Electrochemical Pressure Impedance Spectroscopy As a Diagnostic Method for Hydrogen-Air Polymer Electrolyte Fuel Cells

Abstract

This work introduces a novel in-situ diagnostic method for polymer electrolyte fuel cells (PEFCs) referred to as electrochemical pressure impedance spectroscopy (EPIS). Inspired by electrochemical impedance spectroscopy (EIS), EPIS is a spectroscopic technique that analyses correlations between frequencies in an applied pressure signal and the corresponding voltage response signal in the frequency domain. In EPIS, cathode cell pressure is modulated as a sinusoidal wave by the back-pressure controller (BPC), and the cell voltage is monitored as the response signal. Cell voltage response originates from the membrane electrode assembly (MEA) and, therefore, EPIS can be used to probe cathode transport properties and is sought to develop tools that can be used to study water transport as a function of changes in structure and operating conditions. The cathode reactant gas flows through channels with a pressure drop and, thus, the pressure signal is not identical in different sections of the flow channel. Before studying the relationships between pressure and voltage, it is important to consider the impact of the flow channel on oscillations in the pressure response. The response of the system as a function of correlations between the cathode inlet pressure and the cathode outlet pressure is examined in this work to probe the contributions of the flow channel. Due to instrumental limitations, the BPC can only perform tests at a frequency of 0.1 Hz. Experimental limitations like cathode stoichiometry ratio, cathode flow rate, oxygen partial pressure at cathode, and pressure oscillation amplitude are intensively studied, and therefore, EPIS experimental formalism is defined in this work. Figure 1