Cuboctahedral vs. octahedral platinum nanoclusters: insights into the shape-dependent catalytic activity for fuel cell applications

Abstract

The shape of a catalyst plays an important role in any catalytic reaction. The shape-dependent catalytic activities of two platinum nanoclusters (NCs) with cuboctahedral (Pt₇₉) and octahedral (Pt₈₅) shapes have been investigated toward oxygen reduction reaction (ORR). The energetic stability, thermal stability and dissolution limit of the NCs were investigated for their synthesis and practical usage. The four-electron (H₂O formation) vs. two-electron (H₂O₂ formation) ORR mechanisms are systematically studied on the (111) facet of the NCs to gain more insight into the shape-dependent ORR activity and product selectivity (H₂O vs. H₂O₂). Thermodynamic (reaction free energies) and kinetic (free energy barriers and temperature-dependent reaction rates) parameters are investigated to find out the most favored ORR pathway and product selectivity. The NC-based Pt catalysts are very efficient and selective with respect to the previously reported bulk metal (Pt, Pd, and Ag) based catalysts. Our results show that the rate-determining step is no longer a rate-determining step when the reaction is catalyzed by the cuboctahedral NC. The excellent catalytic activity of the cuboctahedral NC is attributed to the surface energy, compressive strain and d-band center position of the catalyst. Our results are very much consistent with experimental findings, and thereby such NC-based electrodes may serve as good candidates for fuel cell applications.