Xiaoyu Zheng

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.

Two‐Dimensional Porous Carbon: Synthesis and Ion‐Transport Properties

Their chemical stability, high specific surface area, and electric conductivity enable porous carbon materials to be the most commonly used electrode materials for electrochemical capacitors (also known as supercapacitors). To further increase the energy and power density, engineering of the pore structures with a higher electrochemical accessible surface area, faster ion-transport path and a more-robust interface with the electrolyte is widely investigated. Compared with traditional porous carbons, two-dimensional (2D) porous carbon sheets with an interlinked hierarchical porous structure are a good candidate for supercapacitors due to their advantages in high aspect ratio for electrode packing and electron transport, hierarchical pore structures for ion transport, and short ion-transport length. Recent progress on the synthesis of 2D porous carbons is reported here, along with the improved electrochemical behavior due to enhanced ion transport. Challenges for the controlled preparation of 2D porous carbons with desired properties are also discussed; these require precise tuning of the hierarchical structure and a clarification of the formation mechanisms.

A Metal‐Free Supercapacitor Electrode Material with a Record High Volumetric Capacitance over 800 F cm−3

A metal-free supercapacitor electrode material is prepared by the hybridization of graphene and polyaniline in a very compact way without sacrificing their gravimetric capacitance. It exhibits a record high volumetric capacitance over 800 F cm(-3).

Ultra-thick graphene bulk supercapacitor electrodes for compact energy storage

Compact energy storage with high volumetric performance is highly important. However, the state-of-the-art electrodes and devices remain far from the requirements due to the lack of consideration from a device perspective, which not only demands a high specific gravimetric capacity, but also needs to take into account operation voltage, material density and electrode thickness. We develop a novel approach to fabricate a monolithic ultra-thick and dense carbon electrode for symmetric supercapacitors, starting with graphene assembly and taking all the above factors into consideration. We found that zinc chloride is an ideal sacrificial pore former, and taken together with capillary drying can tune the specific surface area of the monolithic graphene from 370 to over 1000 m2 g−1 while the monoliths maintain a high density from 1.6 to 0.6 g cm−3. Having a good balance of porosity and density, the directly sliced graphene pellet electrode with a thickness up to 400 μm delivers a capacitance of 150 F cm−3 in an ionic liquid electrolyte, corresponding to a volumetric energy density of ∼65 W h L−1 for a symmetrical supercapacitor device, the highest value reported to date for supercapacitors. This study presents a design principle for electrode materials towards next-generation energy storage devices, not limited to supercapacitors, which are becoming smaller, lighter but more energetic.

Supercapacitors: A Metal‐Free Supercapacitor Electrode Material with a Record High Volumetric Capacitance over 800 F cm−3 (Adv. Mater. 48/2015)

Energy-storage devices are becoming smaller, lighter, and more energetic. On page 8082, J. Luo, Q.-H. Yang, and co-workers demonstrate the successful preparation of a graphene/polyaniline composite monolith in the most compact way, which delivers a record high volumetric capacitance of over 800 F cm(-3) for a metal-free supercapacitor electrode material.