Porous nitrogen-doped graphene/carbon nanotubes composite with an enhanced supercapacitor performance

MIL-53(Al) assisted in upcycling plastic bottle waste into nitrogen-doped hierarchical porous carbon for high-performance supercapacitors

Disposable aluminum cans and plastic bottles are common wastes found in modern societies. This article shows that they can be upcycled into functional materials, such as metal-organic frameworks and hierarchical porous carbon nanomaterials for high-value applications. Through a solvothermal method, used poly(ethylene terephthalate) bottles and aluminum cans are converted into MIL-53(Al). Subsequently, the as-prepared MIL-53(Al) can be further carbonized into a nitrogen-doped (4.52 at%) hierarchical porous carbon framework. With an optical amount of urea present during the carbonization process, the carbon nanomaterial of a high specific surface area of 1324 m2 g-1 with well-defined porosity can be achieved. These features allow the nitrogen-doped hierarchical porous carbon to perform impressively as the working electrode of supercapacitors, delivering a high specific capacitance of 355 F g-1 at 0.5 A g-1 in a three-electrode cell and exhibiting a high energy density of 20.1 Wh kg-1 at a power density of 225 W kg-1, while simultaneously maintaining 88.2% capacitance retention over 10,000 cycles in two-electrode system. This work demonstrates the possibility of upcycling wastes to obtain carbon-based high-performance supercapacitors.

Graphene Nanoflake- and Carbon Nanotube-Supported Iron-Potassium 3D-Catalysts for Hydrocarbon Synthesis from Syngas

Transformation of carbon oxides into valuable feedstocks is an important challenge nowadays. Carbon oxide hydrogenation to hydrocarbons over iron-based catalysts is one of the possible ways for this transformation to occur. Carbon supports effectively increase the dispersion of such catalysts but possess a very low bulk density, and their powders can be toxic. In this study, spark plasma sintering was used to synthesize new bulk and dense potassium promoted iron-based catalysts, supported on N-doped carbon nanomaterials, for hydrocarbon synthesis from syngas. The sintered catalysts showed high activity of up to 223 μmol_CO/g_Fe/s at 300-340 °C and a selectivity to C₅₊ fraction of ~70% with a high portion of olefins. The promising catalyst performance was ascribed to the high dispersity of iron carbide particles, potassium promotion of iron carbide formation and stabilization of the active sites with nitrogen-based functionalities. As a result, a bulk N-doped carbon-supported iron catalyst with 3D structure was prepared, for the first time, by a fast method, and demonstrated high activity and selectivity in hydrocarbon synthesis. The proposed technique can be used to produce well-shaped carbon-supported catalysts for syngas conversion.

Current Understanding of Water Properties inside Carbon Nanotubes

Confined water inside carbon nanotubes (CNTs) has attracted a lot of attention in recent years, amassing as a result a very large number of dedicated studies, both theoretical and experimental. This exceptional scientific interest can be understood in terms of the exotic properties of nanoconfined water, as well as the vast array of possible applications of CNTs in a wide range of fields stretching from geology to medicine and biology. This review presents an overreaching narrative of the properties of water in CNTs, based mostly on results from systematic nuclear magnetic resonance (NMR) and molecular dynamics (MD) studies, which together allow the untangling and explanation of many seemingly contradictory results present in the literature. Further, we identify still-debatable issues and open problems, as well as avenues for future studies, both theoretical and experimental.

Jellyfish-like few-layer graphene nanoflakes: high paramagnetic response alongside increased interlayer interaction

Jellyfish-like graphene nanoflakes (GNF), prepared by hydrocarbon pyrolysis, are studied with electron paramagnetic resonance (EPR) method. The results are supported by X-ray photoelectron spectroscopy (XPS) data. Oxidized (GNFox) and N-doped oxidized (N-GNFox) flakes exhibit an extremely high EPR response associated with a large interlayer interaction which is caused by the structure of nanoflakes and layer edges reached by oxygen. The GNFox and N-GNFox provide the localized and mobile paramagnetic centers which are silent in the pristine (GNF p ) and N-doped (N-GNF) samples. The change in the relative intensity of the line corresponding to delocalized electrons is parallel with the number of radicals in the quaternary N-group. The environment of localized and mobile electrons is different. The results can be important in GNF synthesis and for explanation of their features in applications, especially, in devices with high sensitivity to weak electromagnetic field.

Graphene/Reduced Graphene Oxide-Carbon Nanotubes Composite Electrodes: From Capacitive to Battery-Type Behaviour

Thanks to the advanced technologies for energy generation such as solar cells and thermo- or piezo-generators the amount of electricity transformed from light, heat or mechanical pressure sources can be significantly enhanced. However, there is still a demand for effective storage devices to conserve electrical energy which addresses the wide range of large stationary applications from electric vehicles to small portable devices. Among the large variety of energy-storage systems available today, electrochemical energy sources and, in particular, supercapacitors (SC), are rather promising in terms of cost, scaling, power management, life cycle and safety. Therefore, this review surveys recent achievements in the development of SC based on composites of such carbon-derived materials as graphene (G) and reduced graphene oxide (rGO) with carbon nanotubes (CNT). Various factors influencing the specific capacitance are discussed, while specific energy and power as well as cycling stability of SC with G/rGO-CNT composite electrode materials are overviewed.

Hybridized Graphene for Supercapacitors: Beyond the Limitation of Pure Graphene

Graphene-based supercapacitors have been attracting growing attention due to the predicted intrinsic high surface area, high electron mobility, and many other excellent properties of pristine graphene. However, experimentally, the state-of-the-art graphene electrodes face limitations such as low surface area, low electrical conductivity, and low capacitance, which greatly limit their electrochemical performances for supercapacitor applications. To tackle these issues, hybridizing graphene with other species (e.g., atom, cluster, nanostructure, etc.) to enlarge the surface area, enhance the electrical conductivity, and improve capacitance behaviors are strongly desired. In this review, different hybridization principles (spacers hybridization, conductors hybridization, heteroatoms doping, and pseudocapacitance hybridization) are discussed to provide fundamental guidance for hybridization approaches to solve these challenges. Recent progress in hybridized graphene for supercapacitors guided by the above principles are thereafter summarized, pushing the performance of hybridized graphene electrodes beyond the limitation of pure graphene materials. In addition, the current challenges of energy storage using hybridized graphene and their future directions are discussed.

Fishnet-Like, Nitrogen-Doped Carbon Films Directly Anchored on Carbon Cloths as Binder-Free Electrodes for High-Performance Supercapacitor

The low specific capacitance and energy density of carbon electrode has extremely limited the wide application of supercapacitors. For developing a high-performance carbon electrode using a simple and effective method, a fishnet-like, N-doped porous carbon (FNPC) film is prepared by calcining the KOH-activated polyindole precoated on carbon cloths. The FNPC film is tightly anchored on carbon cloths without any binder. The FNPC film with 3.8 at% N content exhibits a fairly high specific capacitance of 416 F g^-1 at 1.0 A g^-1. Moreover, the assembled button-type cell with two FNPC film electrodes shows a high energy density of 16.4 Wh kg^-1, a high power density of 67.4 kW kg^-1, and long-term cyclic stability of 92% of the initial capacitance after 10 000 cycles at 10 A g^-1. The high performances mainly came from the integration of pseudocapacitance and electrical double-layer capacitance behavior, wettability, fishnet-like nanostructure, as well as the low interfacial resistivity. This strategy provides a practical, uncomplicated, and low-cost design of binder-free flexible carbon materials electrode for high-performance supercapacitors.

Chemical Simultaneous Synthesis Strategy of Two Nitrogen-Rich Carbon Nanomaterials for All-Solid-State Symmetric Supercapacitor

Present work demonstrates a single step process for simultaneous synthesis of metal-nanoparticle-encapsulated nitrogen-doped bamboo-shaped carbon nanotubes (M/N-BCNTs) and graphitic carbon nitride (G-C₃N₃). The synthesis of two different carbon nanostructures in a single step is recognized for the first time. This process involves the use of inexpensive and nontoxic precursors such as melamine as carbon and nitrogen sources for the growth of G-C₃N₃ and M/N-BCNTs. In this technique, the utilization of unwanted gases such as ammonia and hydrocarbons released during the decomposition of melamine is the key to grow M/N-BCNTs over the catalyst along with the formation of G-C₃N₄. The implementation of M/N-BCNTs as the electrode material for all-solid-state symmetric supercapacitor results in a maximum specific capacitance of ∼368 F g^-1 with excellent electrochemical stability with 97% capacity retention after 10 000 cycles. Furthermore, fabricated symmetric supercapacitor shows maximum high energy and power density up to 10.88 W h kg^-1 and 2.06 kW kg^-1, respectively. The superior electrochemical activity of M/N-BCNTs can be attributed to its high surface to area volume ratio, unique structural characteristics, ultrahigh electrical conductivity, and carrier mobility.

Bioinspired Assembly of Carbon Nanotube into Graphene Aerogel with "Cabbagelike" Hierarchical Porous Structure for Highly Efficient Organic Pollutants Cleanup

Nowadays, physical absorption has become a feasible method offering an efficient and green route to remove organic pollutants from the industrial wastewater. Inspired by polydopamine (PDA) chemistry, one-dimensional PDA-functionalized multiwalled carbon nanotubes (MWCNT-PDA) were creatively introduced into graphene aerogel framework to synthesize a robust graphene/MWCNT-PDA composite aerogel (GCPCA). The whole forming process needed no additional reducing agents, significantly reducing the contamination emissions to the environment. The GCPCA exhibited outstanding repeatable compressibility, ultralight weight, as well as hydrophobic nature, which were crucial for highly efficient organic pollution absorption. The MWCNTs in moderate amounts can provide the composite aerogels with desirable structure stability and extra specific surface area. Meanwhile, the eventual absorption performance of GCPCAs can be improved by optimizing the microporous structure. In particular, a novel "cabbagelike" hierarchical porous structure was obtained as the prefreezing temperature was decreased to -80 °C. The miniaturization of pore size around the periphery of GCPCA enhanced the capillary flow in aerogel channels, and the super-absorption capacity for organic solvents was up to 501 times (chloroform) its own mass. Besides, the GCPCAs exhibited excellent reusable performance in absorption-squeezing, absorption-combustion, and absorption-distillation cycles according to the characteristic of different organic solvents. Because of the viable synthesis method, the resulting GCPCAs with unique performance possess broad and important application prospects, such as oil pollution cleanup and treatment of chemical industrial wastewater.

Nitrogen-enriched carbon spheres coupled with graphitic carbon nitride nanosheets for high performance supercapacitors

A facile two-step method is proposed to synthesize g-CN/NCS composites, which exhibit an excellent electrochemical performance in clean energy storage devices.

Metal-Organic Coordination Polymer to Prepare Density Controllable and High Nitrogen-Doped Content Carbon/Graphene for High Performance Supercapacitors

Design and preparation of carbon-based electrode material with high nitrogen-doping ratio and appropriate density attract much interest for supercapacitors in practical application. Herein, three porous carbon/graphene (NCG_Cu, NCG_Fe, and NCG_Zn) with high doping ratio of nitrogen have been prepared via directly pyrolysis of graphene oxide (GO)/metal-organic coordination polymer (MOCP) composites, which were formed by reacting 4,4'-bipyridine (BPD) with CuCl₂, FeCl₃, and ZnCl₂, respectively. As-prepared NCG_Cu, NCG_Fe and NCG_Zn showed high nitrogen doping ratio of 10.68, 12.99, and 11.21 at. %; and high density of 1.52, 0.84, and 1.15 g cm^-3, respectively. When as-prepared samples were used as supercapacitor electrodes, NCG_Cu, NCG_Fe and NCG_Zn exhibited high gravimetric specific capacitances of 369, 298.5, 309.5 F g^-1, corresponding to high volumetric specific capacitances of 560.9, 250.7, 355.9 F cm^-3 at a current density of 0.5 A g^-1, as well as good cycling stability, nearly 100% of the capacitance retained after 1000 cycles even at a large current density of 10 A g^-1. It is expected that the provided novel strategy can be used to develop electrode materials in high performance energy conversion/storage devices.

A three dimensional N-doped graphene/CNTs/AC hybrid material for high-performance supercapacitors

Single walled carbon nanotubes and activated carbon intercalated N-doped graphene hybrid material was successfully fabricated and exhibited high performance as a supercapacitor.

Inherent N,O-containing carbon frameworks as electrode materials for high-performance supercapacitors

N,O-Containing micropore-dominated materials have been developed successfully via temperature-dependent cross-linking of 4,4'-(dioxo-diphenyl-2,3,6,7-tetraazaanthracenediyl)dibenzonitrile (DPDN) monomers. By employing a molecular engineering strategy, we have designed and synthesized a series of porous heteroatom-containing carbon frameworks (PHCFs), in which nitrogen and oxygen heteroatoms are distributed homogeneously throughout the whole framework at the atomic level, which can ensure the stability of its electrical properties. The as-made PHCFs@550 exhibits a high specific capacitance of 378 F g^-1, with an excellent long cycling life, including excellent cycling stability (capacitance retention of ca. 120% over 20 000 cycles). Moreover, the successful preparation of PHCFs provides new insights for the fabrication of nitrogen and oxygen-containing electrode materials from readily available components via a facile route.

Enhanced capacitive desalination of MnO2 by forming composite with multi-walled carbon nanotubes

The MnO₂/MWCNTs composite shows a high desalination capacity of 6.65 mg g⁻¹ and good efficiency, which can be considered as a promising electrode material for CDI.

Substrate effect on the properties of functionalized multiwalled carbon nanotubes grown by e-beam evaporation for high performance H2O2 detection

In the present study, the properties of functionalized multiwalled carbon nanotube thin films deposited on Ta and Al₂O₃ substrates were compared for better electrochemical sensing performance towards H₂O₂.

Nitrogen-doped reduced graphene oxide and aniline based redox additive electrolyte for a flexible supercapacitor

Nitrogen-doped reduced graphene oxide (N-rGO) with a flexible structure was prepared by simple hydrothermal method. The N-rGO flexible supercapacitor fabricated and improved the performance using aniline as redox additive.