Oxygen Reduction Electrocatalysis on Ordered Intermetallic Pd–Bi Electrodes Is Enhanced by a Low Coverage of Spectator Species

The sluggish rate of the oxygen reduction reaction (ORR) reduces the performance of fuel cell devices. We demonstrated that ordered intermetallic Pd 3 Bi and Pd 31 Bi 12 are up to ∼11× more active than state-of-the-art Pt/C and Pd/C catalysts for the ORR. Temperature-dependent electrochemical measurement indicates that the activation energy ( E a ) for the ORR on Pd 31 Bi 12 and Pd/C is lower than that of Pd 3 Bi and Pt/C under a wide range of overpotentials. The resulting E a indicates that a larger pre-exponential factor (surface site availability) is the primary reason for the enhanced ORR performance on Pd–Bi intermetallics. The increased number of active sites provides more available sites for O 2 activation and conversion, which agrees with the E a measurements. This study deepens our understanding of catalyst–electrolyte and catalyst–adsorbate interaction during the ORR on state-of-the-art Pd–Bi ordered intermetallic catalysts. Fundamental knowledge gained from this study suggests that further increasing the tolerance of the electrode active sites to the adsorption of spectator species by designing appropriate catalysts can improve the ORR performance.