Batteries electrical potential

A battery must use cell reactions that generate and maintain a large electrical potential difference. This requires two half-reactions with substantially different standard reduction potentials. The ideal battery would be compact, inexpensive, rechargeable, and environmentally safe. This is a stringent set of requirements. No battery meets all of them, and only a few come close. 

C19-0137. From the standard reduction potentials appearing in Table 19-1 and Appendix F, identify reaction pairs that are candidates for batteries that would produce more than 5 V of electrical potential under standard conditions. Suggest chemical reasons why no such battery has been commercially developed. 

An electric cattle prod looks a little like a walking stick with an attached battery. A potential from the tip of the stick is applied to a cow s flank, and the induced current hurts the animal. The cow moves where prompted to avoid a reapplication of the pain, thereby simplifying the job of cowherding. 

Galvanic cells in which stored chemicals can be reacted on demand to produce an electric current are termed primary cells. The discharging reaction is irreversible and the contents, once exhausted, must be replaced or the cell discarded. Examples are the dry cells that activate small appliances. In some galvanic cells (called secondary cells), however, the reaction is reversible that is, application of an electrical potential across the electrodes in the opposite direction will restore the reactants to their high-enthalpy state. Examples are rechargeable batteries for household appliances, automobiles, and many industrial applications. Electrolytic cells are the reactors upon which the electrochemical process, electroplating, and electrowinning industries are based. 

While the amount of electricity that can be conducted by polymer films and wires is limited, on a weight basis the conductivity is comparable with that of copper. These polymeric conductors are lighter, some are more flexible, and they can be laid down in wires that approach being one-atom thick. They are being used as cathodes and solid electrolytes in batteries, and potential uses include in fuel cells, smart windows, nonlinear optical materials, LEDs, conductive coatings, sensors, electronic displays, and in electromagnetic shielding. 

Meanwhile, scientists studied the electrical activity of neurons. They discovered that the messages neurons pass to one another consist of brief electrical impulses known as action potentials. Neurons (and most other cells) have a small electrical potential of about 60 millivolts between their interior and exterior—this voltage, which is only about 4 percent as strong as a typical flashlight battery, exists across the cell s membrane. 

Electrodes in a voltaic cell, however, are connected to circuits— paths by which electrons flow. Voltaic cells are sources of electricity, so they can be used to drive electrolytic reactions or perform other activities that require electricity. The term voltaic honors the Italian scientist Alessandro Volta (1745-1827), a pioneer of electrochemistry. A simple voltaic cell can form a battery, invented by Volta in 1800. The unit of electric potential, the volt, also honors Volta. 

This may be why cells use electric signals because these are in principle highly efficient. Electrochemical machines (i.e., storage batteries) are just the type that enable large concentration gradients to be balanced by electrical potential jumps so as to preserve the continuity of the electrochemical potential, which is the requirement for reversibility. The concentration gradients of K+ and Na across cell membranes that... 

We now see that mitochondria contain a variety of molecules—cytochromes, flavins, ubiquinone, and iron-sulfur proteins—all of which can act as electron carriers. To discuss how these carriers cooperate to transport electrons from reduced substrates to 02, it is useful to have a measure of each molecule s tendency to release or accept electrons. The standard redox potential, E°, provides such a measure. Redox potentials are thermodynamic properties that depend on the differences in free energy between the oxidized and reduced forms of a molecule. Like the electric potentials that govern electron flow from one pole of a battery to another, E° values are specified in volts. Because electron-transfer reactions frequently involve protons also, an additional symbol is used to indicate that an E° value applies to a particular pH thus, E° refers to an E° at pH 7. 

A battery (or galvanic or voltaic cell) is a device that uses oxidation and reduction reactions to produce an electric current. In an electrolytic cell, an external source of electric current is used to drive a chemical reaction. This process is called electrolysis. When the electric potential applied to an electrochemical cell is just sufficient to balance the potential produced by reactions in the cell, we have an electrochemical cell at equilibrium. This state also occurs if there is no connections between the terminals of the cell (open-circuit condition). Our discussion in this chapter will be limited to electrochemical cells at equilibrium. 

Alessandro Volta built the first battery in 1800 permitting future research and applications to have a source of continuous electrical current available. The SI unit of electric potential difference is named after him. 

Massive electrochemical attack known as galvanic corrosion [58,59] is the most severe form of copper corrosion. It can completely remove the copper from the structures (Figs. 17.25 and 17.26). It can occur when the wafers are exposed to a corrosive electrolyte for an extended period. It can also occur if the slurry does not contain enough or effective corrosion inhibitor. The source of such a galvanic potential on the patterned copper surface may be due to the fact that some copper structures connected to transistors have a different electrical potential than the rest of the wafer surface. Another possible cause of this type of galvanic potential is related to the barrier material induced metal metal battery effect. Most copper CMP slurries have been developed for Cu structures with Ta or TaN as a barrier material. In some cases, other metals may also be used in addition to the barrier metal. For example, a metal hard mask could contribute to the galvanic corrosion effects. It is also possible that some types of copper are more susceptible to corrosion that others. The grain... 

Now suppose an external electrical potential is applied by connecting the negative terminal of a battery to the p-type region and the positive terminal to the n-type region. The situation represented in Fig. 16.34(b) results. Electrons are drawn toward the positive terminal, and the resulting holes move toward the negative terminal—exactly opposite to the natural flow of electrons at the p-n junction. The junction resists the imposed current flow in this direction and is said to be under reverse bias. No current flows through the system. 

The Electrolysis of Molten Sodium Chloride. Molten sodium chloride (the salt melts at 801° C) conducts an electric current, as do other molten salts. During the process of conducting the current a chemical reaction occurs—the salt is decomposed. If two electrodes (carbon rods) are dipped into a crucible containing molten sodium chloride and an electric potential (from a battery or generator) is applied, metallic sodium is produced at the negative electrode—the cathode—and chlorine gas at the positive electrode—the anode. Such electrical decomposition of a substance is called electrolysis. 

When the current does not flow through battery the measurable diflerence in electric potential between the terminals of the two electrodes is the result of all the equilibrium potential differences at the interphase between the conducting phases in contact. In the example of the Daniell cell, with both electrodes having copper terminals, there are three interfacial potential differences (apart from the small liquid junction potential difference at the contact between the two electrolyte phases) one potential difference at the contact between the zinc rod and the copper terminal (Zn/Cu) and two potential differences at the metal-solution interphases (Zn/Zn + and Cu/Cu +), which are mainly due to the charge transfer processes. 

Since it is impossible to measure the individual electric potential differences at the phase boundaries, we shall hereinafter speak only in terms of the difference in electric potential across the two terminals connected to the electrodes of the battery. When in a battery the current is not flowing or tends to zero, the measurable potential difference across the two terminals is called the open-circuit voltage (OCV), fJc, and it represents the battery s equilibrium potential (or voltage). Since it is related to the free energy of the cell reaction, the OCV is a measure of the tendency of the cell reaction to take place. Indeed, while the conversion of chemical into electric energy is regulated by thermodynamics, the behavior of a battery under current flow (the current is a measure of the electrochemical reaction rate) comes under electrochemical kinetics. 

Years ago, college chemistry textbooks used to contain tables listing in order of electrical potential the metallic elements and carbon. For some odd reason, the tables used in schools and colleges today omit carbon. This is even more strange because the most common of the dry cell batteries until only a few years ago, made use of the electrical potential between zinc and carbon-a relationship illustrated by the table. Reproduced below are two such tables, one of which includes carbon. 

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