An electro-kinetic study of oxygen reduction in polymer electrolyte fuel cells at intermediate temperatures

The oxygen reduction process in polymer electrolyte fuel cells (PEMFCs) was in-situ investigated at intermediate temperatures (80°–130 °C) by using a carbon supported PtCo catalyst and Nafion membrane as electrolyte. To overcome the Nafion dehydration above 100 °C, the experiments were carried out under pressurized conditions. Electro-kinetic parameters such as reaction order and activation energy were determined from the steady-state galvanostatic polarization curves obtained for the PEM single cell. Negative activation energies of 40 kJ mol−1 and 18 kJ mol−1 were observed at 0.9 V and 0.65 V, respectively, in the temperature range 100°–130 °C. This was a consequence of ionomer and membrane dry-out. The ionomer dry-out effect appears to depress reaction kinetics as the temperature increases above 100 °C since the availability of protons at the catalyst–electrolyte interface is linked to the presence of proper water contents. An oxygen reduction reaction of the first order with respect to the oxygen partial pressure was determined at low current densities. Maximum power densities of 990 mW cm−2 and 780 mW cm−2 at 100 °C and 110 °C (H2–O2) with 100% R.H., were achieved at 3 bars abs.

► Oxygen reduction is studied at intermediate temperatures in PEMFCs.
► A positive reaction order is observed at intermediate temperatures.
► The ionomer dry-out negatively affects reaction kinetics at high temperatures.