Effects of flow field combination in proton exchange membrane fuel cells on water management

Abstract

The gas diffusion layer (GDL), a key component of proton exchange membrane fuel cells (PEMFCs), is unevenly compressed by the ribs of both the anode and cathode bipolar plates (BP). The electrical and transport characteristics of the GDL vary with the compression ratio, which influences the supply of reactants, discharge products, and the movement of electrons. This study analyzes the performance differences and overpotentials based on the flow-field combinations. The four combinations, named after the anode flow field, are parallel, rotate, shift, and wavy. The overpotentials of the fuel cell are analyzed using current-voltage curves, electrochemical impedance spectroscopy, and the current interruption method under three operating conditions with different stoichiometric ratios and relative humidity. Through experiments, we decompose the fuel cell overpotential into activation overpotential (ignoring liquid water), ohmic overpotential, concentration overpotential (ignoring liquid water), and liquid water overpotential. The shift combination exhibits excellent performance owing to its high water-discharge effect despite its high ohmic overpotential, whereas the parallel combination exhibits the lowest performance due to flooding. Consequently, by changing the flow field combination under the same operating conditions, the performance improves by up to 33 %.