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Exchange current.

For a more general reaction of the fonn Ox + ne Red, with differing concentrations of Ox and Red, the exchange current density is given by... [Pg.608]

Some values for and (3 for electrochemical reactions of importance are given in table A2.4.6, and it can be seen that the exchange currents can be extremely dependent on the electrode material, particularly for more complex processes such as hydrogen oxidation. Many modem electrochemical studies are concerned with understanding the origin of tiiese differences in electrode perfomiance. [Pg.608]

The exchange current is directiy related to the reaction rate constant, to the activities of reactants and products, and to the potential drop across the double layer. The larger the more reversible the reaction and, hence, the lower the polarization for a given net current flow. Electrode reactions having high exchange currents are favored for use in battery apphcations. [Pg.511]

Fig. 3. Hypothetical Evans diagram and polarization curve for a metal corroding in an acidic solution, where point A represents the current density, /q, for the hydrogen electrode at equiUbrium point B, the exchange current density at the reversible or equiUbrium potential, for M + 2e and point... Fig. 3. Hypothetical Evans diagram and polarization curve for a metal corroding in an acidic solution, where point A represents the current density, /q, for the hydrogen electrode at equiUbrium point B, the exchange current density at the reversible or equiUbrium potential, for M + 2e and point...
The sohd line in Figure 3 represents the potential vs the measured (or the appHed) current density. Measured or appHed current is the current actually measured in an external circuit ie, the amount of external current that must be appHed to the electrode in order to move the potential to each desired point. The corrosion potential and corrosion current density can also be deterrnined from the potential vs measured current behavior, which is referred to as polarization curve rather than an Evans diagram, by extrapolation of either or both the anodic or cathodic portion of the curve. This latter procedure does not require specific knowledge of the equiHbrium potentials, exchange current densities, and Tafel slope values of the specific reactions involved. Thus Evans diagrams, constmcted from information contained in the Hterature, and polarization curves, generated by experimentation, can be used to predict and analyze uniform and other forms of corrosion. Further treatment of these subjects can be found elsewhere (1—3,6,18). [Pg.277]

The exchange current density, depends on temperature, the composition of the electrolyte adjacent to the electrode, and the electrode material. The exchange current density is a measure of the kinetic resistance. High values of correspond to fast or reversible kinetics. The three parameters, a, a. ... [Pg.64]

In this equation /g, is th equilibrium exchange current, and the arrow convention adopted is that / g represents the rate of cathodic reduction... [Pg.77]

If the areas of the electrodes are assumed to be 1 cm, and taking the equilibrium exchange current density /g for the Ag /Ag equilibrium to be 10 A cm", then /g will be 10 A, which is a very high rate of charge transfer. A similar situation will prevail at electrode II, and rates of exchange of silver ions and the potential will be the same as for electrode I. [Pg.77]

It is evident from these expressions that since in the Tafel region / (the current density actually determined) must be greater than /(, (the equilibrium exchange current density), the signs of the overpotentials will conform to equations 1.60 and 1.61, i.e. will be negative and will be positive. [Pg.89]

Fig, 1.24 Tafel lines for a single exchange process. The following should be noted (a) linear f-log I curves are obtained only at overpotentials greater than 0-052 V (at less than 0-052 V E vs. i is linear) b) the extrapolated anodic and cathodic -log / curves intersect at tg the equilibrium exchange current density and (c) /, and the anodic and cathodic current densities... [Pg.89]

The standard electrode trotential, Ep, 2+ Pb = —Q.126V . shows that lead is thermodynamically unstable in acid solutions but stable in neutral. solutions. The exchange current for the hydrogen evolution reaction on lead is very small (-10 - 10"" Acm ), but control of corrosion is usually due to mechanical passivation of the local anodes of the corrosion cells as the majority of lead salts are insoluble and frequently form protective films or coatings. [Pg.724]

Turning now to the acidic situation, a report on the electrochemical behaviour of platinum exposed to 0-1m sodium bicarbonate containing oxygen up to 3970 kPa and at temperatures of 162 and 238°C is available. Anodic and cathodic polarisation curves and Tafel slopes are presented whilst limiting current densities, exchange current densities and reversible electrode potentials are tabulated. In weak acid and neutral solutions containing chloride ions, the passivity of platinum is always associated with the presence of adsorbed oxygen or oxide layer on the surface In concentrated hydrochloric acid solutions, the possible retardation of dissolution is more likely because of an adsorbed layer of atomic chlorine ... [Pg.945]

The most significant parameter in the relationships given above is the equilibrium exchange current density io, which can be evaluated by extra-p>olating the linear t/ vs. log / curve to tj = 0, at which log / = log io. Alternatively, /q may be evaluated from the linear Ep vs. log / curve by extrapolating the curve to the equilibrium potential. ... [Pg.1198]


See other pages where Exchange current. is mentioned: [Pg.214]    [Pg.606]    [Pg.607]    [Pg.607]    [Pg.1923]    [Pg.1923]    [Pg.2718]    [Pg.484]    [Pg.511]    [Pg.514]    [Pg.515]    [Pg.277]    [Pg.67]    [Pg.42]    [Pg.588]    [Pg.523]    [Pg.39]    [Pg.88]    [Pg.90]    [Pg.97]    [Pg.98]    [Pg.100]    [Pg.100]    [Pg.102]    [Pg.109]    [Pg.138]    [Pg.140]    [Pg.228]    [Pg.237]    [Pg.309]    [Pg.322]    [Pg.766]    [Pg.803]    [Pg.1251]    [Pg.346]    [Pg.482]    [Pg.1015]    [Pg.1196]   
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Anode exchange current density

Apparent exchange current density

Batteries exchange current

Butler-Volmer equation exchange current density

Catalyst layer exchange current density

Catalyst layer operation exchange current density

Cathode exchange current density

Co-current Operation of Combined Meso-scale Heat Exchangers and Reactors for Methanol Steam Reforming

Co-current-flow heat exchanger

Continuous counter-current ion-exchang

Counter current heal exchanger

Counter-current exchanger

Counter-current heat-exchanger

Counter-current ion-exchange

Counter-current-flow heat exchange

Current density exchange

Current density exchange-correlation hole

Determination of the Exchange Current Density from Polarization Resistance

Dynamics of a Counter-current Heat Exchanger

Electrocatalysis exchange current density

Electrocatalyst exchange current density

Electrodes exchange current

Equilibrium electrode potential exchange current density

Equilibrium exchange current

Exchange Current Density, io

Exchange current composition dependence

Exchange current densities hydrogen evolution reaction

Exchange current densities, hydrogen

Exchange current density concentration dependence

Exchange current density corrosion

Exchange current density definition

Exchange current density determination

Exchange current density governing kinetics

Exchange current density hydrogen evolution

Exchange current density impedance

Exchange current density local

Exchange current density metal dissolution

Exchange current density of adatoms

Exchange current density of kink atoms

Exchange current density overall

Exchange current density reduction

Exchange current density stainless steel

Exchange current density steady state

Exchange current density table

Exchange current density, Arrhenius

Exchange current, Butler-Volmer model

Exchange currents, and Tafel slopes

Exchange reaction current

Exchange reaction current at the equilibrium potential

Experimental Data on the Exchange Current Density and Symmetry Coefficient

Hydrogen oxidation reaction exchange current density

Hydrogen oxidation, exchange current density

Hydrogen reaction exchange current density

I0, exchange current

Intrinsic exchange current density

Kinetic treatment based on exchange current

Metal exchange current density

Open circuit voltage exchange current density

Oxygen reduction reaction exchange current density

Polarization resistance exchange current density

Proton exchange membrane fuel cell current generation

Standard exchange current density

Superficial exchange current density

Tafel Slope and Exchange Current Density

Tafel lines exchange current density

The Exchange Current Density

Volumetric exchange current density

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