Atomically Dispersed Ni-N 4 Sites Assist Pt 3 Ni Nanocages with Pt Skin to Synergistically Enhance Oxygen Reduction Activity and Stability.

Currently, the rarity and high cost of platinum (Pt)-based electrocatalysts seriously limit their commercial application in fuel cells cathode. Decorating Pt with atomically dispersed metal-nitrogen sites possibly offers an effective pathway to synergy tailor their catalytic activity and stability. Here active and stable oxygen reduction reaction (ORR) electrocatalysts (Pt 3 Ni@Ni-N 4 -C) by in situ loading Pt 3 Ni nanocages with Pt skin on single-atom nickel-nitrogen (Ni-N 4 ) embedded carbon supports are designed and constructed. The Pt 3 Ni@Ni-N 4 -C exhibits excellent mass activity (MA) of 1.92 A mg Pt -1 and specific activity of 2.65 mA cm Pt -2 , together with superior durability of 10 mV decay in half-wave potential and only 2.1% loss in MA after 30 000 cycles. Theoretical calculations demonstrate that Ni-N 4 sites significant redistribute of electrons and make them transfer from both the adjacent carbon and Pt atoms to the Ni-N 4 . The resultant electron accumulation region successfully anchored Pt 3 Ni, that not only improves structural stability of the Pt 3 Ni, but importantly makes the surface Pt more positive to weaken the adsorption of *OH to enhance ORR activity. This strategy lays the groundwork for the development of super effective and durable Pt-based ORR catalysts.