Polymer electrolyte fuel cell experimental and characterization studies using electrochemical impedance spectroscopy

The need for an efficient, nonpolluting power source has resulted in increased attention in Polymer Electrolyte Fuel Cells (PEFC's) powered applications focusing in low cost, high-reliability and high performance. Additionally, the low operating temperatures and high-energy conversion make the PEFC a convenient option. In this research impedance spectroscopy is used for the characterization and understanding of fuel cell performance losses. A H₂/O₂ PEFC with a Pt/Ru-Nafion ® 117 membrane-electrode assembly was used in a range of 3.4 to 9.6 and 1.6 to 5.1 mL/min for H₂ and O₂ flow rates, respectively. Cell temperatures were between 27°C to 47°C. The technique allowed us to determine the sources and nature of the voltage losses and the kinetics effects. Anode charge transfer resistance values were around 0.019 ohms. Membrane resistance values (around 0.5 ohm-cm2) and charge transfer values as a function of overpotential were determined (Cathode charge transfer resistance values presented an average Tafel slope of 116 mv/dec). Other findings include the diffusion problems encountered when reactant gases are not fed stoichiometrically.