Hierarchically nanoperforated graphene as a high performance electrode material for ultracapacitors

Preparation of Ultrahigh Molecular Weight Polyethylene/Graphene Nanocomposite In situ Polymerization via Spherical and Sandwich Structure Graphene/Sio2 Support

Reduced graphene oxide/SiO₂ (RGO/SiO₂) serving as a novel spherical support for Ziegler-Natta (Z-N) catalyst is reported. The surface and interior of the support has a porous architecture formed by RGO/SiO₂ sandwich structure. The sandwich structure is like a brick wall coated with a graphene layer of concreted as skeleton which could withstand external pressures and endow the structure with higher support stabilities. After loading the Z-N catalyst, the active components anchor on the surface and internal pores of the supports. When the ethylene molecules meet the active centers, the molecular chains grow from the surface and internal catalytic sites in a regular and well-organized way. And the process of the nascent molecular chains filled in the sandwich structure polymerization could ensure the graphene disperse uniformly in the polymer matrix. Compared with traditional methods, the porous spherical graphene support of this strategy has far more advantages and could maintain an intrinsic graphene performance in the nanocomposites.

Recent Breakthroughs in Supercapacitors Boosted by Nitrogen-Rich Porous Carbon Materials

Featured with unique mechanical, electronic and chemical properties, nitrogen-doped carbon materials have become the research hotspot of energy storage. As electrode materials in supercapacitors (SCs), N-doped carbons have demonstrated intriguing flexibility and superb performances in a wide electrochemical window, equipped with versatile properties as both cathodes and anodes for constructing high voltage devices. Compared with limited doping level, N-rich and porous carbon materials (NPCs) are of great desire to release the restricted properties of N species and obtain high specific capacitances (>600 F g^-1), pushing the energy density towards the battery level without scarifying the capacitor-level power ability. In this Research News we firstly discuss the key factors influencing the performance of NPC electrodes to disclose related charge storage mechanisms. In addition, the trade-off among N-content, porous structure and electrical conductivity is involved as well as electrochemical behaviors in different electrolytes. Also, various progressive developments are highlighted systematically ranging from asymmetric to symmetric and hybrid configurations, covering both aqueous and non-aqueous systems. Finally, some stubborn and unsolved problems are summarized, with prospective research guidelines on NPC-based SCs.

Materials Design and System Construction for Conventional and New-Concept Supercapacitors

With the development of renewable energy and electrified transportation, electrochemical energy storage will be more urgent in the future. Supercapacitors have received extensive attention due to their high power density, fast charge and discharge rates, and long-term cycling stability. During past five years, supercapacitors have been boomed benefited from the development of nanostructured materials synthesis and the promoted innovation of devices construction. In this review, we have summarized the current state-of-the-art development on the fabrication of high-performance supercapacitors. From the electrode material perspective, a variety of materials have been explored for advanced electrode materials with smart material-design strategies such as carbonaceous materials, metal compounds and conducting polymers. Proper nanostructures are engineered to provide sufficient electroactive sites and enhance the kinetics of ion and electron transport. Besides, new-concept supercapacitors have been developed for practical application. Microsupercapacitors and fiber supercapacitors have been explored for portable and compact electronic devices. Subsequently, we have introduced Li-/Na-ion supercapacitors composed of battery-type electrodes and capacitor-type electrode. Integrated energy devices are also explored by incorporating supercapacitors with energy conversion systems for sustainable energy storage. In brief, this review provides a comprehensive summary of recent progress on electrode materials design and burgeoning devices constructions for high-performance supercapacitors.

Longitudinal unzipped carbon nanotubes with high specific surface area and trimodal pore structure

This study reports unzipped carbon nanotubes (CNTs) with a trimodal (micro–meso–macro) pore structure using KOH as the activating agent.

Non-templated ambient nanoperforation of graphene: a novel scalable process and its exploitation for energy and environmental applications

Nano-perforation of 2D graphene sheets is a recent and strategically significant means to exploit such materials in modern applications such as energy production and storage. However, current options for the synthesis of holey graphene (hG) through nano-perforation of graphene involve industrially undesirable steps viz., usage of expensive/noble metal or silica nanoparticle templates and/or hazardous chemicals. This severely hampers its scope for large scale production and further exploitation. Herein, we report for the first time a scalable non-templated route to produce hG at ambient conditions. Nano-perforation is achieved with tunable pore size via the simple few layer co-assembly of silicate-surfactant admicelles along the surface of graphene oxide. A gentle alkali treatment and a reduction at optimized conditions readily yielded holey graphene with a remarkable capacitance (∼250 F g(-1)) and interesting adsorption abilities for pollutants. Density functional theory based computational studies reveal interesting insights on the template free nano-perforation at a molecular level. This simple rapid process not only excludes the need for expensive templates and harmful chemicals to yield hG at attractively ambient, chemically placid and industrially safer conditions, but also creates no hurdles in terms of scaling up.

Freestanding polyaniline nanorods grown on graphene for highly capacitive energy storage

Freestanding polyaniline (PANI) nanorods grown in situ on microwave-expanded graphene oxide (MEGO) sheets were prepared through a facile solution method. The morphological characterization indicates that large quantity of free-standing PANI nanorods with average diameter of 50 nm were uniformly deposited onto the double sides of the MEGO nanosheets to form a sandwich structure. The hybrid of PANI/MEGO (GPANI) exhibit high specific surface area and high electrical conductivity, compared with pristine PANI nanorods. When evaluated as electrodes for supercapacitors, the GPANI demonstrate high specific capacitance of 628 F g(-1) at a current density of 1.1 A g(-1), high-rate performance, and excellent cycle stability compared to individual component. Such excellent electrochemical performance should be attributed to the combined double-layer capacitance and pseudo -capacitance mechanisms from the MEGO sheets and PANI nanorods.

Natural-gel derived, N-doped, ordered and interconnected 1D nanocarbon threads as efficient supercapacitor electrode materials

Natural gel pectin is transformen into interconnected, N-doped, ordered and Interconnected 1D nano-carbon threads upon high temperature pyrolysis inside SBA-15.

Synergistic fusion of vertical graphene nanosheets and carbon nanotubes for high-performance supercapacitor electrodes

Graphene and carbon nanotubes (CNTs) are attractive electrode materials for supercapacitors. However, challenges such as the substrate-limited growth of CNTs, nanotube bundling in liquid electrolytes, under-utilized basal planes, and stacking of graphene sheets have so far impeded their widespread application. Here we present a hybrid structure formed by the direct growth of CNTs onto vertical graphene nanosheets (VGNS). VGNS are fabricated by a green plasma-assisted method to break down and reconstruct a natural precursor into an ordered graphitic structure. The synergistic combination of CNTs and VGNS overcomes the challenges intrinsic to both materials. The resulting VGNS/CNTs hybrids show a high specific capacitance with good cycling stability. The charge storage is based mainly on the non-Faradaic mechanism. In addition, a series of optimization experiments were conducted to reveal the critical factors that are required to achieve the demonstrated high supercapacitor performance.

Confined growth of carbon nanoforms in one-dimension by fusion of anthracene rings inside the pores of MCM-41

We report a simple two-step procedure that uses anthracene, a cheap polyaromatic hydrocarbon with low melting point, as a molecular precursor to produce carbon nanoforms (CNFs). First, we describe the chemical synthesis of graphite from the fusion of anthracene rings at relatively low temperature (520 °C) followed by cyclodehydrogenation. Next, we extend this protocol to the synthesis of CNFs by confining the molecular precursor in a mesoporous host like MCM-41. The confined environment favors one-dimensional growth of CNFs with sizes controlled by the pores of the mesoporous host.

Hierarchical nanohybrids with porous CNT-networks decorated crumpled graphene balls for supercapacitors

One of the most challenging issues in developing supercapacitor technology is the rational design and synthesis of active electrode materials, at the nanoscale, with favorable morphologies, reasonable porous structure, and excellent conductivity. By transforming a two-dimensional (2D) graphene sheet into a crumpled ball shape, a novel three-dimensional (3D) graphene structure with a large surface area and aggregation-resistant properties has been proposed as an active material in supercapacitors to address the issues associated with the restacking of 2D graphene sheets. To further improve the mass transport/electron transfer and address the issue of limited contact spots between the crumpled graphene balls (CGBs) or between the CGBs and the current collector, we report here a unique hierarchical nanohybrid with porous carbon nanotube (CNT)-networks decorated CGBs (p-CNTn/CGBs), which not only greatly improves the affinity for bridging the active material and the current collector but also maintains favorable features for supercapacitor applications, such as a large surface area, 3D hierarchical nanostructure, excellent electrical conductivity, and outstanding aggregation-resistance. The performance established on the p-CNTn/CGBs far exceeded the bare CGB and reduced graphene oxide (RGO) counterparts in terms of specific capacitance and rate capabilities.

Fe3O4/carbon hybrid nanoparticle electrodes for high-capacity electrochemical capacitors

Fe3O4/carbon hybrid nanoparticles (FeCHNPs) were fabricated using dual-nozzle electrospraying, vapor deposition polymerization (VDP), and carbonization. FeOOH nanoneedles decorated with polypyrrole (PPy) nanoparticles (FePNPs) were fabricated by electrospraying pristine PPy mixed with FeCl3 solution, followed by heating stirring reaction. A PPy coating was then formed on the FeOOH nanoneedles through a VDP process. FeCHNPs were produced through carbonization of PPy and FeOOH phase transitions. These hybrid carbon nanoparticles (NPs) were used to build electrodes of electrochemical capacitors. The specific capacitance of the FeCHNPs was 455 F g(-1), which is larger than that of pristine PPy NPs (105 F g(-1)) or other hybrid PPy NPs. Furthermore, the FeCHNP-based capacitors exhibited better cycle stability during charge-discharge cycling than other hybrid NP capacitors. This is because the carbon layer on the Fe3 O4 surface formed a protective coating, preventing damage to the electrode materials during the charge-discharge processes. This fabrication technique is an effective approach for forming stable carbon/metal oxide nanostructures for energy storage applications.