Taking Advantage of the Operating Heterogeneities in PEMFC: Numerical Study with a Pseudo-3D Model

Abstract

A Proton Exchange Membrane Fuel Cell (PEMFC) is an open system. Its operation is therefore inherently heterogeneous. Indeed, in a cell, electrochemical reactions do not take place homogeneously on the active surface area. It has already been pointed out that operating heterogeneities over a large cell active area can cause a decrease of performance and durability. In fact, studies to date have focused on the relation between operating heterogeneities and local degradation on the active surface area for a small selection of operating conditions.The objective of our study is to find a way to control the current, temperature and water distributions by adjusting the operating conditions to, hopefully, optimize performance and improve durability. In order to define those control strategies, a better understanding of the heterogeneities for a wide range of operating conditions is necessary. To that end, a first numerical approach seems to be the most appropriate.This numerical study is based on a pseudo-3D multi-physics and single-phase model of a large cell, developed on COMSOL Multiphysics®. One novelty of our study, from a methodological point of view, is the calibration of the model. Instead of calibrating the model with the electrochemical response of a large cell for some chosen operating conditions as per usual, it has been calibrated with the electrochemical response of a small cell (1.8 cm²), called differential cell, emulating local operating conditions on a larger cell. Three areas of the large cell were emulated for different operating conditions: inlet, middle and outlet. Once calibrated, the pseudo-3D model was used to calculate the distributions for 108 operating conditions, which were chosen from a full factorial design of experiment defined according to the automobile application of PEMFC. The statistical analysis of these simulation results will give the influence of operating conditions (gases pressure, the magnitude and orientation of the thermal gradient of the cooling fluid, gases temperature and relative humidity) on the current density, temperature and water distributions on the active surface area. These results will later be useful for the design of strategies for controlling heterogeneities, which will be finally tested on PEM stack. Figure 1