Manganese electrode reactions

The direct electrochemical oxidation of manganese alloys was developed and commercialized at the Rustavi Chemical Combine in the Georgian Repubhc (formerly the USSR). The electrode reactions are... 

Consider a salt bridge cell in which the anode is a manganese rod immersed in an aqueous solution of manganese(II) sulfate. The cathode is a chromium strip immersed in an aqueous solution of chromium(in) sulfate. Sketch a diagram of die cell, indicating the flow of the current throughout. Write the half-equations for the electrode reactions, the overall equation, and die abbreviated notation for the celL... 

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 ... 

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 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... 

Titanium covered by platinum or by dioxide of manganese, ruthenium, iridium or other substances is most commonly used as an anode. Graphite and graphite covered with lead dioxide have also been used as anodes. Under some conditions, high pH and absence of salts in the anolyte, nickel can be used as the anode. Stainless steel is commonly used as the cathode. If current reversal is employed, the same material, platinized titanium or graphite, is used for both electrodes. Electrode chambers should be flushed with a large flow of rinse solution in order to remove the electrode reaction products. 

A number of batteries are based on modifications of the technology or the substitution of electrode reactions into either the Ni/Cd or Leclanchd cells the changes usually improve one characteristic of importance to a particular duty but usually only at an increased cost. In an alkaline manganese battery, the cathode is manganese dioxide and graphite in the form of compressed tablets, and the electrolyte is strongly alkaline. The cell reaction is... 

The zinc and manganese dioxide electrode reaction kinetics in alkaline electrolyte are faster than the same reactions in the Leclanche and zinc chloride electrolyte. These differences in reaction rate determine the differences in cell performance. The alkaline cell delivers superior capacity, higher-rate discharge capability, lower internal resistance, lower leakage, and longer shelf life. Alkaline cells have excellent high-rate... 

Figure 9 depicts the effect of temperature on lithium-manganese dioxide compared with zinc-silver and zinc-air cell miniature cell performance. At low temperatures the electrode reactions slow down and severely limit the ability of the cell to deliver current. Cells also lose capacity slowly when stored at room temperature, due to internal self-discharge reactions which are accelerated at higher temperatures. 

We commonly use voltaic cells as convenient, portable sources of energy. Flashlights and radios are examples of devices that are often powered by the zinc-carbon, or Leclanche, dry cell (Figure 20.9). This voltaic cell has a zinc can as the anode a graphite rod in the center, surrounded by a paste of manganese dioxide, ammonium and zinc chlorides, and carbon black, is the cathode. The electrode reactions are complicated but are approximately these ... 

Because the manganese half-reaction has a more negative electrode potential, it repels electrons and proceeds in the reverse direction (oxidation). Because the nickel halfreaction has the more positive (or least negative) electrode potential, it attracts electrons and proceeds in the forward direction. 

Alkaline-manganese cells have a lower internal resistance and give a better performance than the ordinary dry cell but are more expensive. The electrolyte is a potassium hydroxide solution. The primary electrode reactions are as before, but the zinc ions react with the hydroxide ions, resulting in precipitation of zinc hydroxide and oxide, so that the over-all cell reaction is... 

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