Ultrasmall Palladium Nanoclusters as Effective Catalyst for Oxygen Reduction Reaction

The recent prosperity of ultrasmall gold nanoclusters makes it desirable to expand the family of clusters to other metals. Here, we present a one-phase approach for synthesizing thiolate-protected palladium nanoclusters with a mass of approximately 5 kDa. Such nanoclusters are further evaluated for the oxygen reduction reaction in alkaline solutions. Ligand-on palladium nanoclusters exhibit an onset potential of −0.09 V (vs. Ag/AgCl) and superior durability in open air. With ligands removed, the palladium nanoclusters display an onset potential of −0.02 V and a higher mass activity (272.4 A g−1 at the potential of −0.15 V) than that of Pt/C (166.6 A g−1). Kinetic investigation indicates a direct four-electron reduction pathway over palladium nanoclusters, which is preferred in oxygen reduction, owing to enhanced power generation. The efficient catalytic performance of palladium nanoclusters makes them an excellent candidate as electrocatalysts in fuel cell technology.