Zheng-Hong Huang

Towards ultrahigh volumetric capacitance: graphene derived highly dense but porous carbons for supercapacitors

A small volumetric capacitance resulting from a low packing density is one of the major limitations for novel nanocarbons finding real applications in commercial electrochemical energy storage devices. Here we report a carbon with a density of 1.58 g cm−3, 70% of the density of graphite, constructed of compactly interlinked graphene nanosheets, which is produced by an evaporation-induced drying of a graphene hydrogel. Such a carbon balances two seemingly incompatible characteristics: a porous microstructure and a high density, and therefore has a volumetric capacitance for electrochemical capacitors (ECs) up to 376 F cm−3, which is the highest value so far reported for carbon materials in an aqueous electrolyte. More promising, the carbon is conductive and moldable, and thus could be used directly as a well-shaped electrode sheet for the assembly of a supercapacitor device free of any additives, resulting in device-level high energy density ECs.

Adsorption of lead(II) ions from aqueous solution on low-temperature exfoliated graphene nanosheets.

Graphene nanosheets (GNSs) that were obtained by vacuum-promoted low-temperature exfoliation were used to adsorb lead ions from an aqueous system. The pristine and thermally modified GNSs were characterized with scanning electron microscopy observation and X-ray photoelectron spectroscopy analysis. It was interestingly found that the adsorption against lead ions was enhanced by heat treatment, although the oxygen complexes of GNSs showed a significant decrease. In addition, lead ion uptake resulted in an increase in the pH value of the solution. It is supposed that the Lewis basicity of GNSs is improved by heat treatment under a high vacuum, in favor of simultaneous adsorption of lead ions and protons onto GNSs.

Macroscopic 3D Porous Graphitic Carbon Nitride Monolith for Enhanced Photocatalytic Hydrogen Evolution

A macroscopic 3D porous graphitic carbon nitride (g-CN) monolith is prepared by the one-step thermal polymerization of urea inside the framework of a commercial melamine sponge and exhibits improved photocatalytic water-splitting performance for hydrogen evolution compared to g-CN powder due to the 3D porous interconnected network, larger specific surface area, better visible light capture, and superior charge-separation efficiency.

Rational synthesis of MnO2/conducting polypyrrole@carbon nanofiber triaxial nano-cables for high-performance supercapacitors

This study presents a rational synthesis of hierarchical MnO2/conducting polypyrrole (PPy)@carbon nanofiber (CNF) triaxial nano-cables via in situ interfacial redox reaction. Uniform MnO2/PPy multifunctional nanocoatings (∼20 nm) are formed on individual electrospun CNFs, constructing a one-dimensional triaxial configuration. The unique architecture enables a maximum value of the MnO2/PPy pseudocapacitance and a strong synergetic effect of each component. The specific capacitance of the ternary nanocomposite as a freestanding electrode reaches as high as 705 F g−1 at 2 mV s−1. The three-dimensional porous electrode facilitates a large mass loading of active materials up to 2.0 mg cm−2, which leads to a high areal capacitance of 1.4 F cm−2. The improved electrical conductivity and strong structural integrity of the nanocomposite also endow the electrodes with good rate capability and long-term cycling stability. The superior electrochemical performance indicates that this method is an effective strategy for developing multifunctional nanocomposite electrodes for energy storage devices.

Flexible electrodes and supercapacitors for wearable energy storage: a review by category

Supercapacitors are important energy storage devices capable of delivering energy at a very fast rate. With the increasing interest in portable and wearable electronic equipment, various flexible supercapacitors (FSCs) and flexible electrodes (FEs) have been investigated widely and constantly in recent years. Currently-developed FEs/FSCs exhibit myriad physical forms and functional features and form a complicated and extensive system. Herein, we summarize the recent results about FEs/FSCs and present this review by categories. According to different micro-structures and macroscopic patterns, the existing FEs/FSCs can be divided into three types: fiber-like FEs/FSCs; paper-like FEs/FSCs; and three-dimensional porous FEs (and corresponding FSCs). Subsequently each type of the FEs/FSCs is further sub-classified based on their construction rules, and mechanical and electrochemical properties. To our best knowledge, this is the first time such a hierarchical and detailed classification strategy has been propose. We believe it will be beneficial for researchers around the world to understand FEs/FSCs. In addition, we bring up some fresh ideas for the future development of wearable energy storage devices.

Preparation and properties of phenolic resin-based activated carbon spheres with controlled pore size distribution

Abstract Three kinds of phenolic resin-based activated carbon spheres (P-ACS) with different pore size distribution were prepared successfully by adding pore-forming agents to novolac-type phenolic resin. Polyethylene glycol and polyvinyl butyral, serving as pore-forming agents, evaporated during pyrolysis and left a small amount of carbon residue in the matrix of the phenolic resin-based carbon, thus changing the carbonization and activation behavior of the resin. Mesopores between 3 and 5 nm were created in the P-ACS, which possessed excellent adsorption properties for creatinine. Ferrocene has little effect on the carbonization process of the phenolic resin, but has a great impact on the activation process. Mesopores and macropores with a range from 3–5 to 10–90 nm were produced in the P-ACS, which exhibited large adsorption properties for VB 12 , a larger molecule than creatinine. P-ACS without pore-forming agents exhibited a small specific surface area and mainly micropores, which resulted in a very small amount of creatinine and VB 12 adsorbed.

Capacitive deionization of NaCl solutions using carbon nanotube sponge electrodes

Capacitive Deionization (CDI) is a promising method for desalination of brackish water because of its energy-efficiency as compared with conventional techniques such as membrane separation and thermal distillation. Carbon nanotube (CNT) sponges, prepared by chemical vapor deposition, are very flexible and have three-dimensional continuous and mesoporous structures, making them promising electrode materials for capacitive deionization. The CDI characteristics of CNT sponges were investigated for the first time by simply compressing them into a CDI cell without any additives. Desalination of NaCl solutions at different concentrations was conducted with a flow-through CDI cell at 1.2V. Experimental data fit well with the Langmuir model, and the deduced maximum desalination capacity was 40 mg g−1, almost 50% higher than the optimal result reported in the literature. By comparing with other carbon-based materials, the excellent CDI performance of CNT sponges was attributed to higher conductivity and larger effective surface area due to their monolithic continuous flexible framework, crystalline microstructure and preferred pore size distribution.

Enhanced efficiency of graphene/silicon heterojunction solar cells by molecular doping

Graphene (G) films were grown on copper foils by chemical vapor deposition and transferred onto n-type silicon (Si) to form G/Si Schottky heterojunction solar cells. The power conversion efficiencies (PCEs) of the G/Si solar cells were in the range of 1.94–2.66%. Four volatile oxidants HNO3, HCl, H2O2 and SOCl2 were employed to treat the graphene films in the G/Si solar cells, and the PCEs could be greatly enhanced after being treated by all the volatile oxidants and SOCl2 doping showed the best improvement. A solar cell with an initial PCE of 2.45% could be increased to 5.95% upon SOCl2 doping treatment. The PCE stability of the volatile oxidant-treated cells was also investigated. The PCEs decreased with time, while SOCl2 and HCl showed much better PCE stability than HNO3 and H2O2.

Breakthrough of methyethylketone and benzene vapors in activated carbon fiber beds

The breakthrough of low concentration methyethylketone (MEK) and benzene vapors in beds packed with rayon-based activated carbon fiber (ACF) with different surface areas was investigated. The breakthrough characteristics depend on the properties of the ACF and the vapors, as well as on the adsorption conditions. The results of dynamic adsorption in an ACF bed were consistent with those of equilibrium adsorption by gravimetric methods. The breakthrough adsorption indicates that ACF, with an appropriate surface area, could be utilized in controlling volatile organic compounds (VOCs) in indoor air.

Nitrogen-enriched electrospun porous carbon nanofiber networks as high-performance free-standing electrode materials

Nitrogen-enriched porous carbon nanofiber networks (NPCNFs) were successfully prepared by using low-cost melamine and polyacrylonitrile as precursors via electrospinning followed by carbonization and NH3 treatments. The NPCNFs exhibited inter-connected nanofibrous morphology with a large specific surface area, well-developed microporous structure, relatively high-level nitrogen doping and great amount of pyridinic nitrogen. As free-standing new anode materials in lithium-ion batteries (LIBs), the NPCNFs showed ultrahigh capacity, good cycle performance and superior rate capability with a reversible capacity of as high as 1323 mA h g−1 at a current density of 50 mA g−1. These attractive characteristics make the NPCNFs materials very promising anode candidates for high-performance LIBs and, as free-standing electrode materials to be used in other energy conversion and storage devices.