Self-driving cells

Fig. 7.181. In a self-driving cell, the negative electrode is the anode, or an electron sink for deelectronation, and the positive electrode is the cathode, or an electron source for the electronation reaction.

Fig. 7.182. When a self-driving cell delivers current to an external load, the potential of the electron sink shifts in the positive direction, while that of the electron source shifts negatively. The net result is a decrease in the cell potential compared with that at an open circuit.

Thus, to drive a current through the external circuit, the potential of the electron sink has to become more positive and thal of the electron source more negative (Fig. 7.182). But under zero-current, or equilibrium, conditions, the electrode that tends to be a sink is negative with respect to the electrode that tends to be a source. This means that in the course of driving a current, the potentials of the two electrodes climb toward each other the cell potential decreases with cell current in a self-driving cell. 

Fig. 7.185. In a self-driving cell, the plot of cell overpotential vs. log cell current density should be a straight line if the charge transfers at both electrodes are both rate controlling and valid under the high-field approximation. An apparent /0 for the cell as a whole can be deduced.

The fundamental point is that in a self-driving cell (Fig. 7.185)—the case treated above—all the terms on the right-hand side of Eq. (7.323) make the cell potential V at a current / less than the equilibrium potential Ve. In a driven cell with (Fig. 7.184)... 

Consider two half-cell reactions, one for an anodic and the other for a cathodic reaction. The exchange current densities for the anodic and the cathodic reactions are lO-6 A/cm2 and 1(T2 A/cm2, respectively, with transfer coefficients of 0.4 and 1, respectively. The equilibrium potential difference between the two reactions is 1.5 V. (a) Calculate the cell potential when the current density of 1CT5 A/cm2 flows through the self-driving cell, neglecting the concentration overpotentials. The solution resistance is 1000 Q cm2, (b) What is the cell potential when the current density is 10-4 A/cm2 (Kim)... 

According to Bockris et al.,6 the cell voltage of a self-driving cell, Us, is given by... 

The power Ps, which can be obtained from self-driving cells, like batteries and fuel cells, is... 

Parameter Self-driving cell (galvanic cell) Dri ven cell (electrolytic cell)... 

In the cases of self-driving cells (e,g. batteries and fuel cells), ccll positive and the energy consumption is negative, i,e. the cell produces electrical energy. In the latter case, the energy consumption is sometimes referred to as the electrical energy yield. ... 

Before treating cells with currents flowing across them, an expression will be developed for the zero current or equilibrium potential difference across a cell." Since there is zero cell current, the cell is not connected to either an external current source or an external current sink (or (load) one says the cell is on open circuit. It is neither a driven cell nor a self-driving system. Each interface therefore must be at equilibrium because the net current is zero across both interfaces. 

At the outset, consider a self-driving, or energy-producing, cell with two interfaces 1 and 2, and let the equilibrium electrode potentials on the hydrogen scale be Ee j and Ee 2. Suppose Ee t is more positive than Ee Then, if an external load is provided, electrode 2 will taxi to be an electron sink for a net deelectronation reaction and electrode 1 will tend to be an electron source for a net electronation reaction. 

The existence of self-driving electrochemical mechanisms (i.e.. chemical systems that spontaneously produce electrical power) is a concept that has so far been completely neglected in general chemistry (although it has been applied in fuel cells). It may find significant application in biochemistry (Chapter 14). 

Although the notion of monomolecular surface layers is of fundamental importance to all phases of surface science, surfactant monolayers at the aqueous surface are so unique as virtually to constitute a special state of matter. For the many types of amphipathic molecules that meet the simple requirements for monolayer formation it is possible, using quite simple but elegant techniques over a century old, to obtain quantitative information on intermolecular forces and, furthermore, to manipulate them at will. The special driving force for self-assembly of surfactant molecules as monolayers, micelles, vesicles, or cell membranes (Fendler, 1982) when brought into contact with water is the hydrophobic effect. 

Processes which generate heat in organic materials are reviewed. At ordinary temperatures, respiration of living cells and particularly the metabolism of microorganisms may cause self-heating, while at elevated temperatures pyrolysis, abiotic oxidation, and adsorption of various gases by charred materials drive temperatures up whenever the released heat is unable to dissipate out of the material. The crucial rate of pyrolytic heat release depends on exothermicity and rates of the pyrolysis process. 

When it comes to the equilibration of water concentration gradients, the relevant transport coefficient is the chemical diffusion coefficient, Dwp. This parameter is related to the self-diffusion coefficient by the thermodynamic factor (see above) if the elementary transport mechanism is assumed to be the same. The hydration isotherm (see Figure 8) directly provides the driving force for chemical water diffusion. Under fuel-cell conditions, i.e., high degrees of hydration, the concentration of water in the membrane may change with only a small variation of the chemical potential of water. In the two-phase region (i.e., water contents of >14 water molecules... 

Do you accept the idea that self-organization in prebiotic time was the main driving force for the formation of the first living cells (If not, what would you add to the picture )... 

Miniature batteries based on aqueous, non-aqueous and solid electrolytes are manufactured as power sources for microelectronics and other miniaturized equipment. In Fig. 1.2, the sizes and shapes of some representative button cells are shown. A typical application for such cells is in the electric watch, where the oscillator circuit draws a continuous current of 0.2-0.6 pA and depending on the type of frequency divider and display, the complete unit may require a total of up to 0.5-2.0 pA for operation. Hence the total amount of electrical energy consumed in driving the watch for a year is in the range 15-60 mWh. At present, batteries are manufactured which last for 5-10 years. Watch batteries must have exceptionally low self-discharge rates and very reliable seals to prevent leakage. Further, they... 

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