Oxygen Reduction Reaction Catalyzed by Noble Metal Clusters

Highly-efficient catalysts for the oxygen reduction reaction (ORR) have been extensively investigated for the development of proton exchange membrane fuel cells (PEMFCs). The state-of-the-art Pt/C catalysts suffer from high price, limited accessibility of Pt, sluggish reaction kinetics, as well as undesirable long-term durability. Engineering ultra-small noble metal clusters with high surface-to-volume ratios and robust stabilities for ORR represents a new avenue. After a simple introduction regarding the significance of ORR and the recent development of noble metal clusters, the general ORR mechanism in both acidic and basic media is firstly discussed. Subsequently, we will summarize the recent efforts employing Pt, Au, Ag, Pd and Ru clusters, as well as the alloyed bi-metallic clusters for acquiring highly efficient catalysts to enhance both the activity and stability of ORR. Molecular noble metal clusters with definitive composition to reveal the relevant ORR mechanism will be particularly highlighted. Finally, the current challenges, the future outlook, as well as the perspectives in this booming field will be proposed, featuring the great opportunities and potentials to engineering noble metal clusters as highly-efficient and durable cathodic catalysts for fuel cell applications.