Ruijun Zhang

A novel approach of binary doping sulfur and nitrogen into graphene layers for enhancing electrochemical performances of supercapacitors

In this paper, we present a novel route to prepare sulfur and nitrogen co-doped reduced graphene oxide, in which, two main procedures – the preparation of a sulfur doped graphite intercalation compound (S-GIC) and the construction of the sulfur and nitrogen co-doped reduced graphene oxide (SN-RGO) – are included. The loading of sulfur and nitrogen in SN-RGO, which is tracked by X-ray photoelectron spectroscopy, is 1.47 and 3.90 at%, respectively. SN-RGO possesses an almost two times higher specific surface area (SSA) than RGO and a narrow pore size distribution. Electrochemical investigations demonstrate that SN-RGO exhibits an outstanding capacitive performance, its specific capacitance at the scan rate of 5 mV s−1 in a 6 M KOH aqueous electrolyte being up to 402.4 F g−1, which is, to the best of our knowledge, among the highest values so far reported for S/N co-doped carbon materials. Furthermore, SN-RGO also exhibits an excellent cycling stability (almost 95% specific capacitance being retained even after 10 000 cycles). This work suggests that constructing doped graphene-based materials by 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 for supercapacitors.

High-Performance Supercapacitor Based on the NaOH Activated D-Glucose Derived Carbon

In this work, a mechanism of catalytic graphitization of D-glucose derived carbon during NaOH activation process is disclosed. The catalytic graphitization is caused by sodium atom, which is produced in the reaction between NaOH and carbon. Due to the combined action of activation and catalytic graphitization resulting from the NaOH, the activated D-glucose derived carbon behaves as a hierarchical micro- and meso-porous structure and has high electrical conductivity. Electrochemical investigations demonstrate that the activated sample exhibits an outstanding rate capability (70% of capacity retention even at a scan rate of 2V s−1) and high specific capacitance (106F g−1) in 6M KOH aqueous electrolyte, which makes it a promising electrode material for high-power supercapacitors.

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.

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.