Weijiang Si

Hierarchical porous and N-doped carbon nanotubes derived from polyaniline for electrode materials in supercapacitors

Open carbon nanotube materials with hierarchical porosity and N-doping are prepared from polyaniline nanotubes via a combination method of pre-carbonization and post-KOH activation. The morphology, pore texture and surface properties of the carbon materials are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption, X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The prepared carbon materials have a typical hierarchical pore texture and very high specific surface area up to 3253 m2 g−1. The electrochemical capacitive performance of the prepared carbons was systematically investigated in the 6 M KOH electrolyte. HPCT-4 exhibits high charge storage capacity with a specific capacitance of 365.9 F g−1 at a current density of 0.1 A g−1, good rate capability of 60% in the range of 0.1–10 A g−1, and excellent stability over 10 000 cycles. The high capacitive performance could be due to the hierarchical porosity combined with high effective surface area and heteroatom doping effects, resulting in both electrochemical double layer and Faradaic capacitance contributions.

Reduced graphene oxide aerogel with high-rate supercapacitive performance in aqueous electrolytes

Reduced graphene oxide aerogel (RGOA) is synthesized successfully through a simultaneous self-assembly and reduction process using hypophosphorous acid and I2 as reductant. Nitrogen sorption analysis shows that the Brunauer-Emmett-Teller surface area of RGOA could reach as high as 830 m2 g−1, which is the largest value ever reported for graphene-based aerogels obtained through the simultaneous self-assembly and reduction strategy. The as-prepared RGOA is characterized by a variety of means such as scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Electrochemical tests show that RGOA exhibits a high-rate supercapacitive performance in aqueous electrolytes. The specific capacitance of RGOA is calculated to be 211.8 and 278.6 F g−1 in KOH and H2SO4 electrolytes, respectively. The perfect supercapacitive performance of RGOA is ascribed to its three-dimensional structure and the existence of oxygen-containing groups.

Mesoporous Carbons Derived from Citrates for Use in Electrochemical Capacitors

Two mesoporous carbons were prepared by simple pyrolysis of commercial magnesium or barium citrate and tested as electrode materials for electrochemical double-layer capacitors (EDLCs), denoted MgC and BaC, respectively. The as-prepared carbon materials were characterized by N2 adsorption, scanning electron microscopy and Fourier transform infrared spectrometry. Nitrogen adsorption measurements demonstrated that the porosity of the prepared carbons was related to the type of metal cation. BaC possesses a typical bimodal pore size distribution (PSD) at 3.8 and about 15nm, while MgC was between small-size mesoporous and microporous. The carbons were tested as electrode materials using different electrochemical means such as cyclic voltammetry and constant current charge-discharge. Very high specific capacitance (180F•g^(-1) for MgC and 171F•g^(-1) for BaC) was achieved in an ionic liquid electrolyte. BaC proved to be an excellent electrode material with a high rate performance for EDLC application and exhibited an energy density up to 53.3Wh•kg^(-1) and a high maximum specific power density of 20kW•kg^(-1) in IL electrolyte. The good capacitive performance of BaC is attributed to its bimodal PSD and hydrophilic surface properties.

Adsorption of bulky molecules of nonylphenol ethoxylate on ordered mesoporous carbons

Ordered mesoporous carbons (OMCs) with varying pore sizes were prepared using ordered mesoporous silica SBA-15 as hard templates. The OMCs possess abundant mesopores with narrow pore size distribution, on which the adsorption behavior of bulky molecules of nonylphenol ethoxylate (NPE) were investigated. The isotherms of NPE on OMCs can be fitted by Langmuir adsorption model, evidenced by the adsorption data. The surface area of the pores larger than 1.5 nm is a crucial factor to the adsorption capacity of NPE, whereas the most probable pore diameter of OMCs is crucial to the adsorption rate of NPE. The adsorption temperature has more significant effects on adsorption rate than the adsorption capacity. Theoretical studies show that the adsorption kinetics of NPE on OMCs can be depicted with the pseudo-second-order kinetic model. In addition, thermodynamic parameters of adsorption were evaluated based on the equilibrium constants related to the equilibrium of adsorption at different temperatures.

Three-Dimensional Reduced Graphene Hydrogels Using Various Carbohydrates for High Performance Supercapacitors

In present work, three-dimensional (3D) reduced graphene hydrogels (RGHs) are prepared through an efficient and facile strategy by employing three types of carbohydrates (glucose, fructose and sucrose) as reducing agents in aqueous solution of graphene oxide (GO) with ammonia. The formation of RGHs could be confirmed by X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The structures and porosity were characterized by field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and N2 sorption experiments. Benefiting from the abundant porous architectures as fast ionic channels for electrochemical energy storage, the prepared RGHs exhibited a high specific capacitance up to 153.5, 145.0 and 150.3 F g−1 at 0.3 A g−1 for FRGHs (fructose), GRGHs (glucose) and SRGHs (sucrose), which can be maintained for 61.4, 61.5 and 46.9% as the discharging current density was increased up to 20 A g−1. Moreover, it also showed that the electrode based on RGHs has good electrochemical stability and high degree of reversibility in the charge/discharge cycling test.