Zinc alkaline electrolyte

Alkaline batteries were introduced in the early 1960s they last two to five times longer than Zn-carbon cells on continuous discharge and command two or three times the price in the USA (far more in Europe and the East). Alkaline cells became a necessary invention and they succeeded as a result of the requirements of the electronic devices. The essential improvement was the change from ammonium chloride and/or zinc chloride electrolyte to alkaline (KOH) electrolyte, the steel can construction, the outside cathode, and the zinc powder (large surface) anode. A main low-cost feature is that they use pressed cathodes and do not need to follow "jellyroll"... 

It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

Despite the fact that the zinc/ ferricyanide system employs an alkaline electrolyte, the electrode reactions are quite similar to those in zinc/halogen batteries and battery constructions are usually bipolar too. 

The reason for this limited cycle life is the high solubility of the zinc electrode in alkaline electrolyte the zincate ions formed are deposited again during the subsequent charging in the form of dendrites, i.e., of fernlike crystals. They grow in the direction of the counterelectrode and finally cause shorts. 

Metallic zinc was used as a material for the negative electrode in the earliest electrical cell, Volta s pile, and is still employed in a variety of batteries, including batteries with alkaline electrolytes. 

In topochemical reactions all steps, including that of nucleation of the new phase, occur exclusively at the interface between two solid phases, one being the reactant and the other the product. As the reaction proceeds, this interface gradually advances in the direction of the reactant. In electrochemical systems, topochemical reactions are possible only when the reactant or product is porous enough to enable access of reacting species from the solution to each reaction site. The number of examples electrochemical reactions known to follow a truly topochemical mechanism is very limited. One of these examples are the reactions occurring at the silver (positive) electrode of silver-zinc storage batteries (with alkaline electrolyte) ... 

The overall reaction in zinc-air battery with alkaline electrolyte at the beginning of discharge may by written as follows ... 

Two common types of button batteries both use a zinc container, which acts as the anode, and an inert stainless steel cathode, as shown in Figure 11.11 on the next page. In the mercury button battery, the alkaline electrolyte paste contains mercury(II) oxide, HgO. In the silver button battery, the electrolyte paste contains silver oxide, Ag20. The batteries have similar voltages about 1.3 V for the mercury cell, and about 1.6 V for the silver cell. 

The nickel-based systems include the flowing systems nickel—iron (Ni/Fe), nickel—cadmium (NiCd), nickel—metal hydrides (NiMH), nickel—hydrogen (Ni/ H2), and nickel—zinc (Ni/Zn). All nickel systems are based on the use of a nickel oxide active material (undergoing one valence change from charge to discharge or vice versa). The electrodes can be pocket type, sintered type, fibrous type, foam type, pasted type, or plastic roll-bonded type. All systems use an alkaline electrolyte, KOH. 

There are two broad classes of separators employed in nickel—zinc batteries a main separator, which exhibits resistance to dendrite penetration, and an interseparator, which principally acts as an electrolyte reservoir and wicking layer. Both main and interseparator should be resistant to chemical attack by the alkaline electrolyte and resistant to oxidative attack by nascent oxygen, permanently wettable by the electrolyte, flexible, heat sealable, tear resistant, and inexpensive. 

Addition of sodium dodecyl benzene sulfonate to dilute alkaline electrolyte depresses the passivation of zinc surface [275]. Owing to the dodecyl benzene sulfonate adsorption, the passive layer on zinc has a loose and porous structure. Zinc electrodissolution was inhibited by the presence of sodium metasdicate [276] and some acridines [277]. The protection effect was described by a two-parameter equation. 

Cylindrical alkaline cells are zinc-manganese dioxide cells having an alkaline electrolyte, which arc constructed in the standard cylindrical sizes, R2D D, R14 C . R6 AA , ROT AAA, as well as a few other less common sizes, llley can be used in the same types of devices as ordinary Leclanchd and zinc chloride cells. Moreover, die high level of performance makes them ideally suited for applications such as toys, audio devices, and cameras. 

An alkaline cell uses an alkaline electrolyte, with which the zinc electrode does not readily react when the battery is not in use. As a result, alkaline cells have longer lives than dry cells. The uses are the same as those for the dry cell, plus applications that require a long-lasting charge, such as smoke detectors and backup power supplies. 

Corrosion of the zinc anode is a significant side reaction under acidic conditions because zinc reacts with H+(aq) to give Zn2+(aq) and H2(y). Under basic conditions, however, the cell has a longer life because zinc corrodes more slowly. The alkaline cell also produces higher power and more stable current and voltage because of more efficient ion transport in the alkaline electrolyte. 

The curve shown in Fig. 3 cannot proceed indefinitely in either direction. In the cathodic direction, the deposition of copper ions proceeds from solution until the rate at which the ions are supplied to the electrode becomes limited by mass-transfer processes. In the anodic direction, copper atoms are oxidized to form soluble copper ions. While the supply of copper atoms from the surface is essentially unlimited, the solubility of product salts is finite. Local mass-transport conditions control the supply rate so a current is reached at which the solution supersaturates, and an insulating salt-film barrier is created. At that point the current drops to a low level further increase in the potential does not significantly increase the current density. A plot of the current density as a function of the potential is shown in Fig. 5 for the zinc electrode in alkaline electrolyte. The sharp drop in potential is clearly observed at -0.9 V versus the standard hydrogen electrode (SHE). At more positive potentials the current density remains at a low level, and the electrode is said to be passivated. 

Zn(OH)2 is soluble in the alkaline solution as [Zn(OH)3]- until the solution is saturated with K[Zn(OH)3]. In addition Zn(OH)2 can be dehydrated to ZnO. An enhanced power density (when compared with the - Leclanche cell) is accomplished by using particulate zinc (flakes) soaked with the alkaline electrolyte solution. This anode cannot be used as a cell vessel like in the Leclanche cell. Instead it is mounted in the core of the cell surrounded by the separator the manganese dioxide cathode is pressed on the inside of the nickel-plated steel can used as battery container. In order to limit self-discharge by corrosion of zinc in early cells mercury was added, which coated the zinc effectively and suppressed hydrogen evolution because of the extremely low exchange current density... 

The same authors also investigated zinc electrodeposition from acidic and alkaline electrolytes without and with inhibitors [6.82-6.86]. It was suggested that the deposition mechanism involves an autocatalytic step... 

Nikitina, Z. Passivation of a zinc electrode in galvanic elements with alkaline electrolytes. Ya Zh. Prikl. Khim. 1958, 31, 218. 

CVs for the oxidation of ferrate ions in alkaline solution are shown in Figure 10.. 5 (Licht et al., 2001), where an apparently irreversible diffusion-controlled oxidation process is recorded. A primary ferrate(VI) battery contains a Fe(VI) cathode and can use a zinc anode and an alkaline electrolyte such as a conventional alkaline battery. For Ag2FeO4, the general discharge reaction would be ... 

The anodic dissolution experiments of zinc rotating disk electrode were carried out in alkaline electrolyte [278] and in solution at pH 5.5 containing NH4CI and NH4CI +- ZnCb [279], NH4CI -I- NiCb, and NH4CI - NiCh-h ZnCb [280, 281]. The zinc electrode was covered by a porous film composed of a mixture of metallic zinc and zinc hydroxide [279]. In Ni-containing solutions, the passivation of Zn was a result of Zn-Ni alloy formation and Zn(OH)2 precipitation [280]. 

Zinc is also used to make batteries. In fact, the first dry battery produced used a zinc anode, a carbon cathode, and an alkaline electrolyte made from ammonium chloride paste to deliver 1.5 volts of energy. 

The mercury battery is used extensively in medicine and electronic industries and is more expensive than the common dry cell. Contained in a stainless steel cylinder, the mercury battery consists of a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte containing zinc oxide and mercury(ll) oxide (Figure 19.8). The cell reactions are... 

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