Preparation and characterisation of carbon-supported palladium nanoparticles for oxygen reduction in low temperature PEM fuel cells

Pd nanoparticles have been synthesised using different reducing agents, including ethylene glycol (EG), formaldehyde and sodium borohydride and their activity for the oxygen reduction reaction (ORR) evaluated. The use of EG led to the best morphology for the ORR and this synthetic method was optimised by adjusting the system pH. Carbon-supported Pd nanoparticles of approximately 7 nm diameter were obtained when reduction took place in the alkaline region. Pd synthesised by EG reduction at pH 11 presented the highest mass activity 20 A g(-2) and active surface area 15 m(2) g(-1). These synthetic conditions were used in further synthesis. The effect of heat treatment in H-2 atmosphere was also studied; and increased size of the palladium nanoparticles was observed in every case. The Pd/C catalyst synthesised by reduction with EG at pH 11 was tested in a low temperature H-2/O-2 (air) PEMFC with a Nafion (R) 112 membrane, at 20 and 40 degrees C. Current densities at 0.5 V, with O-2 fed to the cathode, at 40 degrees C were 1.40 A cm(-2) and peak power densities 0.79 W cm(-2), approximately; which compared with 1.74 A cm(-2) and 0.91 W cm(-2), respectively for a commercial Pt/C.