Carbon-Based Nanocages: A New Platform for Advanced Energy Storage and Conversion

Energy storage and conversion play a crucial role in modern energy systems, and the exploration of advanced electrode materials is vital but challenging. Carbon-based nanocages consisting of sp² carbon shells feature a hollow interior cavity with sub-nanometer microchannels across the shells, high specific surface area with a defective outer surface, and tunable electronic structure, much different from the intensively studied nanocarbons such as carbon nanotubes and graphene. These structural and morphological characteristics make carbon-based nanocages a new platform for advanced energy storage and conversion. Up-to-date synthetic strategies of carbon-based nanocages, the utilization of their unique porous structure and morphology for the construction of composites with foreign active species, and their significant applications to the advanced energy storage and conversion are reviewed. Structure-performance correlations are discussed in depth to highlight the contribution of carbon-based nanocages. The research challenges and trends are also envisaged for deepening and extending the study and application of this multifunctional material.

Pistachio Shell-Derived Carbon Activated with Phosphoric Acid: A More Efficient Procedure to Improve the Performance of Li-S Batteries

A sustainable and low-cost lithium-sulfur (Li-S) battery was produced by reusing abundant waste from biomass as a raw material. Pistachio shell was the by-product from the agri-food industry chosen to obtain activated carbon with excellent textural properties, which acts as a conductive matrix for sulfur. Pistachio shell-derived carbon activated with phosphoric acid exhibits a high surface area (1345 m²·g^-1) and pore volume (0.67 cm³·g^-1), together with an interconnected system of micropores and mesopores that is capable of accommodating significant amounts of S and enhancing the charge carrier mobility of the electrochemical reaction. Moreover, preparation of the S composite was carried out by simple wet grinding of the components, eliminating the usual stage of S melting. The cell performance was very satisfactory, both in long-term cycling measurements and in rate capability tests. After the initial cycles required for cell stabilization, it maintained good capacity retention for the 300 cycles measured (the capacity loss was barely 0.85 mAh·g^-1 per cycle). In the rate capability test, the capacity released was around 650 mAh·g^-1 at 1C, a higher value than that supplied by other activated carbons from nut wastes.

Effect of Functionalized Carbon Microspheres Combined with Ammonium Polyphosphate on Fire Safety Performance of Thermoplastic Polyurethane

In this article, carbon microspheres (CMSs) synthesized by the hydrothermal method and CMSs-Fe (with Fe³⁺ adsorbed on the surface of CMSs) were combined with ammonium polyphosphate (APP) to achieve the fire safety improvement of thermoplastic polyurethane (TPU). The fire safety performance of TPU composites was investigated by the cone calorimeter test, microscale combustion calorimeter test, thermogravimetric analysis/infrared spectrometry, Raman spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy. The results showed that CMSs and CMSs-Fe can improve the fire safety performance of TPU/APP composites and the effect of CMSs-Fe was better than that of CMSs. The peak heat release rate of the sample containing 0.25 wt % CMSs and 7.75 wt % APP was 16.7% lower than that of the sample containing 8.00 wt % APP, and the content of toxic gases was also reduced in the fire smoke. Also, total heat release and total smoke release of the sample containing CMSs-Fe were 54.7% and 11.6%, respectively, lower than those of the sample containing 0.25% CMSs. It confirmed the contribution of CMSs to the flame retardant system, and the performance of CMSs is improved by adsorbing Fe³⁺.

Electrocatalytic Imprinted Polymer of N-Doped Hollow Carbon Nanosphere-Palladium Nanocomposite for Ultratrace Detection of Anticancer Drug 6-Mercaptopurine

In this work, a nanohybrid-based imprinted polymer consisting of N-doped hollow carbon nanospheres and palladium is reported for the electroanalysis of ultratrace level of anticancer drug, 6-mercaptopurine, used in the treatment of leukemia. For this, N-doped carbon nanospheres decorated with palladium were first developed, and subsequently, a molecular imprinted polymer layer was grown onto their surfaces. The so-produced silica-embedded nanocomposite was made hollow by etching silica moieties with hydrofluoric acid. Finally, the whole system was doped on an ionic-liquid-modified pencil graphite electrode. The underlying synergistic effect of hollow carbon nanosphere-supported palladium nanoparticles inculcated electrocatalytic action. Notably, all rebinding sites in solid core-shells were confined within the shell, which hampers the effective diffusion of template. However, in this work, an effective diffusion of template across the hollow structure of inner and outer surfaces was observed. Consequently, this rendered approximately 2-fold heterogeneous rate constant as compared to the solid core-shell-based sensor. Differential pulse voltammetric transduction was used for ultratrace detection of 6-mercaptopurine through anodic stripping method. The hollow imprinted sensor revealed a linear dependence of current with concentration range 0.80-70.748 ng mL^-1. The limits of detection 0.11-0.22 ng mL^-1 were realized in water, human blood plasma, urine, and pharmaceuticals. Thus, the proposed sensor demonstrated an attractive sensitivity reproducibility, as well as endurance requisite for the treatment of leukemia patients.

Functionalized Natural Carbon-Supported Nanoparticles as Excellent Catalysts for Hydrocarbon Production

We report a one-pot and eco-friendly synthesis of carbon-supported cobalt nanoparticles, achieved by carbonization of waste biomass (rice bran) with a cobalt source. The functionalized biomass provides carbon microspheres as excellent catalyst support, forming a unique interface between hydrophobic and hydrophilic groups. The latter, involving hydroxyl and amino groups, can catch much more active cobalt nanoparticles on surface for Fischer-Tropsch synthesis than chemical carbon. The loading amount of cobalt on the final catalyst is much higher than that prepared with a chemical carbon source, such as glucose. The proposed concept of using a functionalized natural carbon source shows great potential compared with conventional carbon sources, and will be meaningful for other fields concerning carbon support, such as heterogeneous catalysis or electrochemical fields.

L-Cysteine-Assisted Synthesis of Urchin-Like γ-MnS and Its Lithium Storage Properties

MnS has been attracting more and more attentions in the fields of lithium ion batteries (LIBs) because of its high energy density and low voltage potential. In this paper, we present a simple method for the preparation of urchin-like γ-MnS microstructures using L-cysteine and MnCl2 · 4H2O as the starting materials. The urchin-like γ-MnS microstructures exhibit excellent cycling stability (823.4 mA h g-1 at a current density of 500 mA g-1, after 1000 cycles). And the discharge voltage is about 0.75 V, making it a good candidate for the application as the anode material in LIBs. SEM, TEM, and XRD were employed to inspect the changes of the active materials during the electrochemical process, which clearly indicate that the structural pulverization and reformation of the γ-MnS microstructures play important roles for the maintenance of the electrochemical performance during the charge/discharge process.

Unique 1D Co3O4 crystallized nanofibers with (220) oriented facets as high-performance lithium ion battery anode material

A novel one-step hydrothermal and calcination strategy was developed to synthesize the unique 1D oriented Co₃O₄ crystal nanofibers with (220) facets on the carbon matrix derived from the natural, abundant and low cost wool fibers acting as both carbon precursor and template reagent. The resultant W2@Co₃O₄ nanocomposite exhibited very high specific capacity and favorable high-rate capability when used as anode material of lithium ion battery. The high reversible Li⁺ ion storage capacity of 986 mAh g⁻¹ was obtained at 100 mA g⁻¹ after 150 cycles, higher than the theoretical capacity of Co₃O₄ (890 mAh g⁻¹). Even at the higher current density of 1 A g⁻¹, the electrode could still deliver a remarkable discharge capacity of 720 mAh g⁻¹ over 150 cycles.

Scalable synthesis of nanometric α-Fe2O3 within interconnected carbon shells from pyrolytic alginate chelates for lithium storage

By combining naturally abundant iron ions and sodium alginate into conventional wet-spinning and pyrolysis processes, α-Fe₂O₃ could be nanostructured and carbon-coated in a facile and scalable technique.

In situ carbon-coating and Ostwald ripening-based route for hollow Ni3S4@C spheres with superior Li-ion storage performances

Uniform hollow carbon-coated polydymite microspheres, which display superior Li-ion storage performances, were synthesized via an Ostwald ripening-based hollowing route.

In Situ Synthesis of MnS Hollow Microspheres on Reduced Graphene Oxide Sheets as High-Capacity and Long-Life Anodes for Li- and Na-Ion Batteries

Uniform MnS hollow microspheres in situ crystallized on reduced graphene oxide (RGO) nanosheets via a facile hydrothermal method. The MnS/RGO composite material was used as the anode for Na-ion batteries for the first time and exhibited excellent cycling performance, superior specific capacity, and great cycle stability and rate capability for both Li- and Na-ion batteries. Compared with nonencapsulated pure MnS hollow microspheres, these MnS/RGO nanocomposites demonstrated excellent charge-discharge stability and long cycle life. Li-ion storage testing revealed that these MnS/RGO nanocomposites deliver high discharge-charge capacities of 640 mAh g(-1) at 1.0 A g(-1) after 400 cycles and 830 mAh g(-1) at 0.5 A g(-1) after 100 cycles. The MnS/RGO nanocomposites even retained a specific capacity of 308 mAh g(-1) at a current density of 0.1 A g(-1) after 125 cycles as the anode for Na-ion batteries. The outstanding electrochemical performance of the MnS/RGO composite attributed to the RGO nanosheets greatly improved the electronic conductivity and efficiently mitigated the stupendous volume expansion during the progress of charge and discharge.

Ultrafine Pd nanoparticles encapsulated in microporous Co3O4 hollow nanospheres for in situ molecular detection of living cells

Recent progress in the in situ molecular detection of living cells has attracted tremendous research interests due to its great significance in biochemical, physiological, and pathological investigation. Especially for the electrochemical detection of hydrogen peroxide (H2O2) released by living cells, the highly efficient and cost-effective electrocatalysts are highly desirable. In this work, we develop a novel type of microporous Co3O4 hollow nanospheres containing encapsulated Pd nanoparticles (Pd@Co3O4). Owing to the synergy effect between the permeable microporous Co3O4 shell and the ultrafine Pd nanoparticles that encapsulated in it, the resultant Pd@Co3O4 based electrode exhibits excellent electrochemical sensor performance toward H2O2, even when the content of Pd in Pd@Co3O4 hollow nanospheres is as low as 1.14 wt %, which enable it be used for real-time tracking of the secretion of H2O2 in different types of living human cells.

Template-assisted synthesis of multi-shelled carbon hollow spheres with an ultralarge pore volume as anode materials in Li-ion batteries

Double/quadruple shells carbon hollow spheres can be obtained under the assistance of permeably mesoporous silica hollow spheres, which exhibit superior electrochemical performance.

Green synthesis of 3D SnO2/graphene aerogels and their application in lithium-ion batteries

3D SnO₂/GAs were constructed by a simple, facile and environmental friendly process, and show excellent performance when used as anode material in lithium ion batteries.

Cyclodextrin-functionalized hollow carbon nanospheres by introducing nanogold for enhanced electrochemical sensing of o-dihydroxybenzene and p-dihydroxybenzene

A cyclodextrin–gold nanoparticles/hollow carbon nanospheres nanohybrid was prepared for the sensitive simultaneous electrochemical sensing of o- and p-dihydroxybenzene.

Wheat straw carbon matrix wrapped sulfur composites as a superior cathode for Li–S batteries

Wheat straw derived porous carbon with a surface area of 1066 m²g⁻¹and total pore volume of 0.62 cm³g⁻¹is used to synthesize WSC/S (74 wt%) cathode for Li–S batteries, which delivers a stable cycling performance and superior rate capability.

Nickel Oxide Nanoparticle-Assembled Microspheres with a High Rate Capability for Lithium Storage

This paper presents the massive preparation of nickel oxide nanoparticle-assembled mesoporous microspheres using acid-treated carbon microspheres as sacrificial templates. The microstructure and morphology of the hollow NiO microspheres are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption–desorption methods. Scanning electron microscopy and transmission electron microscopy images reveal that these hollow spheres are assembled by NiO particles with sizes of ~20 nm. The nickel oxide nanoparticle-assembled mesoporous microspheres feature high surface area and good electronic conductivity, leading to high capacity and excellent cycling performance as anode materials for lithium-ion batteries.

Ultra-small Co3O4 nanoparticles–reduced graphene oxide nanocomposite as superior anodes for lithium-ion batteries

A facile solution-based method was reported to prepare ultra-small Co₃O₄ nanoparticles–reduced graphene oxide (Co₃O₄–RGO) nanocomposite as anode material for lithium-ion batteries. This Co₃O₄–RGO nanocomposite showed good electrochemical performance.

Porous nano-structured Co3O4 anode materials generated from coordination-driven self-assembled aggregates for advanced lithium ion batteries

A simple and scalable coordination-derived method for the synthesis of porous Co3O4 hollow nanospheres is described here. The initially formed coordination-driven self-assembled aggregates (CDSAAs) could act as the precursor followed by calcination treatment. Then the porous hollow Co3O4 nanospheres are obtained, in which the primary Co3O4 nanoparticles are inter-dispersed. When the nanospheres are used as anode materials for lithium storage, they show excellent coulombic efficiency, high lithium storage capacity and superior cycling performance. In view of the facile synthesis and excellent electrochemical performance obtained, this protocol to fabricate special porous hollow frameworks could be further extended to other metal oxides and is expected to improve the practicality of superior cycle life anode materials with large volume excursions for the development of the next generation of LIBs.

Ge/C nanowires as high-capacity and long-life anode materials for Li-ion batteries

Germanium-based materials (Ge and GeOx) have recently demonstrated excellent lithium-ion storage ability and are being considered as the most promising candidates to substitute commercial carbon-based anodes of lithium-ion batteries. Nevertheless, practical implementation of Ge-based materials to lithium-ion batteries is greatly hampered by the poor cyclability that resulted from the huge volume variation during lithiation/delithiation processes. Herein, uniform carbon-encapsulated Ge and GeOx nanowires were synthesized by a one-step controlled pyrolysis of organic-inorganic hybrid GeOx/ethylenediamine (GeOx/EDA) nanowires in H2/Ar and Ar atmospheres, respectively. The as-obtained Ge/C and GeOx/C nanowires possess well-defined 0D-in-1D morphology and homogeneous carbon encapsulation, which exhibit excellent Li storage properties including high specific capacities (approximate 1200 and 1000 mA h g(-1) at 0.2C for Ge/C and GeOx/C, respectively). The Ge/C nanowires, in particular, demonstrate superior rate capability with excellent capacity retention and stability (producing high stable discharge capacities of about 770 mA h g(-1) after 500 cycles at 10C), making them promising candidates for future electrodes for high-power Li-ion batteries. The improved electrochemical performance arises from synergistic effects of 0D-in-1D morphology and uniform carbon coating, which could effectively accommodate the huge volume change of Ge/GeOx during cycling and maintain perfect electrical conductivity throughout the electrode.