Tian Ouyang

Molten salt synthesis of nitrogen doped porous carbon: a new preparation methodology for high-volumetric capacitance electrode materials

To meet the ever-increasing need for high-efficiency energy storage in modern society, porous carbon materials with large surface areas are typically employed for electrical double-layer capacitors to achieve high gravimetric performances. However, their poor volumetric performances come from low packing density and/or high pore volume resulting in poor volumetric capacitance, which would limit their further applications. Here, a novel and one-step molten salt synthesis of a three-dimensional, densely nitrogen-doped porous carbon (NPC) material by using low-cost and eco-friendly tofu as the nitrogen-containing carbon source is proposed. Hierarchically porous carbon with a specific surface area of 1202 m2 g−1 and a high nitrogen content of 4.72 wt% and a bulk density of ∼0.84 g cm−3 is obtained at a carbonation temperature of 750 °C. As the electrode material for a supercapacitor, the NPC electrode shows both ultra-high specific volumetric and gravimetric capacitances of 360 F cm−3 and 418 F g−1 at 1 A g−1 (based on a three-electrode system), respectively, and excellent cycling stability without capacitance loss after 10 000 cycles at a high charge current of 10 A g−1 in KOH electrolyte. Moreover, the as-assembled symmetric supercapacitor exhibits not only an excellent cycling stability with 97% capacitance retention after 10 000 cycles, but also a high volumetric energy density up to 27.68 W h L−1 at a current density of 0.2 A g−1, making this new method highly promising for compact energy storage devices with simultaneous high volumetric/gravimetric energy and power densities.

From biomass with irregular structures to 1D carbon nanobelts: a stripping and cutting strategy to fabricate high performance supercapacitor materials

One-dimensional (1D) nanostructures have been identified as the most viable structures for high-performance supercapacitors from the view of high ion-accessible surface area and rapid electron transport path as well as excellent mechanical properties. Herein, we report a “stripping and cutting” strategy to produce 1D carbon nanobelts (CNB) from tofu with irregular structures through a molten salts assisted technique. It is a completely novel and green avenue for constructing 1D carbon materials from biomass, showing large commercial potential. The resultant CNB electrode delivers a high specific capacitance (262 F g−1 at 0.5 A g−1) and outstanding cycling stability with capacitance retention up to 102% after 10 000 continuous charging/discharging cycles. Additionally, a CNB//CNB symmetric supercapacitor and CNB//MnO2–CNB asymmetric supercapacitor are assembled and reach energy densities of 18.19 and 29.24 W h kg−1, respectively. Therefore, such a simple, one-pot and low-cost process may have great potential for preparing eco-friendly biomass-derived carbon materials for high-performance supercapacitor electrodes.

Facile synthesis of Co3O4 with different morphology and their application in supercapacitors

In this article, direct growth of Co3O4 with different morphologies on nickel foam is successfully achieved via a simple hydrothermal method by changing the volume ratio between ethanol and water. The morphology and structure of the as-prepared samples are examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The electrochemical performance of the Co3O4 electrodes is investigated as pseudocapacitor material by cyclic voltammetry and galvanostatic charge/discharge test in 3 mol L−1 KOH solution. Results show that the solvent composition plays an important role not only in the morphology but also in the capacitance. Co3O4 with a honeycomb structure obtained from the volume ratio of C2H5OH/H2O = 1 exhibits the highest capacitive performance, 2509.4 F g−1 at 1 A g−1 and 1754 F g−1 at 10 A g−1, which is much larger than that prepared in the pure water and pure ethanol solvent. The electrode also has a satisfactory cycling performance with capacity retention of 74% after 1000 cycles at 10 A g−1. The enhanced electrochemical performance is ascribed to the honeycomb nanostructure allowing facile electrolyte flow which speeds up electrochemical reaction kinetics. These findings may open up the opportunity for optimizing the hydrothermal synthesis conditions to control the morphology and performance of the products.