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.

Currently-developed flexible electrodes/supercapacitors are summarized according a hierarchical and detailed classification strategy.

A cost-effective approach to obtain electrode materials with excellent electrochemical performance is critical to the development of supercapacitors (SCs). Here we report the preparation of a three-dimensional (3D) honeycomb-like porous carbon (HLPC) by the simple carbonization of pomelo peel followed by KOH activation. Structural characterization indicates that the as-prepared HLPC with a high specific surface area (SSA) up to 2725 m(2) g(-1) is made up of interconnected microporous carbon walls. Chemical analysis shows that the HLPC is doped with nitrogen and also has oxygen-containing groups. Electrochemical measurements show that the HLPC not only exhibits a high specific capacitance of 342 F g(-1) and 171 F cm(-3) at 0.2 A g(-1) but also shows considerable rate capability with a retention of 62% at 20 A g(-1) as well as good cycling performance with 98% retention over 1000 cycles at 10 A g(-1) in 6 M KOH. Furthermore, an as-fabricated HLPC-based symmetric SC device delivers a maximum energy density of ∼9.4 Wh kg(-1) in the KOH electrolyte. Moreover, the outstanding cycling stability (only 2% capacitance decay over 1000 cycles at 5 A g(-1)) of the SC device makes it promising for use in a high-performance electrochemical energy system.

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.

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Carbon materials for electrodes of capacitive deionization (CDI) process are reviewed.

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 À1 , almost 50% higher than the optimal result reported in the literature. By comparing with other carbonbased 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.