Surface Manipulation\non Pt<sub>2.2</sub>Ni(111) Nanocatalysts\nfor Boosting Their ORR Performance in Alkaline Media

We have previously shown that Pt–Ni\nalloy nano-octahedra\nwith {111} facets exhibit outstanding electrochemical performance\nin the oxygen reduction reaction (ORR) in acidic media when their\nsurfaces are finely tailored at the atomic level. In this investigation,\nwe further refine the surface structure of Pt<sub>2.2</sub>Ni octahedral\nnanocatalysts to improve ORR performance in a 0.1 M KOH solution using\ndiverse surface manipulation techniques. Through systematic analysis\nusing electrochemical CO stripping, cyclic voltammetry, and X-ray\nphotoelectron spectroscopy, we examined the surfaces of Pt<sub>2.2</sub>Ni octahedral nanocatalysts pretreated with various methods, including\netching in acetic acid or perchloric acid, and subsequent electrochemical\nactivation in an alkaline solution or an acidic solution. Among these\ntreatments, those involving acidic media, particularly electrochemical\ncycling in acidic electrolytes, demonstrated significantly enhanced\nORR activity in 0.1 M KOH. The latter exhibited a mass activity of\n2.95 A/mg<sub>pt</sub> and a specific activity of 8.71 mA/cm<sup>2</sup> at 0.90 V, surpassing state-of-the-art Pt/C by 12-fold and 34-fold,\nrespectively. Furthermore, this identified nanocatalyst displayed\nrobust stability, with negligible activity decay observed after 10,000\ncycles. This study suggests that the improved ORR activity can be\nattributed to the Pt-rich surfaces with well-preserved {111} lattices\non the surface-modified Pt–Ni nano-octahedra.