Water-filled nanopore model

As for effective kinetic parameters of the ORR that should be used in macroscopic models, it seems reasonable to assume that the reaction order for oxygen concentration will be yo2 = 1 for conditions of interest. The effective transfer coefficient of the ORR, ac, will transition through a sequence of discrete values between 1 and 0.5, as a function of electrode potential. The reaction order for proton concentration, yh+, depends strongly on the adsorption regime and, therefore, a prediction of the value is not trivial. The difference ac - yh+ is a key determinant of electrostatic effects in water-filled nanopores inside of catalyst layers, as discussed in the section ORR in Water-Filled Nanopores Electrostatic Effects. ... 

Model OF A Water-Filled Nanopore with Charged Metal Walls... 

The transport properties of water-filled nanopores inside of agglomerates and the properties of the ionomer film at the agglomerate surface define local reaction conditions at the mesoscopic scale. These local conditions, which involve distributions of electrolyte phase potential, proton density (or pH), and oxygen concentration, determine the kinetic regime, under which interfacial electrocatalytic processes must be considered. Combining this information, a local reaction current can be found, which represents the source term to be used in performance modeling of the cathode catalyst layer. 

The model of water-filled nanopores, presented in the section ORR in Water-Filled Nanopores Electrostatic Effects in Chapter 3, was adopted to calculate the agglomerate effectiveness factor. As a reminder, this model establishes the relation between metal-phase potential and faradaic current density at pore walls using Poisson-Nernst-Planck theory. Pick s law of diffusion, and Butler-Volmer equation... 

A model of the ORR in a single water-filled pore with charged walls of Pt will be presented. It affords the definition of an effectiveness factor, by which the performance of any nanoporous CL material could be evaluated. Furthermore, a remarkable conclusion is drawn in view of the coupling of ORR kinetics and metal corrosive dissolution. 

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