Batteries standard potential

Fig. 2. Standard potentials of battery (a) negative electrode and (b) positive electrode reactions (13). Potentials are given in volts.

The mercurous sulfate [7783-36-OJ, Hg2S04, mercury reference electrode, (Pt)H2 H2S04(y ) Hg2S04(Hg), is used to accurately measure the half-ceU potentials of the lead—acid battery. The standard potential of the mercury reference electrode is 0.6125 V (14). The potentials of the lead dioxide, lead sulfate, and mercurous sulfate, mercury electrodes versus a hydrogen electrode have been measured (24,25). These data may be used to calculate accurate half-ceU potentials for the lead dioxide, lead sulfate positive electrode from temperatures of 0 to 55°C and acid concentrations of from 0.1 to Sm. 

Two types of redox systems (Fig. 7) are used for batteries [14]. The standard potential (E°) of MnO 2 should be a good representation of the total energy of the oxide. For two-phase systems such as Pb02, Ag20, HgO, etc., the initial potential (E ) and middle potential (Em ) are equal to E°, from which we can calculate AF (-nFE°). For MnOz, a one-phase system, as shown in Fig. 7(A), the E (initial potential) cannot be used as E°. Ko-zawa proposed the middle potential (Em) of the S-shaped curve to be used as the E°... 

Several significant electrode potentials of interest in aqueous batteries are listed in Table 2 these include the oxidation of carbon, and oxygen evolution/reduction reactions in acid and alkaline electrolytes. For example, for the oxidation of carbon in alkaline electrolyte, E° at 25 °C is -0.780 V vs. SHE or -0.682 V (vs. Hg/HgO reference electrode) in 0.1 molL IC0 2 at pH [14]. Based on the standard potentials for carbon in aqueous electrolytes, it is thermodynamically stable in water and other aqueous solutions at a pH less than about 13, provided no oxidizing agents are present. 

Table 2. Standard potentials for reactions of carbon materials in batteries containing aqueous electrolytes...

Lithium metal had few uses until after World War II, when thermonuclear weapons were developed (see Section 17.11). This application has had an effect on the molar mass of lithium. Because only lithium-6 could be used in these weapons, the proportion of lithium-7 and, as a result, the molar mass of commercially available lithium has increased. A growing application of lithium is in the rechargeable lithium-ion battery. Because lithium has the most negative standard potential of all the elements, it can produce a high potential when used in a galvanic cell. Furthermore, because lithium has such a low density, lithium-ion batteries are light. 

Lithium (Li) is a silver-colored soft metal, and the lightest of aU the metallic elements. li is oxidized by atmospheric nitrogen to form lijN. Though li melts at 453.7 K, its boiling point temperature is very much higher at 1620 K. A deep-violet flame is formed when Li is burned in air. Its standard potential is about 3.5 V and a relatively high electric current is formed when it is used in batteries. 

Although the nickel-containing systems have been extensively studied also by electrochemical methods [1] due to their practical importance, for example, in electrochemical power sources (Ni—Fe, Ni—Cd, Fi—NiF2 batteries), in corrosion-resistant alloys (tableware, coins, industrial instruments) as well as due to their interesting (magnetic, spectral, catalytic) properties most of the standard potentials of electrode... 

The emf of a cell or battery depends on the concentration of electrolyte. Calculate the emf of a charged and discharged lead-acid cell that has 29% by weight of sulfuric acid when it is fully charged. On discharge of this cell, the concentration of acid reduces to 21 % by weight. Assume that the temperature is 25 °C and the standard potential (E°) for both concentration is 2.0359 V. (Bhardwaj)... 

Iodine — Iodine, L, is a halogen which occurs naturally mainly as iodide, I- [i]. Iodine (Greek ioeides for colored violet ) is a black solid with a melting point of 113.6 °C which is readily undergoing sublimation to form a violet gas. Iodine occurs in the oxidation states -1,0, +1, +3, +5, +7 and it possesses a rich redox chemistry [ii]. In aqueous solution the formation of I2 from I- occurs with a standard potential of 0.621V vs. SHE and this oxidation process is preceded by the formation of I3 with a standard potential of 0.536 V vs. SHE. For the reaction I2(cryst) + 2e - 21 E = 0.535 V. The I—/I3 redox couple is employed, for example, in solar cells [iii] and in long-lived lithium-iodine battery systems. The oxidation of I2 in organic solvents results formally in I+ intermediates which is a powerful oxidant and useful, for example, in electro-synthetic chemical processes [ii]. 

The theoretical voltage of the battery represents the maximum potential that can be obtained from the battery. It is measured experimentally. The theoretical voltage is the same standard potential of the battery that was defined in Sect. 7.5.1. As explained before, it can also be calculated from the standard potentials of each of the electrodes with respect to a reference electrode. For the Mercad cell, the standard potential of each of the electrodes with respect to a SHE in aqueous solution at 25 °C is = 0.81 V and t HgO = 0.10 V, for Eqs (40) and (41), respectively [1], Adding both potentials gives the standard open-circuit potential of the cell, Ue = 0.91 V. 

This is one of the most negative standard potentials of any of the elements, which is why lithium is excellent for use in batteries. The lithium ion rechargeable battery used in cell phones and other mobile devices has a lithium cobalt(III) oxide cathode, with graphite as the anode, and an organic solvent as the electrolyte. It works by ... 

Table 5.2 Standard potentials of various battery electrode reactions (25°C)...

Other systems, for example, the standard potential of Mg (—2.37 V) is more negative than that of zinc (—0.76 V) and the electrochemical equivalent of magnesium (0.45 gA h ) is less than that of zinc (1.22 gA h ). The electrochemical reactions of the Mg-air battery can be expressed by the following equations ... 

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