Correlating electrochemical active surface area with humidity and its application in proton exchange membrane fuel cell modeling

The electrochemical active surface area has a vital influence on the performance of proton exchange membrane fuel cells. In this study, a universal semi-empirical equation of the electrochemical active surface area in the catalyst layer of fuel cells is proposed based on self-designed experiments, aiming to improve the predictive accuracy of numerical models under low humidity conditions. The generalization of this equation is also verified with the other nine catalyst layers of different compositions. At very low water content corresponding to low inlet humidification operations, the electrochemical active surface area is generally low and increases sharply with the increment of water content. When the water content exceeds a certain threshold value, the electrochemical active surface area becomes independent of water content. In addition, the electrochemical active surface area significantly decreases as the operating temperature increases. Consequently, including this newly proposed electrochemical active surface area equation in conventional full-cell models is of significant importance to accurately predict the activation loss and performance of fuel cells under both cold-start and normal operation conditions, especially at low humidification, which is validated against experimental data. In contrast with the conventional constant electrochemical active surface area assumption, this equation improves the model accuracy from about 70% to be higher than 90% under low humidity conditions.