Electrolytic manganese dioxide reactions

The alkaline cell has an open-circuit voltage of 1.5 V that can deliver 150 Wh/kg and 460 Wh/1. The reactions have fast kinetics and can deliver full capacity, even at high-rate discharges. Since its introduction in 1959, there has been a steady increase in performance of the alkaline cell as new materials and cell components were incorporated into the structure. The present alkaline cell designs are based on the use of nanostructured electrolytic manganese dioxide, a thinner polymer gasket seal with sealant to increase internal volume and improve shelf Ufe. Mercury has been eliminated by using new zinc alloy compositions. These improvements have resulted in about a 40 % improvement in performance over the same-size cells produced in 1959. 

The most significant nonferrous use of manganese compounds is for primary batteries, where manganese dioxide is the principal constituent of the cathode mix. In the standard Leclanchn ceU, 2inc and ammonium chloride are mixed to form the electrolyte, a mixture of carbon and MnO forms the cathode, and 2inc acts as the anode (221). The principal ceU reaction is as foUows ... 

In the case of the alkaline manganese dioxide cell, only high quaUty synthetic manganese dioxide, typically an EMD (224), is used and graphite is the cathode. The anode is an amalgamated 2inc. Potassium hydroxide serves as the electrolyte and the reaction can be summari2ed as follows ... 

The initial voltage of an alkaline-manganese dioxide battery is about 1,5 V. Alkaline-manganese batteries use a concentrated alkaline aqueous solution (typically in the range of 30-45 % potassium hydroxide) for electrolyte. In this concentrated electrolyte, the zinc electrode reaction proceeds, but if the concentration of the alkaline solution is low, then the zinc tends to passivate. 

The design of a AA-size alkaline manganese dioxide cell is shown in Fig. 1 (Sec. 3.1). Primary and secondary alkaline batteries are constructed in the same way and can be manufactured on essentially the same machinery. The separator material, electrode formulation, and the Mn02 Zn balance are different. Rechargeable cells are zinc-limited to prevent a discharge beyond the first electron-equivalent of the MnOz reduction. The electrolyte is 7-9 mol L KOH. The electrode reactions are ... 

Oxygen can be produced by electrolysis of water using a salt as an electrolyte that produces hydrogen at the opposite electrode. When potassium chlorate (KClOj) is heated in a test tube with a small amount of manganese dioxide (MnO ) as a catalyst, the chemical reaction that releases the oxygen from potassium chlorate will be accelerated. Use of potassium nitrate (KNOj) will also produce small amounts of oxygen. 

The nitrosodisulfonate salts, particularly the dipotassium salt called Fremy s salt, are useful reagents for the selective oxidation of phenols and aromatic amines to quinones (the Teuber reaction). - Dipotassium nitrosodisulfonate has been prepared by the oxidation of a hydroxylaminedisulfonate salt with potassium permanganate, " with lead dioxide, or by electrolysis. This salt is also available commercially. The present procedure illustrates the electrolytic oxidation to form an alkaline aqueous solution of the relatively soluble disodium nitrosodisulfonate. This procedure avoids a preliminary filtration which is required to remove manganese dioxide formed when potassium permanganate is used as the oxidant. " ... 

The Leclanche cell, the inexpensive disposable flashlight-type cell, has been on the market for over 100 years, yet its chemistry is not completely understood. The cell consists of an outer zinc shell that acts as the anode (seen by the external circuit as the source of electrons and hence the negative terminal) and oxidizes away during operation of the cell, a carbon rod or disk that serves as the cathodic current collector (positive terminal), and a moist paste of manganese dioxide, ammonium chloride, and zinc chloride that fills the cell and acts as both the electrolyte and the source of the cathodic reaction (reduction of MnIV). Usually, graphite in the form of carbon black is added to the paste to increase the electrical conductivity. The basic reactions are... 

Calculations of the emf of cells based on these reactions provide values within the wide range of 1.5-1.7 V, characteristic of undischarged cells formed with different samples of manganese dioxide and electrolyte pH. However, during the discharge of practical cells, inhomogeneities in the solution and cathode phases may produce a much more complicated reaction sequence, as will be discussed below. 

The alkaline dry cell is a modified version of the Leclanche cell in which the acidic NH4C1 electrolyte of the Leclanche cell is replaced by a basic electrolyte, either NaOH or KOH. As in the Leclanche cell, the electrode reactions involve oxidation of zinc and reduction of manganese dioxide, but the oxidation product is zinc oxide, as is appropriate to the basic conditions ... 

Leclanche cells are the least expensive primary batteries. The first zinc-manganese dioxide cell was developed by Georges Leclanche in 1866. He developed the primary battery with an ammonium chloride and zinc chloride electrolyte, and with a natural Mn02 and carbon (usually acetylene black) cathode inserted into a zinc can. His name is still associated with this chemistry today. The battery reactions are given in Equation 10.1. 

Zinc-Manganese Dioxide. In 1866 Leclanche invented a galvanic cell in which the reduction of Mn02 is the cathodic reaction in the cell s discharge. The corresponding anodic dissolution reaction is the oxidation of zinc. The Leclanche cell is a (so-called) dry cell, i.e., the ammonium electrolyte is immobilized in the form of a paste. There are three forms of the zinc-manganese dioxide batteries ... 

Leclanche cell — Primary cell (-> Leclanche 1866) containing a manganese dioxide cathode in an aqueous electrolyte solution of NF14C1 (20 wt %) in a zinc beaker used as anode (negative electrode, negative mass). Gelatin is added to enhance the viscosity of the electrolyte solution. Electrode reactions are... 

The actual cell voltage is about 1.5 V, it does not depend on the actual pH-value of the electrolyte solution as obvious from the absence of protons and hydroxide ions in the cell reaction equation. It slightly depends on the source of the used manganese dioxide. Initially naturally occurring manganese dioxide was used. The battery required a quality of less than 0.5% copper, nickel, cobalt, and arsenic to avoid undue corrosion of the zinc electrode. Currently synthetic manganese dioxide is prepared either by chemical (CMD) or electrochemical (EMD) procedures. For improved electrical conductivity graphite or acetylene black are added. Upon deep... 

Leclanche s cells have been around for more than 100 years. They are also known as zinc/carbon cells or dry cells. They use a chemically produced manganese dioxide cathode (positive electrode), a zinc (foil or sheet) anode (negative electrode), and an aqueous electrolyte. Typical electrolyte mixtures include ammonium chloride and zinc chloride dissolved in water. The electrodes are separated by a cereal paste wet with electrolyte or a starch or polymer-coated absorbent kraft paper. The reactions... 

Alkaline manganese dioxide batteries have been around since 1959. They are usually known as alkaline batteries. They are a variation of Leclanche s cells. They use an electrolyte produced manganese dioxide as cathode (to improve its purity and increase the capacity of the cell), powdered zinc as anode (to provide a larger surface area for the reaction), and a highly... 

The most common dry cell, that is, a cell without a fluid component, is the Leclanche cell used in flashlights and transistor radios. The anode of the cell consists of a zinc can or container that is in contact with manganese dioxide (Mn02) and an electrolyte. The electrolyte consists of ammonium chloride and zinc chloride in water, to which starch is added to thicken the solution to a pastelike consistency so that it is less likely to leak (Figure 19.7). A carbon rod serves as the cathode, which is immersed in the electrolyte in the center of the cell. The cell reactions are... 

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