Porous Nitrogen-doped Graphene Research Articles

An all-in-one material with excellent electrical double-layer capacitance and pseudocapacitance performances for supercapacitor

3D porous nitrogen-doped graphene nanosheets (PNGs) are facilely prepared via a simple one-step segmented thermal annealing method, using graphene oxide (GO) as carbon source, urea as nitrogen source and pore generator. During the pyrolysis process at 300 °C, urea and oxygenous groups on GO sheets can release large amounts of gas such as NH3, HCNO and H2O, which act as pore generators to tear and strike GO nanosheets to form 3D porous nanostructured material. When the temperature is increased up to 800 °C, a large amount of nitrogen-containing gas can react with the functional groups on GO. Consequently, the pore forming and nitrogen doping processes of GO are successfully realized and 3D PNGs are prepared. The research results show that the PNGs with an optimal N-doping content of 6.9% display a high surface area of 490.2 m2 g−1 and excellent electrochemical capacitive performance. The outstanding electrical double-layer capacitance and the increasing pseudocapacitance are attributed to the large specific surface area and the high nitrogen content, respectively. In 1 M H2SO4 electrolyte, the PNGs exhibit a specific capacitance of 337.0 F g−1 and a low capacitance loss of 2.4% after 5000 cycles. Moreover, a symmetric supercapacitor with a cell voltage of 1.3 V is assembled, which displays both high energy density and high power density of 19.9 W h kg−1 and 650 W kg−1, respectively. The all-in-one material with excellent electrical double-layer capacitance and pseudocapacitance is promising in supercapacitor.

A multidimensional and nitrogen-doped graphene/hierarchical porous carbon as a sulfur scaffold for high performance lithium sulfur batteries

Constructing 3D heteroatom-doped carbon framework from sp2-hybridized nanocarbon (graphene) and sp3-hybridized porous carbon (activated carbon) has been considered as an effective method to achieve excellent performance in energy conversion and storage due to the synergistic effect between building blocks. Herein, a facile assembly of graphene oxide and porous carbon is reported to fabricate the inherent nitrogen-doped porous carbon and graphene composited nanostructures. When used as the sulfur scaffold for lithium sulfur batteries, the materials suggest outstanding electrochemical properties, including a high reversible capacity (1372 mAh g−1 at 0.1C), excellent rate performance (451 mAh g−1 at 3C) and cycling stability (579 mAh g−1 at 1C after 500 cycles). The enhancement in electrochemical properties can be ascribed to the 3D hierarchical porous structure of the carbon hybrid, in which, besides, the inherent doping of nitrogen can generate homogeneous active sites and defects that can effectively improve the interfacial adsorption. Thus, the simple strategy of pyrolysis and self assembly of graphene oxide and porous carbon provided in this work opens a new avenue for combining different dimensional nanocarbons to construct nitrogen-doped, multi-dimensional carbon architecture for high performance lithium sulfur batteries.

M-N-Doped Carbon Nanofibers Modified Separators for Lithium-Sulfur Batteries

A novel lightweight, multi-functional layer comprised of 1D porous metal-embedded nitrogen-doped carbon nanofibers (M-N-C) and 2D graphene sheets is introduced to modify a commercial polyolefin separator for using in lithium-sulfur batteries. Benefiting from the high electrical conductivity and strong lithium polysulfides (LiPSs) chemical adsorption ability of M-N-C, the porous intercalation-structured modified layer exhibits excellent ability to suppress LiPSs shuttling while maintaining high lithium-ion transport, and the modified layer functions as a highly conductive upper current collector to reutilize active sulfur species. The cell assembled with the modified multifunctional separator shows a high rate capability and excellent cycling stability. These exciting results indicate that this multifunctional membrane could be a promising separator candidate for Li-S batteries.

Role of Nitrogen Moieties in N-Doped 3D-Graphene Nanosheets for Oxygen Electroreduction in Acidic and Alkaline Media.

This study elucidates the synthesis-structure-property correlations of nitrogen moieties present in nitrogen-functionalized graphene nanomaterials toward oxygen reduction reactions (ORRs) and their electrochemical pathways in acidic and alkaline electrolytes. Porous three-dimensional nitrogen-doped graphene nanosheets (N/3D-GNSs) were fabricated using the sacrificial support method and doped with nitrogen using 10 atom % NH3 under thermal pyrolysis at T = 650, 850, and 1050 °C for evaluating the nitrogen species formed under different temperatures. The abundances of the various nitrogen species formed under pyrolytic conditions were evaluated with X-ray photoelectron spectroscopy. Using rotating ring-disk electrode, we analyzed the role played by the nitrogen moieties influencing the electrochemical activity of the N/3D-GNS supports for oxygen reduction reactions (ORRs) in both acidic and alkaline media. It was demonstrated that the concentrations of the nitrogen moieties: graphitic-N, quaternary, hydrogenated-N (hydrogenated nitrogen combined pyrrolic nitrogen and hydrogenated pyridine) and pyridinic-N varied considerably with pyrolysis temperatures. A decrease in graphitic-N content and an increase in the ratio of hydrogenated-N/pyridinic-N significantly improved the activity of the material. The half-wave and onset potentials as well as the current densities and hydrogen peroxide (H2O2)/(HO2-) yields of the N/3D-GNS materials also varied between acidic and alkaline electrolytes but followed the general trend in terms of pyrolysis temperatures and abundance of the nitrogen moieties. Among the synthesized materials, the 3D-graphene nanosheets that were doped with nitrogen at 850 °C, optimized to have the highest hydrogenated-N and lowest pyridinic-N as well as better catalyst-ionomer integration, showed the highest ORR performance. This strategy for the tunable synthesis of nitrogen-doped graphene materials with controlled nitrogen functionalization offers a platform for developing active supports or catalytic nanomaterials for fuel cell applications.

Supramolecular assembly promoted synthesis of three-dimensional nitrogen doped graphene frameworks as efficient electrocatalyst for oxygen reduction reaction and methanol electrooxidation

Nitrogen-doped three-dimensional porous graphene frameworks (NGAs) are fabricated through a unique strategy of adopting the supramolecular assembly-assisted method with GO as building block, and supramolecular aggregate of self-assembled melamine and cyanuric acid as not only a “spacer” to suppress the re-stacking of graphene nanosheets but a self-sacrificial pore-forming agent as well as a nitrogen source leading to simultaneous N-doping. Supramolecular aggregates function as the structure-directing agent playing a vital role in generating the loose porous and free-stacking structure and guiding the formation of unique 3D architecture. The resulting metal-free NGA products possess high specific surface area, porous structure and free-stacking properties, and exhibit enhanced ORR performance in terms of positive half-wave potential which is only ∼43 mV lower than that of a commercial Pt/C, four-electron-transfer process, good durability and outstanding methanol poisoning tolerance. Besides, it also performs as a good support for Pt particles. Consequently, Pt/NGA catalyst displays impressive catalytic activity and stability towards efficient methanol electrooxidation reaction. This simple and robust synthetic strategy of 3D N-doped graphene has put forward a new prospect for rational synthesis of heteroatoms doped carbon materials for sustainable energy conversion applications.

Amino acid-mediated N-doped graphene aerogels and its electrochemical properties

Three-dimensional porous nitrogen-doped graphene aerogels (NGAs) were synthesized via a facile and green hydrothermal process by using graphene oxide and different amino acids as nitrogen source. The morphology and structure of the as-prepared NGAs were characterized by means of FESEM, XRD, FTIR, Raman and XPS spectroscopy. The microstructure, nitrogen content and doping configuration of NGAs could be facilely controlled by selecting different amino acids. The formation mechanism of different nitrogen doping configurations was proposed. It has been proved that the NGAs prepared with amino acids as nitrogen doping source had enhanced electrochemical performance than pristine graphene aerogels. The pyrrolic N as main doping configuration plays important role in determining the electrochemical performance of NGAs. The NGA with pyrrolic N (content up to 13.82 at.%) exhibited a high specific capacitance, superior rate capability and excellent cycling life. This study gives inspiration to fabricate NGAs for a broad range of technological applications.

Scalable Self-Supported Graphene Foam for High-Performance Electrocatalytic Oxygen Evolution.

Developing efficient electrocatalysts consisting of earth-abundant elements for oxygen evolution reaction (OER) is crucial for energy devices and technologies. Herein, we report self-supported highly porous nitrogen-doped graphene foam synthesized through the electrochemical expansion of carbon-fiber paper and subsequent nitrogen plasma treatment. A thorough characterization, such as electron microscopy and synchrotron-based near-edge X-ray absorption fine structure, indicates the well-developed porous structures featuring homogeneously doped nitrogen heteroatoms. These merits ensure enriched active sites, an enlarged active surface area, and improved mass/electron transport within the continuous graphene framework, thus leading to an outstanding capability toward electrocatalyzing OER in alkaline media, even competitive with the state-of-the-art noble-/transition-metal and nonmetal electrocatalysts reported to date, from the perspectives of the sharp onset potential, a small Tafel slope, and remarkable durability. Furthermore, a rechargeable Zn-air battery with this self-supported electrocatalyst directly used as the air cathode renders a low charge/discharge overpotential and considerable life span. The finding herein suggests that a rational methodology to synthesize graphene-based materials can significantly enhance the oxygen electrocatalysis, thereby promoting the overall performance of the energy-related system.

Pt nanoparticles supported on nitrogen-doped porous graphene for sensitive detection of Tadalafil

Graphene (GR) is one of the most promising candidates for utilization in the electroanalytical field because of its superior electrocatalytic activity, excellent electronic conductivity, and high chemical stability. However, the GR sheets usually tend to stack together with π-π interaction. The spontaneous stacking leads to the aggregation of the GR sheets and imposes a negative feedback in the surface area of the GR, which obviously limits its electrochemical application. In this study, nitrogen-doped porous GR (NPGR) with different pore sizes is prepared by using silica (SiO2) as a template. The NPGR exhibits high surface area and porous structure, fulfilling the requirement for supporting materials. Being a support, the structural uniqueness and N dopants of NPGR facilitate the deposition of Pt nanoparticles (Pt NPs). The Pt NPs/NPGR composites integrate the structural properties of NPGR and catalytic properties of Pt NPs. A selective and sensitive electrochemical sensor was successfully developed for sensitive determination of Tadalafil (TAD), showing a concentration range of 1.30–488.9μM and limit of detection of 0.268μM.

Fe-N-doped carbon nanofiber and graphene modified separator for lithium-sulfur batteries

A novel lightweight, multi-functional layer comprised of 1D porous Fe-embedded nitrogen-doped carbon nanofibers (Fe-N-C) and 2D graphene sheets is introduced to modify a commercial polypropylene (PP) separator for use in lithium-sulfur batteries. Benefiting from the high electrical conductivity and strong lithium polysulfide (LiPS) chemical adsorption ability of Fe-N-C, the porous intercalation-structured modified layer exhibits excellent ability to suppress LiPS shuttling while maintaining high lithium-ion transport, and the modified layer functions as a highly conductive upper current collector to reutilize active sulfur species. The cell assembled with the modified multifunctional separator shows a high rate capability and excellent cycling stability, exhibiting a capacity of 847.9 mAh g−1 at 2 C and a low degradation rate of 0.053% per cycle over 500 cycles at 0.5 C.

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.

Facile synthesis of nitrogen-doped graphene aerogels functionalized with chitosan for supercapacitors with excellent electrochemical performance

Three-dimensional porous nitrogen-doped graphene aerogels (NGAs) were synthesized by using graphene oxide (GO) and chitosan via a self-assembly process by a rapid method. The morphology and structure of the as-prepared aerogels were characterized. The results showed that NGAs possesed the hierarchical pores with the wide size distribution ranging from mesopores to macropores. The NGAs carbonized at different temperature all showed excellent electrochemical performance in 6mol/L KOH electrolyte and the electrochemical performance of the NGA-900 was the best. When working as a supercapacitor electrode, NGA-900 exhibited a high specific capacitance (244.4F/g at a current density of 0.2A/g), superior rate capability (51.0% capacity retention) and excellent cycling life (96.2% capacitance retained after 5000 cycles).

3D nitrogen-doped graphene foam with encapsulated germanium/nitrogen-doped graphene yolk-shell nanoarchitecture for high-performance flexible Li-ion battery

Flexible electrochemical energy storage devices have attracted extensive attention as promising power sources for the ever-growing field of flexible and wearable electronic products. However, the rational design of a novel electrode structure with a good flexibility, high capacity, fast charge–discharge rate and long cycling lifetimes remains a long-standing challenge for developing next-generation flexible energy-storage materials. Herein, we develop a facile and general approach to three-dimensional (3D) interconnected porous nitrogen-doped graphene foam with encapsulated Ge quantum dot/nitrogen-doped graphene yolk-shell nano architecture for high specific reversible capacity (1,220 mAh g−1), long cycling capability (over 96% reversible capacity retention from the second to 1,000 cycles) and ultra-high rate performance (over 800 mAh g−1 at 40 C). This work paves a way to develop the 3D interconnected graphene-based high-capacity electrode material systems, particularly those that suffer from huge volume expansion, for the future development of high-performance flexible energy storage systems.

Nitrogen-doped porous graphene as a highly efficient cathodic electrocatalyst for aqueous organic redox flow battery application

The redox flow battery (RFB) is considered one of the most attractive energy storage technologies because of its high efficiency, long service life and great safety.

Hierarchical nitrogen-doped porous graphene/reduced fluorographene/sulfur hybrids for high-performance lithium-sulfur batteries.

It is a great challenge to obtain high performance cathodes with a high sulfur loading and good cycle performance due to the dissolution of intermediate lithium polysulfides in lithium-sulfur batteries. Herein, we report a novel hierarchical hybrid composed of nitrogen-doped porous graphene (NG), reduced fluorographene or graphene fluoride (RFG), and sulfur as a composite cathode in the Li-S batteries. In comparison with sulfur composites based on only either nitrogen-doped porous graphene or pure reduced fluorographene, the hierarchical hybrid of RFG, NG, and sulfur (NG-RFG/S) shows a better reversible capacity and rate capability performance due to a better confinement effect of lithium polysulfides and sulfur. The NG-RFG/S cathode with ∼63.2% S content exhibits a high discharge capacity of 1120 mA h g-1 and retains 632 mA h g-1 after 100 cycles at 0.1C. At the higher rate of 0.5C, the cell still maintains a discharge capacity of about 300 mA h g-1 after 800 cycles, which reveals the great potential of this hybrid cathode for long-cycle-life, high energy density storage applications.

Hierarchically porous nitrogen-doped graphene aerogels as efficient metal-free oxygen reduction catalysts

Nitrogen-doped graphene aerogels with hierarchically porous architectures (N-Gs) are fabricated through the co-assembly of graphene oxide and o-phthalonitrile in a solvothermal process and the thermal treatment of the obtained composites at different temperatures. The structural characterizations indicate that both mesopores and macropores exist in the monolithic N-Gs. More importantly, the architectures, porosities and compositions show obvious dependence on the thermal treatment temperature. As the metal-free catalyst for oxygen reduction reaction in basic media, the sample thermally treated at 750°C shows the best catalytic performances among the three N-Gs, which is owing to its advantages in the surface areas and content of active N species.

Facile synthesis of porous nitrogen-doped holey graphene as an efficient metal-free catalyst for the oxygen reduction reaction

Nitrogen-doped graphene is a promising candidate for the replacement of noble metal-based electrocatalysts for oxygen reduction reactions (ORRs). The addition of pores and holes into nitrogen-doped graphene enhances the ORR activity by introducing abundant exposed edges, accelerating mass transfer, and impeding aggregation of the graphene sheets. Herein, we present a straightforward but effective strategy for generating porous holey nitrogen-doped graphene (PHNG) via the pyrolysis of urea and magnesium acetate tetrahydrate. Due to the combined effects of the in situ generated gases and MgO nanoparticles, the synthesized PHNGs featured not only numerous out-of-plane pores among the crumpled graphene sheets, but also interpenetrated nanoscale (5–15 nm) holes in the assembled graphene. Moreover, the nitrogen doping configurations of PHNG were optimized by post-thermal treatments at different temperatures. It was found that the overall content of pyridinic and quaternary nitrogen positively correlates with the ORR activity; in particular, pyridinic nitrogen generates the most desirable characteristics for the ORR. This work reveals new routes for the synthesis of PHNG-based materials and elucidates the contributions of various nitrogen species to ORRs.

Porous nitrogen-doped graphene for high energy density supercapacitors in an ionic liquid electrolyte

Porous nitrogen-doped graphene (PNG) has been prepared via simple thermal treatment of graphene oxide and urea, and the morphology and structure of the PNG have been characterized by using a range of electron microscopy, X-ray photoelectron spectroscopy, and other techniques. The electrochemical performances of the PNG have been investigated in an ionic liquid electrolyte by cyclic voltammetry and galvanostatic charge-discharge via both three-electrode and two-electrode configurations. The PNG electrode delivers a specific capacitance of 310 F g−1 at 1 A g−1 with good cycling stability over 4000 cycles. The high electrochemical performance is ascribed to the porous structure and nitrogen-doping in the PNG. The porous structure enables high specific surface area and rapid ion mobility, contributing to double layer capacitance, while the N-doping enhances electrochemical activity and electric conductivity, contributing to pseudocapacitance. Meanwhile, the ionic liquid electrolyte enables a very wide working voltage of 3 V, leading to a high energy density up to 163.8 W h kg−1. The fabricated supercapacitor can light up a LED for a long while with low self-discharge, showing good potential for practical application.

Bi2O3 nanoparticles encapsulated by three-dimensional porous nitrogen-doped graphene for high-rate lithium ion batteries

A composite consisting of Bi2O3 nanoparticles encapsulated by three-dimensional (3D) porous nitrogen-doped graphene is reported. Due to the 3D porous structure, the composite has large specific surface area of 112 m2 g−1, which can increase the contact area between active material and electrolyte. In addition, the 3D porous conductive framework can not only facilitate the fast electron transport and Li+ diffusion but also enhance the electrical conductivity of the composite. As expected, the composite shows an outstanding rate capability of 273 mAh g−1 at 10000 mA g−1 and a capacity of 417 mAh g−1 over 100 cycles at a current density of 200 mA g−1. Therefore, the composite is a promising candidate as an anode material for high-rate lithium ion batteries.

One Step Synthesis of Me (Fe, Co, Ni) and Nitrogen co-doped Porous Graphene for ORR in Alkaline Electrolyte

This article reports the influence of different transition metals (Fe, Co, Ni) on improving electrochemical property of porous nitrogen-doped graphene and their electrocatalytic activity toward oxygen reduction reaction (ORR) in alkaline media. The catalysts were prepared through a simple one step synthesis method along with the high-temperature pyrolysis process. The electrocatalystic activity of the obtained catalysts for ORR was performed with cyclic voltammetry (CV) and linear sweep voltammetry (LSV) employing a rotating disk electrode (RDE). In addition, the rotating ring-disk electrode (RRDE) measurements were performed to survey the peroxide yield (H2O2%) and electron transfer number (n) on the Me (Fe, Co, Ni) and nitrogen co-doped graphene (ie., Me-PNG, Me = Fe, Co, Ni) catalyzed electrode to further study the ORR catalytic pathway of the catalysts. The electrochemical properties are found to depend strongly on the kinds of transition metals, where the Fe-PNG, with onset potential at 0.197 V and half-wave potential at 0.071 V, showed much better catalytic activity than Co-PNG and Ni-PNG.

Nitrogen-Doped Porous Carbon/Graphene Aerogel with Much Enhanced Capacitive Behaviors

Hierarchically porous hybrids of strongly coupled nitrogen-doped porous carbons and graphene aerogel (NPC-GA) are fabricated through the solid-state oxidation polymerization and carbonization of m-phenylenediamine on the interconnected macroporous frameworks of GA. The hierarchically porous hybrids provide abundant storage sites and short transport paths for electrolyte ions. By adjusting the pyrolysis temperature, the specific surface areas and nitrogen content of NPC-GA can be easily modified, further influencing the electrochemical performance of the hybrids. In a three-electrode system, NPC-GA electrode shows high specific capacitance of 608Fg−1 at 0.1Ag−1 in 1M H2SO4. An all-solid-state flexible supercapacitor based on NPC-GA delivers superior energy density (12.4 Wh Kg−1) and power density (2432W Kg−1) as well as good cycling stability (92% specific capacitance retention after 10 000 cycles).