Silver and Copper Ion Conductors

The family of Ag + and Cu + superionic conductors have been extensively studied for many decades, using a wide range of experimental and computational techniques see also Chapter 7. They are principally of interest for fundamental reasons, as model systems in which to characterize the nature ofthe dynamic disorder and to probe the factors which promote high values of ionic conductivity within the solid state. Their commercial applications are generally limited by factors such as chemical stability, the high cost of silver, and their relatively high mass when compared, for example, to lithium-based compounds. 

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In spite of the extraordinarily high ionic conductivity of silver- and copper-ion conductors, these materials suffer from their low capacity and energy density. In addition, only a few positive electrode materials have been found until now. 

Cul) is not due to point defects but to partial occupation of crystallographic sites. The defective structure is sometimes called structural disorder to distinguish it from point defects. There are a large number of vacant sites for the cations to move into. Thus, ionic conductivity is enabled without use of aliovalent dopants. A common feature of both compounds is that they are composed of extremely polarizable ions. This means that the electron cloud surrounding the ions is easily distorted. This makes the passage of a cation past an anion easier. Due to their high ionic conductivity, silver and copper ion conductors can be used as solid electrolytes in solid-state batteries. 

The use of known solid silver and copper ion conductors in display devices has also been proposed (U9). 

Electroless plating — An autocatalytic process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons. It is promoted by specific reductants, namely formaldehyde, sodium hypophosphide, sodium boro-hydride, dialkylamine borane, and hydrazine. Electroless deposition has been used to produce different metal (e.g., nickel, cobalt, copper, gold, platinum, palladium, silver) and alloy coatings. It can be applied to any type of substrate including non-conductors. Some substrates are intrinsic catalytic for the electroless deposition other can be catalyzed usually by sensibilization followed by Pd nucleation also, in some non-catalytic metallic substrates the electroless process can be induced by an initial application of an appropriate potential pulse. In practical terms, the evaluation of the catalytic activity of a substrate for the electroless deposition of a given metal is... 

An electrochemical cell consists of two conductors called electrodes, each of which is immersed in an electrolyte solution. In most of the cells that will be of interest to us, the solutions surrounding the two electrodes are different and must be separated to avoid direct reaction between the reactants. The most common way of avoiding mixing is to insert a salt bridge, such as that shown in Figure 18-2, between tire solutions. Conduction of electricity from one electrolyte solution to the other then occurs by migration of potassium ions m the bridge in one direction and chloride ions in the other. However, direct contact between copper metal and silver ions is prevented. 

Copper was called cuprum in Latin, hence its symbol, Cu. It is used in the minting of one cent pieces and for pans, but an even more important use is in the wires and switches that carry electricity. Copper is the second-best conductor of electricity (silver is first). It is alloyed with other metals to make bronze and brass. The Cu+2 ion is necessary in the human body, in very small, or trace, amounts, as a catalyst in making blood. At ordinary temperatures, copper is the best conductor of heat. 

C rystalline membranes arc also available thal consist of a homogeneous mixture of silver sulfide with sulfides of copper(U), lead, or cadmiunt. Toward these divalent cations, electrodes from these materials have electrical responses similar to electrodes of the third kind (Section 23C-3). Note that these divalent sulfides, by themselves, are not conductors and thus do not exhibit ion-selectivc activity. 

A phenomenon of great practical relevance is the increase of ion conductivity by adding second surface active particles (a). The earliest example was LiI Al203, [11] later examples are silver, copper, and thallium halides which showed similar effects [4, 5]. Similar effects can also be observed for anion conductors examples (e.g., PbF2 Si02) (b) [4]. They all find their explanation in the concept of... 

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