Lu Mao

Nanostructured MnO2/graphene composites for supercapacitor electrodes: the effect of morphology, crystallinity and composition

Nanostructured MnO2 with different morphologies, i.e. amorphous, lamellar and needle-like, is incorporated with tetrabutylammonium hydroxide stabilized graphene (GTR) with different mass ratios. A systematical approach has been used to investigate the morphology, structure and electrochemical performances of these materials for supercapacitor electrodes. It is found that the morphology, crystallinity and composition all play important roles in the capacitor performance. Needle-like MnO2 (N-Mn)/GTR composites with high surface area and good crystallinity show better performance compared with the other two systems. A new morphology emerges in N-Mn/GTR13; meanwhile high specific capacitances of 280 F g−1 for the N-Mn/GTR13 composite and 631 F g−1 for MnO2 are achieved. The inclusion of graphene significantly improves the cycling stability.

Surfactant-intercalated, chemically reduced graphene oxide for high performance supercapacitor electrodes

A series of surfactant-stabilized graphene materials were prepared by intercalation of graphene oxide (GO) with different surfactants, tetrabutylammonium hydroxide (TBAOH), cetyltrimethylammonium bromide (CTAB) and sodium dodecylbenzene sulfonate (SDBS), followed by reduction using hydrazine. The materials were fully characterized, and the surfactants were found to be successfully intercalated in both GO and the reduced graphene oxide. As well as stabilizing the morphology of single layer or few-layer structure of graphene sheets during reduction, the presence of surfactants in graphene materials can also enhance the wettability of the graphene surface and thus improve its performance as a supercapacitor electrode. When the graphene materials were used as an electrode for a supercapacitor, the highest specific capacitance of 194 F g−1 was obtained from the TBAOH stabilized graphene at a specific current density of 1 A g−1 in 2 M H2SO4 electrolyte.

Surfactant-stabilized graphene/polyaniline nanofiber composites for high performance supercapacitor electrode

Polyaniline nanofibers were prepared by in situ polymerization of aniline in the presence of surfactants such as tetrabutylammonium hydroxide and sodium dodecyl benzenesulfonate stabilized graphene under acidic condition. A homogeneous dispersion of individual graphene sheets within the polymer matrix was achieved due to the good dispersibility of surfactant-stabilized graphene in aqueous phase. The morphology and electrochemical properties of both components were well preserved due to the mild reaction conditions. The composite materials were used for supercapacitor electrode and a high specific capacitance of 526 F g−1 was obtained at a current density of 0.2 A g−1 with good cycling stability.

Iron Oxide-Decorated Carbon for Supercapacitor Anodes with Ultrahigh Energy Density and Outstanding Cycling Stability

Supercapacitor with ultrahigh energy density (e.g., comparable with those of rechargeable batteries) and long cycling ability (>50000 cycles) is attractive for the next-generation energy storage devices. The energy density of carbonaceous material electrodes can be effectively improved by combining with certain metal oxides/hydroxides, but many at the expenses of power density and long-time cycling stability. To achieve an optimized overall electrochemical performance, rationally designed electrode structures with proper control in metal oxide/carbon are highly desirable. Here we have successfully realized an ultrahigh-energy and long-life supercapacitor anode by developing a hierarchical graphite foam-carbon nanotube framework and coating the surface with a thin layer of iron oxide (GF-CNT@Fe2O3). The full cell of anode based on this structure gives rise to a high energy of ∼74.7 Wh/kg at a power of ∼1400 W/kg, and ∼95.4% of the capacitance can be retained after 50000 cycles of charge-discharge. These performance features are superior among those reported for metal oxide based supercapacitors, making it a promising candidate for the next generation of high-performance electrochemical energy storage.

Synthesis, Self-Assembly, and Charge Transporting Property of Contorted Tetrabenzocoronenes

A facile route has been developed for the preparation of a new family of contorted 1.2,3.4,7.8,9.10-tetrabenzocoronenes (TBCs). A two-step cyclization reaction, i.e., oxidative photocyclization followed by FeCl(3)-mediated intramolecular cyclodehydrogenation, was carried out on the olefin precursors to obtain the final TBC compounds. These new TBC molecules have contorted conformation due to steric overcrowding as disclosed by single-crystal crystallographic analysis. Nevertheless, they showed extended π-conjugation compared with coronene and exhibited strong aggregation in solution. The thermal behavior and self-assembly of TBC-C8 in solid were studied by a combination of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Compound TBC-C8 showed very good thermal and photostability and exhibited long-range ordered π-stacking in the bulk state. Moreover, uniform nanofibers with tens of micrometer length are formed in the drop-casted thin films. TBC-C8 also possesses a desirable HOMO energy level (-5.10 eV), which allows efficient charge injection from electrodes such as gold electrode. The charge carrier mobilities were determined by using the space-charge limited-current (SCLC) technique and high average hole mobility of 0.61 cm(2) V(-1) s(-1) was obtained for TBC-C8.

3D TiO2@Ni(OH)2 Core-shell Arrays with Tunable Nanostructure for Hybrid Supercapacitor Application.

Three dimensional hierarchical nanostructures have attracted great attention for electrochemical energy storage applications. In this work, self-supported TiO2@Ni(OH)2 core-shell nanowire arrays are prepared on carbon fiber paper via the combination of hydrothermal synthesis and chemical bath deposition. In this core-shell hybrid, the morphology and wall size of the interconnected nanoflake shell of Ni(OH)2 can be tuned through adjusting the concentration of ammonia solution. Heterogeneous nucleation and subsequent oriented crystal growth are identified to be the synthesis mechanism affecting the nanostructure of the shell material, which consequently determines the electrochemical performance in both energy storage and charge transfer. Superior capabilities of 264 mAhg−1 at 1 A g−1 and 178 mAh g−1 at 10 A g−1 are achieved with the core-shell hybrids of the optimized structure. The asymmetric supercapacitor prototype, comprising of TiO2@Ni(OH)2 as the anode and mesoporous carbons (MCs) as the cathode, is shown to exhibit superior electrochemical performance with high energy and power densities. The present work provides a clear illustration of the structure-property relationship in nanocrystal synthesis and offers a potential strategy to enhance the battery type Ni(OH)2 electrode in a hybrid supercapacitor device.

Activation of sucrose-derived carbon spheres for high-performance supercapacitor electrodes†

Mesoporous carbons were prepared from carbon spheres derived from hydrothermal carbonization of sucrose, followed by KOH activation. The porous structure was tuned by adjusting the ratio of KOH to sucrose-derived carbon spheres. Activated carbons exhibited bi-modal pore size distribution consisting of both micropores and mesopores within 1–5 nm in size, and high surface areas up to 2823 m2 g−1 can be achieved. The activated porous carbons derived from an optimal KOH/carbon weight ratio of 2.5 demonstrated the highest specific capacitance of 316 F g−1 with excellent high-rate performance and good cycling stability. A high power density of 151.8 kW kg−1 with a reasonable energy density of 10.7 W h kg−1 in 6 M KOH aqueous electrolyte could be achieved. Similarly, a high energy density of 32.8 W h kg−1 at a decent power density of 52.5 kW kg−1 in organic electrolyte can be realized, attributed to the high surface area and micro/mesoporous structure. The current study provides a simple, low cost and effective method for the preparation of electrode materials for supercapacitors from biomass.

Cetyltrimethylammonium bromide intercalated graphene/polypyrrole nanowire composites for high performance supercapacitor electrode

Polypyrrole (PPy) nanowires were prepared by in situ polymerization of pyrrole in the presence of cetyltrimethylammonium bromide stabilized graphene (GCR). PPy nanowire/GCR composites with different loading ratios were tested as supercapacitor electrode materials in both 1 M H2SO4 (aq) and 1 M KCl (aq) electrolytes, and different electrochemical behaviors were observed. The incorporation of GCR nanosheets into the PPy nanowire matrix obviously improved the electrochemical performance of PPy and a high specific capacitance of 492 F g−1 can be obtained for PPyGCR91 in 1 M H2SO4 at a current density of 0.2 A g−1 with good cycling stability.

Bendable graphene/conducting polymer hybrid films for freestanding electrodes with high volumetric capacitances

Bendable freestanding films composed of reduced graphene oxide (RGO) and one dimensional conducting polymers (CPs) including polyaniline (PANI) and polypyrrole (PPy) are successfully fabricated by self-assembly assisted filtration method. The morphology and intrinsic properties of both components are well preserved and the desired synergetic effects are achieved. The intercalated one dimensional CPs act as not only pseudocapacitors to improve the overall capacitances but also an effective framework to open the penetrative channels for the electrolyte. The hybrid freestanding electrodes thus obtained exhibit superior performance in terms of gravimetric capacitance, volumetric capacitance and cycling stability. For example, at the current density of 0.2 A g−1, the RGO/PPy film electrode gives rise to a gravimetric capacitance of 374 F g−1 and a volumetric capacitance of 355 F cm−3; while the RGO/PANI film electrode yields a high gravimetric capacitance of 540 F g−1 and a volumetric capacitance of 616 F cm−3. Both RGO/PANI and RGO/PPy hybrid film electrodes deliver good cycling stabilities with ∼86% of original capacitances being retained after 5000 cycles.

Mesoporous Hollow Carbon Derived from Soft-Templated Hydrothermal Process for Supercapacitor Electrode

Supercapacitors have been emerged as an important energy storage device, owing to their high power density, excellent cycle ability, fast charge-discharge processes and low self-discharging. In this work, we have developed a facile soft-templated hydrothermal procedure to produce hollow mesoporous carbon spheres, which can deliver a relatively high capacitance (~190 F/g) and an energy density of ~26.38 Wh/kg at the discharging current of 1 A/g. The hollow cavity and micropore volume are shown to be the main factors that contribute to the good capacitive behavior.