Longsheng Zhang

Flexible Hybrid Membranes with Ni(OH)2 Nanoplatelets Vertically Grown on Electrospun Carbon Nanofibers for High-Performance Supercapacitors

The practical applications of transition metal oxides and hydroxides for supercapacitors are restricted by their intrinsic poor conductivity, large volumetric expansion, and rapid capacitance fading upon cycling, which can be solved by optimizing these materials to nanostructures and confining them within conductive carbonaceous frameworks. In this work, flexible hybrid membranes with ultrathin Ni(OH)2 nanoplatelets vertically and uniformly anchored on the electrospun carbon nanofibers (CNF) have been facilely prepared as electrode materials for supercapacitors. The Ni(OH)2/CNF hybrid membranes with three-dimensional macroporous architectures as well as hierarchical nanostructures can provide open and continuous channels for rapid diffusion of electrolyte to access the electrochemically active Ni(OH)2 nanoplatelets. Moreover, the carbon nanofiber can act both as a conductive core to provide efficient transport of electrons for fast Faradaic redox reactions of the Ni(OH)2 sheath, and as a buffering matrix to mitigate the local volumetric expansion/contraction upon long-term cycling. As a consequence, the optimized Ni(OH)2/CNF hybrid membrane exhibits a high specific capacitance of 2523 F g(-1) (based on the mass of Ni(OH)2, that is 701 F g(-1) based on the total mass) at a scan rate of 5 mV s(-1). The Ni(OH)2/CNF hybrid membranes with high mechanical flexibility, superior electrical conductivity, and remarkably improved electrochemical capacitance are condsidered as promising flexible electrode materials for high-performance supercapacitors.

Cotton Wool Derived Carbon Fiber Aerogel Supported Few-Layered MoSe2 Nanosheets As Efficient Electrocatalysts for Hydrogen Evolution

Recent studies have proven that newly emerging two-dimensional molybdenum diselenide (MoSe2) is a promising noble-metal-free electrocatalyst for hydrogen evolution reaction (HER). Increasing the exposures of the active edges of MoSe2 nanostructures is a key issue to fully realize the excellent electrochemical properties of MoSe2. In this work, a few-layered MoSe2/carbon fiber aerogel (CFA) hybrids have been facilely obtained through the combination of high-temperature carbonization and one-pot solvothermal reaction. CFA derived from cotton wool is used as a three-dimensional conductive network for construction of hierarchical MoSe2/CFA hybrids, where few-layered MoSe2 nanosheets are uniformly and perpendicularly decorated on the surfaces of CFA. In the designed and prepared hybrids, CFA effectively increases the exposures of the active edges of MoSe2 nanosheets as well as provides reduced lengths for both electron transportation and ion diffusion. Therefore, the obtained optimal MoSe2/CFA hybrid exhibits excellent electrochemical activity as HER electrocatalyst with a small onset potential of -0.104 V vs reversible hydrogen electrode and a small Tafel slope of 62 mV per decade, showing its great potential as a next-generation Pt-free electrocatalyst for HER.

3D porous hybrids of defect-rich MoS2/graphene nanosheets with excellent electrochemical performance as anode materials for lithium ion batteries

In recent years, the global energy crisis and environmental concerns have put forward an ever-growing demand for efficient energy storage, which has accelerated the development of lithium ion batteries with higher power density and longer cycle life. Herein, we demonstrate a facile and scalable process to prepare three-dimensional (3D) porous hybrids comprised of ultrathin defect-rich MoS2 nanosheets (dr-MoS2 NSs) and conductive graphene nanosheets (GNS) via a hydrothermal co-assembly process. The resulting dr-MoS2/graphene (dr-MoS2/GNS) hybrids possess a 3D porous structure with large specific surface area, which enables rapid diffusion of lithium ions to access active materials. The ultrathin dr-MoS2 NSs with exposure of additional active edge sites significantly facilitate the intercalation of lithium ions, thus leading to higher specific capacity. The interconnected graphene network not only provides highly conductive pathways facilitating the charge transfer and lithium ion transport, but also maintains its structural stability during the lithiation/delithiation process. As a consequence, the dr-MoS2/GNS (6:1) hybrid exhibits a high reversible capacity of 1130.9 mA h g−1 at a current density of 0.1 A g−1, with excellent cyclic stability and rate capability. The outstanding electrochemical performance of the dr-MoS2/GNS hybrids can be ascribed to their 3D porous structure and the synergetic effect between ultrathin dr-MoS2 NSs and the conductive graphene network, making them promising anode materials for high performance lithium ion batteries.

A flexible free-standing defect-rich MoS2/graphene/carbon nanotube hybrid paper as a binder-free anode for high-performance lithium ion batteries

The rapid development of flexible energy storage devices has motivated people to seek reliable electrodes with both high mechanical flexibility and excellent electrochemical performance. Herein, we demonstrate a facile and scalable process to fabricate a flexible free-standing defect-rich MoS2/graphene/carbon nanotube (dr-MGC) hybrid paper, which can be directly used as a flexible binder-free anode for lithium ion batteries. Benefiting from the excellent dispersibility of defect-rich MoS2 nanosheets (dr-MoS2 NSs) and graphene oxide/carbon nanotube (GO/CNT) hybrids in aqueous solution, a unique three-dimensional (3D) nanoporous architecture with ultrathin dr-MoS2 NSs homogeneously embedded in graphene/CNT frameworks is nicely constructed by a simple vacuum filtration and thermal reduction process. As a consequence, the flexible free-standing dr-MGC21 hybrid paper exhibits a high reversible capacity of 1137.2 mA h g−1 at a current density of 0.1 A g−1 with excellent cyclic stability and rate capability. The superior electrochemical performance of the dr-MGC hybrid paper is ascribed to the 3D nanoporous architecture as well as the synergistic effect between the dr-MoS2 NSs and conductive graphene/CNT network. Moreover, the idea of utilizing graphene/CNT hybrids as flexible conductive frameworks provides a novel pathway for the large-scale fabrication of various flexible binder-free electrodes for high-performance flexible energy storage devices.

Three-Dimensional Nanoporous Graphene-Carbon Nanotube Hybrid Frameworks for Confinement of SnS2 Nanosheets: Flexible and Binder-Free Papers with Highly Reversible Lithium Storage.

The practical applications of transition-metal dichalcogenides for lithium-ion batteries are severely inhibited by their inferior structural stability and electrical conductivity, which can be solved by optimizing these materials to nanostructures and confining them within conductive frameworks. Thus, we report a facile approach to prepare flexible papers with SnS2 nanosheets (SnS2 NSs) homogeneously dispersed and confined within the conductive graphene-carbon nanotube (CNT) hybrid frameworks. The confinement of SnS2 NSs in graphene-CNT matrixes not only can effectively prevent their aggregation during the discharge-charge procedure, but also can assist facilitating ion transfer across the interfaces. As a result, the optimized SGC papers give an improved capacity of 1118.2 mA h g(-1) at 0.1 A g(-1) along with outstanding stability. This report demonstrates the significance of employing graphene-CNT matrixes for confinement of various active materials to fabricate flexible electrode materials.

Immobilization of NiS nanoparticles on N-doped carbon fiber aerogels as advanced electrode materials for supercapacitors

NiS nanoparticles (NPs) with excellent electrochemical capacitance have attracted considerable attention as cost-effective energy-storage materials for supercapacitors in recent years. Preventing the aggregation and increasing the conductivity of NiS NPs are key to fully realizing their excellent electrochemical properties. In this work, NiS/N-doped carbon fiber aerogel (N-CFA) nanocomposites were obtained easily through the combination of polymerization, carbonization, and a one-step solvothermal reaction. N-CFA derived from polydopamine (PDA)-coated cotton wool was used as a template for the construction of hierarchical NiS/N-CFA nanocomposites, in which NiS NPs are uniformly immobilized on the surface of N-CFA. In this nanostructured system, N-CFA containing abundant nanofibers not only provides active regions for the growth of NiS NPs to prevent their aggregation, but also offers short pathways for the transport of electrons and ions. The electrochemical properties of the obtained NiS/N-CFA nanocomposites were investigated by cyclic voltammetry, galvanostatic charge–discharge, and alternating current impedance measurements. The optimized NiS/N-CFA nanocomposite exhibits a high specific capacitance of 1,612.5 F·g‒1 at a charge/discharge current density of 1 A·g‒1 and excellent rate capacitance retention of 66.7% at 20 A·g‒1. The excellent electrochemical properties of NiS/N-CFA nanocomposites make these materials promising electrode materials for supercapacitors.

Polymer/Carbon-Based Hybrid Aerogels: Preparation, Properties and Applications

Aerogels are synthetic porous materials derived from sol-gel materials in which the liquid component has been replaced with gas to leave intact solid nanostructures without pore collapse. Recently, aerogels based on natural or synthetic polymers, called polymer or organic aerogels, have been widely explored due to their porous structures and unique properties, such as high specific surface area, low density, low thermal conductivity and dielectric constant. This paper gives a comprehensive review about the most recent progresses in preparation, structures and properties of polymer and their derived carbon-based aerogels, as well as their potential applications in various fields including energy storage, adsorption, thermal insulation and flame retardancy. To facilitate further research and development, the technical challenges are discussed, and several future research directions are also suggested in this review.

Porous graphene–carbon nanotube hybrid paper as a flexible nano-scaffold for polyaniline immobilization and application in all-solid-state supercapacitors

Polyaniline (PANI) has been recognized as an ideal candidate for electrode materials in supercapacitors. However, the relatively low electrical conductivity and poor cyclic stability severely limit its potential applications. Therefore, a proper substrate with carefully designed nanostructures for PANI immobilization is highly desirable for realizing its full performance. In this study, three-dimensional porous graphene–carbon nanotube (p-GC) hybrid papers with high porosity, excellent electrical conductivity and good flexibility were utilized as a nano-scaffold for the in situ polymerization of PANI, thus obtaining flexible p-GC/PANI ternary hybrid papers with hierarchical nanostructures. The good electrical conductivity and optimized porous nanostructure of the p-GC hybrid paper provides improved conductive pathways and high surface area, ensuring the efficient utilization of the pseudocapacitance of PANI. Thus, the ternary hybrid paper exhibits a high specific capacitance of up to 409 F g−1 at a current density of 10 A g−1, as well as excellent rate and cyclic performance. Furthermore, the dimensional confinement of PANI particles within the p-GC framework effectively prohibits volume expansion and shrinkage upon electrolyte soakage and cycling. Therefore, the p-GC hybrid paper with tunable hierarchical nanostructures can act as a promising substrate to enhance the electrochemical properties of PANI or other electroactive materials and can be easily extended to the design of next-generation high-performance flexible supercapacitors.

Flexible hierarchical membranes of WS2 nanosheets grown on graphene-wrapped electrospun carbon nanofibers as advanced anodes for highly reversible lithium storage

It is still very challenging to achieve effective combination of carbon nanofibers and graphene sheets. In this study, a novel and facile method is developed to prepare flexible graphene/carbon nanofiber (GCNF) membranes with every carbon nanofiber wrapped by conductive graphene sheets, resulting in a remarkable improvement of their electrical conductivity. This method only entails a moderate process of soaking the pre-oxidized electrospun polyacrylonitrile (oPAN) nanofiber membranes in graphene oxide (GO) aqueous dispersion, and subsequent carbonization of the GO/oPAN hybrid membranes. By using the highly conductive GCNF membrane as a template, hierarchical WS2/GCNF hybrid membranes with few-layer WS2 nanosheets uniformly grown on GCNF nanofibers were fabricated as high-performance anodes for lithium ion batteries. Benefiting from the synergistic effects of GCNF nanofibers and WS2 nanosheets, the resulting WS2/GCNF hybrid membranes possessed a porous structure, large specific surface area, high electrical conductivity and good structural integrity, which are favorable for the rapid diffusion of lithium ions, fast transfer of electrons and overall electrochemical stability. As a result, the optimized WS2/GCNF hybrid membrane exhibited a high initial charge capacity of 1128.2 mA h g-1 at a current density of 0.1 A g-1 and outstanding cycling stability with 95% capacity retention after 100 cycles.

Elastic Carbon Aerogels Reconstructed from Electrospun Nanofibers and Graphene as Three-Dimensional Networked Matrix for Efficient Energy Storage/Conversion

Three-dimensional (3D) all-carbon nanofibrous aerogels with good structural stability and elasticity are highly desirable in flexible energy storage/conversion devices. Hence, an efficient surface-induced co-assembly strategy is reported for the novel design and reconstruction of electrospun nanofibers into graphene/carbon nanofiber (CNF) composite aerogels (GCA) with hierarchical structures utilizing graphene flakes as cross-linkers. The as-obtained GCA monoliths possess interconnected macropores and integrated conductive networks, which exhibit high elasticity and great structural robustness. Benefitting from the largely increased surface area and charge-transfer efficiency derived from the multi-form firm interconnections (including pillaring, bridging and jointing) between graphene flakes and CNF ribs, GCA not only reveals prominent capacitive performance as supercapacitor electrode, but also shows excellent hydrogen evolution reaction activity in both acidic and alkaline solutions as a 3D template for decoration of few-layered MoSe2 nanosheets, holding great potentials for energy-related applications.