Cathodic anodic reactions, battery

Figure 10. Model battery anodic-cathodic reactions...

Battery type Anode Cathode Reaction mechanism V g/Ah Ah/kg Specific energy Wh/kg Nominal voltage V Specific energy Wh/kg Energy density Wh/L... 

In a battery, the anode and cathode reactions occur ia different compartments, kept apart by a separator that allows only ionic, not electronic conduction. The only way for the cell reactions to occur is to mn the electrons through an external circuit so that electrons travel from the anode to the cathode. But ia the corrosion reaction the anode and cathode reactions, equations 8 and 12 respectively, occur at different locations within the anode. Because the anode is a single, electrically conductive mass, the electrons produced ia the anode reaction travel easily to the site of the cathode reaction and the 2iac acts like a battery where the positive and negative terminals are shorted together. 

Zinc—Silver Oxide Batteries. Miniature 2inc—silver oxide batteries have a 2inc anode, and a cathode containing silver oxide [20667-12-3] Ag20. The cathode reaction... 

The electrons sustain the current via external load and are used to reduce the active material of the cathode (positive). In the case of storage batteries, the ideal anodic and cathodic reactions are completely reversible. 

Aluminum is directly applied in its metallic form when it serves as battery anode. The battery concepts considered are in general single-use types (primary batteries). The most developed systems belong to the metal-air batteries, using the reduction of atmospheric oxygen as the cathode reaction, e.g., (-) A1 / KOH / 02 (+) or (-) A1 / seawater / 02 (+). The main discharge reactions are ... 

The organization of the Handbook of Battery Materials is simple, dividing between aqueous electrolyte batteries and alkali metal batteries and further in anodes, cathodes, electrolytes and separators. There are also three more general chapters about thermodynamics and mechanistics of electrode reactions, practical batteries and the global competition of primary and secondary batteries. 

The Zinc-air battery is more expensive than the dry cell and deteriorates relatively quickly once it is exposed to air. High capacity and a cell potential that does not vary with use offset these disadvantages. Like the dry cell, a zinc-air battery uses zinc for the anode reaction. Uniquely among batteries in common use, this battery relies on molecular oxygen from the atmosphere for its cathode reaction. 

Anodic chlorine evolution by electrolysis of concentrated chloride solutions is used for the large-scale industrial production of chlorine. The cathodic reaction, which is the ionization of molecular chlorine, is used in certain types of batteries. 

Cathodic reaction in this battery chemistry is described by equation (1). Anodic reaction may be written in a form of reaction (10) ... 

This equation has a standard electrode potential of -0.447 V. Thus, the solution containing mercuric and chloride ions in contact with iron forms a battery. The reduction of the complex ions to metallic mercury is the cathodic reaction. The dissolution of iron is the anodic reaction. The overall reaction in the battery is given by the addition of Equation (13.42) and Equation (13.43). Due to the high value of its reversible cell voltage under standard conditions (0.85 V), it is expected that a very low equilibrium concentration of the complex ion can be achieved. 

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 ... 

Some commonly used batteries are shown in Table 15.5, and two are drawn schematically in Fig. 15.10. From these it can be seen that important components are the container, the anode/cathode compartment separators, current collectors to transport current from the electrode material (usually a porous, particulate paste), the electrode material itself, and the electrolyte. It should be noted that the electrode reactions can be significantly more complex than those indicated in Table 15.5, and there will probably be parallel reactions. By stacking the batteries in series, any multiple of the cell potential can be obtained. 

Battery technology Electrolyte Mobile species in electrolyte Anode reaction during discharge Cathode reaction during discharge Standard cell potential / V Gravimetric energy density/ Wh kg-1 Notes... 

Mn02 has a number of uses in chemical processes as an oxidizing agent, and it is also used in dry cell and alkaline batteries. In both cases the anode is made of zinc. The anode reaction (oxidation) and cathode reaction (reduction) are as follows for an alkaline cell ... 

The mercury battery shown in Figure 21-8c is smaller yet and is used to power devices such as hearing aids and calculators. The mercury battery uses the same anode half-reaction as the alkaline battery, with this cathode halfreaction. 

A third primary dry cell is the zinc-mercuric oxide cell depicted in Figure 17.7. It is commonly given the shape of a small button and is used in automatic cameras, hearing aids, digital calculators, and quartz-electric watches. This battery has an anode that is a mixture of mercury and zinc and a steel cathode in contact with solid mercury(II) oxide (HgO). The electrolyte is a 45% KOH solution that saturates an absorbent material. The anode half-reaction is the same as that in an alkaline dry cell,... 

An electron is removed from the Ni (OH)2 at the anode, and the reverse reaction occurs to yield NiOOH and H+, which goes to the cathode to react to produce the metal hydride. The merits of this type of battery are that the cathode reaction is simple, and the metalhydride can store large amount of hydrogen. It is possible to replace the liquid electrolyte by the solid polymer electrolyte. 

Combining both anode and cathode reactions, the overall cell reaction of the alkaline Zn/Mn02 battery can be described as follows ... 

Unlike the cathode reaction, the anode reaction is not a homogenous single-phase reaction, but rather a two-phase [Cd and Cd(OH)2] charge transfer reaction. Therefore, the anode potential is independent of its SOC. The anode reaction mechanism plays a significant role in impacting the reduction in battery capacity... 

Electrolysis, the splitting of compounds by electricity, occurs when two electrodes, an anode and a cathode, are inserted into a liquid electrolyte such as molten sodium chloride and connected to a source of electrical energy such as a battery. When electrical current flows into the electrolytic cell, chemical reactions occur. Anions and cations conduct the current by moving freely through the liquid. In the external circuit, electrons move out of the anode, through the battery, and into the cathode. 

Because the three-dimensional battery has not yet been made, the question remains whether there is enough electrode area to have a nucleation event such that the anodic or cathodic reaction can occur. 

Battery performance is related to the available voltage and current while the battery is discharging. The terminal voltage of a battery depends on the thermodynamic free-energy change of the anode and cathode reactions, according to Equation (26.19) and by the various activation (kinetic), concentration, and resistance overpotentials that lower the battery s voltage (as discussed in Section 26.3.4) ... 

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