Oxygen reduction reaction polarization curves

Fig. 4.23 Schematic representation of polarization curves for the analysis of galvanic coupling when diffusion control of the oxygen reduction reaction is the dominant factor governing the corrosion rate...

The cathodic polarization curve is constructed using the oxygen electrode equilibrium potential and the cathodic slope, 6<- = —0.05V/decade. The equilibrium cathode potential, geq,c is calculated by applying the Nemst equation to the oxygen reduction reaction, Eq. (4.13), for an oxygen concentration of 1.0x10 mol/1 at pH= 11. 

Fuel Cells, Non-Precious Metal Catalysts for Oxygen Reduction Reaction, Fig. 4 (a) Polarization curves of several Me-N-C catalysts all examined under the same experimental conditions (1.5 bar H2/O2, 1 mg cm see Ref. [12] et al. for details), (b) today s most active NPMC catalysts (p-Fe-N-C) as prepared by the pore-filling method (PFM) described in Lefevre et al. [44] and by the method described by Proietti et al. [10]. The values... 

Two different reaction mechanisms following a two-electron reduction were suggested on the basis of detailed mechanistic studies of the reduction. The polarization curves are characterized by two waves the first with a limiting current close to the current that correspcMids to the oxygen... 

Figure 15.17. ORR polarization curves for W-Co-Se and Pt/C in 0.5 M H2SO4 at 25 C. Potential scan rate 5 mV/s. Pt/C loading is 122 pg/cm [HO]. (Reprinted from Electrochemistry Communications, 9(7), Lee Kunehan, Zhang Lei and Zhang Jiujun, Ternary non-nohle metal chalcogenide (W-Co-Se) as eleetrocatalyst for oxygen reduction reaction, 1704—8, 2007, with permission from Elsevier.)...

In attempts to simulate the experimentally observed oxygen reduction reaction, several kinetic models have been reported in the literature, based on various proposed ORR mechanisms [38—41]. These models employed either the associative or the dissociative model. The former was used by Antoine et al. [38] in their simulation of a polarization curve and impedance spectra, and by Du et al. [40] in a model-based electrochemical impedance spectroscopy study. Antoine et al. considered the following reaction steps ... 

Figure 10.5 Polarization curves for oxygen reduction reaction over Pd3Pt,/C and Pt/C in 02-saturated 0.5 mol I" HCIO4 in the presence or absence of 0.1 mol I" methanol at room...

Hinton and co-workers found based on analysis of polarization curves for AA7075 that corrosion rates decreased when 1000 ppm of CeCl3, LaCl3, PrClj or NdClj were added to 0.1M NaCl solutions. The surface films formed on AA7075 decreased the susceptibility to corrosion by reducing the rate of the oxygen reduction reaction at cathodic sites. ... 

Figure 3-8 shows how the cell polarization curve is formed, by subtracting the activation polarization losses, ohmic losses, and concentration polarization losses from the equilibrium potential. Anode and cathode activation losses are lumped together, but, as mentioned before, a majority of the losses occiu on the cathode because of sluggishness of the oxygen reduction reaction. 

In the presence of oxidizing species (such as dissolved oxygen), some metals and alloys spontaneously passivate and thus exhibit no active region in the polarization curve, as shown in Fig. 6. The oxidizer adds an additional cathodic reaction to the Evans diagram and causes the intersection of the total anodic and total cathodic lines to occur in the passive region (i.e., Ecmi is above Ew). The polarization curve shows none of the characteristics of an active-passive transition. The open circuit dissolution rate under these conditions is the passive current density, which is often on the order of 0.1 j.A/cm2 or less. The increased costs involved in using CRAs can be justified by their low dissolution rate under such oxidizing conditions. A comparison of dissolution rates for a material with the same anodic Tafel slope, E0, and i0 demonstrates a reduction in corrosion rate... 

In analyzing the polarization data, it can be seen that the cathodic reaction on the copper (oxygen reduction) quickly becomes diffusion controlled. However, at potentials below -0.4 V, hydrogen evolution begins to become the dominant reaction, as seen by the Tafel behavior at those potentials. At the higher anodic potentials applied to the steel specimen, the effect of uncompensated ohmic resistance (IRohmk) can be seen as a curving up of the anodic portion of the curve. 

The objective of the mass transport lab is to explore the effect of controlled hydrodynamics on the rate at which a mass transport controlled electrochemical reaction occurs on a steel electrode in aqueous sodium chloride solution. The experimental results will be compared to those predicted from the Levich equation. The system chosen for this experiment is the cathodic reduction of oxygen at a steel electrode in neutral 0.6 M NaCl solution. The diffusion-limited cathodic current density will be calculated at various rotating disk electrode rotation rates and compared to the cathodic polarization curve generated at the same rotation rate. 

Cathodic polarization curves for mild steel exposed to air-saturated tap water and tap water containing 200 ppm of CeCl3 [7] showed that oxygen reduction is the primary cathodic reaction in aerated solutions devoid of CeCl3 and the current density is considerably reduced by the addition of CeCb. A pale yellow film was also observed on the sample. 

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