Disk electrodes limiting current density

Figure 3a is an illustration of the effect of surface overpotential on the limiting-current plateau, in the case of copper deposition from an acidified solution at a rotating-disk electrode. The solid curves are calculated limiting currents for various values of the exchange current density, expressed as ratios to the limiting-current density. Here the surface overpotential is related to the current density by the Erdey Gruz-Volmer-Butler equation (V4) ... 

Fig. 9. Logarithmic plot of apparent limiting-current density as a function of current increase rate at a rotating-disk electrode i — apparent limiting current density i, = true steady-state limiting current density di/dt = current increase rate (A cm-2 sec-1) (u = rotation rate (rad sec-1). [From Selman and Tobias (S10).]...

Using the rotating disk electrode, Seliv-anov et al. [214] have investigated the zinc electrodeposition from zincate electrolyte containing polyethylene polyamine. The limiting current density of [Zn(OH)4] ion diffusion through a film of zinc oxides and hydroxides is shown to be responsible for the formation of dark zinc deposits in the potential range from —1.33 to —1.47 V. 

Influence of Rotating Disk Electrode Condition (Stationary or Rotating) on the Diffusion-Layer Thickness and the Limiting Current Density for the Reaction... 

Fig. 8.3. ATafel line. No special effort is made to reduce the limiting current density in case 1 and the Tafel line has a relatively small range, e.g., only 102 times in current density. In case 2, a rotating disk electrode is used to cause an increased limiting current density, and hence a larger range (say, 104 times) of current density.

As z app approaches iL, the cathodic overpotential, r c, becomes very large and the cathodic reaction rate becomes independent of overpotential. For a completely mass transport limited cathodic reaction, the concentration of the reacting specie in solution, Cb, approached zero at the electrode interface and z COff = iL. This is shown at Vi and V2 in Fig. 2. The limiting current density is increased by increasing solution stirring or rotation rate, co, in the case of a rotating cylinder or disk electrode. The corrosion rate would be increased. 

Figure 7 (a) Cathodic polarization data for a low carbon steel rotating disk electrode in 0.6 M NaCl with ambient aeration. Oxygen reduction limiting current densities are shown for the indicated rotation rates, (b) Plot of experimental limiting current density versus square root of the rotation rate, showing the experimental and predicted linear behavior. 

Figure 3 Plots of the total number of electrons Ut (a), of the Tafel slope b (b), of the limiting current density IjA,-, (c) and of the exchange current density I/A (d), versus the platinum loading for the reduction of oxygen on a platinum-modified polyaniline-glassy carbon rotating disk electrode (O2 saturated 0.5 M H2SO4 2mVs 25 °C A, is the true surface...

Effect of velocity on the corrosion of active-passive stainless is analyzed using a rotating disk electrode (RDE) technique. The hydrodynamics of the rotating disk electrode have been studied extensively [42-46]. The Levich equation provides the limiting current density as a function of angular velocity of the electrode [42] ... 

In the Rotating Disk Electrode (RDE) technique, the current-potential curves on smooth platinum exhibit an anodic limiting current density, which depends on rotation rate in both acidic and alkaline media [46]. These plots are well described by equation (19), which holds for a diffusion overpotential alone. Similar relationships have been observed in acidic solutions for Ir, Rh, and Pd, and well-characterized Pt-Ru, Pt-Rh, Pt-Sn [53], and Pt-Au [51] alloys, and also for Ni in alkaline solutions. In the case of platinum, a evolution of the limiting diffusion current density to a limiting reaction current density ( x) independent of rotation rate, is observed as a consequence of the rate-determining H2 adsorption. 

According to the Levich equation (4.105) the limiting current density for a rotating disk electrode is proportional to Cg. On the other hand, the Nernst model (equation 4.81) indicates that the limiting current is proportional to the product Cb Db- By combining these two equations we find that 5has a Db dependence. This result reveals the artificial character of the Nernst diffusion layer model. Every dissolved species that reacts in an electrochemical system has its own speeifie Nernst diffusion layer. 

According to the Levich equation (4.105), the limiting current density of a rotating-disk electrode can be written as ... 

Figure 445 Anodic dissolution of Fe in FeCl2 Variation of anodic limiting current density with bulk concentraion for different rotation rates of a rotating disk electrode [19].

The saturation concentration of FeCl2 in water is equal to 4.25 mol 1". Calculate the anodic limiting current density for iron dissolution from a rotating disk electrode in a binary electrolyte of 2.0 mol 1 FeCl2 at a rotation rate of 200 rpm. The temperature... 

The film diffusion limiting current density and the adsorption limiting current density are both independent of disk electrode rotation rates and applied potential (E), thus it is impossible to dissociate them and Eq. 9.29 can be written ... 

In the laboratory one frequently uses rotating-disk electrodes for the study of mass transport effects. According to the Levich equation [9], the limiting current density for a cathodic reaction at a rotating-disk electrode under laminar flow conditions varies linearly with the square root of the rotation rate. 

The primary potential distribution is, by definition, uniform adjacent to the electrode surface, but the current distribution is highly nonuniform (Fig. 10). It is a general characteristic of the primary current distribution that the current density is infinite at the intersection of an electrode and a coplanar insulator. This condition obtains at the periphery of the disk electrode, and the current density becomes infinite at that point. Additional resistance due to kinetic limitations invariably reduces the nonuniformity of the current distribution. In this system the current distribution becomes more uniform as the Wagner number increases. Theoretically, the current distribution is totally uniform as the Wagner number approaches infinity. 

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