Characterization of water transport and flooding conditions in polymer electrolyte membrane fuel cells by electrochemical pressure impedance spectroscopy (EPIS)

The manuscript focuses on the use of pressure induced impedance spectroscopy (EPIS) to investigate transport phenomena in a membrane fuel cell in the presence of liquid water. A step-by-step approach is used to differentiate the different phenomena. Experiments were conducted in oxygen or air, at different currents, flowrates or relative humidities, with different GDLs (with or without MPL and PTFE) and in new or aged assemblies. In the presence of oxygen, over the whole frequency range (1-10 0 0 mHz), the greater the amount of liquid water, the higher the impedance modulus. This observation is accentuated with the absence of MPL, PTFE, and for an aged assembly. For frequencies below 10mHz, water transport is problematic, while gas transport appears impacted for frequencies above 100mHz. For a less efficient GDL with a large water excess, the phase shift is shifted toward negative values over 100mHz. In the presence of air, diffusion is superimposed on the previous phenomena: increase in the EPIS modulus at high frequencies and strong decrease in the phase shift. In the case of air and conditions close to flooding, the EPIS modulus increases severely in the range 0.1-1Hz and the phase shift increases strongly in positive values between 1-30 mHz.(c) 2022 Elsevier Ltd. All rights reserved.