A model for water transport in the membrane and an impedance spectroscopy study of the effect of relative humidity on PEM fuel cell parameters

TL;DR

This study presents a comprehensive impedance model for water transport in PEM fuel cell membranes, validated by experimental spectra, revealing how humidity and current density influence water management and electrochemical activity.

Contribution

The paper introduces a coupled impedance and two-phase model for water transport in PEM fuel cells, validated with experimental data across various humidity levels and current densities.

Findings

Higher humidity increases double layer capacitance.

Liquid water transport affects electrochemically active surface area.

Water transport dynamics vary with current density and humidity.

Abstract

Effective water management is essential for the optimal performance of PEM fuel cells. We have developed an impedance model for liquid water transport through the membrane and coupled it with the two-phase model for cathode side impedance. The complete model was fitted to experimental spectra measured at anode/cathode relative humidities (RH) of 32/32\%, 50/50\% and 100/100\% within a current density range of 100 to 1000 mA cm$^{-2}$ and an air flow stoichiometry of 2. Cathode catalyst layer (CCL) saturation decreases with current density due to a growing liquid pressure gradient. For all RH values, the CCL oxygen diffusivity increases dramatically with cell current due to progressive involvement of larger pores into the proton current conversion. Higher RH leads to higher double layer capacitance, which indicates that liquid water increases the electrochemically active surface area.