Nitrogen-doped Graphene Network Research Articles

Combustion synthesis of N-doped three-dimensional graphene networks using graphene oxide–nitrocellulose composites

We demonstrate a novel method to prepare high-quality and uniform nitrogen-doped, three-dimensional, graphene networks through combustion of graphene oxide (GO)–nitrocellulose composites. The N-doped 3D graphene networks have tunable porous morphology and the pore size can be controlled by adjusting the concentration of GO in the nitrocellulose matrix. This new method is a simple method to obtain nitrogen-doped graphene networks and has potential applications in energy storage and conversion, catalysis, and sensors.

Efficient polysulfides anchoring for Li-S batteries: Combined physical adsorption and chemical conversion in V2O5 hollow spheres wrapped in nitrogen-doped graphene network

Lithium-sulfur (Li-S) batteries are attracting intense attention due to its high specific capacity and low cost. However, serious lithium polysulfides (LiPS) shuttle effect and the insulating property of sulfur restrict the practical application of Li-S batteries. In this work, we put forward an efficient strategy to anchor soluble LiPS through a combination of physical adsorption and chemical conversion, which is accomplished by using a heterostructure of V2O5 hollow spheres wrapped in nitrogen-doped graphene network (VOHS/NG) as the sulfur host. The nitrogen-doped graphene (NG) network not only provides excellent conductivity but also traps the LiPS rapidly with high specific surface area. The initially adsorbed LiPS chemically react with V2O5 hollow spheres (VOHS) to form thiosulfate intermediates. These intermediates convert the soluble “high-order” LiPS to insoluble “low-order” LiPS. Hence, the shuttle effect can be restrained efficiently. Owing to the physical and chemical synergy of the two components, the VOHS/NG heterostructure with 71 wt% sulfur can deliver superior rate performance and excellent cycling stability. A high specific capacity of 970 mAh g−1 can be obtained after 100 cycles at 0.2 C. Even cycled at 2 C for 1000 times, a reversible capability of 623 mAh g−1 can still be achieved with the decay rate as low as 0.017% per cycle.

Bimetal phosphide Ni1.4Co0.6P nanoparticle/carbon@ nitrogen-doped graphene network as high-performance anode materials for lithium-ion batteries

Transition metal phosphides (TMPs) have attracted much considerable interest for electrochemical energy storage, due to their high theoretical capacity and earth-abundant. In this work, we report ultrafine carbon-coated bimetal phosphide nanoparticles embedded into the nitrogen-doped graphene network (NGN) through a solution-phase self-assembly strategy. The unique carbon-coated Ni1.4Co0.6P nanoparticles and strongly coupled with NGN can not only provide more active sites for lithium-ions reaction and enhance the conductivity of electrode, but also restrain the volume expansion during the charge/discharge process. When evaluated as anode material for lithium-ion batteries, the as-prepared hybrid electrode exhibits high specific capacities (1320 mAh g−1 at 120 mA g−1), superior rate capability (227 mAh g−1 at a current density of 3000 mA g−1) and excellent cycling stability (350 mAh g−1 at 1200 mA g−1 after 1000 cycles). This work can be extended to develop advanced electrode materials for next-generation energy storage systems.

An efficient carbon-based ORR catalyst from low-temperature etching of ZIF-67 with ultra-small cobalt nanoparticles and high yield

Low-temperature etching of ZIF-67 is proposed for ultra-small cobalt/cobalt-oxide nanoparticles in nitrogen-doped graphene-networks as an efficient electrocatalyst for the oxygen reduction reaction.

Hollow SnO2 nanospheres with oxygen vacancies entrapped by a N-doped graphene network as robust anode materials for lithium-ion batteries.

The practical application of tin dioxide (SnO2) in lithium-ion batteries has been greatly hindered by its large volumetric expansion and low conductivity. Thus, a rational design of the size, geometry and the pore structure of SnO2-based nanomaterials is still a dire demand. To this end, herein we report an effective approach for engineering hollow-structured SnO2 nanospheres with adequate surface oxygen vacancies simultaneously wrapped by a nitrogen-doped graphene network (SnO2-x/N-rGO) through an electrostatic adsorption-induced self-assembly together with a thermal reduction process. The close electrostatic attraction achieved a tight and uniform combination of positively charged SnO2 nanospheres with negatively charged graphene oxide (GO), which can alleviate the aggregation and volume expansion of the entrapped SnO2 nanospheres. Subsequent thermal treatment not only ensures a significant reduction of the GO sheets accompanying nitrogen-doping, but also induces the generation of oxygen vacancies on the surface of the SnO2 hollow nanospheres, together building up a long-range and bicontinuous transfer channel for rapid electron and ion transport. Because of these structural merits, the as-built SnO2-x/N-rGO composite used as the anode material exhibits excellent robust cycling stability (∼912 mA h g-1 after 500 cycles at 0.5 A g-1 and 652 mA h g-1 after 200 cycles at 1 A g-1) and superior rate capability (309 mA h g-1 at 10 A g-1). This facile fabrication strategy may pave the way for the construction of high performance SnO2-based anode materials for potential application in advanced lithium-ion batteries.

Metal-Organic Framework-Derived Metal Oxide Embedded in Nitrogen-Doped Graphene Network for High-Performance Lithium-Ion Batteries.

Metal-organic frameworks (MOFs) are hybrid inorganic-organic materials that can be used as effective precursors to prepare various functional nanomaterials for energy-related applications. Nevertheless, most MOF-derived metal oxides exhibit low electrical conductivity and mechanical strain. These characteristics limit their electrochemical performance and hamper their practical application. Herein, we report a rational strategy for enhancing the lithium storage performance of MOF-derived metal oxide. The hierarchically porous Co3O4@NGN is successfully prepared by embedding ZIF-67-derived Co3O4 particles in a nitrogen-doped graphene network (NGN). The high electrical conductivity and porous structure of the NGN accelerates the diffusion of electrolyte ions and buffers stress resulting from the volume changes of Co3O4. As an anode material, the Co3O4@NGN shows high capacity (1030 mA h g-1 at 100 mA g-1), outstanding rate performance (681 mA h g-1 at 1000 mA g-1), and good cycling stability (676 mA h g-1 at 1000 mA g-1 after 400 cycles).

Nitrogen-doped graphene aerogel as both a sulfur host and an effective interlayer for high-performance lithium–sulfur batteries

Lithium–sulfur batteries have attracted great concern because of the high theoretical capacity of sulfur (1675 mA h g−1). However, the poor electrical conductivity and volumetric expansion of sulfur along with the dissolution of lithium polysulfides largely limit their practical application. In this study, nitrogen-doped graphene aerogel (NGA) with high nitrogen content and porosity is used as a host for the impregnation of sulfur. The effects of sulfur impregnation on the specific surface area, pore volume, and microstructure of NGA supported sulfur composite (S@NGA) are well investigated. Furthermore, NGA is also processed into a NGA film, which is sandwiched between a separator and S@NGA cathode. The lithium–sulfur battery with such a configuration delivers a high reversible capacity of 1514 mA h g−1 at 0.1 C, excellent rate performance (822 mA h g−1 at 2.0 C), and good cycling stability (946 mA h g−1 at 0.5 C even after 100 cycles). The enhanced electrochemical performance can be ascribed to the introduction of the NGA interlayer, the unique interconnected porous structure, and strong interaction between the three-dimensional nitrogen-doped graphene network and the homogeneously dispersed sulfur and/or lithium polysulfides.

Nitrogen doped graphene – Silver nanowire hybrids: An excellent anode material for lithium ion batteries

Abstract We present an in-situ polyol assisted synthesis approach for the preparation of silver nanowires (AgNW) over the nitrogen doped graphene (NG) sheets and has been tested as a viable LIBs anode material for the first time. The use of NG serves as nucleation sites, thereby facilitating the growth of AgNWs. The specific material design of the as-prepared NG-AgNW hybrids involves some advantages, including a continuous AgNW-graphene conducting network. Since AgNWs are electrically conductive, it provides an electrical contact with NG sheets which can effectively help the charge transport process and limit the variations in volume during the lithiation/de-lithiation processes. Apart from this, the insertion of metallic Ag nanowires into a percolated NG network increases the interlayer distance of NG sheets and prevent its restacking. Moreover, the more porous nature of the hybrid structure accommodating the large volume changes of AgNWs. As an anode material for LIBs, the NG-AgNW hybrid displays a remarkable initial discharge capacity of 1215 mAh g −1 and attains a stable capacity of 724 mAh g −1 at a current density of 100 mA g −1 after 50 cycles. The electrode exhibits a stable reversible capacity of 714, 634, 550 and 464 mA h g −1 at 0.1, 0.2, 0.5, 1 Ag −1 respectively. The reversible capacity (710 mAh g −1 ) at 0.1 Ag −1 is recovered after the cycling at various current densities confirming outstanding rate performance of the material. In addition, the coulombic efficiency, the NG-AgNW anode retains nearly 99% after the second cycle, further indicating its excellent reversibility. The hybrid material exhibits better cycling stability, greater rate capability, capacity retention and superior reversible capacity than that of bare AgNW and NG sheets. Our smart design will pave way for the development of efficient electrode materials for high capacity and long cycle life LIBs.

An ultralight and highly compressible anode for Li-ion batteries constructed from nitrogen-doped carbon enwrapped Fe3O4 nanoparticles confined in a porous 3D nitrogen-doped graphene network

Anode materials made of nanohybrids of graphene and transition metal oxides have been widely investigated. However, less attention has been paid to their density and compressibility. In this study, we synthesized an ultralight, highly compressive, and porous nanohybrid. This nanohybrid integrates nitrogen-doped graphene (NG), Fe3O4 nanoparticles, and N-doped carbon (NC) shell on each Fe3O4 nanoparticle. The Fe3O4 nanoparticles with NC shell are connected to and confined by 3D NG which forms a three-dimensional (3D) interconnected conductive scaffold. This sophisticated nanostructure was synthesized by a facile and scalable one-step hydrothermal reaction followed by calcination. The resultant Fe3O4/NC/NG nanohybrid with highly porous structure exhibits ultralow density (8.47mgcm−3) and supercompressibility. In addition, the Fe3O4/NC/NG nanohybrid delivers high reversible capacity of 952mAhg−1 at 200mAg–1, excellent high rate capacity (427mAhg−1 at 4000mAg–1), and prolonged cycling life (905mAhg−1 at 200mAg–1 after 100 cycles). The Fe3O4/NC/NG nanohybrid is a very efficient Fe3O4-based anode material for Li-ion batteries. These promising results demonstrate that this facile and scalable strategy holds great potential in the fabrication of high-performance compressive and ultralight metal oxide-graphene electrochemical devices.

Microwave-Assisted Synthesis of Highly Dispersed PtCu Nanoparticles on Three-Dimensional Nitrogen-Doped Graphene Networks with Remarkably Enhanced Methanol Electrooxidation.

A well-dispersed PtCu alloy nanoparticles (NPs) on three-dimensional nitrogen-doped graphene (PtCu/3D N-G) electrocatalyst has been successfully synthesized by a conventional hydrothermal method combined with a high-efficiency microwave-assisted polyol process. The morphology, composition, and structures are well-characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammograms illustrate that the as-prepared PtCu/3D N-G electrocatalyst possesses the larger electrochemical active surface area, lower onset potential, higher current density, and better tolerance to CO poisoning than PtCu NPs on reduced graphene oxide and XC-72 carbon black in acid solution. In addition, long-time chronoamperometry reveals that the PtCu/3D N-G catalyst exhibits excellent stability even longer than 60 min toward acid methanol electrooxidation. The remarkably enhanced performance is related to the combined effects of uniformly interconnected three-dimensional porous graphene networks, nitrogen doping, modified Pt alloy NPs, and strong binding force between Pt alloy NPs and 3D N-G structures.

Cobalt-doped edge-rich MoS2/nitrogenated graphene composite as an electrocatalyst for hydrogen evolution reaction

Co-doped MoS2/nitrogenated graphene composite has been successfully fabricated through a facile hydrothermal method and is investigated as an electrocatalyst for hydrogen evolution reaction (HER). The results reveal that Co2+ ions have been successfully incorporated into MoS2 lattice which can give rise to structural strain and dislocation. As a result, the Co-doped MoS2 nanosheets are characteristic of few layers (3–6 layers) and abundant exposed active edges. Meanwhile, Co-doped MoS2 nanosheets are well implanted into the nitrogen-doped graphene networks to form robust composite. When evaluated as a catalyst for HER, the obtained composite demonstrates superior electrocatalytic activities towards HER including low onset potential (∼90mV), large cathodic current density and small Tafel slope of 59mV dec−1. It is believed that the desirable catalytic properties can be credited to the unique microstructures including few-layer features, plentiful exposed active sites as well as intimate integration with highly electroconductive nitrogenated graphene.

Triethylenetetramine-assisted hydrothermal synthesis of sulfur-doped few-layer MoSe2/nitrogenated graphene hybrids and their catalytic activity for hydrogen evolution reaction

S-doped MoSe2/nitrogenated graphene hybrid has been successfully fabricated through a facile triethylenetetramine-assisted hydrothermal method and is investigated as an electrocatalyst for hydrogen evolution reaction (HER). The obtained products are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Electrochemical impendence spectroscopy (EIS). The results reveal that S-doped MoSe2 nanosheets which are characteristic of few layers (2–4 layers) and abundant exposed active edge sites are well implanted into the nitrogen-doped graphene networks to form robust 2D hybrid. When evaluated as a catalyst for HER, the obtained hybrid demonstrates superior electrocatalytic activities toward HER in comparison with the bare MoSe2. It is believed that the desirable electrochemical performances benefit from the unique microstructures including few-layer features, plentiful exposed active sites as well as intimate integration with highly electroconductive nitrogenated graphene.

Nitrogen-doped graphene network supported copper nanoparticles encapsulated with graphene shells for surface-enhanced Raman scattering.

In this study, we demonstrated nitrogen-doped graphene network supported few-layered graphene shell encapsulated Cu nanoparticles (NPs) (Cu@G-NGNs) as a sensing platform, which were constructed by a simple and scalable in situ chemical vapor deposition (CVD) technique with the assistance of a self-assembled three-dimensional (3D) NaCl template. Compared with pure Cu NPs and graphene decorated Cu NPs, the graphene shells can strengthen the plasmonic coupling between graphene and Cu, thereby contributing to an obvious improvement in the local electromagnetic field that was validated by finite element numerical simulations, while the 3D nitrogen-doped graphene walls with a large surface area facilitated molecule adsorption and the doped nitrogen atoms embedded in the graphene lattice can reduce the surface energy of the system. With these merits, a good surface enhanced Raman spectroscopy (SERS) activity of the 3D Cu@G-NGN painting film on glass was demonstrated using rhodamine 6G and crystal violet as model analytes, exhibiting a satisfactory sensitivity, reproducibility and stability. As far as we know, this is the first report on the in situ synthesis of nitrogen-doped graphene/copper nanocomposites and this facile and low-cost Cu-based strategy tends to be a good supplement to Ag and Au based substrates for SERS applications.