Analysis of gas transport phenomena in a polymer electrolyte fuel cell by electrochemical pressure impedance spectroscopy

Electrochemical pressure impedance spectroscopy (EPIS) was introduced in view to differentiating transport/transfer phenomena of gas and liquid occurring in electrochemical cells. This work aimed at measuring EPIS impedance in a 100 cm(2) membrane fuel cell upon predominant control from gas transport, in conditions where the presence of liquid water is little significant. Operating the fuel cell with pure oxygen allowed observation of gas convection: EPIS impedance modulus was below 1 mu V Pa(-1 )in the frequency range 1 mHz-1 Hz, whereas the phase shift decrease did not exceed 30 degrees near 200 mHz with an MPL-free gas diffusion layer (GDL). Conversely, occurrence of diffusion phenomena with oxygen diluted into nitrogen or helium is revealed by the strong increase in the EPIS modulus up to 12-30 mu V Pa-1 near 500 mHz depending on the nature of the diluting gas, the GDL, and the excess in fed oxygen. Corresponding phase shift decreased regularly from nearly 0 degrees at 1 mHz to approx. -200 degrees at 1 Hz. The presence of liquid water and its poor management by the MPL-free GDL aggravates gas transport situation in the porous layers, in particular with more negative phase shifts and higher modulus at high frequency.

Automated summary

Electrochemical pressure impedance spectroscopy (EPIS) is used to differentiate gas and liquid transport/transfer phenomena in electrochemical cells. This study investigates EPIS impedance in a membrane fuel cell under predominant gas transport control, with little presence of liquid water. Results show that operating the fuel cell with pure oxygen allows observation of gas convection, while oxygen dilution leads to diffusion phenomena. The presence of liquid water and poor management of it worsen gas transport situation in the porous layers.