A novel nitrogen-doped porous graphene material (NPGM) was prepared by freeze-drying a graphene/melamine-formaldehyde hydrogel and subsequent thermal treatment. The use of melamine-formaldehyde resin as a cross-linking agent and nitrogen source enhances the nitrogen content. NPGM possesses a hierarchical porous structure, a large Brunauer-Emmett-Teller surface area (up to 1170 m 2 g -1 ), and a considerable nitrogen content (5.8 at%). NPGM displays a discharge capacity of 672 mA h g -1 at a current density of 100 mA g -1 when used as an anode material for lithium ion batteries, much higher than that observed for a nitrogen-free graphene porous material (450 mA h g -1 ). The NPGM electrode also possesses superior cycle stability.No capacity loss was observed even after 200 charge/discharge cycles at a current density of 400 mA g -1 . The enhanced electrochemical performance is attributed to nitrogen doping, high specific surface area, and the three-dimensional porous network structure.Melamine-formaldehyde resin (MF) was synthesized by adding formaldehyde (1.01 g, 37 wt%) and 0.63 g melamine into ultrapure water (7.86 g), followed by the addition of aqueous sodium hydroxide solution (0.5 mL, 0.1 M). This mixture was heated at 80 °C for 15 min till it turned clear. The resultant soluble MF (1.0 g) was 13 of graphene material. In addition, a great amount of crumpled sheets can be observed in the TEM images of NPGM and PGM, and these sheets are entangled with each other (Figs. 4c and d). Both NPGM and PGM possess a 3D interconnected network structure as expected, which may deliver superior electrochemical properties. Fig. 4 SEM images of NPGM (a) and PGM (b), TEM images of NPGM (c) and PGM (d).A nitrogen adsorption-desorption measurement was applied to further investigate porous properties. Both NPGM and PGM exhibit type IV isotherms, and their nitrogen adsorption-desorption isotherms show high uptake at a low relative pressure of 0-0.1, suggesting the microporous nature. Compared with PGM, NPGM displays a larger hysteresis at the relative pressure range of 0.45-1.0 (Fig. 5a), indicating the presence of 21 graphene sheets, which is helpful to the adsorption and infiltration of lithium ions into electrode. 23 The reduced charge-transfer resistance is beneficial to the electron transfer and lithium ion transport between the electrode and electrolyte. Fig. 9 (a) Electrochemical impedance spectra of NPGM and PGM electrodes (Inset is the corresponding simulation results for NGPM and PGM electrodes), (b) the simulated Randles equivalent circuit for NPGM and PGM electrodes. (CPE and R stand for the constant phase element and resistance, respectively.) ConclusionsIn this work, we prepared a graphene-based hydrogel by using melamine-formaldehyde resin as a cross-linking agent. NPGM was fabricated through freeze-drying of GMF hydrogel and subsequent thermal treatment. The as-prepared NPGM possessed a hierarchical porous structure, large specific surface area, and

The capacity of manganese dioxide (MnO 2 ) deteriorates with cycling due to the irreversible changes induced by the repeated lithiation and delithiation processes. To overcome this drawback, MnO 2 /nitrogen-doped graphene hybrid aerogels (MNGAs) were prepared via a facile redox process between KMnO 4 and carbon within nitrogen-doped graphene hydrogels. The three-dimensional nitrogen-doped graphene hydrogels were prepared and utilized as matrices for MnO 2 deposition. The MNGAs-120 obtained after a deposition time of 120 min delivered a very high discharge capacity of 909 mA h g -1 after 200 cycles at a current density of 400 mA g -1 , in sharp contrast to only 280 and 70 mA h g -1 delivered from nitrogen-doped graphene aerogels and MnO 2 . This discharge capacity is superior to that of the previously reported MnO 2 /carbon based hybrid materials. This material also exhibited an excellent rate capability and cycling performance. Its superior electrochemical performance can be ascribed to the synergistic interaction between uniformly dispersed MnO 2 particles with high capacity and the conductive three-dimensional nitrogen-doped graphene network with a large surface area and an interconnected porous structure. Tel.: +86 10 8254 5576. E-mail: hanbh@nanoctr.cn.Tel.: +61 2 4221 3127. E-mail: gwallace@uow.edu.au. AbstractThe capacity of manganese dioxide (MnO 2 ) deteriorates with cycling due to the irreversible changes induced by the repeated lithiation and delithiation processes. To overcome this drawback, MnO 2 /nitrogen-doped graphene hybrid aerogels (MNGAs) were prepared via a facile redox process between KMnO 4 and carbon within nitrogen-doped graphene hydrogels. The three-dimensional nitrogen-doped graphene hydrogels were prepared and utilized as matrices for MnO 2 deposition. The MNGAs-120 obtained after a deposition time of 120 min delivered a very high discharge capacity of 909 mA h g -1 after 200 cycles at a current density of 400 mA g -1 , in sharp contrast to only 280 and 70 mA h g -1 delivered from nitrogen-doped graphene aerogels and MnO 2 . This discharge capacity is superior to that of the previously reported MnO 2 /carbon based hybrid materials. This material also exhibited an excellent rate capability and cycling performance.Its superior electrochemical performance can be ascribed to the synergistic interaction between uniformly dispersed MnO 2 particles with high capacity and the conductive three-dimensional nitrogen-doped graphene network with a large surface area and interconnected porous structure.

In this study, we reported a novel and facile method for the fabrication of highly porous nitrogen-doped carbon nanoribbons (NCNs) by using KOH as an activating agent and polypyrrole nanoribbons as carbon and nitrogen precursors. The as-prepared NCNs exhibited an ultrahigh specific surface area (2230 m 2 g −1 ), large pore volume (1.2 cm 3 g −1 ), high nitrogen content (8.4 at %), and excellent thermal stability. Given the above features, the NCNs as gas adsorbents possessed a high uptake capacity for carbon dioxide (24.5 wt %) and methane (3.0 wt %) at 1.0 bar and 273 K. Furthermore, the NCNs as anode materials for lithium ion batteries delivered a high reversible capacity, good rate capacity, and excellent cycling performance due to the combined advantages of the high accessible porosity and enhanced electrochemical activity of doped nitrogen atoms. Therefore, the highly porous NCNs may hold promise in the fields of energy and environment.

Lithium-sulfur batteries have attracted great concern because of the high theoretical capacity of sulfur (1675 mA h g). 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 at 0.1 C, excellent rate performance (822 mA h g at 2.0 C), and good cycling stability (946 mA h g 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.

In this study, a facile method for synthesizing a novel graphene oxide/pyrrole-formaldehyde (GOP-1) composite hydrogel was developed via in situ polymerization of pyrrole and formaldehyde in the presence of graphene oxide sheets without any additional catalyst. During the polymerization, graphene oxide can act as a two-dimensional template to regulate the aggregation state of polymer and as an acid catalyst to accelerate the reaction rate of pyrrole and formaldehyde. The morphology and microstructure were investigated by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, respectively. The chemical properties were analyzed via X-ray photoelectron spectroscopy, infrared spectroscopy, and Raman spectroscopy. The freeze-dried GOP-1 composite hydrogel exhibited a large specific surface area, high nitrogen content, and three-dimensional network structure. Based on the above features, the freeze-dried GOP-1 composite hydrogel used as a gas adsorbent showed a high carbon dioxide uptake capacity at 1.0 bar and 273 K (11.1 wt%), in sharp contrast to that of graphene oxide (7.4 wt%). Furthermore, the as-prepared composite hydrogel may possess attractive potential in the fields of electrode material, tissue engineering, and water treatment.

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