Control-oriented modeling and exploration of hygrothermal characteristics of air-cooled proton exchange membrane fuel cell

Achieving high output performance of air-cooled proton exchange membrane fuel cells relies on appropriate temperature and water content management. However, the open-cathode structure of the fuel cell stack leads to the coupling of thermal-water controls and makes the development of management strategies more challenging. This paper studies the effects of temperature and water content on the system performance theoretically and experimentally. The results show that there exists an optimum temperature at a specific current, at which we can optimize the stack output voltage. We analyzed the stack voltage changes and various voltage losses under three anode purge strategies. The results reveal that the losses of stack activation and mass transfer increase significantly when the purge valve closes for a long time, 20 min for the system under this study. With electrochemical impedance spectroscopy technology, we found that the voltage drops rapidly and irreversibly when the stack activation loss exceeds a certain limit, defined as the protective activation resistance. A control-oriented dynamic model based on water transport, electrochemistry, and heat balance theories was developed and verified by experiments. The relationship curves of the current-optimal temperature and the current-protective activation resistance were obtained from the experiment results, which can be used as the controller's reference input and upper limit, respectively. Finally, we proposed an automatic purge strategy for air-cooled PEMFC based on electrochemical impedance spectroscopy.