Measurement and analysis on current density distribution of long-channel proton exchange membrane fuel cell: Insights from operational conditions and electrochemical impedance

This work extensively examines how various operational conditions (temperature, pressure, humidity, and stoichiometric ratio) affect both the local current density (LCD) uniformity and performance of a long-channel proton exchange membrane fuel cell (PEMFC), utilizing a segmented anode flow field plate equipped with LCD measurement capabilities. As current density increases, charge transfer resistance (Rct) decreases rapidly before stabilizing at a lower level, while mass transfer resistance (Rmt) exhibits an exponential increase. Under full humidification, LCD linearly decreases along the channel and pronounced non-uniformities in LCD arise due to the “flooding” of the cathode outlet at higher current densities. Higher temperatures, pressures, and stoichiometric ratios effectively mitigate “flooding”, decreasing Rmt and improving LCD uniformity, thereby enhancing PEMFC performance. However, lower cathode relative humidities can improve voltage but worsen the LCD uniformity under medium and high current densities, and both the voltage and LCD uniformity can be improved by appropriately reducing anode relative humidity. Crucially, a linear relationship between LCD non-uniformity and Rmt/Rct has been identified, which is useful for comparing the LCD non-uniformity under different combinations of operating conditions, particularly under high current densities. These findings highlight the value in quickly screening suitable operating conditions through electrochemical impedance spectroscopy to optimize the PEMFC performance, as well as the guidelines for the development of high-power-density and long-life PEMFCs.