Lattice Boltzmann Simulation of Transport Phenomena in Nanostructured Cathode Catalyst Layer for Proton Exchange Membran
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Lattice Boltzmann Simulation of Transport Phenomena in Nanostructured Cathode Catalyst Layer for Proton Exchange Membrane Fuel Cells Christopher D. Stiles and Yongqiang Xue College of Nanoscale Science and Engineering, State University of New York, Albany, New York 12203, USA ABSTRACT A multi-component, multiple-relaxation-time (MRT) lattice Boltzmann (LB) model has been employed to study transport processes in the nanostructured cathode catalyst layer of a prototype proton exchange membrane (PEM) fuel cell. The electrode consists of an array of ordered and aligned nanorods that are continuously coated with platinum (Pt). The effect of spacing between the nanorods was studied. Simulation results showed that smaller spacing in nanorods leads to lower utilization of the Pt catalyst due to O2 mass transport limitations. Results from the LB model were found to be in good agreement with the continuum model using the finite element method (FEM) with the same boundary conditions until the systems reached the O2 mass transport limited regions, where the solutions diverged. INTRODUCTION As the fossil fuel crisis becomes more critical, it is imperative to develop renewable sources of power generation. Proton exchange membrane fuel cells (PEMFC) are considered as viable options. However, the cost of the Pt catalyst has hindered their commercialization. Efforts towards further reducing Pt loading are currently underway utilizing nanostructured electrodes [1]. The inherent advantages of nanostructured catalyst layers as compared to the tortuous carbon black (CB) catalyst layers are that they would enhance the transport of oxygen and improve the catalytic reactivity at the catalyst-membrane-gas triple phase boundaries, postulated to result in better catalyst utilization with reduced precious metal loading, thus yielding higher fuel cell performance [1]. However, a common consequence of increased Pt utilization is flooding which is detrimental to fuel cell performance. Flooding refers to the phenomenon of accumulation of liquid water on the electrode surface, in the gas diffusion layer (GDL) or in gas channels resulting in blockage of active electrochemical sites. Flooding causes a two-fold impact on cell performance: a drop in cell voltage and a rise in parasitic pumping power to overcome the increased pressure drop, which together result in a significant reduction in system efficiency [2]. Proper water management is therefore crucial for optimum performance of the fuel cell and also for enhancing membrane durability. Due to the difficulty in performing experiment measurements without modifying cell and system designs, numerical modeling is critical for better mechanistic understanding of PEMFC operation. The Lattice Boltzmann (LB) method is a powerful numerical tool for simulating fluid flow [3], which has received increasing attention in PEMFC transport modeling. The majority of the LB studies have focused on transport processes and their dependence on the pore structure and wettability in GDL [4-6]. Although transport phenomen
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