Abstract
We report the first investigation into a quaternary-doped graphene catalyst material for the oxygen reduction reaction (ORR) under alkaline conditions. The material was synthesized via direct pyrolysis of graphene oxide (GO) with boron, nitrogen, phosphorus and sulfur precursors. The resulting BNPS-Gr catalyst was thoroughly characterized and its composition found via XPS to be 6.4% (B), 6.1% (N), 2.6% (P) and 0.5% (S), while HR-TEM imaging shows a few-layered graphene structure. Electrochemical investigations into the catalytic activity towards the ORR show improved performance of the quaternary-doped graphene with the effective number of electrons transferred being ca. 3.7, compared to single-doped graphenes (2.9–3.2) and significantly lower peroxide production. This demonstrates BNPS-Gr to be a promising alternative to current Pt-group catalysts for the ORR, especially in methanol-fuelled fuel cells, where the presence of methanol in the cathode side from the fuel crossover is shown not to affect the performance of the quaternary-doped graphene catalyst.
Highlights
Graphene is increasingly finding application within catalysis due to its intrinsic properties [1,2,3], and in particular its catalytic activity towards the oxygen reduction reaction (ORR) has generated significant interest [4,5]
This catalyst is physically characterized using high-resolution transmission electron microscopy (HR-TEM), scanning TEM (STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS), and its electrochemical ORR performance is compared with the equivalent singledoped catalysts
The incorporation of B, N, P and S into the graphene structure is clearly visualized from the STEM-EDX images reflected in Fig. 2, where it can be observed that a great amount of oxide groups still remain after the thermal treatment
Summary
Graphene is increasingly finding application within catalysis due to its intrinsic properties [1,2,3], and in particular its catalytic activity towards the oxygen reduction reaction (ORR) has generated significant interest [4,5]. Several methods have been proposed for the doping of graphene with heteroatoms, including chemical vapour deposition (CVD), ball milling, bottom-up synthesis, thermal annealing, wet chemical method, plasma treatment with heteroatom atmosphere or arc-discharge [31] Among these methods, CVD is one of the most widespread, it is a relatively complex process whose application entails the use of hazardous precursors and gases, contamination by transition metal reagents, high cost of the process and a low yield [32]. We present a novel metal-free quaternary-doped graphene synthesized via an easy method of GO thermal annealing in presence of B, N, P and S dopant precursors under an inert atmosphere This catalyst is physically characterized using high-resolution transmission electron microscopy (HR-TEM), scanning TEM (STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS), and its electrochemical ORR performance is compared with the equivalent singledoped catalysts
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