Negative plates reactions

The drying of negative plates is not possible without precautions, because of the tendency to spontaneous oxidation. This oxidation reaction is much ac-celerated by water, and the active material of a moist negative electrode is spon-taneously converted into lead oxide when exposed to air. When, on the other hand, the charged plate is dry, a thin layer of oxide covers the surface of the active material, and prevents... 

Nickel-cadmium batteries use a hydrate nickel oxide as positive electrode, a metallic cadmium as negative electrode and an aqueous solution of potassium hydroxide as electrolyte [17]. The production of electrons at the negative plate during discharge occurs via the following semi-reaction ... 

Two other reactions must be taken into account during the charging of a VRLA cell. These are, the evolution of hydrogen at the negative plate ... 

The reaction between the ions of the solution and the initial solid porous phases proceeds in a reaction layer, which is located between the zone of the initial phases and the zone occupied by the reaction products. The reaction layer shifts in space and penetrates the volume of the initial phase zone. Thus, the volume of the zone occupied by the reaction products grows at the expense of the initial phase zone. The direction in which the reaction product zone grows depends on the transport hindrances experienced by the ions on their way from the solution volume to the reaction layer and/or on the transport difficulties met by the ions formed in the reaction layer on their way to the solution volume. On soaking and formation of the positive and negative plates, some zonal processes occur. During soaking, only chemical reactions proceed in the reaction layer (i.e., chemical zonal processes). 

The electrochemical reactions that proceed during formation of negative plates can be represented by the following equations. represents the equilibrium potential... 

Negative-plate formation. The stages in the formation of negative plates have been determined in terms of the zonal processes as presented in Fig. 3.45. The reactions involved in each of the formation stages are presented schematically in Figs. 3.43 and 3.44, and are summarized in Fig. 3.59. The formation can be divided into the following stages. 

Resolution of the above problems is made more difficult by the sensitivity of negative plates to various secondary reactions, such as those caused by impurities and additives. These may affect the self-discharge rate, as well as the charge-acceptance and the efficiency at which the charge input is subsequently used. The transient nature of these effects increases the difficulty of understanding their influence. Several studies are now underway to increase this understanding and... 

During the initial stages of the discharge of a fully charged negative plate, eleetron transfer can take place at any location because the entire plate is conduetive. Accordingly, the discharge process (both dissolution and deposition steps) oeeurs both on the surfaces and in the interior of the plate. Nevertheless, the reaction in the... 

Fig. 17.4. Discharge and charge reactions at the negative plate of a lead-acid cell.

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