Size-Selected Platinum Subnanocluster Catalysts Alloyed with Nickel (Pt_nNi_m, n = 3–7, m = 1–3) or Cobalt (Pt_nCo_m, n = 4–8, m = 1–2) for the Oxygen Reduction Reaction

Proton-exchange membrane fuel cells (PEMFCs) are promising candidates for sustainable energy due to their low operating temperatures and carbon-neutral potential. However, their widespread deployment is hindered by the high cost and limited activity of conventional platinum (Pt)-based catalysts for the oxygen reduction reaction (ORR). In this study, we present a structure-based investigation of the ORR activity of atomically precise Pt-based subnanoclusters (sub-NCs), alloyed with nickel (Ni) or cobalt (Co), prepared via size- and composition-selective deposition using magnetron sputtering. For a series of carbon-supported alloyed sub-NCs, Pt n Ni m ( n = 3–7) and Pt n Co m ( n = 4–8), the ORR mass activities were evaluated, with Pt 5 Ni 1, Pt 5 Co 1, Pt 6 Ni 2, and Pt 6 Co 2 exhibiting activities 2.1–2.5 times higher than that of commercial standard Pt/C. Combined structural analysis using X-ray absorption fine structure and density functional theory revealed charge redistribution within the alloyed sub-NCs, where bonding to the carbon support is mediated by two Pt anchor atoms, while Ni and Co atoms remain unanchored. These findings demonstrate that atomicity-controlled alloy sub-NCs provide a rational design platform for next-generation PEMFC catalysts with enhanced activity and a tunable electronic structure.