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

Nitrogen-Doped Carbon Polyhedra Nanopapers: An Advanced Binder-Free Electrode for High-Performance Supercapacitors

Metal–organic framework (MOF)-derived nitrogen-doped porous carbon as electrode material for supercapacitors has recently drawn much attention. However, the development of flexible electrodes composed of MOF-derived carbon is still a great challenge. Herein, nitrogen-doped porous carbon polyhedra (NC) derived from zeolitic imidazolate framework-8 (ZIF8) are assembled into flexible nanopapers assisted with reduced graphene oxide (rGO). The resultant NC/rGO nanopaper shows a hierarchical structure of NC nanoparticle-imbedded rGO framework. A uniform dispersion of NC nanoparticles is achieved due to the rGO framework, and meanwhile, the uniform decoration of NC nanoparticles on rGO nanosheets prevents easy restacking of rGO. A conductive rGO framework further accelerates the electron/ion transportation inside the NC/rGO nanopaper. Furthermore, excellent mechanical performance of rGO framework endows high flexibility to the NC/rGO nanopaper. As a result, the NC/rGO nanopaper as a binder-free electrode delivers high specific capacitance of 280 F g–1 at 1 A g–1, high capacitance retention after 5000 cycles, and high energy density of 19.45 W h kg–1

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

In-Situ Growth of Few-Layered MoS₂ Nanosheets on Highly Porous Carbon Aerogel as Advanced Electrocatalysts for Hydrogen Evolution Reaction

Molybdenum disulfide-based hybrids, acting as cost-effective and acid-stable electrocatalysts for hydrogen evolution reaction (HER), have been developed fast for providing sustainable hydrogen energy in recent years. Herein, few-layered molybdenum disulfide (MoS₂) nanosheets/carbon aerogel (CA) hybrids were successfully obtained through the combination of sol–gel process, aging, freeze-drying, high temperature carbonization, and solvothermal reaction. CA with highly continuous porosity and high specific surface area is used as a matrix material for construction of hierarchical MoS₂/CA hybrids where few-layered MoS₂ nanosheets are uniformly covered on a CA surface. In this heterostructured system, CAs not only provide three-dimensional (3D) conductive pathway for fast transportation of electrons and ions, but also offer highly active regions for the growth of MoS₂, greatly preventing the aggregation of MoS₂ nanosheets. Due to the rationally designed hybrids with 3D porous nanostructures, the as-prepared MoS₂/CA hybrids with optimized MoS₂ content exhibit enhanced catalytic performance for electrocatalytic HER with a low onset potential of −0.14 V, large current density, and excellent stability

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

Self-Assembly-Assisted Facile Synthesis of MoS₂‑Based Hybrid Tubular Nanostructures for Efficient Bifunctional Electrocatalysis

In this work, MoS₂-based hybrid tubular nanostructures are facilely synthesized via a self-assembly-assisted process and evaluated as a bifunctional electrocatalyst for hydrogen evolution reactions (HERs) and oxygen reduction reactions (ORRs). By simply mixing the reactants under ambient conditions, (NH₄)₂MoS₄/polydopamine (PDA) hybrid nanospheres are formed. The protonated dopamine is linked to tetrahedral [MoS₄]^2– via weak N–H···S and O–H···S interactions, causing the PDA nanospheres merging together and forming nanorods under stirring-induced shear force. Moreover, the oxidative polymerization of dopamine proceeds on the surface of the nanorods, whereas it is prohibited inside the nanorods owing to lack of oxygen, leading to outward diffusion of dopamine and hence cavitation. After annealing, the tubular morphology is perfectly retained, while ultrafine MoS₂ monolayers are formed due to the confinement of the framework. Benefiting from these unique structural features, the MoS₂/C hybrid nanotubes possess abundant active sites and high surface area, as well as boost electronic and ionic transport, remarkably enhancing their electrocatalytic activities. The onset and half-wave potentials are 0.91 and 0.82 V, respectively, for ORR, close to those of Pt/C. Moreover, low onset potential and small Tafel slope are also observed for HER, demonstrating the potential of the hybrid nanotubes as a promising non-noble metal bifunctional electrocatalyst

Robust Lignin-Based Aerogel Filters: High-Efficiency Capture of Ultrafine Airborne Particulates and the Mechanism

In this article, we report a new type of lignin-based wood-like aerogel filters composed of aligned micrometer-sized pores and cross-linked lignin-based cell walls, as well as their air filtration-related properties. The aerogel filters were prepared via facile unidirectional ice-crystal-induced self-assembly from an aqueous solution, followed by annealing at 300 °C. The cross-linking of lignin and reinforcement with a very small amount of graphene significantly enhance the mechanical stiffness, thermal stability, and humidity/water resistance of the aerogels. Simultaneously, abundant functional groups retained from lignin and the aligned pore channels lead to high filtration efficiency for ultrafine particles accompanied by fairly low pressure drop. Moreover, these low-cost and renewable biomass-based filters also exhibit outstanding long-term filtration efficiency. Through filtration tests with particles of various sizes, it is revealed that the air filtration by this type of aerogel filters is dominated by diffusion, rather than impaction or interception mechanism, which offers a new avenue for design of novel high-performance air filters

Molybdenum Carbide Anchored on Graphene Nanoribbons as Highly Efficient All-pH Hydrogen Evolution Reaction Electrocatalyst

The demand for exploiting hydrogen as a new energy source has driven the development of feasible, efficient, and low-cost electrocatalysts for hydrogen evolution reaction (HER) in different reaction media. Herein, we report the synthesis of molybdenum carbide (Mo₂C) nanoparticles anchored on graphene nanoribbons (GNRs) as HER electrocatalyst that can function well under acidic, basic, and neutral conditions. GNRs obtained by unzipping carbon nanotubes (CNTs) display strip-like structure, offering abundant active sites for growing Mo₂C nanoparticles. Furthermore, GNRs could provide a fast electron transport pathway as well as large exposed surface area to allow full impregnation of electrolytes. Coupling with the anticorrosion feature of Mo₂C nanoparticles, the Mo₂C–GNR hybrid exhibits outstanding electrocatalytic performance in all of the acidic, basic, and neutral media, making it promising as a highly efficient electrocatalyst under conditions at all pH values

Ultralight and Highly Elastic Graphene/Lignin-Derived Carbon Nanocomposite Aerogels with Ultrahigh Electromagnetic Interference Shielding Performance

Ultralight and highly elastic reduced graphene oxide (RGO)/lignin-derived carbon (LDC) composite aerogels with aligned micron-sized pores and cell walls are prepared using a facile freeze-drying method. The presence of a small fraction of LDC in the cell walls enhances the interfacial polarization effect while almost maintaining the amount of charge carriers and conductivity of the cell walls, greatly boosting the wave absorption capability of the cell walls. RGO/LDC aerogels also show a greater number of large cell walls with better integrity than RGO aerogels, further improving the multiple reflection ability of the aligned cell walls. Synergistic effects of the multiphase cell walls and the preferred microstructures of the RGO/LDC aerogels lead to their high electromagnetic interference (EMI) shielding effectiveness of 21.3–49.2 dB at an ultralow density of 2.0–8.0 mg/cm³. This corresponds to the surface-specific SE (SE divided by density and thickness) up to 53 250 dB·cm²/g, which is higher than the values reported for other carbon- and metal-based shields. Furthermore, the critical roles that microstructures play in determining the EMI shielding performance are directly revealed by comparing the shielding performance in directions parallel and normal to cell walls, as well as in an in situ compression process