Fangyuan Su

Hierarchical porous carbon microtubes derived from willow catkins for supercapacitor applications

With willow catkins as highly accessible carbon sources, hierarchical porous carbon microtubes (denoted as HPNCTs) have been successfully prepared by a facile carbonization and subsequent KOH activation process. The resulting materials not only inherited the natural tubular morphology of willow catkins, but also developed a hierarchical porous structure by activation, with nitrogen from the biomass being self-doped in the resulting carbon. A maximum specific surface area of 1775.7 m2 g−1 with a pore volume of 0.8516 cm3 g−1 was achieved for HPNCT-800. When evaluated as an electrode by a three-electrode system in 6 M KOH aqueous solution, the material exhibited a high gravimetric capacitance of 292 F g−1 at a current density of 1 A g−1, with a good rate capability of 83.5% retention at 10 A g−1. HPNCT-800 was further employed in a coin-type symmetric device with 1 M LiPF6 electrolyte, and exhibited a high energy density of 37.9 W h kg−1 at a power density of 700 W kg−1, with excellent cycling stability with 90.6% retention after 4000 cycles. By taking advantage of the unique structure of abundant biomass from nature, this work sheds light on the creation of advanced porous carbon materials towards energy storage applications.

Self‐Assembled 3D Graphene‐Based Aerogel with Co3O4 Nanoparticles as High‐Performance Asymmetric Supercapacitor Electrode

Using graphene oxide and a cobalt salt as precursor, a three-dimensional graphene aerogel with embedded Co3 O4 nanoparticles (3D Co3 O4 -RGO aerogel) is prepared by means of a solvothermal approach and subsequent freeze-drying and thermal reduction. The obtained 3D Co3 O4 -RGO aerogel has a high specific capacitance of 660 F g(-1) at 0.5 A g(-1) and a high rate capability of 65.1 % retention at 50 A g(-1) in a three-electrode system. Furthermore, the material is used as cathode to fabricate an asymmetric supercapacitor utilizing a hierarchical porous carbon (HPC) as anode and 6 M KOH aqueous solution as electrolyte. In a voltage range of 0.0 to 1.5 V, the device exhibits a high energy density of 40.65 Wh kg(-1) and a power density of 340 W kg(-1) and shows a high cycling stability (92.92 % capacitance retention after 2000 cycles). After charging for only 30 s, three CR2032 coin-type asymmetric supercapacitors in series can drive a light-emitting-diode (LED) bulb brightly for 30 min, which remains effective even after 1 h.

Nitrogen- and oxygen-enriched 3D hierarchical porous carbon fibers: synthesis and superior supercapacity

A nitrogen- and oxygen-enriched hierarchical porous carbon fiber was fabricated by phase-separable wet-spinning and the subsequent chemical activation of polyacrylonitrile (PAN) precursors. The wet-spinning could readily offer an interpenetrating 3D meso-/macro-porous network owing to the phase-separation of PAN in the coagulation bath (DMSO/H2O), caused by the different solubility of PAN in DMSO and H2O, and the different content of PAN in the fiber and the coagulation bath. The latter chemical activation introduced abundant small-sized nanopores within the meso-/macro-porous network skeleton. The obtained hierarchical porous carbon fiber exhibited a high specific surface area of 2176.6 m2 g−1 and a large pore volume of 1.272 cm3 g−1, and was highly doped with heteroatoms of nitrogen and oxygen. When it was used as a supercapacitor electrode, high performance of reversible specific capacitances of 329 F g−1 at 0.1 A g−1 and 223 F g−1 at 20 A g−1 as well as the capacitance retention of 97.6% after 2000 cycles were achieved in a two-electrode cell.

Layered NiO/reduced graphene oxide composites by heterogeneous assembly with enhanced performance as high-performance asymmetric supercapacitor cathode

A layered NiO/reduced graphene oxide composite (NiO/RGO) was prepared by a facile heterogeneous assembly approach with subsequent in situ thermal reduction. The two-dimensional hydroxide and graphene oxide nanosheets achieved nanoscale dispersion in the composites, with high interfacial interaction between each other. The as-obtained material exhibits a high specific capacitance of 782 F g−1 at 0.5 A g−1 and an excellent cycling stability with 94.1% retention at 2 A g−1 after 3000 cycles in a three-electrode system. To further evaluate the NiO/RGO electrode for practical application, an asymmetric supercapacitor NiO/RGO//AC was fabricated using the NiO/RGO as cathode and AC as anode. It exhibits maximum energy density of 32.5 W h kg−1 at a power density of 375 W kg−1 and even retains 19.78 W h kg−1 at 7500 W kg−1. This asymmetric device also shows a high cycling stability along with 92.7% retention after 3000 cycles, and is able to light up an LED bulb. The success of the NiO/RGO composite sheds light on designing advanced hybrid materials for next-generation supercapacitive energy storage.

Hollow carbon microtubes from kapok fiber: structural evolution and energy storage performance

Hollow carbon microtubes, with tunable porosity and surface chemistry, are highly desired for advanced energy conversion and storage applications. Although most natural fibers possess a hollow tubular structure, their original morphology is easily destroyed when they are carbonized directly due to the pyrolysis reactions. In this study, using kapok fiber as a precursor, hollow carbon microtubes were obtained by pre-stabilization and subsequent carbonization–activation in the presence of (NH4)2HPO4. During structural evolution from an organic biomass fiber to a hollow carbon fiber, (NH4)2HPO4 acts not only as a porogen and nitrogen/phosphorus source for in situ activation and doping but also as a crosslinking agent for chemical stabilization. The material exhibited good electrochemical performance in an organic electrolyte when evaluated as a supercapacitor electrode due to highly accessible surface area, convenient ion diffusion, and electron transfer. This study provides insights for the design of an anisotropic porous carbon structure towards next-generation high-power smart devices.