Computational Exploration of Ultra-High Current PEFC Operation with Porous Flow Field

Abstract

A comprehensive 2D+1 computational model has been developed to explore the operation of a polymer electrolyte fuel cell (PEFC) with a porous flow field, also called open metallic element (OME), in the ultra-high current density regime (>2A/cm 2 ). The computational model has been validated to a greater extent than previously published multi-phase models, including in-situ experimental measurement of performance, high frequency resistance (HFR) and net water drag coefficient under a wide range of input relative humidity (RH) conditions. The combined experimental and modeling investigation found that, with the OME used as the flow field, gas phase transport of oxygen is not the limiting factor, even in the ultra-high current regime. The use of OME results in significant performance improvement compared to the conventional land-channel architecture at high current. Instead of oxygen transport limitation, however, anode dry-out limits performance, as confirmed by net water drag data from both experiment and model. With the OME architecture, diffusion flow is the dominant transport mechanism of water from the catalyst layer to the flow field, compared to capillary action and convection. Results also highlight the utility of experimentally-determined anode dry-out limits for validating multi-phase models.

Measurement of Net Water Drag Coefficients in Polymer Electrolyte Fuel Cells under Cathode-Dry Conditions

“…Their results indicated that α NWD increased with i, though α NWD remained negative when i was less than about 2.5 A cm −2 . Zheng and Srouji et al 19,20 reported the dependency of α NWD on T cell at a constant i of 2 A cm −2 using the same cell as Zheng et al, 18 and reported that α NWD increased with T cell and turned from negative to positive when T cell exceeded a certain threshold value. Gandomi et al 21,22 investigated the effect of MPL properties on α NWD under various conditions, including cathode-dry condition.…”

“…The effect of operating parameters (cell temperature, pressure, stoichiometric ratio and relative humidity of the inlet gases) and the specifications of the cell components (membrane, electrode, and gas diffusion layer) on the water transport behavior in the cell has been examined by evaluating α NWD . [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Some of those studies focused on the effect of a micro-porous layer (MPL) on the water transport behavior in the cell, 12,13,16,17 because there is a hypothesis that the presence of an MPL on the cathode gas diffusion layer (GDL) would enhance the back-diffusion of water through the membrane from the cathode to anode. 23,24 Based on water balance measurements, Kim et al 16 reported that water transport toward the anode from the cathode increased significantly when an MPL was added to GDL.…”

“…The experimental evaluation of α NWD under cathode-dry condition was reported by Mench and his co-researchers. [18][19][20][21][22] Zheng et al 18 presented the dependency of α NWD on the current density (i) under cathode dry condition when the cell temperature (T cell ) was 60°C and a commercial GDL with MPL (SGL25BC) was applied to the both sides of the cell. Their results indicated that α NWD increased with i, though α NWD remained negative when i was less than about 2.5 A cm −2 .…”

Performance and mass transport in open metallic element architecture fuel cells at ultra-high current density

“…The results of this study provide a comparison between conventional parallel C/L design and an open metallic element for the first time in literature, and show different origins of performance limitation of the two designs. The experimental work also provides validation data for simultaneous modeling efforts of the open metallic element design [23].…”

Modeling of two-phase transport in proton exchange membrane electrolyzer cells for hydrogen energy

“…Among all types of electrolyzer cell systems, PEMEC is providing a promising solution for hydrogen and oxygen production and receiving more and more attention due to their higher energy efficiency/density, faster charging/discharging, and a more compact design [1][2][3][4][5]. A PEMEC has a similar configuration and operating components to a PEM fuel cell (PEMFC) [6][7][8][9][10][11]. Figure 1 shows a three-dimensional geometry schematic of a typical single-cell PEMEC, which consists of flow channels, liquid/gas diffusion layers (LGDL), catalyst layers (CL), and the PEM.…”