Electrically active complex current density

In order to obtain a definite breakthrough of current across an electrode, a potential in excess of its equilibrium potential must be applied any such excess potential is called an overpotential. If it concerns an ideal polarizable electrode, i.e., an electrode whose surface acts as an ideal catalyst in the electrolytic process, then the overpotential can be considered merely as a diffusion overpotential (nD) and yields (cf., Section 3.1) a real diffusion current. Often, however, the electrode surface is not ideal, which means that the purely chemical reaction concerned has a free enthalpy barrier especially at low current density, where the ion diffusion control of the electrolytic conversion becomes less pronounced, the thermal activation energy (AG°) plays an appreciable role, so that, once the activated complex is reached at the maximum of the enthalpy barrier, only a fraction a (the transfer coefficient) of the electrical energy difference nF(E ml - E ) = nFtjt is used for conversion. 

In order to identify EPHs of the cell or electrode reactions from the experimental information, there had been two principal approaches of treatments. One was based on the heat balance under the steady state or quasi-stationary conditions [6,11, 31]. This treatment considered all heat effects including the characteristic Peltier heat and the heat dissipation due to polarization or irreversibility of electrode processes such as the so-call heats of transfer of ions and electron, the Joule heat, the heat conductivity and the convection. Another was to apply the irreversible thermodynamics and the Onsager s reciprocal relations [8, 32, 33], on which the heat flux due to temperature gradient, the component fluxes due to concentration gradient and the electric current density due to potential gradient and some active components transfer are simply assumed to be directly proportional to these driving forces. Of course, there also were other methods, for instance, the numerical simulation with a finite element program for the complex heat and mass flow at the heated electrode was also used [34]. 

Substantial part of my scientific activity was devoted to physicochemical properties of aqueous solutions of citric add and various inoiganic citrates. They included formation of metal-mixed complexes, determinations of solubiUties, vapour pressures of water above citric acid and citrates solutions, densities, melting points, sound velocities and electrical conductances. Unquestionably, the industrial and biological importance of citric acid was the main motivation that more than 25 sdentific papers I pubhshed together with my coworkers on systems with citrate ions. Our results up to 1994,1 summarized in the review entitled Thermodynamic and Transport Properties of Aqueous Solutions of Hydroxycaiboxylic Acids. The current book came as a desire to enlarge the information about citric acid properties presented there, to incorporate some subjects which were entirely omitted (chemistry of citric acid and properties of inorganic citrate solutiorrs) and finally to include our and others new relevant results. 

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