Synthesis and plasma treatment of nitrogen-doped graphene fibers for high-performance supercapacitors

Graphene fiber-based supercapacitor has aroused great interest as a flexible power source in future wearable electronics. However, the low electrochemical performance of graphene fibers (GFs) usually causes the serious limitation of use in practical applications due to the material stacking, hydrophobicity and fabrication process complexity. In this work, a facile and effective plasma-assisted strategy is put forward to increase specific surface area, tune hierarchically porous structure and promote wettability of nitrogen-doped graphene fibers (NGFs), resulting in the improvement of electrochemical performance. The supercapacitor assembled from plasma-treated NGFs shows superior capacitance (878 mF/cm² at 0.1 mA/cm² current density) and high energy density (19.5 μW h/cm² at 40 mW/cm² power density), which is 23.7% and 131.4% higher than that of NGFs and GFs, respectively. Additionally, the fiber-based supercapacitor based on plasma-treated NGFs exhibits high rate capability of 59.8% and excellent cyclic performance (95.8% retention over 10,000 cycles). These plasma-treated NGFs can be promising candidates for high-performance and flexible power sources in future wearable electronics.     

Mesoporous nitrogen-doped graphene aerogels with enhanced rate capability towards high performance supercapacitors

In this work, a novel preparation method and architecture of mesoporous nitrogen-doped graphene aerogels (GAs) using electrostatic attraction are reported. The sacrificial template, positively charged SiO₂ nanoparticles by using (3-Animopropyl) triethoxysilane (3-APTS), can significantly decrease the spacing between graphene oxide sheets, due to the strong electrostatic attraction between the graphene oxide and SiO₂. After the etching of templates, the ratio of mesopores is greatly increased, and the electrochemical performances of electrodes are enhanced. The mesoporous GAs yield an enhanced specific capacitance of 203 F/g at a current density of 1 A/g, and a capacitance fade of only 8.95% at a high current density of 20 A/g, indicating improved ion transport in mesoporous architecture. The controllable synthesized method can be further applied to prepare other mesoporous materials and such mesoporous nitrogen-doped GAs have great potential in high rate performance supercapacitors.     

Preparation of scale-like nickel cobaltite nanosheets assembled on nitrogen-doped reduced graphene oxide for high-performance supercapacitors

Ultrathin scale-like nickel cobaltite (NiCo₂O₄) nanosheets supported on nitrogen-doped reduced graphene oxide (N-rGO) are successfully synthesized through a facile co-precipitation of Ni²⁺ and Co²⁺ in the presence of sodium citrate and hexamethylenetetramine and subsequent calcination treatment. The composition and morphology of NiCo₂O₄ nanosheets@nitrogen-doped reduced graphene oxide (denoted as NiCo₂O₄ NSs@N-rGO) were characterized by Scanning electron microscope, Transmission electron microscope, X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller and thermogravimetric analysis. The thickness of NiCo₂O₄ nanosheets anchored on the reduced graphene oxide is around 4 nm. The capacitance of NiCo₂O₄ NSs@N-rGO is evaluated by cyclic voltammogram and galvanostatic charge/discharge with the result that the NiCo₂O₄ NSs@N-rGO could deliver a specific capacitance of 1540 F g⁻¹ after 1000 cycles at 10 A g⁻¹.     

KOH活化对超级电容器用氮掺杂石墨烯的影响

为了制备高比表面积、适宜孔径的石墨烯基材料,从而使其具备良好的电化学性能,化学活化法已经被广泛地研究。本文以氧化石墨烯(GO)为基体,密胺树脂预聚体为氮掺杂剂,采用KOH活化法制备超级电容器用氮掺杂石墨烯材料。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、比表面积和孔隙度分析(BET)、循环伏安法(CV)及恒电流充放电法(GCD)等对其微观形貌和电化学性质进行分析。结果表明:在活化温度800℃,活化倍率3.0时,样品的比表面积为554.32 m2/g,比电容达到312 F/g,具有更好的电化学特性。     

One-pot hydrothermal synthesis of nitrogen-doped hierarchically porous carbon monoliths for supercapacitors

The nitrogen-doped hierarchically porous carbon monoliths (N-HPCMs) were successfully synthesized by using dicyandiamide (DCDA) as nitrogen source, phenolic resol as carbon precursor and mixed triblock copolymers as templates via a one-pot hydrothermal approach. The obtained carbon monoliths possess tunable mesopore size (4.3–11.4 nm), large surface area (552–660 m²/g), and high nitrogen content (up to 12.1 wt%). Ascribed to the nitrogen-doped frameworks and hierarchical porosity, N-HPCMs exhibit good electrochemical performance as the supercapacitor electrode with specific capacitance of 268.9 F/g (in 6 M KOH) at a current density of 1 A/g, and a 4.1 % loss of the specific capacitance after 5,000 charge–discharge cycles, indicating a long-term cycling stability. Such unique features make N-HPCMs promising electrode materials for high performance supercapacitors.     

The preparation of graphene decorated with manganese dioxide nanoparticles by electrostatic adsorption for use in supercapacitors

Graphene decorated with manganese dioxide nanoparticles are prepared by electrostatic adsorption. The manganese dioxide is synthesized by a microemulsion route using the cationic surfactant hexadecyltrimethyl ammonium bromide, which dispersed in water is converted to be positively charged. The surface charge of graphene in water is negative, allowing two forms of manganese dioxide-decorated graphene to be synthesized by electrostatic adsorption: (a) free in situ synthesis and (b) layer-by-layer self-assembly. By electrochemical analysis, the specific capacitances of two materials are found to be about 40% and 250% larger than that of manganese dioxide. The improvement is because of the tighter contact between graphene and manganese dioxide, and the higher conductive and capacitive characteristics of graphene.     

Thermochemistry of nitrogen-doped reduced graphene oxides

The thermodynamic stability of a series of nitrogen - doped reduced graphene oxides prepared by ammonolysis of graphene oxide has been investigated by high temperature oxidation calorimetry. In terms of enthalpy and depending on the concentration of nitrogen, the nitrogen - doped reduced graphene oxides can be up to 73 kJ·mol⁻¹ more stable than graphite plus nitrogen. There is a linear relationship between the nitrogen content and the formation enthalpy, which indicates a decrease in stability with increasing nitrogen content.     

Multiscale patterning of graphene oxide and reduced graphene oxide for flexible supercapacitors

A simple and facile method for multiscale, in-plane patterning of graphene oxide and reduced graphene oxide (GO–rGO) was developed by region-specific reduction of graphene oxide (GO) under a mild irradiation. The UV-induced reduction of graphene oxide was monitored by various spectroscopic techniques, including optical absorption, X-ray photoelectron spectroscopy (XPS), Raman, and X-ray diffraction (XRD), while the resultant GO–rGO patterned film morphology was studied on optical microscope, scanning electron microscope (SEM), and atomic force microscope (AFM). Flexible symmetric and in-plane supercapacitors were fabricated from the GO–rGO patterned polyethylene terephthalate (PET) electrodes to show capacitances up to 141.2 F/g.     

Synthesis of ruthenium-embedded nitrogen-doped graphene for carbon dioxide hydrogenation

Two-dimensional (2D) layered materials have attracted great interest in the energy storage and catalysis field due to their graphene-like structure and excellent performance. Ruthenium-embedded nitrogen-doped graphene (Ru-NG) have been obtained by a novel method, using montmorillonite as hard template and Ru-phenanthroline chelate as precursor. After calcination in N₂ atmosphere at 800℃, Ru-NG were obtained and further characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nitrogen sorption. Ru-NG have 2D layered structure just like the montmorillonite template, and C, N, O and Ru are homogeneously distributed on them. The average sizes of Ru nanoparticles do not change much with the increasing of Ru content, and they keep at about 1.2 to 1.4 nm. The XPS results indicate that phenanthroline has been successfully transformed to nitrogen-doped carbon during pyrolysis, and the peaks at 398.5, 400.1 and 401.5 eV suggest the presence of pyridine-like, pyrrole-like and quaternary nitrogen atoms, respectively. Compared with the Ru catalyst supported on activated carbon prepared by the traditional impregnation-reduction method, Ru-NG exhibits excellent catalytic activity in the reaction of hydrogenation of carbon dioxide to formic acid.     

负载钌的氮掺杂石墨烯催化剂的制备及应用

利用人工合成的蒙脱石做硬模板,以插层的邻菲罗啉-钌络合物为前体,在惰性气氛下热解后用氢氟酸和盐酸刻蚀除去蒙脱石模板制备出负载钌纳米粒子的氮掺杂石墨烯催化剂(Ru-NG)。Ru-NG具有与模板蒙脱石类似的层状石墨烯结构,C、N、O及Ru元素在其上分布均匀。Ru-NG中钌的含量随钌前体的加入量的增加而增加,但受蒙脱石片层的物理限域作用及与含氮物种的配位作用,钌纳米粒子的粒径却无显著变化,且粒径均一,平均粒径在1.2～1.4 nm范围内。与传统浸渍-还原法制备的活性炭负载的Ru催化剂相比,Ru-NG在二氧化碳加氢生成甲酸反应中表现出优异的催化活性。     

Functionalized three-dimensional graphene networks for high performance supercapacitors

Three-dimensional (3D) thermal reduced graphene network (TRGN) deposition on Ni foam without any conductive agents and polymer binders was successfully synthesized by dipping Ni foam into graphene oxide (GO) suspension and subsequent thermal reduction process. The direct and close contact between thermal reduced graphene and Ni foam is beneficial to the enhanced conductivity of the electrode, as well as the improvement of ion diffusion/transport into the electrode. Additionally, low-temperature reduction of GO possesses a large amount of stable oxygen-containing groups that can provide high pseudocapacitance. As a result, the TRGN electrode delivers a high specific capacitance of 442.8 F g⁻¹ at 2 mV s⁻¹ in 6 mol L⁻¹ KOH. Moreover, symmetric supercapacitor based on TRGN exhibits a maximum energy density of 30.4 Wh kg⁻¹ based on the total mass of the two electrodes in 1 mol L⁻¹ Na₂SO₄ electrolyte, as well as excellent cycling stability with 118% of its initial capacitance after 5000 cycles.     

Pore-size-tunable nitrogen-doped polymeric frameworks for high performance sodium ion storage and supercapacitors

Sodium-ion batteries (SIBs) is considered as a promising alternative to lithium-ion batteries. Supercapacitors (SCs) are receiving great attention for their significantly higher power density than batteries and prolonged cycle life. Herein, SIBs and SCs based on N-doped amorphous multi-size pores dominated polymeric frameworks were fabricated and examined. The enlarged interlayer spacing and multi-size-pore dominated interconnected architecture with high specific surface area, high pore volume and high N content optimize the electrochemical performance of N-PPF-20. As an anode material, N-PPF-20 exhibited a sodium ion storage capacity of 432.2 mAh g^?1 at a current density of 0.05 A g^?1, while maintaining a reversible capacity of 61.1 mAh g^?1 at an ultrahigh current density of 20 A g^?1. Additionally, a specific capacity of 158.3 mAh g^?1 at 1 A g^?1 was obtained after 1000 cycles, indicating an excellent cycling stability. When tested as an electrode material for SCs, N-PPF-20 delivered a high specific capacitance of 438.7 F g^?1 at 0.1 A g^?1, and a specific capacitance of 111.2 F g^?1 was achieved even at a high current density of 10 A g^?1. Meanwhile, a long-term cycling life test demonstrated a specific capacitance of 120 F g^?1 at an ultrahigh current density of 10 A g^?1 after 10,000 cycles.     

超盐环境下含氮碳气凝胶的制备及其在超级电容器中的应用

多孔碳材料因其优异的导电性和稳定性,以及成本低廉等优点而成为当今的研究热点之一。以苯酚、甲醛和三聚氰胺为原料,利用高浓度氯化锌来提供超盐环境,经溶剂热反应后,在氮气中800℃下热解制得了含氮碳气凝胶(NCA)。扫描电子显微镜、拉曼光谱、X射线光电子能谱和氮气吸附等表征结果表明,该含氮碳气凝胶具有分级多孔蜂窝状结构,其比表面积高达729.6 m2/g。采用三电极测试体系测试了含氮碳气凝胶的电化学性能,结果表明,在三电极体系中,以0.5 mol/L H₂SO₄作为电解液,含氮碳气凝胶在电流密度为1 A/g时比电容达到350.7 F/g;在电流密度为20 A/g时,经过10000次充放电后,含氮碳气凝胶的电容保持率仍高达97.8%。在双电极体系中,含氮碳气凝胶在800 W/kg的功率密度下,能量密度可达26.8 (W·h)/kg。上述结果表明,该含氮碳气凝胶是一种非常理想的超级电容器电极材料。     

Simple preparation of nanoporous few-layer nitrogen-doped graphene for use as an efficient electrocatalyst for oxygen reduction and oxygen evolution reactions

We prepared nitrogen-doped graphene (NG) by simple pyrolysis of graphene oxide and polyaniline, which was selected as the N source. The resulting NG contains 2.4 at.% N, of which as high as 1.2 at.% is quaternary N. Electrochemical characterizations reveal that the NG has excellent catalytic activity toward oxygen reduction reaction (ORR) in an alkaline electrolyte, including a desirable four-electron pathway for the formation of water, large kinetic-limiting current density, long-term stability and good tolerance to methanol crossover. In addition, we demonstrate that the NG also has high catalytic activity toward oxygen evolution reaction (OER), rendering its potential application as a bi-functional catalyst for both ORR and OER.     

Enhancement of weak localization for nitrogen-doped graphene by short range potentials

We have prepared pristine graphene and nitrogen-doped graphene on copper foils by chemical vapor deposition. Compared with the pristine graphene, an increased disorder in nitrogen-doped graphene was confirmed by Raman spectra studies. Temperature dependent Hall resistances and magnetoresistances were measured for both samples. The carrier densities can be extracted from the experimental datum. Abrupt decreases of magnetoresistances near zero magnetic field strongly suggest weak localization effects for both samples. Furthermore, more obvious decreases of magnetoresistances near zero magnetic field and valleys at higher magnetic fields were observed due to an enhancement of weak localization for nitrogen-doped graphene. The whole field dependence of magnetoresistance at different temperatures can be well fitted by a revised McCann model. By defining characteristic magnetic fields, visual phase diagrams were obtained. In addition, larger weak localization area was found for nitrogen-doped graphene than the one for pristine graphene. Our results manifest that an increased elastic intervalley scattering which comes from the increased disorder with short range potentials should account for the expected enhancement of the weak localization for nitrogen-doped graphene.     

Restacking-inhibited nitrogen-incorporated mesoporous reduced graphene oxides for high energy supercapacitors

Graphene is considered a promising active electrode material due to a large surface area, high electronic conductivity, and chemical and mechanical stabilities for supercapacitor (SC) applications. However, the current bottleneck is the fabrication of restacking-inhibited graphene on an electrode level which otherwise loses the capability to achieve the aforementioned properties. Herein, we demonstrate the synthesis of restacking-inhibited nitrogen (N)-incorporated mesoporous graphene for high energy SCs. The melamine-formaldehyde acts as a restacking inhibitor by forming a bonding with reduced graphene oxide (RGO) through a condensation reaction and as an N precursor to be decomposed to create open pores and N sources upon heat treatment. The d-spacing increases up to 0.352 nm and the surface area is as high as 698 m² g^?1 with high mesoporosity, confirming restacking inhibition by N incorporation decomposed by melamine-formaldehyde. The restacking-inhibited RGO-based SC cells in organic electrolyte show the specific capacitance of 25.8 F g^?1, the energy density of 21.8 kW kg^?1 and 85% of capacitance retention for 5000 cycles, which are better than those of pristine RGO-based cells. These improved SC performances are attributed to the fast ion transport through a mesoporous channel in crumpled structure and the doping effect of N incorporation. This work provides a simple yet effective chemical approach to fabricate restacking-inhibited RGO electrodes for improved SC performances.     

Far-infrared reduced graphene oxide as high performance electrodes for supercapacitors

We report a novel far-infrared (FIR) thermal reduction process to effectively reduce graphene oxide films for supercapacitor electrode applications. The binder-free graphene oxide films used in this study were produced by electro-spray deposition of a graphene oxide colloidal solution onto stainless steel current collectors. The reduction of graphene oxide was performed using a commercial FIR convection oven that is ubiquitous in homes for cooking and heating food. The reduction process incorporated a simple, one-step FIR irradiation carried out in ambient air. Further, the FIR irradiation process was completed in ∼3 min, wherein neither special atmosphere nor high temperature was employed, resulting in an economic, efficient and simplified processing technique. The as-produced FIR graphene electrode gave a specific capacitance of ∼320 F/g at a current density of ∼0.2 A/g with less than 94% loss in specific capacitance over 10,000 charge/discharge cycles. This is one of the best specific capacitances reported for all-carbon electrodes without any additives. Even at ultrafast charge/discharge rates (current densities as high as ∼100 A/g), the FIR graphene electrode still delivered specific capacitances in excess of 90 F/g. The measured energy and power densities of the FIR supercapacitors were found to be ∼3–6 times higher than commercial (activated carbon) supercapacitor devices. This excellent electrochemical performance of the FIR graphene coupled with its ease of production (in air at low temperatures) using a commercial home-use FIR convection oven indicates the significant potential of this concept for large-scale commercial electrochemical supercapacitor applications.     

All-gel-state supercapacitors of polypyrrole reinforced with graphene nanoplatelets

The development of supramolecular structures (conducting hydrogels) obtained from the charge–charge interaction of sodium dodecyl sulfate micelles and oppositely charged polypyrrole chains represents an important step to obtain self-supported and flexible electrodes for supercapacitors. Herein, the energy density of polypyrrole hydrogel-based supercapacitors is enhanced by the incorporation of graphene nanoplatelets that introduced the electrical double capacitance contribution to the overall response. The electrochemical performance of synthesized electrodes was optimized from the relative variation in the concentration of supramolecular arrangements (micelles of sodium dodecyl sulfate), pyrrole, and graphene nanoplatelets. As result, higher capacitive retention is observed for modified electrodes (with the incorporation of graphene) – in order of 90% after 1000 cycles of use, preserving the high conductivity and intrinsic mechanical properties (flexibility and stretchability) reaching an areal capacitance of 210.7 mFcm⁻².     

Chemical reduction-induced fabrication of graphene hybrid fibers for energy-dense wire-shaped supercapacitors

The emerging one-dimensional wire-shaped supercapacitors(SCs) with structural advantages of low mass/volume structural advantages hold great interests in wearable electronic engineering. Although graphene fiber(GF) has full of vigor and tremendous potentiality as promising linear electrode for wire-shaped SCs, simultaneously achieving its facile fabrication process and satisfactory electrochemical performance still remains challenging to date. Herein, two novel types of graphene hybrid fibers, n...