The effect of oxygen partial pressure and humidification in proton exchange membrane fuel cells at intermediate temperature (80–120 °C)

Abstract

The integration of proton exchange membrane fuel cells (PEMFCs) in heavy-duty vehicles would be facilitated if operating temperatures above 100 °C were possible. In this work, the effect of temperature in the intermediate range of 80–120 °C is investigated for a commercial membrane electrode assembly (MEA) through polarization curves and electrochemical impedance spectroscopy. The importance of oxygen partial pressure on voltage is systematically studied by decoupling it from humidity and temperature. The results show that adequate operation at intermediate temperature is achievable if the oxygen partial pressure is sufficient. Although the cathode kinetics is faster with rising temperatures, the voltage gain is counteracted by the decreasing equilibrium potential. At intermediate temperature, the water transport is enhanced, levelling out the relative humidity difference between anode and cathode. However, ionic conductivity in the polymer can become limiting at high currents, due to a smaller relative humidity increase at these temperatures. To conclude, a higher operating temperature does not inherently cause a decrease in obtained current density. Rather, the difficulty to simultaneously have sufficient oxygen partial pressure and high relative humidity causes limitations within the cathode that to some extent can be solved by pressurizing the cell.