Oxygen evolution reaction relations

Furthermore, BDD anodes have a high overpotential for the oxygen evolution reaction compared with the platinum anode (Fig. 1.3). This high overpotential for oxygen evolution at BDD electrodes is certainly related to the weak BDD-hydroxyl radical interaction, what results in the formation of H202 near to the electrode s surface (1.14), which is further oxidized at the BDD anode (1.15) ... 

In the discussion of the hydrogen and oxygen evolution reactions, we saw that the current-potential relationship is influenced, and sometimes determined completely, by the potential dependence of the coverage 9. Thus, one may expect that the kinetic parameters will depend on the adsorption isotherm, which relates the surface concentration to the bulk concentration, and more importantly in electrochemistry, to the potential. In the preceding derivations it was tacitly assumed that the Langmuir isotherm applies. In Section 19 we discuss the limitations of this assumption and show how the kinetic parameters change when different isotherms are applicable. 

FIGURE 1.14 Current density related to real surface area for the oxygen evolution reaction on perovskites at 0.30 V of overpotential versus the M-OH bond strength. The transition metals, M, of the perovskites are indicated in the plot. This plot is a simplified representation of that in [21]. 

Anode performance depends on the brine quality and the operating parameters such as pH, current density, NaCl concentration, and NaOH concentration (in diaphragm and membrane cells). The contribution of the anode to the cell inefficiency, as mentioned in Section 4.4, is directly related to the losses arising from the oxygen evolution reaction, and indirectly by chlorate formation. Thus, as the %02 increases, the pH at the anode-solution interface decreases, and hence, the amount of chlorate formed will decrease as the bulk pH is lowered. The amount of O2 generated at the anode is a function of the current density, pH, the composition and surface area of the anode coating, and the salt concentration. 

The high-temperature performance of nickel-metal hydride batteries is directly related to the behavior of the nickel hydroxide electrode materials, which determines the cell capacity. Due to oxygen evolution on the positive electrode at a temperature higher than 50°C, the charge efficiency of positive electrodes is significantly diminished when the rmdesirable oxygen evolution reaction occurs. 

Initial studies on electrocatalysis for fuel cell application using amorphous alloys were related to the oxygen evolution reaction (OER) [131,132], Ni-based amorphous alloys have a significant contribution to the development of materials for application in fuel cells due to their high stability in alkaline medium, relative low overpotential, low cost, and high corrosion resistance. The synthesis of the alloys is relatively simple. The catalyst can be obtained via the mechanical alloy technique, where the metallic elements are placed in a planetary ball mill for several hours, at the desired ratio. An important observation is that the as-synthesized catalyst does not display significant catalytic activity as compared to the crystalline material. An acid treatment with HE or HF-HNO3 is required for activation of the material surface [133,134],... 

The character of the oxide layers influences the kinetics and mechanism of the electrochemical reactions occurring on the platinum anode surface. The relation between the rate of oxygen evolution and oxide layer thickness is complex. In the region where the a-oxides exist, the reaction rate decreases with increasing oxide layer thickness. In the region where the P-oxides exist, the reaction rate depends little on oxide layer thickness or, according to some data, increases with increasing oxide layer thickness. 

In Figure 16 is shown the photo-current / potential relation for an n-type GaP anode and a p-type GaP cathode. The current at zero applied potential is larger in this case, but this is because the anodic reaction is dissolution of the GaP and not oxygen evolution. 

While the flavonoids suppress oxygen uptake in isolated mitochondria and oxygen evolution from chloroplasts, there has been too little work to establish these organelle effects as the only mechanisms of action. Flavonoids are known to protect membrane lipids against destructive reactions and, based on current evidence, these compounds do not readily fit the model of Figure 11.2. The flavonol rutin did not show an effect on soybean seedling water relations.64 It is... 

Several oxides with perovskite related stmctures can also be intercalated with oxygen ions by an electrochemical method. The oxide Sr2Fe20s with the brownmillerite stmcture has been electrochemically oxidized to SrFeOs. The reaction was carried out by controlled potential electrolysis at a potential below that for oxygen evolution in 1 M aqueous KOH at room temperature. Bulk oxidation was confirmed by Mossbauer spectroscopy and X-ray difflaction. Similar results have been obtained for electrochemical oxidation... 

The effect of the dopant was considered in relation to the formation of oxide ion vacancies and simultaneous oxygen evolution. The equilibrium reaction of the oxygen evolution and absorption in Ce02 is expressed by the following equation. 

---