Influence of Gas Composition on the Polymer Membrane Fuel Cell (PEFC) Performance

Kurzfassung

Polymer electrolyte fuel cells (PEFCs) are one of the most interesting alternatives for a pollution-free energy production. One of the major challenges in the development of PEFCs is to exploit the whole capacity that inherits a given membrane electrode assembly (MEA). Mass transport effects lead to an inhomogeneous electrochemical activity over the electrode area. In order to investigate in detail the influence of gas composition on the cell performance and to elucidate mass transport effects in the cell current-voltage curves and electrochemical impedance spectra (EIS) were recorded. The cathode of the PEFC was fed with gas with different oxygen content ranging from 100% to 5%. The other gas component was helium or nitrogen. Results can be used to improve cell components, to validate models and to detect inappropriate detrimental operating conditions of the fuel cell. The measured EIS can be simulated using an equivalent circuit taking into account the uncompensated membrane resistance (electrolyte resistance), kinetics of the oxygen reduction reaction, the kinetics of hydrogen oxidation reaction and the porous structure of anode and cathode. The used model is the cylindrical-pore model proposed by Göhr, where the impedance elements of the pore’s wall surface are the double layer capacity (Cdl), charge transfer resistance (Rct) and impedance elements of oxygen diffusion (Zdiff).