Electrodes flooded agglomerate

The membrane electrode assembly (MEA), which consists of three components (two gas diffusion electrodes with a proton exchange membrane in between), is the most important component of the PEMFC. The MEA exerts the largest influence on the performance of a fuel cell, and the properties of each of its parts in turn play significant roles in that performance. Although all the components in the MEA are important, the gas diffusion electrode attracts more attention because of its complexity and functions. In AC impedance spectra, the proton exchange membrane usually exhibits resistance characteristics the features of these spectra reflect the properties of the gas diffusion electrode. In order to better understand the behaviour of a gas diffusion electrode, we introduce the thin-film/flooded agglomerate model, which has been successfully applied by many researchers to... 

The characteristics of a gas diffusion electrode can also be illustrated by the thin-film/flooded agglomerate model. Paganin et al. [4] summarized the parameters that often appear in the impedance spectra of H2/02 and H2/air fuel cells ... 

Springer TE, Raistrick ID (1989) Electrical impedance of a pore wall for the flooded-agglomerate model of porous gas-dilFusion electrodes. J Electrochem Soc 136 1594-603... 

Electrode Kinetic and Mass Transfer for Fuel Cell Reactions For the reaction occurring inside a porous three-dimensional catalyst layer, a thin-film flooded agglomerate model has been developed [149, 150] to describe the potential-current behavior as a function of reaction kinetics and reactant diffusion. For simplicity, if the kinetic parameters, such as flie exchange current density and diffusion limiting current density, can be defined as apparent parameters, the corresponding Butler-Volmer and mass diffusion relationships can be obtained [134]. For an H2/air (O2) fuel cell, considering bofli the electrode kinetic and the mass transfer, the i-rj relationships of the fuel cell electrode reactions within flie catalyst layer can be expressed as Equations 1.130 and 1.131, respectively, based on Equation 1.122. The i-rj relationship of the catalyzed cathode reaction wifliin the catalyst layer is... 

Similar agglomerate approaches were adopted by Iczkowski and Cutlip [30] and by Bjbmbom [31], Those works already identified the doubling of the apparent Tafel slope as a universal signature of the interplay of mass transport limitations and interfacial electrochemical kinetics. Flooded agglomerate models have been employed since then to analyze sources of irreversible voltage losses, optimum electrode thickness, and effectiveness of catalyst utilization. Moreover, it was... 

In addition to the equivalent circuit method, the impedance results can also be analyzed using mathematical models based on physicochemical theories. Guo and White developed a steady-state impedance model for the ORR at the PEM fuel cell cathode [15]. They assumed that the electrode consists of flooded ionomer-coated spherical agglomerates surrounded by gas pores. Stefan-Maxwell equations were used to describe the multiphase transport occurring in both the GDL and the catalyst layer. The model predicted a high-frequency loop due to the charge transfer process and a low-frequency loop due to the combined effect of the gas-phase transport resistance and the charge transfer resistance when the cathode is at high current densities. 

The catalytic layers (CLs) of fuel cell electrodes can be represented as an assembly of two interconnected porous systems (1) a microstructure of porous catalysts (together with their supports) flooded by electrolyte, and (2) a macroslructure in hydrophilic CLs of wide gas pores or, in hydrophobized CLs, agglomerates of hydrophobic particles with gas pores between the particles. 

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