Anode gas diffusion

Eor the purpose of modeling, consider a planar SOEC divided into anode gas channel, anode gas diffusion electrode, anode interlayer (active electrode), electrolyte, cathode interlayer (active electrode), cathode gas diffusion electrode, and cathode gas channel. The electrochemical reactions occur in the active regions of the porous electrodes (i.e., interlayers). In an SOFC, oxidant reduction occurs in the active cathode. The oxygen ions are then transported through the electrolyte, after which oxidation of the fuel occurs in the active anode by the following reactions. 

Figure 12.1 is a schematic view of a typical PEM fuel cell. A membrane electrode assembly (MEA) usually refers to a five-layer structure that includes an anode gas diffusion layer (GDL), an anode electrode layer, a membrane electrolyte, a cathode electrode layer, and a cathode GDL. Most recently, several MEA manufacturers started to include a set of membrane subgaskets as a part of their MEA packages. This is often referred to as a seven-layer MEA. In addition to acting as a gas and... 

Ohmic overpotential is the loss associated with resistance to electron transport in the gas diffusion layers. For a given nominal current density, the magnitnde of this overpotential is dependent on the path of the electrons. The potential field in the cathodic and the anodic gas diffusion electrodes are shown in Figure 3.17. The potential distribntions are normal to the flow charmel and the sidewalls, while there is a gradient into the land areas where electrons flow into the bipolar plate. The distributions exhibit gradients in both x and y direction due to... 

The velocity fields inside the cathodic and anodic gas diffusion layers are shown in Figures 4.2 and 4.3 for both gas and liquid phase. The pressure gradient induces bulk gas flow from... 

The MEA consists of an anodic electrode, PEM, and a cathodic electrode. Because the electrode reactions take place in the MEA, it is the heart of a H2/air PEM fuel cell. The components of an MEA include the anode gas diffusion medium (A-GDM), anode microporous layer (A-MPL), anode catalyst layer (A-CL), PEM, cathode catalyst layer (C-CL), cathode microporous layer (C-MPL), and cathode gas diffusion medium (C-GDM), as shown in Fig. 2.1. A commonly used term is gas diffusion layer (GDL), which actuaUy contains the gas-diffusion-medium layer and the microporous layer. Each component shown in Fig. 2.1 has specific characteristics and functions in fuel cell operation and performance. Therefore, they differ significantly in their design and fabrication. These topics wUl be addressed in the following sections. 

In a PEM fuel cell, hydrogen molecules can diffuse from the anode and then cross over the membrane to the cathode, which is a diffusion-controlled process. As discussed in Chapter 2, a typical MEA usually consists of an anode gas diffusion layer (GDL(a)), anode catalyst layer (CL(a)), PEM, cathode... 

Effective cathode gas diffusivity Effective anode gas diffusivity Volume fraction porosity Surface exchange coefficient Impedance at angular frequency Imaginary part of admittance Real part of admittance Anode thickness Cathode thickness Electrolyte thickness Exchange current density Anode limiting current density Cathode limiting current density Three phase boundary length Transfer coefficient of symmetry factor... 

Diffusion media are generally made hydrophobic to avoid flooding in their bulk. Typically, both cathode and anode gas diffusion media are PTFE treated. A wide range of PTFE loadings have been used in PEMFC diffusion media (5% to 30%), most typically by dipping the diffusion media into a PTFE solution followed by drying and sintering. 

Hydrogen domain includes anode channel, anode gas diffusion layer, and anode catalyst layer, with no boundary conditions required at the interfaces between these layers. 

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