Effects of Using a 3-D Micro-lattice Flow Structure on Oxygen Transport Characteristics in the Cathode Medium of Polymer Electrolyte Membrane Fuel Cells

Abstract

This work is primarily concerned with alleviating the concentration loss in Polymer Electrolyte Membrane fuel cells. One of the suggested solutions is utilizing a unique flow structure such as a 3-D micro-lattice flow pattern. A 3-D micro-lattice flow configuration is used to enhance the dynamic mechanisms of reactants and water removal capability, thus mitigating the overall transport resistance. In this work, the measured oxygen transport resistances of two unit cells each assembled with a different flow pattern are quantitatively compared to understand the detailed transport mechanisms in the cathode diffusion media. Conventionally, the oxygen transport resistance is obtained from analyzing the corresponding limiting current density. The calculated total resistance is segmented into different resistances induced by three transport mechanisms, which include molecular diffusion, Knudsen diffusion, and ionomer permeation. By systematically varying the experimental conditions, the overall transport resistances of two different unit cells are measured and disintegrated. The resistance caused by the molecular diffusion is determined from varying pressure, while the ionomer permeation portion of the resistance is segmented by considering multiple relative humidity points, and the rest is considered to be induced by Knudsen diffusion. When comparing the two sets of dissected measurements, the unit cell with the 3-D micro-lattice flow configuration showed a noticeably smaller resistance. Additionally, the analyzed results showed that the molecular diffusion portion of the resistance is the most, if not only, responsible segment for the decrease in the overall resistance. To understand the solitary change in the quantity, the flow rate was increased to identify the effect and presence of advection on the oxygen transport in the cathode medium. It is shown that the presence of advection is evident

as with the 3-D micro-lattice, the only change is shown in the molecular diffusion portion of the resistance, whereas the effect is absent with the parallel channel.