Oxygen reduction reaction associative mechanism

In practice, in all fuel cells that involve the utilization of 02 from air (Section 13.4.5), the oxygen reduction reaction [Eqs. (13.4) and (13.24)] is always rate determining for terrestrial applications. One can seejust how important it is to attempt to develop electrocatalysts for the cathodes of fuel cells on which the enhanced current density is high and Tafel slope is low and the efficiency of energy conversion, therefore, maximal. The direct relation of the mechanism of oxygen reduction and the associated Tafel parameters to the economics of electricity production and transportation is thus clearly seen. 

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 ... 

The mechanism in hepatic cellular metabolism involves an electron transport system that functions for many drugs and chemical substances. These reactions include O-demethylation, N-demethyla-tion, hydroxylation, nitro reduction and other classical biotransformations. The electron transport system contains the heme protein, cytochrome P-450 that is reduced by NADPH via a flavoprotein, cytochrome P-450 reductase. For oxidative metabolic reactions, cytochrome P-450, in its reduced state (Fe 2), incorporates one atom of oxygen into the drug substrate and another into water. Many metabolic reductive reactions also utilize this system. In addition, there is a lipid component, phosphatidylcholine, which is associated with the electron transport and is an obligatory requirement for... 

L-Ascorbic acid is also added to food in essentially a non-nutrient capacity such as a preservative or oxygen acceptor, as an acidulant, as a stabilizer of cured meat color, or as a flour improver. Because of the ene-diol group, it has a marked inhibitory influence on the oxidation-reduction reactions responsible for undesirable color, flavor, and odor development. Its mechanism of action is dependent upon the characteristics of the food or food ingredient, the associated environments, the processing technology, and the storage expectancy of the product. 

Currently, several air-side contamination models have been published in the literature, ranging from simple empirical and adsorption models to general kinetic models. These models have been applied to simulate and predict SO2, NO2, NH3, and toluene contamination. The kinetic model is a very general one based on the associative oxygen reduction mechanism. It takes into account contaminant reactions, such as surface adsorption, competitive adsorption, and electrochemical oxidation, and has the capability of simulating and predicting both transient and steady state cell performance. The model can be applied to other cathode contaminants, e.g., SO2 and NO2. 

There is still no consensus concerning the mechanism for the WGSR over Au/ceria catalysts. Two reaction mechanisms have mainly been considered in the literature — the so-called redox mechanism and the associative mechanism, which needs further discussion for the type of intermediate bicarbonate, formate, or carboxyl.According to the redox mechanism, the WGS reaction proceeds via consecutive steps of reduction and oxidation at the catalyst s surface.These steps include GO adsorption on the metal surface and interaction with lattice oxygen in the ceria to... 

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