Synergistic increase of oxygen reduction favourable Fe–N coordination structures in a ternary hybrid of carbon nanospheres/carbon nanotubes/graphene sheets

Abstract

A Fe/N co-doped ternary nanocarbon hybrid, with uniform bamboo-like carbon nanotubes (CNTs) in situ grown on/between the single/few-layer graphene sheets interspaced by carbon nanosphere aggregates, was prepared through a one-pot heat treatment of a precursor mixture containing graphene oxide, Vulcan XC-72 carbon nanospheres, nitrogen rich melamine and small amounts of Fe ions. Physical characterization including electron microscopic images, N2 adsorption-desorption isotherms, pore size distribution, XPS, XRD, Mössbauer spectra, and EDX revealed that the 0-D/1-D/2-D ternary hybrid architecture not only offered an optimized morphology for high dispersion of each nanocarbon moiety, while the carbon nanosphere interspaced graphene sheets have provided a platform for efficient reaction between Fe ions and melamine molecules, resulting in uniform nucleation and growth of CNTs and formation of high density Fe-N coordination assemblies that have been believed to be the active centers for the oxygen reduction reaction (ORR) in carbon-based nonprecious metal electrocatalysts. In the absence of graphene oxides or carbon nanospheres, a similar heat treatment was found to result in large amounts of elemental Fe and Fe carbides and entangled CNTs with wide diameter distributions. As a result, the ternary Fe/N-doped nanocarbon hybrid exhibits ORR activity much higher than the Fe-N doped single or binary nanocarbon materials prepared under similar heat treatment conditions, and approaching that of the state-of-the-art carbon-supported platinum catalyst (Pt/C) in acidic media, as well as superior stability and methanol tolerance to Pt/C.

Iron–nitrogen co-doped hierarchically mesoporous carbon spheres as highly efficient electrocatalysts for the oxygen reduction reaction

“…Precious works reported two different models to describe the active sites in M-N/C catalyst for ORR. One is the M-N x species, 27,29,47 and the other is the doping N atoms in the carbon surface. [48][49][50] In our control experiment (Fig.…”

Rational Design and Synthesis of Low-Temperature Fuel Cell Electrocatalysts

“…16c produced a measured area current activity of 9.9 mA cm −2 at 0.9 V iR-free and a peak power density of 0.9 W cm −2 . Other framework substrate methods, such as a combination of various carbon materials [164][165][166] and synthesis with silica template [131,167,168] or NaCl template [169], were also found to create abundant channels/pores to facilitate mass transportation.…”

Surfactant-Template Preparation of Polyaniline Semi-Tubes for Oxygen Reduction

“…The multi-technique characterization have suggested that the enviable performance should be ascribed to the formation of metal-N complexion structures as well as the carbon nanostructures such as thin graphene sheets and nanofibers [10][11][12]. It has been generally accepted that the formation of uniform and ordered carbon nanostructures is very important in enhancing the catalytic activity [10][11][12][13][14][15][16][17][18][19].…”

“…We also prepared the composite of PANIs with graphene nanosheets (GS) that were prepared by high temperature thermal reduction of graphene oxide [17,18]. In this case, 30 mg of GS were added into the CTAB solution to prepare the PANI, which corresponded to a PANI/GS ratio of 1/8.…”