Using Computational Fluid Dynamics to Analyze Water Transport in PEM Fuel Cells

Proton-Exchange Membrane Fuel Cells (PEMFCs) are clean alternative power sources that harness the chemical energy of hydrogen through an electrochemical reaction with oxygen to form water.

Central to the operation of PEMFCs is the transport of protons from the anode to the cathode through the membrane. This transport is favoured by high water content inside the membrane. However, the protons ‘drag’ water along with them as they travel, thereby resulting in water flux across the catalyst (triple phase boundary) and membrane. This flux results in a non-uniform distribution of water in these layers, thereby reducing proton conductivity. Humidification of the membrane is then essential to reduce Ohmic losses from resistance to ionic transport. Since water is produced at the cathode triple phase boundary (TPB), the reaction can proceed such that there is an over-abundance of water, leading to flooding of the cell. Such flooding conditions may inhibit reactant delivery to the TPB, thereby limiting power production. As a result, a defining challenge of PEMFC operation is the management of water. The aim of this study is to understand the extent to which membrane humidification affects overall fuel cell performance. This is achieved by analysis of water transport in the TPB and membrane, with a focus on water phase changes under different temperatures.

Computational Fluid Dynamics (CFD) was used to model power production in a PEMFC with a fifteen-channel serpentine flow field. The simulation was set up such that the fuel cell would run under near-dehydrating conditions, with the cathode temperature varying from the operating temperature of 353K. From the polarization curves generated, it was found that lower temperatures resulted in higher power production, and peak power production occurred at 0.45V. The phase change of water from vapor to dissolved phase was found to be correlated with higher peak power production under dehydrating conditions.