Polarization curves for oxygen reduction

Fie. 3.18 Illustration of the effect of exchange current density on the polarization curve for oxygen reduction in aerated environments of pH = 0.56 and Pq2 = °-2 atm- Curves converge to the same diffusion limit and are identical when the hydrogen ion reduction is the dominant reaction. 

Figure 3.9. Steady-state polarization curve for oxygen reduction (1 atm.) on ClFeTMPP/ RB electrode of different loadings with a Pt/C (E-Tek) electrode for comparison in an H2/O2 minifuel ceU with hydrated Nation 117 at 60 C (A, dark squares) 12.3% ClFeTMPP (0.17 mgF/cm ) on RB (800°C H.T.) (B, dark circles) 24.2% ClFeTMPP (0.34 mgFe/cm ) on RB (800 C H.T.) and (C, open triangles) Pt/Xc-72 (E-Tek, 2 mg Pt/cm ) (according to Figure 9 in ref. [64] reproduced with permission of Springer Science and Busmes Media).

Figure 27 presents the polarization curves for oxygen reduction on carbon black promoted by different cobaltitesin alkaline solution. In these rotating disk-ring electrode experiments an extremely thin layer of a catalyst was applied to the pyrographite disk electrode. The analysis of the experimental data has shown that the O2 in the presence of the cobaltites is reduced mainly to water without the formation of hydrogen peroxide. 

Equations (4.91) to (4.93) can be applied to any cathodic partial reaction for which the charge-transfer step obeys the Butler-Volmer equation. In corrosion, oxygen reduction is often under mixed control. Figure 4.25 shows the cathodic polarization curve for oxygen reduction, measured on a platinum electrode [6]. The shape of the curve suggests a relatively low value for the ratio I o/ltil-... 

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...

Polarization curves for oxygen reduction on the platinum disk electrode are shown in curves d-f in Fig. 6, at various methanol concentrations without bpy. The... 

Table 3 Effect of additives on polarization curves for oxygen reduction and methanol oxidation ...

Figure 20.5 Schematic presentation of the current-potential relationship in a fuel cell. Lines 1 and 2 show the polarization curves for oxygen reduction and hydrogen oxidation, respectively. Line 3 shows the power as a...

Figure 7. Electrode polarization curves for oxygen-containing solutions with a mixed potential resulting from oxygen reduction accompanied by Fe2+ oxidation. Curves are schematic but in accord with available data at significant points...

FIGURE 1.12 Polarization curves for the reduction of oxygen on a bare platinum disk in oxygen-saturated 0.5 M H2S04 at different rotation speeds. (From Ayad, A., et al., J. Power Sources, 149, 66, 2005.)... 

For reasons stated previously, it is considerably more difficult to construct illustrative polarization curves for the reduction of dissolved oxygen. Reasonable estimates of the exchange current densities, Tafel slopes, and diffusion rates have been used to construct the curves of Fig. 3.17 (Ref 3, 6). These curves, identified by letters, are described as follows ... 

Figure 7.4 (A) Polarization curves for O2 reduction on platinum monolayers (PIml) on Ru(OOOI), lr(111), Rh(111), Au(111), and Pd(111) surfaces in 02-saturated 0.1 M HCIO4 solution on a disk electrode. The rotation rate is 1600 rpm, and the sweep rate is 20 mV s (50 mV s for R(111)) y= current density, RHE = reversible hydrogen electrode. (Reprinted with permission from Ref. 6) (B) kinetic currents (yi< square symbols) at 0.8 V for O2 reduction on the platinum monolayers supported on different single-crystal surfaces in 02-saturated 0.1 M HCIO4 solution and calculated binding energies of atomic oxygen (BEO filled circles) as functions of calculated d-band center (fd cp relative to the Fermi level) of the respective clean Pt monolayers. Labels (1) PtMi/Ru(0001),(2) RMi/lrOU). (3) PtMi/Rh(111),(4) PtMi/Au(111), (5) Pt(111), (6) PtML/Pd(111). Reprinted with permission from Ref. 22.

Figure 13.7. Polarization curves for O2 reduction reaction on Au/Pt/C (A) and Pt/C (C) catalysts on a rotating disk electrode, before and after 30,000 potential cycles. Sweep rate 10 mV/s rotation rate 1600 rpm. Voltammetric curves for Au/Pt/C (B) and Pt/C (D) catalysts before and after 30,000 cycles sweep rates 50 and 20 mV/s, respectively. The potential cycles were from 0.6 to 1.1 V in an 02-saturated 0.1 M HCIO4 solution at room temperature. For aU electrodes, the Pt loading was 1.95 mg (or 10 nmol) on a 0.164 cm glassy carbon rotating disk electrode. The shaded area in (D) indicates the lost Pt surface area [31]. (From Zhang J, Sasaki K, Sutter E, Adzic RR. Stabilization of platinum oxygen-reduction electrocatalysts using gold clusters. Science 2007 315 220-2. Reprinted with permission from AAAS.)...

FIGURE 22.2 Schematic polarization curves for spontaneous dissolution (a) of active metals (h) of passivated metals. (1,2) Anodic curves for active metals (3) cathodic curve for hydrogen evolution (4) cathodic curve for air-oxygen reduction (5) anodic curve of the passivated metal. 

Figure 1, Polarization curve for the electrochemical reduction of oxygen coupled with the electrochemical oxidation of an unspecified organic impurity O.C, designates the open circuit potentials...

Figure 9 Polarization curve of carbon steel in deaerated, pH 13.5 solution at 65°C. Sample was initially held potentiostatically at —1.2 V(SCE) for 30 min before initiation of the potentiodynamic scan in the anodic direction at 0.5 m V/s. The cathodic loop results from the fact that the passive current density is only 1 pA/cm2, which is less than the diffusion-limited current density for oxygen reduction for the 0.5 ppm of dissolved oxygen present. (From Ref. 8.)...

Ahn et al. have developed fibre-based composite electrode structures suitable for oxygen reduction in fuel cell cathodes (containing high electrochemically active surface areas and high void volumes) [22], The impedance data obtained at -450 mV (vs. SCE), in the linear region of the polarization curves, are shown in Figure 6.22. Ohmic, kinetic, and mass transfer resistances were determined by fitting the impedance spectra with an appropriate equivalent circuit model. 

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. 

Figure 10. Polarization curves (IR-free) for oxygen reduction at LSM cathode without (O) and with ( ) loading Pt catalysts in O2 at 7 ceii = 800 °C. Pt(A) 0.5 ing/cnr A Pt(A) 0.1 mg/em Pt(C) 0.1 mg/cm. Reproduced from Ref. 30, Copyright (1996), by permission from The Electrochemical Society of Japan.

Figure 11. Polarization curves (IR-free, measured in O2) for oxygen reduction at LSC cathodes. A LSC1050/SDC400, O LSC1050/ SDCl 150.

Oxygen Electrocatalytic Properties Oxygen Reduction. Figure 8 compares steady-state polarization curves for the electroreduction of Op on a typical pyrochlore catalyst, Pb2(Rui.42Pbo.53)06.5 15 w/o platinum on carbon. The latter was considered representative of conventional supported noble metal electrocatalysts. The activities of both catalysts are quite comparable. While the electrodes were not further optimized, their performance was close to the state of the art, considering that currents of 1000 ma/cm could be recorded, at a relatively moderate temperature (75 C) and alkali concentration (3M KOH). Also, the voltages were not corrected for electrolyte resistance. The particle size of the platinum on the carbon support was of the order of 2 nanometers, as measured by transmission electron microscopy. 

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...

Fig. 4.28 Idealized anodic polarization curves for metals A and B and for hydrogen and oxygen reduction. An explanation for the use of these curves for estimating the corrosion potentials, currents and rates for aerated and deaerated environments and for galvanic coupling can be found in the text.

Fig. 5.11 Schematic representation of relative positions of anodic metal, cathodic oxygen, cathodic hydrogen, and cathodic water reduction polarization curves. pH = 1. Po, = 0-2 atm. Curve M, anodic polarization curve for metal (e.g., Fe-18% Cr) curve H, cathodic polarization curve for H+ curve W, cathodic polarization curve for H20 curve O, cathodic polarization for 02...

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