Dampening Humidifier Effects on Electrochemical Pressure Impedance Spectroscopy (EPIS) Fuel Cell Diagnostics
Authors: Schneider-Coppolino Merissa , Zhang Qingxin , Niroumand Amir , Homayouni Hooman , Gates Byron D. 
Published: August 2024

Fuel cells are versatile, low-emission alternative energy sources, but their optimization and failure analyses are complex due to their black-box nature. Conventional in-situ diagnostic techniques such as electrochemical impedance spectroscopy (EIS), are widely used to deconvolute transient processes within operating fuel cells. EIS is invaluable to understanding some of these processes, but other processes within the cell, such as mass transport and individual water fluxes, get overshadowed and are hard to detect.
In an effort to provide information that is currently unattainable with conventional fuel cell diagnostic techniques, this project focuses on the further development of electrochemical pressure impedance spectroscopy (EPIS). EPIS is based on a pressure alternating frequency response analysis (pFRA). This diagnostic method is similar to EIS, except that it implements mechanical perturbations in the form of gas pressure oscillations, rather than voltage or current oscillations, to achieve an electrochemical response. Since EIS is based on electrical perturbations, the results are primarily based on the transport of electrons and provides electron-based performance metrics, including charge transfer, adsorption, diffusion, and double-layer behaviors. Conversely, the mechanical perturbations in EPIS enable the investigation of non-electron-based mechanisms, such as flow and gas transport resistances.
This project builds from the work of Zang et al., who developed an experimental setup for EPIS and showed that pressure perturbations affect local reaction rates and transport phenomena within the cell, providing a sinusoidal voltage response.1 Prior work focused on the EPIS signal at the outlet, as the oscillation diminished by the time it reached the inlet of the cell. Shirsath et al. proposed that the excess volume of the humidifier before the fuel cell dampens the pressure oscillation signal and acts as an extra capacitor.2 To mitigate this, this project focused on the implementation of additional hardware between the humidifier and the cell inlet to act as a counter resistance and amplify the inlet pressure oscillation and subsequent EPIS response. The setup was fully explored through a series of targeted tests focused on identifying the most effective system parameters to validate the configuration and achieve optimal results. This hardware implementation aims to reduce the system effects and provide a more consistent pressure oscillation down the channel to further decouple the EPIS response and provide more accurate diagnostics of the cell.

1 Zhang, Q., Homayouni, H., Gates, B. D., Eikerling, M. H., & Niroumand, A. M. (2022). Electrochemical Pressure Impedance Spectroscopy for Polymer Electrolyte Fuel Cells via Back-Pressure Control. Journal of The Electrochemical Society, 169(4), 044510.

2 Shirsath, A. V., Raël, S., Bonnet, C., Schiffer, L., Bessler, W., & Lapicque, F. (2020). Electrochemical pressure impedance spectroscopy for investigation of mass transfer in polymer electrolyte membrane fuel cells. Current Opinion in Electrochemistry, 20, 82–87.