Experimental evaluation of the dynamic behavior of an air-breathing fuel cell stack

The performance of an air breathing proton exchange membrane (PEM) fuel cel l stack has been experimentally measured to investigate the steady-state an d transient effects of temperature, humidity and air flowrate. The results show that hydrogen leaks to the cathode through the membrane causing intern al heating of the fuel cell. The leakage rate is found to be linearly depen dent on the pressure difference between the hydrogen side and air side whic h is at atmospheric pressure. Temperature was found to not have a significa nt effect on the PEM performance, except through its indirect effect on hum idity. The humidity of the membrane is found to be the most significant var iable in determining the fuel cell performance. The airflow also influences the performance of the fuel cell directly by supplying oxygen and indirect ly by influencing the humidity of the membrane. Experiments show that an op timum air flowrate exists that is much larger than required for stoichiomet ric oxidation of the fuel.