Youfang Zhang

Nitrogen-Doped Carbon Nanofiber/Molybdenum Disulfide Nanocomposites Derived from Bacterial Cellulose for High-Efficiency Electrocatalytic Hydrogen Evolution Reaction

To remit energy crisis and environmental deterioration, non-noble metal nanocomposites have attracted extensive attention, acting as a fresh kind of cost-effective electrocatalysts for hydrogen evolution reaction (HER). In this work, hierarchically organized nitrogen-doped carbon nanofiber/molybdenum disulfide (pBC-N/MoS2) nanocomposites were successfully prepared via the combination of in situ polymerization, high-temperature carbonization process, and hydrothermal reaction. Attributing to the uniform coating of polyaniline on the surface of bacterial cellulose, the nitrogen-doped carbon nanofiber network acts as an excellent three-dimensional template for hydrothermal growth of MoS2 nanosheets. The obtained hierarchical pBC-N/MoS2 nanocomposites exhibit excellent electrocatalytic activity for HER with small overpotential of 108 mV, high current density of 8.7 mA cm(-2) at η = 200 mV, low Tafel slope of 61 mV dec(-1), and even excellent stability. The greatly improved performance is benefiting from the highly exposed active edge sites of MoS2 nanosheets, the intimate connection between MoS2 nanosheets and the highly conductive nitrogen-doped carbon nanofibers and the three-dimensional networks thus formed. Therefore, this work provides a novel strategy for design and application of bacterial cellulose and MoS2-based nanocomposites as cost-effective HER eletrocatalysts.

Graphene/carbon aerogels derived from graphene crosslinked polyimide as electrode materials for supercapacitors

Carbon aerogels with hierarchical porous structures are highly promising for developing novel electrode materials for supercapacitors due to their substantial active sites for ion and electron transfer. Herein, a new type of graphene/carbon aerogels with multimodal pores have been facilely synthesized via carbonization of graphene crosslinked polyimide aerogels. Compared to most carbon aerogels based on organic aerogels reported previously, this preparation process is facilitated by the exclusion of harmful formaldehyde. Moreover, graphene is demonstrated as a powerful crosslinking agent, allowing acceleration of the gelation process, improvement of the porous structures inside carbon aerogels, and enlargement of specific surface area and conductivity of carbon aerogels. SEM observation shows the multimodal pores and three-dimensional nano-network of carbon aerogels, which provide short diffusion lengths for both charge and ion transport and high electroactive regions. With graphene involved, the as-prepared carbon aerogels possess high specific surface area up to 998.7 m 2 g � 1 and specific capacitance up to 178.1 F g � 1 at a current density of 1 A g � 1 , which is much higher than that of pure carbon aerogels (193.6 m 2 g � 1 and 104.2 F g � 1 ). This work provides a new and facile avenue for

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.

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.

Quasi-one-dimensional graphene nanoribbon-supported MoS2 nanosheets for enhanced hydrogen evolution reaction

Electrolysis of water is a sustainable and environmentally friendly way to produce hydrogen, which has motivated people to develop efficient and earth-abundant electrocatalysts that minimize energy consumption. Herein, graphene nanoribbon@MoS2 (GNR@MoS2) hybrids with hierarchical structure have been facilely fabricated as efficient electrocatalysts for the hydrogen evolution reaction (HER). Derived from longitudinally unzipping of multi-walled carbon nanotubes, GNR sheets can provide a greater surface area for the decoration of MoS2, which not only stems from the outer wall sheets, but also from the additional exfoliated inner wall space, as well as from the unique ribbon edges. Furthermore, the interconnected GNR sheets can form a conductive pathway for fast electron transportation and an open structure for convenient electrolyte permeation. As a consequence, the GNR@MoS2 hybrids exhibit excellent electrochemical activity as HER catalysts with a low onset potential of −0.11 V vs. the reversible hydrogen electrode and a small Tafel slope of 43.4 mV per decade. The outstanding electrocatalytic performance of the GNR@MoS2 hybrids can be ascribed to their unique hierarchical architecture with numerous active sites, as well as synergistic effects between the electrocatalytic MoS2 nanosheets and conductive GNR framework, making them promising materials for future electrocatalysts in the HER.

Simultaneous growth of carbon nanotubes on inner/outer surfaces of porous polyhedra: Advanced sulfur hosts for lithium-sulfur batteries

Metal-organic framework (MOF)-derived functional carbon matrices have recently attracted considerable attention as energy-storage materials. However, the development of MOF-derived carbon materials with hierarchical structures, capable of thoroughly preventing the “shuttling᾿of polysulfides, is still a major challenge. Herein, we synthesized cobalt nanoparticle-containing porous carbon polyhedra with in situ grown N-doped carbon nanotube (CNT) backbone (NCCNT-Co), using zeolitic imidazolate framework-67 (ZIF-67) as starting material. The obtained NCCNT-Co, with interconnected N-doped CNTs on both inner and outer surfaces, possesses an integrated conductive network, which can further accelerate the transport of electrons/ions inside the whole sulfur cathode. The mesoporous structure derived from the ZIF-67 matrix and the densely immobilized CNTs, coupled with the homogeneously doped N atoms and Co nanoparticles, can efficiently trap lithium polysulfides (LiPSs) by physical confinement and chemical interactions. Furthermore, the hierarchical structure of the porous carbon polyhedra enables a high sulfur loading of up to 76 wt.% and can also buffer the volume changes of active sulfur during the lithiation process. As a result, the NCCNT-Co-S cathode delivers a high initial specific capacity of 1,300 mAh·g−1 at 0.1 C, along with a high capacity of 860 mAh·g−1 after 500 cycles at 1 C, with an extremely low capacity decay of 0.024% per cycle.