Towards new routes to increase the electrocatalytic activity for oxygen reduction reaction of n-doped graphene nanofibers (original) (raw)
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Nitrogen and fluorine co-doped graphite nanofibers (N–F/GNFs) were synthesized using melamine and ammonium fluoride as precursors, respectively, for use as metal-free catalysts for oxygen reduction reaction (ORR). The N–F/GNF catalyst undergoes structural transformation resulting in wrinkled graphene structures with many open-edge sites when F is doped into N/GNF. The developed catalyst has no effect on CH3OH or CO, which makes it highly desirable as a metal-free electrocatalyst for the ORR. The developed catalyst was subjected to 20,000 repeated potential cycles, no degradation of ORR activity was observed in acidic media. X-ray photoelectron spectroscopy analysis of the N–F/GNF catalyst reveals the presence of active pyridine and graphitic type N with highly active semi-ionic C–F bond in the graphitic structure. First-principles density functional theory calculations further support the formation of graphene structures from the GNF with the interlayer distance increasing from 3.9 to 5.1 Å. The Bader charge analysis predicts the site specificity of F doping in N-doped GNF. This N–F/GNF catalyst delivers a peak power density of 165 mW cm−2 at a load current density of 850 mA cm−2 in a H2/O2 polymer electrolyte fuel cell, as a nonmetallic electrocatalyst in acidic media.
Electrocatalytic oxygen reduction on nitrogen-doped graphene in alkaline media
Applied Catalysis B: Environmental, 2014
Nitrogen-doped graphene nanosheets were prepared from nitrogen precursor and graphene oxide (GO), which was synthesised from graphite by modified Hummers' method. Melamine, urea and dicyandiamide (DCDA) were used as nitrogen precursors and the doping was achieved by pyrolysing GO in the presence of these nitrogen-containing compounds at 800 • C. The N-doped graphene (NG) samples were characterised by scanning electron microscopy and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The oxygen reduction reaction (ORR) was examined on NG-modified glassy carbon (GC) electrodes in alkaline media using the rotating disk electrode (RDE) method. It was found on the basis of the RDE results that nitrogen-containing catalysts possess higher electrocatalytic activity towards the ORR than the annealed GO. Oxygen reduction on this GO material and on NG catalysts prepared by pyrolysis of GO-melamine and GO-urea followed a two-electron pathway at low overpotentials, but at higher cathodic potentials the desirable four-electron pathway occurred. For NG catalyst prepared from GO-DCDA a four-electron O 2 reduction pathway dominated in a wide range of potentials. The half-wave potential of O 2 reduction on this NG catalyst was close to that of Pt/C catalyst in 0.1 M KOH. These results are important for the development of alkaline membrane fuel cells based on non-platinum cathode catalysts.
Bulletin of Materials Science, 2015
Here we report a remarkable transformation of nitrogen-doped multiwalled carbon nanotubes (MWCNTs) to size selective nitrogen-doped graphene quantum dots (N-GQDs) by a two-step electrochemical method. The sizes of the N-GQDs strongly depend on the applied anodic potential, moreover increasing potential resulted in a smaller size of N-GQDs. These N-GQDs display many unusual size-dependant optoelectronic (blue emission) and electrocatalytic (oxygen reduction) properties. The presence of N dopants in the carbon framework not only causes faster unzipping of MWCNTs but also provides more low activation energy site for enhancing the electrocatalytic activity for technologically daunting reactions like oxygen reduction. The smaller size of N-GQDs has shown better performance as compared to the large N-GQDs. Interestingly, N-GQDs-3 (size = 2.5 ± 0.3 nm, onset potential = 0.75 V) show a 30-mV higher positive onset potential shift compared to that of N-GQDs-2 (size = 4.7 ± 0.3 nm, onset potential = 0.72 V) and 70 mV than that of N-GQDs-1 (size = 7.2 ± 0.3, onset potential = 0.68 V) for oxygen reduction reaction (ORR) in a liquid phase. These result in the size-dependent electrocatalytic activity of N-GQDs for ORR as illustrated by the smaller sized N-GQDs (2.5 ± 0.3 nm) undoubtedly promising metal-free electrocatalysts for fuel cell applications.
The effect of nitrogen species on the catalytic properties of N-doped graphene
Scientific Reports, 2021
The production of effective catalysts in the oxygen reduction reaction (ORR) continues to be a great challenge for scientists. A constant increase in demand for energy storage materials is followed by a proportionate increase in the number of reports on electrocatalyst synthesis. The scientific world focuses on environmentally friendly materials synthesized in accordance with the safest possible. In this work, we developed a facile method of obtaining heavy-metal-free electrode materials that are effective in ORR. Graphene-based catalysts were doped using azodicarbonamide (ADC) as the source of nitrogen, then carbonized at high temperatures in the range of 700–900 °C under inert gas flow. The produced materials were tested as catalysts for ORR, which is the most important reaction for Zn–air batteries and fuel cells. All obtained nitrogen-doped graphene foams showed increased catalytic activity in ORR owing to active sites created by nitrogen functional groups on the graphene surfac...
Carbon, 2014
In this work the electrocatalysis of oxygen reduction on nitrogen-doped few-layer graphene/multi-walled carbon nanotube (FLG/MWCNT) composite catalyst has been investigated. These composite materials were prepared from different nitrogen precursors, acid-treated MWCNTs and graphene oxide (GO), which was synthesised from graphite by the modified Hummers' method. Urea and dicyandiamide were used as nitrogen precursors and the doping was achieved by pyrolysing the mixture of GO and MWCNTs in the presence of these nitrogen-containing compounds at 800°C. The N-doped composite catalyst samples were characterised by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The oxygen reduction reaction (ORR) was studied in 0.1 M KOH on glassy carbon electrodes modified with N-doped FLG/MWCNT electrocatalysts employing the rotating disk electrode (RDE) method. The RDE results indicated that these metal-free nitrogen-doped nanocarbon catalysts possess remarkable electrocatalytic activity towards the ORR in alkaline media similar to that of commercial Pt/C catalyst. The results obtained in this work are particularly important for the development of non-Pt cathode catalysts for alkaline membrane fuel cells.
Nitrogen-Doped Carbon Nanotube and Graphene Materials for Oxygen Reduction Reactions
Catalysts, 2015
Nitrogen-doped carbon materials, including nitrogen-doped carbon nanotubes (NCNTs) and nitrogen-doped graphene (NG), have attracted increasing attention for oxygen reduction reaction (ORR) in metal-air batteries and fuel cell applications, due to their optimal properties including excellent electronic conductivity, 4e − transfer and superb mechanical properties. Here, the recent progress of NCNTs-and NG-based catalysts for ORR is reviewed. Firstly, the general preparation routes of these two N-doped carbon-allotropes are introduced briefly, and then a special emphasis is placed on the developments of both NCNTs and NG as promising metal-free catalysts and/or catalyst support materials for ORR. All these efficient ORR electrocatalysts feature a low cost, high durability and excellent performance, and are thus the key factors in accelerating the widespread commercialization of metal-air battery and fuel cell technologies.
Electrocatalytic N-Doped Graphitic Nanofiber - Metal/Metal Oxide Nanoparticle Composites
Small (Weinheim an der Bergstrasse, Germany), 2018
Carbon-based nanocomposites have shown promising results in replacing commercial Pt/C as high-performance, low cost, nonprecious metal-based oxygen reduction reaction (ORR) catalysts. Developing unique nanostructures of active components (e.g., metal oxides) and carbon materials is essential for their application in next generation electrode materials for fuel cells and metal-air batteries. Herein, a general approach for the production of 1D porous nitrogen-doped graphitic carbon fibers embedded with active ORR components, (M/MOx , i.e., metal or metal oxide nanoparticles) using a facile two-step electrospinning and annealing process is reported. Metal nanoparticles/nanoclusters nucleate within the polymer nanofibers and subsequently catalyze graphitization of the surrounding polymer matrix and following oxidation, create an interconnected graphite-metal oxide framework with large pore channels, considerable active sites, and high specific surface area. The metal/metal oxide@N-doped...
Eco-Friendly Nitrogen-Doped Graphene Preparation and Design for the Oxygen Reduction Reaction
Molecules, 2021
Four N-doped graphene materials with a nitrogen content ranging from 8.34 to 13.1 wt.% are prepared by the ball milling method. This method represents an eco-friendly mechanochemical process that can be easily adapted for industrial-scale productivity and allows both the exfoliation of graphite and the synthesis of large quantities of functionalized graphene. These materials are characterized by transmission and scanning electron microscopy, thermogravimetry measurements, X-ray powder diffraction, X-ray photoelectron and Raman spectroscopy, and then, are tested towards the oxygen reduction reaction by cyclic voltammetry and rotating disk electrode methods. Their responses towards ORR are analysed in correlation with their properties and use for the best ORR catalyst identification. However, even though the mechanochemical procedure and the characterization techniques are clean and green methods (i.e., water is the only solvent used for these syntheses and investigations), they are t...
2022
Recently, electrocatalysts for oxygen reduction reactions (ORRs) as well as oxygen evolution reactions (OERs) hinged on electrospun nanofiber composites have attracted wide research attention. Transition metal elements and heteroatomic doping are important methods used to enhance their catalytic performances. Lately, the construction of electrocatalysts based on metal-organic framework (MOF) electrospun nanofibers has become a research hotspot. In this work, bimetallic NixCoy-ZIF nanocrystals were synthesized in an aqueous solution, followed by NixCoy-ZIF/PAN electrospun nanofiber precursors, which were prepared by a simple electrospinning method. Bimetal (Ni-Co) porous carbon nanofiber catalysts doped with nitrogen, oxygen, and sulfur elements were obtained at high-temperature carbonization treatment in different atmospheres (Ar, Air, and H2S), respectively. The morphological properties, structures, and composition were characterized by SEM, TEM, SAED, XRD, and XPS. Also, the speci...