Island-in-Sea Structured Pt 3 Fe Nanoparticles-in-Fe Single Atoms Loaded in Carbon Materials as Superior Electrocatalysts toward Alkaline HER and Acidic ORR.

In this work, Pt 3 Fe nanoparticles (Pt 3 Fe NPs) with the ordered internal structure and Pt-rich shells surrounded by plenty of Fe single atoms (Fe SAs) as active species (Pt 3 Fe NP-in-Fe SA) loaded in the carbon materials are successfully fabricated, which are abbreviated as island-in-sea structured (IISS) Pt 3 Fe NP-in-Fe SA catalysts. Moreover, the synergistic effect of O-bridging between Pt 3 Fe NPs and Fe SAs, and the ordered internal structured Pt 3 Fe NPs with Pt-rich shells of an optimal thickness contributes to the achievement of the local acidic environments on the surfaces of Pt 3 Fe NPs in the alkaline hydrogen evolution reaction (HER) and the enhancement of the desorption rate of *OH intermediate in the acidic oxygen reduction reaction (ORR). In addition, the electronic interactions between Pt 3 Fe NPs and dispersed Fe SAs cannot only provide efficient electrons transfer, but also prevent the aggregation and dissolution of Pt 3 Fe NPs. Furthermore, the overpotential and the half wave potential of the as-prepared IISS Pt 3 Fe NP-in-Fe SA catalysts toward the alkaline HER and toward the acidic ORR are 8 mV at a current density of 10 mA cm -2 and 0.933 V, respectively, which is 29 lower and 86 mV higher than those (37 mV and 0.847 V) of commercial Pt/C catalysts.