Active and Stable Pt-Ni Alloy Octahedra Catalyst for Oxygen Reduction via Near-Surface Atomical Engineering

Shape-controlled Pt-based bimetallic nanocrystals with ultrathin Pt-rich surfaces are appealing electrocatalysts for some key electrochemical reactions such as the oxygen reduction reaction (ORR) because of the synergistic tuning of topological atom configuration and strengthened electronic effects. However, it is rather challenging to fabricate such particular structures that can remain intact in harsh electrochemical environments, as such Pt-based nanocatalysts are unable to simultaneously achieve both unparalleled activity and robust stability. Here, a facile surface engineering strategy is proposed and employed to atomically tailor the near-surface structure of the Pt1.5Ni octahedra. The engineered Pt-Ni octahedra consist of an ultrathin Pt-rich shell (similar to two atomic layers) and Pt-rich bulk composition. The optimized octahedral catalyst exhibits superior specific and mass activity (7.7 mA/cm(2) Pt and 1.9 A/mg Pt at 0.9 V) for ORR, similar to 20 and similar to 10 times higher than commercial Pt/C, respectively. The ligand and strain effects arising from the near-surface engineering are unraveled to be responsible for the remarkable ORR activity. Moreover, it shows robust stability with just 9.2% decay in mass activity after accelerated degradation tests (ADTs), as its compositional nature prevents surface Pt atoms and interior Ni atoms from diffusion and dissolution, compared with a decrease of 33% for commercial Pt/C. Our atomical engineered surface strategy illustrates a facile and effective design for a class of Pt-based nanocatalysts with excellent activity and stability.