Cathode oxygen reduction reaction

If the potential of a metal surface is moved below line a, the hydrogen reaction line, cathodic hydrogen evolution is favored on the surface. Similarly a potential below line b, the oxygen reaction line, favors the cathodic oxygen reduction reaction. A potential above the oxygen reaction line favors oxygen evolution by the anodic oxidation of water. In between these two lines is the region where water is thermodynamically stable. 

Electrode A is called the anode because the anodic reaction is favored over the cathodic reaction. In a fuel cell, the anodic oxidation of H2 is favored. The corresponding reaction at the cathode, electrode B, is the cathodic oxygen reduction reaction,... 

As discussed above, if the exchange current density of anode hydrogen oxidation is i nMc =0,1 Acni 2 and that of the cathode oxygen reduction reaction (ORR) is... 

During the processes described by equations 1 and 2, dissolution from the coating layer gives rise to the deposition of a hydroxide layer impeding the cathodic oxygen reduction reaction. [8] This reaction involves the rapid hydrolysis of water via equations 3 and 4. 

Iron hydroxide ion formation, Fe(OFI), depends on solution pFl, that is, the availability of OH ions. As bivalent Fe ions are formed through Eq. (12.6), OH ions are transported from the bulk to the surfice to maintain electroneutrality. Flydroxide ions are also produced via the cathodic oxygen reduction reaction, causing an increase in surface pH. At high pH, the formation of adsorbed [Fe(OH)]ads on the iron surface becomes more favorable than bivalent Fe ions, Eq. (12.6). The electrode potential tends to shift into a more anodic direction to accommodate the formation of Fe(OH)". As time increases, the Fe(OH) concentration at the surface increases. In the next step, Fe(OH) oxidizes to ferric oxide at e° = —0.084Vvs.SCE, resulting in a barrier oxide layer ... 

Currently used electrode-catalysts (anode and cathode) consist of an assembly of metallic nanoparticles usually deposited on an electronic conducting substrate and embedded in a hydrated membrane [10, 11], which is the polymer electrolyte proton-conductive material (Figure 17.1). What differs between cathode and anode is the catalyst material, and also the significantly slow kinetics of the cathode oxygen reduction reaction compared to that of the anode hydrogen oxidation reaction. For this reason, several... 

Snyder J, McCue I, Livi K, Erlebacher J (2012) Structure/processing/properties relationships in nanoporous nanoparticles as applied to catalysis of the cathodic oxygen reduction reaction. J Am Chem Soc 134 8633-8645... 

The development of cheap and efficient electrocatalysts, especially the oxygen reduction electrocatalyst, is another task for the large-scale commer-ciahzation of PEMFCs. In any PEMFCs, there are two types of electrocatalysts one catalyzes the anodic hydrogen oxidation reaction and the other the cathodic oxygen reduction reaction. Both electrocatalysts rely heavily on the use of precious metals, especially the Pt-based electrocatalysts. The tasks in the development of electrocatalysts include the improvement of electrocatalytic activity, the reduction of the loading of precious metals, or even the replacement of precious metals with cheap metals, and the... 

The slow kinetics of the cathode oxygen reduction reaction (ORR) plays the key role in limiting PEMFC performance when pristine hydrogen is used as the fuel. Therefore, improving the catalytic activity for the ORR has drawn most of the research attention in catalysis studies. Cathode contamination has attracted less attention compared with anode contamination, and only a limited number of papers have been published. Pollutants in air include NOx (NO2 and NO), SOx (SO2 and... 

Kalman et al. (1994) studied the inhibition mechanism of HEDP on carbon steel corrosion in neutral oxygen containing NaC104 solution by polarization and impedance techniques. The results obtained indicated that the major effects of the inhibitor below 10 M concentration are to shift the corrosion potential in the anodic direction and to reduce the anodic current. The inhibitor has little or no effect on the cathodic oxygen reduction reaction. Therefore it is suggested that inhibition in this concentration range is due to repair of oxide layer as a result of the adsorption of HEDP molecules. Increasing the HEDP concentration decreases the inhibition efficiency due to dissolution of the oxide layer. 

The cathodic oxygen reduction reaction cannot be sustained in the crevice area, making it the anode of a differential aeration cell. This anodic imbalance may lead to the creation of highly corrosive microenvironmental conditions in the crevice, conducive to further metal dissolution. It is also thought that subsequent pH changes at anodic and cathodic sites further stimulate local cell action [Fig. 6.21(c)]. The aggravating factors present in a fully developed crevice can be summarized in the following points ... 

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