Solid electrolyte relative humidity

With many electrolytes, AP is so large that the solid, when exposed to moist air, picks up water (deliquesces). This occurs with calcium chloride, whose saturated solution has a vapor pressure only 30% that of pure water. If dry CaCl2 is exposed to air in which the relative humidity is greater than 30%, it absorbs water and forms a saturated solution. Deliquescence continues until the vapor pressure of the solution becomes equal to that of the water in the air. 

The substitution of the two-sided tape with a film of an ionic conductor gives (Fig. 24) a triple-layered muscle working in air.114 The tape now acts as a solid electrolyte. Nevertheless, the system only works if the relative humidity in air surpasses 60%. Under these conditions, movements and rates similar to those shown by a triple layer working in aqueous solution were obtained. This device was developed in cooperation with Dr. M. A. De Paoli from the Campinnas University (Campinnas, Brazil). At the moment several groups are developing actuators, muscles, and electrochemomechanical devices based on bilayer or multilayer structures.115-125... 

Atmospheric corrosion of metals is differentiated from the other forms of corrosion due to exposure of metals to different atmospheres rather than immersion in electrolytes. The spontaneous atmospheric corrosion of materials is controlled by the temperature, the relative humidity, the time of wetness, the pH of the electrolyte, and the presence of contaminants such as chlorides, NH3, SO2, NO2, and acidic fogs. In most cases, the rate equations have hmited validity due to different local atmospheric conditions. Metals spontaneously form a solid metal oxide film when exposed to dry atmospheres. The barrier oxide film reaches a maximum thickness of 2-5 nm [1-6]. The corrosion rate of metals exposed to a wet atmosphere is similar to that observed during immenion in aerated water in the presence of dissolved oxygen. Atmospheric corrosion rates decrease in dry atmospheres with corrosion mechanisms that are different from those in wet atmospheres. 

Opekar F, Stulik K (1999) Electrochemical sensors with solid polymer electrolytes. Anal Chim Acta 385 151-162 Opekar F, Svozil D (1995) Electric resistance in a Nation membrane exposed to air after a step change in the relative humidity. J Electroanal Chem 385 269-271 Osada Y, De Rossi DE (eds) (2000) Polymer sensors and actuators. Springer, Berlin... 

In a recent article [5] dealing with the properties of adsorbed water layers and the effect of adsorbed layers on interparticle forces, it was clearly stated that even under common room conditions (relative humidity in the region 40-60%), two or three adsorbed monolayers of water are often present on particles, dominating the interactions, and therefore the physical characteristics of the material. For a two-phase equilibrium system containing hydrophilic silica plates (surface of a-quartz covered by silanol groups) and water molecules, a molecular dynamic simulation expected at least one adsorbed monolayer to be present. Quite different behavior would be expected for less hydrophilic surfaces. The material character and chemical properties of solid materials are of crucial importance in the hydration interaction. Therefore, some common adsorbents which are Irequently used in aqueous electrolyte solutions are discussed separately. 

Fig. 7.16 Dependence of proton conductivity on relative humidity of a hybrid octane membrane at (a) 120°C and (b) 160°C. Reprinted with permission from Ref. [56] I. Honma, et al.. Organic/ inorganic nano-composites for high temperature proton conducting polymer electrolytes. Solid State Ionics 162-163, 237-245 (2003). Copyright Elsevier...

PEO has also been used as polymer matrix for the preparation of electrolytes containing KI, h and the ionic liquid 1-ethyl 3-methyl imidazolium thiocyanate." The final room-temperature conductivity of PEO/ionic Uquid/KFF solid film was 2.3 x 10 S cm at 50% relative humidity. The DSSC prepared with the electrolyte containing 80% of ionic liquid showed Jsc = 1.9 mA cm . Foe = 0.65 V, FF = 0.52 and rj = 0.6%." ... 

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