Rsc_cc_c2cc37413g 1..3

Platinum (Pt) with foreign components has been considered as an effective approach to overcome CO poisoning, enhance the activity and decrease the usage of expensive Pt in fuel cells. In particular, PtFe is one of the superior binary Pt-based nanomaterial electrocatalysts for formic acid oxidation, which exhibits high resistance to CO poisoning and is a potential candidate for CO-tolerant alloyed catalysts. Graphene, with a 3D self-supported structure, is promising for catalyst loading to facilitate the mass transfer and maximize the accessibility. We have recently fabricated graphene-based cathodic catalysts for fuel cell applications, and developed shape-defined ternary Pt/PdCu nanoboxes anchored onto a 3D graphene framework (3DGF) as an efficient anodic catalyst for ethanol oxidation. Herein, we design a new complex catalyst system in which a network of ternary Pd2/PtFe nanowires is supported by an open-pore 3DGF. The heterogeneous structure derived from Pd with PtFe under 3DGF support presents a significantly enhanced synergetic role for formic acid oxidation, remarkably outperforming the Pd or PtFe, and the well-established commercial Pt/C catalysts (E-TEK 20% Pt/C). We first developed a facile solvothermal strategy to fabricate 3DGF with in situ formed PtFe nanowires. Ternary heterogeneous Pd2/PtFe network is subsequently formed by reducing PdCl2 through the second solvothermal process (See Experimental details in ESIw). This solvothermal approach works well for the formation of defined 3DGF (Fig. 1a and Fig. S1, ESIw). PtFe nanowires, tens of nanometers in length and 2–5 nm in diameter, are anchored on the graphene sheets (Fig. 1b). The X-ray energy dispersive spectroscopy (EDS) reveals that the sample is mainly composed of C, Pt and Fe elements plus O associated with the solvothermally reduced GO (Fig. 1c). The atomic ratio of Pt and Fe is ca. 1/1.0, consistent with the stoichiometric proportion of initial reactants and the analysis of inductively coupled plasma-mass spectrometry (ICP-MS) (Table S1, ESIw). X-ray diffraction (XRD) pattern of PtFe/3DGF (Fig. 1d) shows the typical (111) diffraction peak of PtFe at ca. 411, apart from the broad peak at 2y E 231 assigned to the (002) plane of stacked graphene. The initial formation of PtFe nanowires is strongly dependent on the graphene planar structure within 3DGF as compared with commercial XC-72 carbon black (Fig. S2, ESIw). Fig. 2a shows the SEM images of Pd2/PtFe attached 3DGF. The 3D microstructures of graphene sheets maintained well after deposition of Pd. Fig. 2b shows the typical TEM image of Pd2/PtFe network on graphene sheets, which has a nanowire diameter of ca. 5–10 nm slightly larger than that of initial PtFe nanowires due to the effective deposition of Pd. Fig. 2c exhibits a high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image of a single Pd2/ PtFe wire. The elemental mappings reveal that Pd, Pt, and Fe are distributed along the nanowire (Fig. 2d–f), where Pt and Fe elements have relatively narrow spatial distributions along the nanowire. Since the deposition of single-phase Pd on 3DGF produces nanoparticles instead of nanowires (Fig. S3, ESIw),