A mesoscale simulation is developed to simulate transport and electrochemistry in a small section of a proton exchange membrane fuel cell ͑PEMFC͒ cathode catalyst layer. Oxygen, proton, and electron transport are considered in the model. Many simulations are run with a wide variety of different parameters on stochastically reconstructed microstructures with a resolution of 2 nm. Knudsen diffusion plays an important role in limiting the transport of oxygen through the catalyst layer. Using larger carbon spheres in the catalyst layer increases the effective diffusivity of oxygen through the catalyst layer. The effective proton conductivity increases when larger spheres are used, a normal distribution of spheres is used, or a higher overlap tolerance is used. Increasing the overlap tolerance or overlap probability results in an increase in the effective electron conductivity. When electrochemical reactions are considered in a part of the catalyst layer that is close to the gas diffusion layer, the critical parameter that determines oxygen consumption is the carbon sphere radius. Oxygen consumption at a given carbon volume fraction is larger in microstructures containing spheres with smaller radii, because there is more surface area available for electrochemical reactions.Catalyst layers in proton exchange membrane fuel cells ͑PEM-FCs͒ have a complex structure due to the presence of carbon, platinum, ionomer, and pores. Carbon provides a pathway for electron conduction, platinum is used as a catalyst for electrochemical reactions, the ionomer allows for the conduction of protons, and oxygen or hydrogen travel through pores to reaction sites. It is difficult to make experimental observations of the catalyst layer, because its thickness is close to 10 m. To obtain a greater understanding of the transport properties and electrochemistry in the catalyst layer, numerical simulation can be used. Several different approaches have been used to model the catalyst layer in fuel cell models. In simulations which consider the entire fuel cell, the catalyst layer is often treated as an infinitely thin interface. 1-4 Alternatively, some have modeled the catalyst layer using porous electrode models 5-8 or agglomerate models. 9-15 These models do not resolve the porous structure of the catalyst layer, but rather rely on a bulk-averaged representation of the porous media in conjunction with the prescription of effective transport parameters. While this approach allows computationally efficient simulations of larger scale models, there are challenges in the determination of the effective transport parameters.There have been several efforts to simulate catalyst layer transport and reactions at the nanoscale level. A two-dimensional finite difference simulation of oxygen, proton, and electron transport along with electrochemical reactions through a regular microstructure was done by Wang. 16 This model was later extended to three dimensions and applied to a regular microstructure 17 and a random microstructure. 18 In the three-dimension...

No abstract

No abstract

No abstract