Xingbin Yan

Fabrication of Free-Standing, Electrochemically Active, and Biocompatible Graphene Oxide−Polyaniline and Graphene−Polyaniline Hybrid Papers

In this work, we report a low-cost technique via simple rapid-mixture polymerization of aniline using graphene oxide (GO) and graphene papers as substrates, respectively, to fabricate free-standing, flexible GO-polyaniline (PANI) and graphene-PANI hybrid papers. The morphology and microstructure of the obtained papers were characterized by FESEM, FTIR, Raman, and XRD. As results, nanostructural PANI can be deposited on the surfaces of GO and graphene papers, forming thin, lightweight, and flexible paperlike hybrid papers. The hybrid papers display a remarkable combination of excellent electrochemical performances and biocompatibility, making the paperlike materials attractive for new kinds of applications in biosciences.

Flexible and conductive nanocomposite electrode based on graphene sheets and cotton cloth for supercapacitor

There is currently a strong demand for energy storage devices which are cheap, light weight, flexible, and possess high power and energy densities to meet the various requirements of modern gadgets. Herein, we prepare a flexible and easily processed electrode via a simple “brush-coating and drying” process using everyday cotton cloth as the platform and a stable graphene oxide (GO) suspension as the ink. After such a simple manufacturing operation followed by annealing at 300 °C in argon atmosphere, the as-obtained graphene sheets (GNSs)–cotton cloth (CC) composite fabric exhibits good electrical conductivity, outstanding flexibility, and strong adhesion between GNSs and cotton fibers. Using this GNSs–CC composite fabric as the electrode material and pure CC as the separator, a home-made supercapacitor was fabricated. The supercapacitor shows the specific capacitance of 81.7 F g−1 (two-electrode system) in aqueous electrolyte, which is one of the highest values for GNSs-based supercapacitors. Moreover, the supercapacitor also exhibits satisfactory capacitance in ionic-liquid/organic electrolyte. An all-fabric supercapacitor was also fabricated using pure CC as separator and GNSs–CC composite fabric as electrode and current collector. Such a conductive GNSs–CC composite fabric may provide new design opportunities for wearable electronics and energy storage applications.

Promising Porous Carbon Derived from Celtuce Leaves with Outstanding Supercapacitance and CO2 Capture Performance

Business costs and energy/environmental concerns have increased interested in biomass materials for production of activated carbons, especially as electrode materials for supercapacitors or as solid-state adsorbents in CO₂ adsorption area. In this paper, waste celtuce leaves were used to prepare porous carbon by air-drying, pyrolysis at 600 °C in argon, followed by KOH activation. The as-prepared porous carbon have a very high specific surface area of 3404 m²/g and a large pore volume of 1.88 cm³/g. As an electroactive material, the porous carbon exhibits good capacitive performance in KOH aqueous electrolyte, with the specific capacitances of 421 and 273 F/g in three and two-electrode systems, respectively. As a solid-state adsorbent, the porous carbon has an excellent CO₂ adsorption capacity at ambient pressures of up to 6.04 and 4.36 mmol/g at 0 and 25 °C, respectively. With simple production process, excellent recyclability and regeneration stability, the porous carbon that was derived from celtuce leaves is among the most promising materials for high-performance supercapacitors and CO₂ capture.

A hybrid supercapacitor based on flower-like Co(OH)2 and urchin-like VN electrode materials

A series of hybrid electrochemical capacitors were fabricated by using the flower-like cobalt hydroxide (Co(OH)2) and urchin-like vanadium nitride (VN) as the positive and negative electrode materials, respectively. Both Co(OH)2 and VN electrode materials showed excellent electrochemical performance due to their unique structure and fast reversible Faradic reaction characteristics. With different operation voltage window (OVW) and negative/positive mass ratios, the impact on capacitance performance of the hybrid supercapacitor was investigated thoroughly, which demonstrated that both mass ratio and OVW played an important role in their capacitance performance. Furthermore, theoretical modeling was performed and the simulation result was found to be in agreement with the experimental result for the influence of the negative/positive mass ratio on capacitance performance of the hybrid supercapacitor. When an optimized negative/positive mass ratio was located, the Co(OH)2//VN hybrid supercapacitor could be cycled reversibly in the high-voltage region of 0–1.6 V and delivered a high energy density of 22 W h kg−1. Even at a large power density of 15.9 kW kg−1, the hybrid supercapacitor still possessed a desirable specific energy density of 9 W h kg−1. Such an impressive hybrid supercapacitor was expected to be a highly promising candidate for application in high-performance energy storage systems.

Novel and high-performance asymmetric micro-supercapacitors based on graphene quantum dots and polyaniline nanofibers

In comparison with graphene sheets, graphene quantum dots (GQDs) exhibit novel chemical/physical properties including nanometer-size, abundant edge defects, good electrical conductivity, high mobility, chemical inertia, stable photoluminescence and better surface grafting, making them promising for fabricating various novel devices. In the present work, an asymmetric micro-supercapacitor, using GQDs as negative active material and polyaniline (PANI) nanofibers as positive active material, is built for the first time by a simple and controllable two-step electro-deposition on interdigital finger gold electrodes. Electrochemical measurements reveal that the as-made GQDs//PANI asymmetric micro-supercapacitor has a more excellent rate capability (up to 1000 V s(-1)) than previously reported electrode materials, as well as faster power response capability (with a very short relaxation time constant of 115.9 μs) and better cycling stability after 1500 cycles in aqueous electrolyte. On this basis, an all-solid-state GQDs//PANI asymmetric micro-supercapacitor is fabricated using H3PO4-polyvinyl alcohol gel as electrolyte, which also exhibits desirable electrochemical capacitive performances. These encouraging results presented here may open up new insight into GQDs with highly promising applications in high-performance energy-storage devices, and further expand the potential applications of GQDs beyond the energy-oriented application of GQDs discussed above.

Superior asymmetric supercapacitor based on Ni-Co oxide nanosheets and carbon nanorods

Nickel and cobalt (Ni-Co) binary oxide nanosheets with mesoporous structure are prepared by a facile approach based on the formation and disassociation of nickel/cobalt-citrate complex, and they show an ultra-high Faradaic capacitance up to 1846 F g−1 and excellent rate capability. On this basic, advanced aqueous asymmetric supercapacitors (AASs) are successfully built by using the Ni-Co oxide as the positive electrode and three kinds of activated carbons respectively as the negative electrode. As-made AASs are able to work reversibly in a full operated voltage region of 0–1.6 V and exhibit outstanding electrochemical performance. Among them, activated polyaniline-derived carbon (APDC)//Ni-Co oxide AASs shows the highest specific capacitance of 202 F g−1, the maximum energy density of 71.7 Wh kg−1, and superior combination of high energy and power density (a energy density of 41.6 Wh kg−1 at a high power density of 16 kW kg−1).

Free-Standing Three-Dimensional Graphene/Manganese Oxide Hybrids As Binder-Free Electrode Materials for Energy Storage Applications

Novel three-dimensional (3D) hybrid materials, i.e., free-standing 3D graphene-supported MnO2 nanosheets, are prepared by a simple and controllable solution-phase assembly process. Characterization results show that MnO2 nanosheets are uniformly anchored on a 3D graphene framework with strong adhesion and the integral hybrids show desirable mechanical strength. Such unique structure of 3D graphene/MnO2 hybrids thus provides the right characteristics of binder-free electrode materials and could enable the design of different kinds of high-performance energy storage devices. Especially, an advanced asymmetric supercapacitor is built by using a 3D graphene/MnO2 hybrid and a 3D graphene as two electrodes, and it is able to work reversibly in a full operation voltage region of 0-3.5 V in an ionic liquid electrolyte and thus exhibits a high energy density of 68.4 Wh/kg. As the cathode materials for Li-O2 and Li-MnO2 batteries, the 3D graphene/MnO2 hybrids exhibit outstanding performances, including good catalytic capability, high reversible capacity and desirable cycling stability. The results presented here may pave a way for new promising applications of such 3D graphene/MnO2 hybrids in advanced electrochemical energy storage devices.

Facile Synthesis of Fe2O3 Nano-Dots@Nitrogen-Doped Graphene for Supercapacitor Electrode with Ultralong Cycle Life in KOH Electrolyte.

Fe2O3 nanodots supported on nitrogen-doped graphene sheets (denoted as Fe2O3 NDs@NG) with different loading masses are prepared through a facile one-pot solvothermal method. The resulting Fe2O3 NDs@NG composites exhibit outstanding electrochemical properties in aqueous KOH electrolyte. Among them, with the optimal loading mass of Fe2O3 NDs, the corresponding Fe2O3 NDs@NG-0.75 sample is able to deliver a high specific capacitance of 274 F g(-1) at 1 A g(-1) and the capacitance is still as high as 140 F g(-1) even at a ultrahigh current density of 50 A g(-1), indicating excellent rate capability. More remarkably, it displays superior capacitance retention after 100,000 cycles (about 75.3% at 5 A g(-1)), providing the best reported long-term cycling stability for iron oxides in alkaline electrolytes to date. Such excellent electrochemical performance is attributed to the right combination of highly dispersed Fe2O3 NDs and appropriately nitrogen-doped graphene sheets, which enable the Fe2O3 NDs@NG-0.75 to offer plenty of accessible redox active sites, facilitate the electron transfer and electrolyte diffusion, as well as effectively alleviate the volume change of Fe2O3 NDs during the charge-discharge process.

A super-high energy density asymmetric supercapacitor based on 3D core–shell structured NiCo-layered double hydroxide@carbon nanotube and activated polyaniline-derived carbon electrodes with commercial level mass loading

Realization of high cell energy density at high mass loading is a critical requirement for the practical applications of supercapacitors. To date, the cell energy density of supercapacitor devices has been mainly limited by the low utilization efficiency of electroactive materials on positive electrodes at high mass loading and the low capacitance value of common activated carbon materials on negative electrodes. In this study, a super-high energy density asymmetric supercapacitor device with commercial mass loading was successfully fabricated by using a 3D core–shell structured NiCo-layered double hydroxide@carbon nanotube (NiCo-LDH@CNT) composite as the positive electrode and activated polyaniline-derived carbon (APDC) as the negative electrode. Due to its unique core–shell structure, the NiCo-LDH@CNT/nickel foam (NF) electrode with a mass loading of 8.5 mg cm−2 delivered a high capacitance of 2046 F g−1 at 1 A g−1, and still retained a high capacitance of 1335 F g−1 as the current density increased up to 15 A g−1. Coupled with the high performance APDC-based negative electrode with a capacitance of 487 F g−1 at 1 A g−1, the asymmetric NiCo-LDHs@CNT/NF//APDC/NF supercapacitor device delivered a maximum energy density of 89.7 W h kg−1 with an operational voltage of 1.75 V, and a maximum power density of 8.7 kW kg−1 at an energy density of 41.7 W h kg−1, suggesting its promising applications in future.

Facile Preparation of One-Dimensional Wrapping Structure: Graphene Nanoscroll-Wrapped of Fe3O4 Nanoparticles and Its Application for Lithium-Ion Battery

Graphene nanoscroll (GNS) is a spirally wrapped two-dimensional (2D) graphene sheet (GS) with a 1D tubular structure resembling that of a multiwalled carbon nanotube (MWCNT). GNS provide open structure at both ends and interlayer galleries that can be easily intercalated and adjusted, which show great potential applications in energy storage. Here we demonstrate a novel and simple strategy for the large-scale preparation of GNSs wrapping Fe3O4 nanoparticles (denoted as Fe3O4@GNSs) from graphene oxide (GO) sheets by cold quenching in liquid nitrogen. When a heated aqueous mixed suspension of GO sheets and Fe3O4 nanoparticles is immersed in liquid nitrogen, the in-situ wrapping of Fe3O4 nanoparticles with GNSs is easily realized. The structural conversion is closely correlated with the initial temperature of mixed suspension, the zeta potential of Fe3O4 nanoparticles and the immersion way. Remarkably, such hybrid structure provides the right combination of electrode properties for high-performance lithium-ion batteries. Compared with other wrapping structure, such 1D wrapping structure (GNSs wrapping) effectively limits the volume expansion of Fe3O4 nanoparticles during the cycling process, consequently, a high reversible capacity, good rate capability, and excellent cyclic stability are achieved with the material as anode for lithium storage. The results presented here may pave a way for the large-scale preparation of GNS-based materials in electrochemical energy storage applications.