Oxygen reduction polarization

If, however, it is assumed from Eq. (2-40) that the protection current density corresponds to the cathodic partial current density for the oxygen reduction reaction, where oxygen diffusion and polarization current have the same spatial distribution, it follows from Eq. (2-47) with = A0/7 ... 

Systematic studies of cathodic oxygen reduction, unlike those of its anodic evolution, were only started in the 1950s when required for the realization of fuel cells. The large polarization of this reaction is one of the major reasons that the efficiency of the fuel cells developed so far is not very high. 

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. 

The effects of impurities are less important for oxygen-depolarized than for hydrogen-depolarized corrosion, since the values of polarization for oxygen reduction found at different metafs differ fess strongfy than those for hydrogen evofution. 

Various carbon-based catalysts for the electrochemical oxygen reduction have been tested in the air gas-diffusion electrodes [7]. The polarization curves of the air electrodes were measured when operating against an inert electrode in 2 N NaCl-solution. The potential of the air electrodes was measured versus saturated calomel electrode (SCE). 

Figure 3. Current density versus electrode polarization (Ag/AgCl ref. electrode) for oxygen reduction in 1MKOH at20°C on Co-Ni modified AG-3 carbon.

Lee et al. [30] used in situ X-ray photo electron spectroscopy (XPS) measurement on La0 9Sr0 Mn03 as a function of cathodic polarization. The XPS results showed the peaks of Mn 2p spectra were shifted to the lower binding energy as the applied potential became more cathodic, indicating the reduction of Mn ions. The oxygen reduction and the concomitant formation of Mn2+ ions and oxygen vacancies are proposed as ... 

The impedance polarization performance of LSM electrode is closely related to the mechanism and kinetics of the oxygen reduction reactions. 02 reduction at SOFC cathodes is the most heavily studied subject, and this subject is sufficiently broad and complex to warrant its own review. Interested readers should consult the recent excellent articles by Adler [1] and Fleig [55], Here, only the polarization performance and its influencing factors are discussed. 

The initial polarization behavior for the oxygen reduction on LSM-based cathodes is characterized by a well-known activation phenomenon, as shown in... 

Fig. 14.19 Polarization curves of oxygen reduction on nitrogen-doped CNTs with different nitrogen content. Operating conditions 0.1 M KOH, 5 mVs-1 scan rate, 1600 rpm rotation speed,...

Oxygen/reduction polarization curves from RDE measurements for Ru,92MO(,Q8Se04, Ru/C, and Pt/C in 0.6 M H2SO4,60°C. (T. J. Schmidt et al.. Journal of the Electrochemical Society, 4 2620 (2000). Reproduced by permission of The Electrochemical Society.)... 

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...

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