electrolyte systems [23, 30, 31,145] or Nafion membranes [23]. The EPOC phenomenon leads to apparent Faradaic efficiencies, A, well in excess of 100% (values up to 105 have been measured in solid-state electrochemistry and up to 102 in aqueous electrochemistry). This is due to the fact that, as shown by a variety of surface science and electrochemical techniques [23, 40, 195-198, 206-209], the NEMCA effect is due to electrocatalytic (Faradaic) introduction of promoting species onto catalyst-electrode surfaces [23, 196], each of these promoting species being able to catalyze numerous (A) catalytic turnovers. 

There are many types of electrolyzers high temperature, high pressure, low temperature and low pressure, and liquid electrolyte and solid electrolyte forms. For solar hydrogen production, low to medium pressure, low temperature liquid electrolyte electrolyzers are preferred. When compared to the cost of high temperature, high pressure systems and/or solid electrolyte systems, they are inexpensive to make, purchase and maintain. 

Bhoga. S.S. and Singh. K. (2005) Performance of electr ochemical CO2 gas sensor with NASICON dispersed in a binar y solid electrolyte system. Indian J. Phys.. 79 (7). 725-6. 

Kennedy, I.H., Thin films solid electrolyte systems. Thin Solid Films 43 (1977) 41-92. Skliar, M. and Tathireddy, R, Approximation of evolutional system using singular forcing, Comput. Chem. Eng. 26 (2002) 1013—1021. 

L. Elikan, J. P. Morris, and C. K. Wu, Development of a solid electrolyte system for oxygen reclamation, report prepared under Contract NASI-8896, Westinghouse Electric Corporation for NASA, 1971. 

In 1973, Peter Wright and coworkers first reported [39-41] the ionic conductivity of poly(ethylene oxide), [CH2CH20]n, (PEO), with alkali metal salts. This was followed by the visionary suggestion of M. Armand for the use of PEO as a solid electrolyte system for the transport of ions [42-43]. Since then, the area of polymer electrolytes has attracted considerable interest. In the following account, first a discussion is presented on the general features applicable to polymer electrolytes. This is followed by an account on individual polymer electrolytes, par-... 

Recently (5,6,7) solid electrolyte systems based on poly(vinyl alcohol), PVOH,... 

---