Effects of pumping power on oxygen transport and performance of proton exchange membrane fuel cell

Abstract

BackgroundPumping power (PP), determined by the resistance of the gaseous reactants flowing in flow fields, significantly affects the net output power density of proton exchange membrane fuel cells (PEMFCs), especially on the air-cooled PEMFCs. No previous studies on the oxygen transport performance of PEMFCs operated at high PPs are available. Novel flow channels are needed to serve the PEMFC applications with intermediate PP. MethodsThe fluid flow, heat, and mass transport processes in a steady-state PEMFC were simulated using a three-dimensional, two-phase, and non-isothermal model, with the oxygen concentration distributions, its interfacial fluxes, and the so-yielded pressure difference and electric current density being reported. Three flow fields were studied: parallel, serpentine, and a novel bamboo shape. Significant findingsThere is a threshold PP above which the current density reaches a plateau, counterbalanced by the increasing resistance built up by water accumulation at the cathode. Both the threshold PP and the maximum current density of the serpentine flow field (0.8 W, 1.83 A cm−2) are higher than those of the parallel flow field (0.1 W, 1.71 A cm−2) since the governing oxygen transport for the former depends on the convection and for the latter, the diffusion. A bamboo shape flow field has been proposed to compensate for the drawback of high PP needed for the serpentine flow field. The threshold PP is reduced to 0.5 W, with a maximum current density of 1.78 A·cm−2. The parallel flow field can be applied at a high mass flow rate and low PP scenario; at a low mass flow rate and high PP case, the serpentine flow field can be applied; in between, the bamboo flow field can be applied to be an appropriate alternative.