Yanyan Liu

Comparative study on three commercial carbons for supercapacitor applications

Three commercial carbon materials for supercapacitor were investigated by physicochemical characterization, electrochemical measurements and surface treatment to explore the effects of specific surface area, electrolyte and surface functional groups on the specific capacitance, charge storage mode and high rate performance of carbon materials. Results indicate that the specific surface area of carbon material plays dominate role in the specific capacitance. The electrolytes have remarkable effects on the specific capacitance and high rate performance. Investigation of HNO3 treated Vulcan XC-72 carbon material reveals that the treatment can increase the specific surface area and surface functional groups, which observably improve the specific capacitance of the XC-72 carbon material. The surface functional groups contribute to the pseudo-capacitance of the carbon material.

Floss-like Ni–Co binary hydroxides assembled by whisker-like nanowires for high-performance supercapacitor

AbstractFloss-like Ni–Co binary hydroxides (FL-NCOH), assembled by whisker-like nanowires, are synthesized via a facile hydrothermal process with sodium dodecyl benzene sulfonate (SDBS) as the soft template. The forming process of FL-NCOH is clarified by tuning the hydrothermal reaction time. The result indicates that floccule-like nickel–cobalt hydroxide nanoclusters gradually become longer and slenderer nanowires to form FL-NCOH with the increase of reaction time. The dissolution–recrystallization of hydroxide plays an important role in the morphology control of nickel–cobalt hydroxide. The high specific surface area (106.5xa0m2xa0g−1) and the suitable 3D structure endow the as-prepared FL-NCOH material high specific capacitance (up to 918.9xa0Fxa0g−1 at the current density of 0.2xa0Axa0g−1), good high-rate performance (594.2xa0Fxa0g−1 even at 10.0xa0Axa0g−1), and long cycle life (98.7xa0% capacitance retention after 3000 charge–discharge cycles at 2.0xa0Axa0g−1).n Graphical Abstractᅟ

A Novel and facile synthesis approach of porous carbon/graphene composite for the supercapacitor with high performance

We propose a novel and facile synthesis approach to a porous carbon/graphene composite. Graphene is obtained from room-temperature expanded graphite (RTEG), not involving the use of graphite oxide (GO). Porous carbon is acquired by carbonization and KOH-activation of polyvinylpyrrolidone (PVP), which is used to exfoliate RTEG into graphene and inhibit the restacking of the resultant graphene in the present work. The prepared porous carbon/graphene composite has a high specific surface area (SSA) (3008 m2 g-1) and a hierarchical micro- and meso- pore structure (dominant pores in the range of 1-5 nm). Electrochemical measurement demonstrates that the as-prepared porous carbon/graphene composite can deliver an outstanding specific capacitance of up to 340 F g-1 at 5 mV s-1 in 6 M KOH electrolyte. This specific capacitance is among the highest reported so far for porous carbon/graphene materials. Moreover, the prepared composite as an electrode material also exhibits excellent cycling stability (94.4% capacitance retention over 10 000 cycles). The as-fabricated symmetrical supercapacitor exhibits a high energy density of 10.9 W h kg-1 (based on total mass of electrode materials) and an outstanding energy density retention, even at high power density. Compared with conventional preparation routes for porous carbon/graphene composites, the present approach is significantly simple, convenient and cost-effective, which will make it more competent in the development of electrode materials for high-performance supercapacitors.

Ultrahigh-power supercapacitors based on highly conductive graphene nanosheet/nanometer-sized carbide-derived carbon frameworks

In order to develop energy storage devices with high power performance, electrodes should hold well-defined pathways for efficient ionic and electronic transport. Herein, we demonstrate a highly conductive graphene nanosheet/nanometer-sized carbide-derived carbon framework (hcGNS/nCDC). In this architecture, nCDC possesses short transport paths for electrolyte ions, thus ensuring the rapid ions transportation. The excellent electrical conductivity of hcGNS can reduce the electrode internal resistance for the supercapacitor and thus endows the hcGNS/nCDC composite electrodes with excellent electronic transportation performance. Electrochemical measurements show that the cyclic voltammogram of hcGNS/nCDC can maintain a rectangular-like shape with the increase of the scan rate from 5 mV s-1 to 20 V s-1, and the specific capacitance retention is up to 51% even at a high scan rate of 20 V s-1, suggesting ultrahigh power performance, which, to the best of our knowledge, is among the best power performances reported so far for the carbon materials. Furthermore, the hcGNS/nCDC composite also shows an excellent cycling stability (no drop in its capacitance occurs even after 10000 cycles). This work demonstrates the advantage in the ultrahigh power performance for the framework having both short transport pathways for electrolyte ions and high electrical conductivity.

Fabrication and enhanced electrochemical performance of a nitrogen-doped porous graphene/nanometer-sized carbide-derived carbon composite for supercapacitors

Herein, we fabricated a nitrogen-doped porous graphene/nanometer-sized carbide-derived carbon (NPG/nCDC) composite. In this architecture, the nCDC with a hierarchical pore structure is used as spacer to inhibit the agglomeration of NPG ensuring the in-plane diffusion paths for electrolyte ions and has contribution to the specific surface area and the pore structure of the composite as well. The nano-sized pores existing on the NPG sheets can provide the cross-plane diffusion paths for electrolyte ions. Furthermore, the nitrogen doping to NPG can further enhance the capacitive performance of the composite. Benefiting from these advantages, the NPG/nCDC composites exhibit outstanding supercapacitive performance. Its specific capacitance is up to 336xa0Fxa0g−1 at 5xa0mVxa0s−1 in 6xa0molxa0L−1 KOH electrolyte, and 99.3% capacitance can be maintained even after 10,000xa0cycles, demonstrating the great potential as the electrode material for supercapacitors.

Fabrication and enhanced supercapacitive performance of sulfur and nitrogen co-doped porous graphene

In this paper, we present a strategy to prepare the sulfur and nitrogen co-doped porous graphene electrode, in which, three main procedures—the pore-formation in the natural graphite, the preparation of sulfur doped porous graphite intercalation compounds (S-PGIC) and the construction of the sulfur/nitrogen co-doped porous reduced graphite oxide (SN-PRGO) are included. The as-prepared SN-PRGO sample can behave relatively high specific surface area (SSA) and simultaneously provide through-plane and in-plane diffusion paths for electrolyte ions, thus exhibiting an outstanding capacitive performance. Its specific capacitance at the scan rate of 5xa0mVxa0s−1 in 6xa0M KOH aqueous electrolyte can reach up to 438xa0Fxa0g−1, which is, to the best of our knowledge, among the highest values so far reported for heteroatoms doped carbon materials. Besides, SN-PRGO also exhibits an excellent cycling stability with almost 94% of its initial capacitance being retained after the long-term consecutive cycling. This work suggests that constructing the doped graphene-based materials by generating the pores in the graphite sheets and using the intercalated substances among the graphite layers as the dopant sources can be considered as a promising strategy for the development of high performance electrodes in supercapacitors.

One-step room-temperature exfoliation of graphite to 100% few-layer graphene with high quality and large size

Large scale application of graphene is still facing a great challenge due to the lack of cost-effective methods for its production. Herein, we report a simple and cost-effective method for scalable production of few-layer graphene (FLG) with high quality and large size in only one step at room temperature. In this method, a novel binary-component system, which is composed of sodium percarbonate (SPC) and concentrated H2SO4, has been developed for the chemical exfoliation of graphite, where sodium percarbonate is used to exfoliate graphite for the first time, furthermore, the amount of the concentrated H2SO4 used as an intercalating agent is reduced dramatically by 83–85% in comparison to those in the other chemical exfoliation methods. It is found that SPC plays a key role in the exfoliation of graphite. Considering the analysis results, a possible mechanism for the exfoliation of graphite to FLG is proposed. The exfoliated graphene sheets exhibit a few-layer feature (average layer number <5 layers), and possess large areal sizes (the maximum areal size can be up to 538 μm2, and the average sheet area is 276.8 μm2) and few structural defects (the oxygen content is only 1.65%), thereby exhibiting an outstanding electrical conductivity of 1.90 × 105 S m−1.