In Situ Fabrication of PtCo Alloy Embedded in Nitrogen‐Doped Graphene Nanopores as Synergistic Catalyst for Oxygen Reduction Reaction

Abstract

embedded metal nanoparticles in nanopores is essential for catalytic investigation.In the present study, we demonstrate a general and scalable synthesis approach to PtCo nanoparticles embedded in nitrogen-doped graphene nanopores (PtCo/NPG) through direct in situ etching by platinum phthalocyanine (PtPc) and cobalt phthalocyanine (CoPc) in pristine graphene. To our knowledge, no attention has been given to the use of PtPc as precursor to alloy formation. Nitrogen-rich PtPc and CoPc supply abundant N sources, as well as in situ-formed nano pores and alloy nanoparticles generated on the graphene sheets. Nanopore edges act as the anchoring sites for PtCo nanoparticles and exert a synergetic coupling effect between nanopores and PtCo nanoparticles. The strong interactions between PtCo nanoparticles and nanopores supply a possible means to modulate the electronic properties of PtCo nanoparticles, which helps to partially inhibit Pt oxidation and dissolution during ORR. Furthermore, this unique structure may reduce the dissociation activation energy of molecular O 2 and sequentially enhance the electrocatalytic ORR activity and durability. The obtained PtCo/NPG showed superb electrocatalytic activity and stability for ORR, outperforming the state-of-the-art catalyst Pt/C.The fabrication of PtCo/NPG hybrid is demonstrated in Scheme 1 . Amounts of PtPc, CoPc, dipyridylacetylene (dpa), glucose, and graphene were mixed together and stirred in water for 12 h. CoPc and PtPc can be easily coordinated to both ends of dpa through the bond formed between the pyridine of dpa and the Co, Pt center in CoPc, PtPc, respectively, during refl ux, and then the molecules can be dispersed on the basal plane of graphene uniformly. The mixture was further coated with a thin layer of amorphous carbon via hydrothermal carbonization of glucose. The thin carbon layer can reduce the sublimation of PtPc and CoPc during pyrolysis and obviously decrease agglomeration. The obtained nanocomposites were fi nally annealed under N 2 atmosphere at 700 °C for 2 h to yield PtCo/ NPG nanohybrid. For comparison, a similar reaction procedure was conducted using only PtPc as precursor (Pt/NPG). Moreover, potassium tetrachloroplatinate (II) and cobalt nitrate were reduced on nitrogen-doped graphene (NG) and pristine graphene (G) by adding sodium borohydride to obtain PtCo-supported materials, which were denoted as PtCo/NG and PtCo/G.Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to investigate the microstructures and morphology of PtCo/NPG. As depicted in Figure 1 a and Figure S1 (Supporting Information), PtCo/NPG displays Recently, graphene has attracted considerable attention for its several advantages, such as extraordinarily large surface area and enhanced conductivity; moreover, graphene has been used to disperse metal nanoparticles and thus improve the performance of oxygen reduction reaction (ORR). [ 1 ] The distribution and morphology of metal nanoparticles in graphene can be easily controlled. However, the dist...

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