IMPEDANCE SPECTROSCOPY GENETIC PROGRAMMING (ISGP) ANALYSES SETTING PROPER WORKING CONDITIONS OF A POLYMER ELECTROLYTE MEMBRANE FUEL CELL

Abstract

This study demonstrates application of Impedance Spectroscopy Genetic Program (ISGP) for the investigation of a polymer electrolyte membrane fuel cell (PEMFC). It further demonstrates the procedures to optimize the operating conditions of a single cell in a test station. To do that, the effects of temperature, hydrogen/air, and dew point temperature (DPT) on the cell were examined using an Arbin test station. ISGP followed a two-iteration procedure. First, find an out-of-range peak (at high frequencies) that corresponds to the ohmic (series) resistance of the system. Second, finding the models after subtracting the ohmic resistance from the real part of the measured spectrum. This two- step procedure allows solving a Fredholm equation of the second kind with a reasonable accuracy. The resulting peaks making the distribution function of relaxation time (DFRT) were partially assigned to different physical processes in the PEMFCs. ISGP seeks for a distribution of relaxation times that has the form of a peak or a sum of several peaks, assuming the Debye kernel, where each peak is represented by a known analytic function. As a part of the analysis, the peak areas, which correspond to the contribution of the relevant process to the total impedance, were calculated obtaining tendentious behavior depending on the changing environmental parameters. ISGP of PEMFC results in three peaks. The optimized conditions were found to be the ratio of gas flow fuel to air rate 1:7, fuel cell temperature 60°C and dew point temperature 50°C.