CVD generated mesoporous hollow carbon spheres as supercapacitors

Biomass-based controllable morphology of carbon microspheres with multi-layer hollow structure for superior performance in supercapacitors

The electrochemical properties of corn starch (CS)-based hydrothermal carbon microsphere (CMS) electrode materials for supercapacitor are closely related to their structures. Herein, cetyltrimethyl ammonium bromide (CTAB) was used as a soft template to form the corn starch (CS)-based carbon microspheres with radial hollow structure in the inner and middle layers by hydrothermal and sol-gel method. Due to the introduction of multi-layer hollow structure of carbon microsphere, more micropores were produced during CO2 activation, which increased the specific surface area and improved the capacitance performance. Compared to commercial activated carbon, the four different morphologies of corn starch CMS had better electrochemical performances. Consequently, the proposed CO2-(CTAB)-CS-CS exhibits a high discharge specific capacitance of 242.5F/g at 1 A/g in three-electrode system with 6 M KOH electrolyte, better than commercial activated carbon with 208.5F/g. Moreover, excellent stability is achieved for CO2-(CTAB)-CS-CS with approximately 97.14 % retention of the initial specific capacitance value after 10,000 cycles at a current density of 2 A/g, while the commercial activated carbon has 86.96 % retention. This implies that the corn starch-based multilayer hollow CMS could be a promising electrode material for high-performance supercapacitors.

High-Performance Lithium-Ion Batteries with High Stability Derived from Titanium-Oxide- and Sulfur-Loaded Carbon Spherogels

This study presents a novel approach to developing high-performance lithium-ion battery electrodes by loading titania-carbon hybrid spherogels with sulfur. The resulting hybrid materials combine high charge storage capacity, electrical conductivity, and core-shell morphology, enabling the development of next-generation battery electrodes. We obtained homogeneous carbon spheres caging crystalline titania particles and sulfur using a template-assisted sol-gel route and carefully treated the titania-loaded carbon spherogels with hydrogen sulfide. The carbon shells maintain their microporous hollow sphere morphology, allowing for efficient sulfur deposition while protecting the titania crystals. By adjusting the sulfur impregnation of the carbon sphere and varying the titania loading, we achieved excellent lithium storage properties by successfully cycling encapsulated sulfur in the sphere while benefiting from the lithiation of titania particles. Without adding a conductive component, the optimized material provided after 150 cycles at a specific current of 250 mA g-1 a specific capacity of 825 mAh g-1 with a Coulombic efficiency of 98%.

Facile and Controllable Synthesis of CuS@Ni-Co Layered Double Hydroxide Nanocages for Hybrid Supercapacitors

The synthesis of battery-type electrode materials with hollow nanostructures for high-performance hybrid supercapacitors (HSCs) remains challenging. In this study, hollow CuS@Ni-Co layered double hydroxide (CuS-LDH) composites with distinguished compositions and structures are successfully synthesized by co-precipitation and the subsequent etching/ion-exchange reaction. CuS-LDH-10 with uniformly dispersed CuS prepared with the addition of 10 mg of CuS shows a unique hollow polyhedral structure constituted by loose nanosphere units, and these nanospheres are composed of interlaced fine nanosheets. The composite prepared with 30 mg of CuS addition (CuS-LDH-30) is composed of a hollow cubic morphology with vertically aligned nanosheets on the CuS shell. The CuS-LDH-10 and CuS-LDH-30 electrodes exhibit high specific capacity (765.1 and 659.6 C g^-1 at 1 A g^-1, respectively) and superior cycling performance. Additionally, the fabricated HSC delivers a prominent energy density of 52.7 Wh kg^-1 at 804.5 W kg^-1 and superior cycling performance of 87.9% capacity retention after 5000 cycles. Such work offers a practical and effortless route for synthesizing unique metal sulfide/hydroxide composite electrode materials with hollow structures for high-performance HSCs.

Nanohollow Carbon for Rechargeable Batteries: Ongoing Progresses and Challenges

Among the various morphologies of carbon-based materials, hollow carbon nanostructures are of particular interest for energy storage. They have been widely investigated as electrode materials in different types of rechargeable batteries, owing to their high surface areas in association with the high surface-to-volume ratios, controllable pores and pore size distribution, high electrical conductivity, and excellent chemical and mechanical stability, which are beneficial for providing active sites, accelerating electrons/ions transfer, interacting with electrolytes, and giving rise to high specific capacity, rate capability, cycling ability, and overall electrochemical performance. In this overview, we look into the ongoing progresses that are being made with the nanohollow carbon materials, including nanospheres, nanopolyhedrons, and nanofibers, in relation to their applications in the main types of rechargeable batteries. The design and synthesis strategies for them and their electrochemical performance in rechargeable batteries, including lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, and lithium-sulfur batteries are comprehensively reviewed and discussed, together with the challenges being faced and perspectives for them.

From Hollow to Solid Carbon Spheres: Time-Dependent Facile Synthesis

Here, we report a facile route for obtaining carbon spheres with fully tunable shell thickness. Using a hard template in chemical vapor deposition (CVD), hollow carbon spheres, solid carbon spheres, and intermediate structures can be obtained with optimized process time. The resulting carbon spheres with particle diameters of ~400 nm, as well as a controllable shell thickness from 0 to 70 nm, had high Brunauer–Emmett–Teller (BET) specific surface area (up to 344.8 m²·g⁻¹) and pore volume (up to 0.248 cm³·g⁻¹). The sphere formation mechanism is also proposed. This simple and reproducible technique can deliver carbon materials for various applications, e.g., energy storage and conversion, adsorption, catalytic, biomedical, and environmental applications.

Dual active nitrogen doped hierarchical porous hollow carbon nanospheres as an oxygen reduction electrocatalyst for zinc-air batteries

Developing non-platinum catalysts for the oxygen reduction reaction (ORR) has become urgent for electrochemical energy devices. Herein, we synthesize N-doped hollow carbon nanospheres (N-HCNs) which only contain active pyridinic-N and graphitic-N by using polystyrene spheres and aniline as the corresponding template and precursor. The electrochemical measurements show that N-HCNs possess superior ORR electrocatalytic activity (half-wave potential is 15 mV higher than that of the precious Pt/C electrocatalyst), durability and anti-toxicity to Pt/C in alkaline media. Simultaneously, N-HCNs also reveal comparable ORR activity and superior stability to Pt/C in acidic media. Such high ORR performance can be ascribed to their hierarchical porous structure, ultra-high specific surface area, plenty of edge defects and high contents of active N atoms. It is noteworthy that when used as the catalyst for the air electrode of zinc-air batteries, N-HCNs present a higher power density and a larger operating voltage than Pt/C at the same discharge current density.

Recent progress in hollow sphere-based electrodes for high-performance supercapacitors

Hollow spheres have drawn much attention in the area of energy storage and conversion, especially in high-performance supercapacitors owing to their well-defined morphologies, uniform size, low density and large surface area. And quite some significant breakthroughs have been made in advanced supercapacitor electrode materials with hollow sphere structures. In this review, we summarize and discuss the synthesis and application of hollow spheres with controllable structure and morphology as electrode materials for supercapacitors. First, we briefly introduce the fabrication strategies of hollow spheres for electrode materials. Then, we discuss in detail the recent advances in various hollow sphere-based electrode materials for supercapacitors, including single-shelled, yolk-shelled, urchin-like, double-shelled, multi-shelled, and mesoporous hollow structure-based symmetric and asymmetric supercapacitor devices. We conclude this review with some perspectives on the future research and development of the hollow sphere-based electrode materials.

Generation of open-ended, worm-like and graphene-like structures from layered spherical carbon materials

The generation of open ended worm-like, graphene-like carbon nanostructures from polydispersed Au@SiO₂ spheres and SiO₂ spheres.

Study on size effect of the silica nanospheres with solid core and mesoporous shell on cellular uptake

The properties of mesoporous silica nanoparticles including large surface area, large pore volume, easy surface functionalization and control of structure and pore size has made them promising drug carriers. In this study, the effect of different diameters (50 nm, 70 nm, 90 nm, 110 nm and 140 nm) of silica nanospheres with a solid core and mesoporous shell (mSiO2/SiO2) on cellular internalization in mouse fibroblast cells (L929) was evaluated. The physical properties of the nanostructures were characterized with various methods, such as transmission electron microscopy with x-ray dispersion spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy and zeta potential. In order to define the cellular uptake, the nanostructures were labelled with fluorescent dye Alexa647, and imaging and quantitative methods were applied: laser scanning confocal microscopy, flow cytometry and thermogravimetry. Our results indicate that cellular uptake of the studied nanospheres is size-dependent, and nanospheres of 90 nm in diameter showed the most efficient cell internalization. Thus, particle size is an important parameter that determines cellular uptake of nanoparticles and should be considered in designing drug delivery carriers.

Reduced graphene oxide paper based nanocomposite materials for flexible supercapacitors

A flexible supercapacitor is developed by combining reduced graphene oxide (rGO), cellulose and RTIL. The device exhibited good electrochemical performance with an energy density of 6.28 W h kg⁻¹ at a power density of 1.32 kW kg⁻¹ in a 6 M KOH electrolyte.

Mesoporous carbons: recent advances in synthesis and typical applications

Mesoporous carbon materials have been extensively studied because of their vast potential applications ranging from separation and adsorption, catalysis, and electrochemistry to energy storage.

Ordered multimodal porous carbon with hierarchical nanostructure as high performance electrode material for supercapacitors

Unique hierarchical nanostructure of OMPC facilitates fast mass transport along with large surface area for electrical charge storage.