Henghui Xu

Synthesis of functionalized 3D hierarchical porous carbon for high-performance supercapacitors

Functionalized three-dimensional hierarchical porous carbon (THPC) is prepared via a facile modified chemical activation route with polypyrrole microsheets as precursor and KOH as activating agent. The as-obtained THPC presents a large specific surface area (2870 m2 g−1), high-level heteroatom doping (N: 7.7 wt%, O: 12.4 wt%), excellent electrical conductivity (5.6 S cm−1), and hierarchical porous nano-architecture containing macroporous frameworks, mesoporous walls and microporous textures. Such unique features make the THPC an ideal electrode material for electrochemical energy storage. As the electrode material for a supercapacitor, the THPC exhibits a high capacitance, excellent rate performance and long-term stability in both aqueous and organic electrolytes.

A bamboo-inspired nanostructure design for flexible foldable and twistable energy storage devices

Flexible energy storage devices are critical components for emerging flexible electronics. Electrode design is key in the development of all-solid-state supercapacitors with superior electrochemical performances and mechanical durability. Herein, we propose a bamboo-like graphitic carbon nanofiber with a well-balanced macro-, meso-, and microporosity, enabling excellent mechanical flexibility, foldability, and electrochemical performances. Our design is inspired by the structure of bamboos, where a periodic distribution of interior holes along the length and graded pore structure at the cross section not only enhance their stability under different mechanical deformation conditions but also provide a high surface area accessible to the electrolyte and low ion-transport resistance. The prepared nanofiber network electrode recovers its initial state easily after 3-folded manipulation. The mechanically robust membrane is explored as a free-standing electrode for a flexible all-solid-state supercapacitor. Without the need for extra support, the volumetric energy and power densities based on the whole device are greatly improved compared to the state-of-the-art devices. Even under continuous dynamic operations of forceful bending (90°) and twisting (180°), the as-designed device still exhibits stable electrochemical performances with 100% capacitance retention. Such a unique supercapacitor holds great promise for high-performance flexible electronics.

Encapsulation of MnO Nanocrystals in Electrospun Carbon Nanofibers as High-Performance Anode Materials for Lithium-Ion Batteries

A novel and controllable approach is developed for the synthesis of MnO nanocrystals embedded in carbon nanofibers (MnO/CNFs) through an electrospinning process. The as-formed MnO/CNFs have a porous structure with diameters of 100–200 nm and lengths up to several millimeters. When used as an anode material for lithium-ion batteries, the resulting MnO/CNFs exhibit superior electrochemical performances with high specific capacity, good cyclability, and excellent rate capability. The unique porous carbon nanofibers (PCNFs) can not only improve the contact area between the electrode and the electrolyte, but also alleviate the impact of the large volume effect of MnO during the electrochemical cycling. It is expected that the present synthetic strategy can be extended to synthesize other nanostructured oxides encapsulated in carbon nanofibers for extensive energy transfer and storage applications.

Flexible fiber-shaped supercapacitors based on hierarchically nanostructured composite electrodes

A novel all-solid-state, coaxial, fiber-shaped asymmetric supercapacitor has been fabricated by wrapping a conducting carbon paper on a MnO2-modified nanoporous gold wire. This energy wire exhibits high capacitance of 12 mF·cm−2 and energy density of 5.4 μW·h·cm−2 with excellent cycling stability. Hierarchical nanostructures and coaxial architectural design facilitate effective contacts between the two core@sheath electrodes and active layers with high flexibility and high performance. This work provides the first example of coaxial fibershaped asymmetric supercapacitors with an operation voltage of 1.8 V, and holds great potential for future flexible electronic devices.

Conformal N-doped carbon on nanoporous TiO2 spheres as a high-performance anode material for lithium-ion batteries

Conformal N-doped carbon (NC) on nanoporous TiO2 spheres has been successfully synthesized via a facile solution-phase process and subsequent heat treatment. The highly conductive and uniform NC layer coated on the surface of nanoporous TiO2 spheres facilitates lithium ion diffusion and electronic transport. The resulting TiO2@NC nanohybrid not only delivers a high capacity of ∼170 mA h g−1 at a current density of 0.1 A g−1, but also exhibits excellent rate capability (∼102 mA h g−1 at a current density of 2.0 A g−1). The as-formed porous TiO2@NC electrode is promising for secondary battery applications with high power and energy densities.

Assembly of NiO/Ni(OH)2/PEDOT Nanocomposites on Contra Wires for Fiber-Shaped Flexible Asymmetric Supercapacitors

Fiber-shaped solid-state supercapacitors have aroused much interest in the fields of portable devices because of their attractive features such as high flexibility and safety, tiny volume, and high power density. In this work, NiO/Ni(OH)2 nanoflowers encapsulated in three-dimensional interconnected poly(3,4-ethylenedioxythiophene) (PEDOT) have been fabricated on contra wires through a mild electrochemical route. The as-formed hybrid electrode made of NiO/Ni(OH)2/PEDOT delivered a high specific capacitance of 404.1 mF cm(-2) (or 80.8 F cm(-3)) at a current density of 4 mA cm(-2) and a long cycle life with 82.2% capacitance retention after 1000 cycles. Furthermore, a fiber-shaped flexible all-solid-state asymmetric supercapacitor based on the resulting hybrid electrode was assembled. The energy density of 0.011 mWh cm(-2) at a power density of 0.33 mW cm(-2) was achieved under an operating voltage window of 1.45 V. This work provides an effective strategy to fabricate high-performance electrodes for fiber-shaped flexible asymmetric supercapacitors through a facile and low-cost route.

VO2/TiO2 Nanosponges as Binder-Free Electrodes for High-Performance Supercapacitors.

VO2/TiO2 nanosponges with easily tailored nanoarchitectures and composition were synthesized by electrostatic spray deposition as binder-free electrodes for supercapacitors. Benefiting from the unique interconnected pore network of the VO2/TiO2 electrodes and the synergistic effect of high-capacity VO2 and stable TiO2, the as-formed binder-free VO2/TiO2 electrode exhibits a high capacity of 86.2 mF cm−2 (~548 F g−1) and satisfactory cyclability with 84.3% retention after 1000 cycles. This work offers an effective and facile strategy for fabricating additive-free composites as high-performance electrodes for supercapacitors.

Synthesis of Amorphous FeOOH/Reduced Graphene Oxide Composite by Infrared Irradiation and Its Superior Lithium Storage Performance

A new hybrid nanostructure composed of mildly reduced graphene oxide (mRGO) nanosheets and homogeneous loading of amorphous FeOOH with ultrafine particles (∼2 nm) is successfully synthesized via a facile infrared irradiation approach. Surprisingly, the as-prepared FeOOH/mRGO hybrid exhibits high reversible capacity, long-term stability, and excellent rate performance, when used as an anode material for lithium-ion batteries. A high reversible capacity of 767 mA h g(-1), with a coulombic efficiency of ∼100%, can be achieved at a high current density of 1000 mA g(-1) even after 600 discharge/charge cycles. The superior electrochemical performances are attributed to the synergistic effects of the small particle size, amorphous structure, and conductive mRGO.

3D interconnected porous NiMoO4 nanoplate arrays on Ni foam as high-performance binder-free electrode for supercapacitors

3D interconnected NiMoO4 nanoplate arrays (NPAs) are grown on Ni foam (NPAs@Ni) via a facile hydrothermal reaction. The obtained NPAs@Ni is directly used as a binder-free integrated electrode for supercapacitors. The optimized electrode exhibits a specific capacitance as high as 3.4 F cm−2 (2138 F g−1) at a current density of 2 mA cm−2, and an excellent cyclability with 87% retention of the initial specific capacitance after 3000 cycles. The remarkable electrochemical performance can be attributed to the interconnected architecture in which the electrons and ions readily transport along the conductive 3D channels.

Hierarchical core-shell NiCo2O4@NiMoO4 nanowires grown on carbon cloth as integrated electrode for high-performance supercapacitors

Hierarchical core-shell NiCo2O4@NiMoO4 nanowires were grown on carbon cloth (CC@NiCo2O4@NiMoO4) by a two-step hydrothermal route to fabricate a flexible binder-free electrode. The prepared CC@NiCo2O4@NiMoO4 integrated electrode was directly used as an electrode for faradaic supercapacitor. It shows a high areal capacitance of 2.917 F cm−2 at 2 mA cm−2 and excellent cycling stability with 90.6% retention over 2000 cycles at a high current density of 20 mA cm−2. The superior specific capacitance, rate and cycling performance can be ascribed to the fast transferring path for electrons and ions, synergic effect and the stability of the hierarchical core-shell structure.