Lead aqueous electrolyte

In an aqueous electrolyte, the anodic behaviour of lead vanes greatly depending on the conditions prevailing. Extensive reviews of the anodic behaviour of lead have been produced Under certain conditions, the passive film may be converted to lead dioxide which has an electronic resistivity of 1 - 4 x 10" Ohm cm. Two polymorphs of PbO, exist, a and... 

Zinc/carbon and alkaline/manganese cells are primary battery systems lead, nickel/cadmium, and nickel/metal hydride accumulators are secondary batteries with aqueous electrolyte solutions. Their per-... 

Aqueous electrolytes proposed in the literature for cathodic electrodeposition of lead selenide are generally composed of dissolved selenous anhydride and a lead salt, such as nitrate or acetate. Polycrystalline PbSe films have been prepared by conventional electrosynthesis from ordinary acidic solutions of this kind on polycrystalline Pt, Au, Ti, and Sn02/glass electrodes. The main problem with these applications was the PbSe dendritic growth. Better controlled deposition has been achieved by using EDTA in order to prevent PbSeOs precipitation, and also acetic acid to prevent lead salt hydrolysis. 

Electrorefining has been used for the purification of many common as well as reactive metals. It has been seen that the emf or the potential required for such a process is usually small because the energy needed for the reduction of the ionic species at the cathode is almost equal to that released by the oxidation of the crude metal at the anode. Some metals, such as copper, nickel, lead, silver, gold, etc., are refined by using aqueous electrolytes whereas molten salt electrolytes are necessary for the refining of reactive metals such as aluminum,... 

Several metallophthalocyanines have been reported to be active toward the electroreduction of C02 in aqueous electrolyte especially when immobilized on an electrode surface.125-127 CoPc and, to a lesser extent, NiPc appear to be the most active phthalocyanine complexes in this respect. Several techniques have been used for their immobilization.128,129 In a typical experiment, controlled potential electrolysis conducted with such modified electrodes at —1.0 vs. SCE (pH 5) leads to CO as the major reduction product (rj = 60%) besides H2, although another study indicates that HCOO is mainly obtained.129 It has been more recently shown that the reduction selectivity is improved when the CoPc is incorporated in a polyvinyl pyridine membrane (ratio of CO to H2 around 6 at pH 5). This was ascribed to the nature of the membrane which is coordinative and weakly basic. The microenvironment around CoPc provided by partially protonated pyridine species was suggested to be important.130,131 The mechanism of C02 reduction on CoPc is thought to involve the initial formation of a hydride derivative followed by its reduction associated with the insertion of C02.128... 

In order to study the identity and nature of the intermediate, Aylmer-K.elly et al. (1973) employed modulated specular reflectance spectroscopy. They studied the reduction reaction at a lead cathode in both aqueous and non-aqueous electrolytes. A phase-sensitive detection system was employed by the authors, locked-in to the frequency of the potential modulation. The potential was modulated at 30 Hz between the reference potential of — 1.0 V vs. Ag/AgCl and a more cathodic limit. 

The charge carriers may reduce or oxidize the semiconductor itself leading to decomposition. This poses a serious problem for practical photoelectrochemical devices. Absolute thermodynamic stability can be achieved if the redox potential of oxidative decomposition reaction lies below the valence band and the redox potential of the reductive decomposition reaction lies above the conduction band. In most cases, usually one or both redox potentials lie within the bandgap. Then the stability depends on the competition between thermodynamically possible reactions. When the redox potentials of electrode decomposition reactions are thermodynamically more favored than electrolyte redox reactions, the result is electrode instability, for example, ZnO, Cu20, and CdS in an aqueous electrolyte. 

Smith-Magowan, D. Goldberg, R. N. "A Bibliography of Sources of Experimental Data Leading to Thermal Properties of Binary Aqueous Electrolyte Solutions" Nat. Bur. Stand. Special Publ. No. 537, March 1979. 

Anodic oxide formation suggests itself as a passivating mechanism in aqueous electrolytes, as shown in Fig. 6.1a. However, pore formation in silicon electrodes is only observed in electrolytes that contain HF, which is known to readily dissolve Si02. For current densities in excess of JPS a thin anodic oxide layer covers the Si electrode in aqueous HF, however this oxide is not passivating, but an intermediate of the rapid dissolution reaction that leads to electropolishing, as described in Section 5.6. In addition, pore formation is only observed for current densities below JPS. Anodic oxides can therefore be excluded as a possible cause of pore wall passivation in PS layers. Early models of pore formation proposed a... 

The aqueous batteries use water based electrolytes (e.g., KOH electrolyte for NiCd and NiMH and H2-SO4 electrolyte for lead acid), which are less resistive then nonaqueous electrolytes. Polyolefin materials are generally suitable for use in the manufacture of separators for these batteries, but they are not inherently wettable by aqueous electrolytes. Such electrolytes are therefore unable to penetrate the pores of a separator formed from such a material, so that ion migration through the pores in solution will not occur without modification. This problem is sometimes overcome by treating the polyolefin material with a surfactant, which allows an aqueous electrolyte to wet the material. However, such surfactant can be removed from the surfaces of the polyolefin material when electrolyte is lost from the device, for example during charging and discharging cycles, and it is not subsequently replaced on the material when the electrolyte is replenished. 

Similar types of electric double layer may also be formed at the phase boundary between a solid electrolyte and an aqueous electrolyte solution [7]. They are formed because one electrically-charged component of the solid electrolyte is more readily dissolved, for example the fluoride ion in solid LaFs, leading to excess charge in the solid phase, which, as a result of movement of the holes formed, diffuses into the soUd electrolyte. Another possible way a double layer may be formed is by adsorption of electrically-charged components from solution on the phase boundary, or by reactions of such components with some component of the solid electrolyte. For LaFa this could be the reaction of hydroxyl ions with the trivalent lanthanum ion. Characteristically, for the phase boundary between two immiscible electrolyte solutions, where neither solution contains an amphiphilic ion, the electric double layer consists of two diffuse electric double layers, with no compact double layer at the actual phase boundary, in contrast to the metal electrode/ electrolyte solution boundary [4,8, 35] (see fig. 2.1). Then, for the potential... 

Traditionally, anodic oxygen evolution from acid solution—particularly from aqueous electrolytes containing sulfuric acid—has been performed at lead anodes that are passivated and stabilized against corrosion by a selfforming coating of Pb02. 

The manufacture of secondary batteries based on aqueous electrolytes forms a major part of the world electrochemical industry. Of this sector, the lead-acid system (and in particular SLI power sources), as described in the last chapter, is by far the most important component, but secondary alkaline cells form a significant and distinct commercial market. They are more expensive, but are particularly suited for consumer products which have relatively low capacity requirements. They are also used where good low temperature characteristics, robustness and low maintenance are important, such as in aircraft applications. Until recently the secondary alkaline industry has been dominated by the cadmium-nickel oxide ( nickel-cadmium ) cell, but two new systems are making major inroads, and may eventually displace the cadmium-nickel oxide cell - at least in the sealed cell market. These are the so-called nickel-metal hydride cell and the rechargeable zinc-manganese dioxide cell. There are also a group of important but more specialized alkaline cell systems which are in use or are under further development for traction, submarine and other applications. 

Apart from liquid-liquid transitions, liquid-vapor transitions in aqueous electrolyte solutions have played a crucial role in debates on ionic criticality [142-144], The liquid-vapor transition is usually associated with a mechanical instability with diverging density fluctuations, while liquid-liquid transitions are associated with a material instability with diverging concentration fluctuations. This requires, however, that both regimes are well-separated. Their interference can lead to complex phase behavior with continuous transitions from liquid-liquid demixing to liquid-gas condensation [9, 145, 146]. It is then not trivial to define the order parameter [147-149]. 

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