Dazhang Zhu

Development of MnO2/porous carbon microspheres with a partially graphitic structure for high performance supercapacitor electrodes

We report the development of MnO2/porous carbon microspheres with a partially graphitic structure for high performance supercapacitor electrode materials. Micro- and mesoporous carbon microspheres were fabricated based on a hydrothermal emulsion polymerization and common activation process. Manganese nitrate was introduced into the pores of the carbon microspheres, followed by thermal treatment to transform it into amorphous MnO2. As-prepared MnO2/porous carbon microspheres with high specific surface area (up to 1135 m2 g−1) and regular geometry (0.5–1.0 μm in diameter) benefit fast ion-transport and rapid charge–discharge, and contribute double layer capacitance to the hybrid electrode. Besides, manganese dioxide shows high pseudocapacitive behaviour due to faradaic redox reaction. Furthermore, the introduction of MnO2 greatly promotes the graphitization degree of the carbon matrix. A typical MnO2/carbon sample shows a partially graphitic structure with a very low intensity ratio of Raman D to G band (ID/IG = 0.27), which substantially increases the electronic conductivity and reduces the internal resistance (decreased from 0.42 to 0.20 Ω). As a result, the MnO2/porous carbon microspheres as supercapacitor electrodes exhibit excellent electrochemical performance (459 F g−1 at 1.0 A g−1 and 354 F g−1 at 20.0 A g−1 in 6 M KOH electrolyte). The well-developed MnO2/carbon hybrid materials with a high charge–discharge rate capability coupled with a high electrochemical capacitance highlight the great potential for widespread supercapacitor applications.

A facile synthesis of a novel mesoporous Ge@C sphere anode with stable and high capacity for lithium ion batteries

Tremendous volume expansion of germanium during cycling causes much difficulty to its use in high performance anodes for lithium ion batteries (LIBs). In this paper, we report a facile synthesis of novel mesoporous Ge@C spheres as stable and high capacity LIB anodes. A Ge–catechol complex obtained via a simple chelation reaction was introduced into resorcinol–formaldehyde polymer spheres prepared by the extended Stober method. After carbonization and carbothermic reduction at 800 °C in an Ar atmosphere, carbon spheres loaded with Ge nanoparticles (∼8 nm) were fabricated. The Ge@C spheres have a uniform diameter of ∼500 nm, a mesopore size of ∼14 nm and a specific surface area of 348 m2 g−1. Mesoporosity between Ge particles and the carbon matrix creates a buffer layer that effectively stabilizes the encapsulated Ge particles for huge volume change and mitigates the aggregation of active particles during the lithiation/delithiation process. The mesoporous Ge@C sphere anode shows initial discharge and charge specific capacities of 1653 and 1440 mA h g−1 at 0.1 C. Even at a high rate of 10 C, the Ge@C electrode still has a reasonable discharge–charge specific capacity of 753/708 mA h g−1, exhibiting excellent high-rate discharge–charge performance. The Ge@C anode maintains a high discharge capacity of 1099 mA h g−1 at 0.1 C with a coulombic efficiency of 99% after 100 cycles. The simple method for the design of mesoporous Ge@C spheres with a high capacity coupled with an excellent cycling stability opens up a new opportunity of Ge-based anode materials for widespread applications in LIBs.

Core–shell ultramicroporous@microporous carbon nanospheres as advanced supercapacitor electrodes

In this paper, we report a novel design and synthesis of core–shell ultramicroporous@microporous carbon nanospheres (UMCNs) for advanced supercapacitor electrodes. Polymer colloids (10–14 nm) are obtained by time-controlled polymerization of phloroglucinol and terephthalaldehyde (P/T). UMCNs with ultramicropores in the inner core and abundant micropores in the outer shell are fabricated by the copolymerization of resorcinol and formaldehyde (R/F) on the surfaces of P/T colloids with the presence of ammonia, followed by carbonization and further KOH activation. The as-prepared UMCNs have an adjustable diameter (52–74 nm) and a high specific surface area (up to 2156 m2 g−1). Inter-particle mesoporosity among UMCNs creates ion buffer reservoirs and reduces the ion diffusion distance, while micropores offer highly efficient ion channels and also show high capability for charge accumulation. Moreover, regular ultramicropores benefit the fast transportation and diffusion of electrolyte ions. Consequently, UMCNs with a unique 3D core–shell nanostructure exhibit superb electrochemical performance such as very high specific capacitance (411 F g−1 at 1 A g−1), ultra-high rate capability (charge–discharge operation under an extremely high current density of 100 A g−1), excellent long-term cycle stability (10 000 cycles) and reasonable energy density at high power density (5.94 W h kg−1 at 50 kW kg−1) in a 6 M KOH electrolyte. This finding opens up a new window for well-developed carbon nanoarchitectures to support advanced supercapacitor devices for high rate electrochemical energy storage.

Mesoporous size controllable carbon microspheres and their electrochemical performances for supercapacitor electrodes

In this paper, size controllable SiO2 nanoparticles synthesized by adjusting the hydrolysis–condensation time and the concentration of tetraethyl orthosilicate (TEOS) in ethanol–water solution in the presence of ammonia as a catalyst were encapsulated within resorcinol–formaldehyde polymer microspheres which were fabricated in the same ethanol–water–ammonia system. After carbonization and following etching with NaOH solution, a series of mesoporous carbon microspheres (MCMs) with an average diameter of 500 nm, a mesopore size of 3.2–14 nm and surface areas of 659–872 m2 g−1 are obtained. As electrode materials for supercapacitors, typical samples of MCMs with a mesopore size of 3.2 nm and 13.5 nm show an initial specific capacitance of 289 and 268 F g−1 under a current density of 1.0 A g−1. After 10 000 charge–discharge cycles, the specific capacity remains 261 and 254 F g−1 with the retention of 90.3% and 94.7%. Besides, electrochemical performances influenced by the mesopore size were investigated.

Novel mesoporous Si@C microspheres as anodes for lithium-ion batteries

In this paper, we demonstrate the design and synthesis of novel mesoporous Si@C microspheres as anode materials for high-performance lithium-ion batteries. SiO2 nanoparticles modified with hexadecyl trimethyl ammonium bromide are enveloped within resorcinol-formaldehyde polymer microspheres which form in the ethanol-water-ammonia system. Mesoporous voids between Si nanoparticles and the carbon framework are generated after carbonization at 800 °C and magnesiothermic reduction at 650 °C. The resultant Si@C microspheres show regular spherical shapes with a mean diameter of about 500 nm, a mesopore size of 3.2 nm and specific surface areas of 401-424 m(2) g(-1). Mesoporosity of Si@C microspheres effectively buffers the volume expansion/shrinkage of Si nanoparticles during Li ion insertion/extraction, which endows mesoporous Si@C microspheres with excellent electrochemical performance and cycle stability when they are used as lithium-ion battery anode materials. A typical sample of mesoporous Si@C microspheres presents a specific capacity of 1637 and 1375 mA h g(-1) at first discharge and charge under a current density of 50 mA g(-1). After 100 cycles, the charge capacity remains 1053 mA h g(-1) with a coulombic efficiency of 99%, showing good cycle stability of the anode. This finding highlights the potential application of mesoporous Si@C microspheres in lithium-ion battery anode materials.

A seeded synthetic strategy for uniform polymer and carbon nanospheres with tunable sizes for high performance electrochemical energy storage

We established a novel and facile strategy to synthesize uniform polymer and carbon nanospheres, the diameters of which can be precisely programmed between 35-105 and 30-90 nm, respectively, via time-controlled formation of colloidal seeds. The carbon nanospheres show promising prospects in high rate performance electrochemical energy storage.

Supramolecular core-shell nanosilica@liposome nanocapsules for drug delivery.

The fabrication of core-shell structural nanosilica@liposome nanocapsules as a drug delivery vehicle is reported. SiO(2) nanoparticles are encapsulated within liposomes by a W/O/W emulsion approach to form supramolecular assemblies with a core of colloidal particles enveloped by a lipid bilayer shell. A nanosilica core provides charge compensation and architectural support for the lipid bilayer, which significantly improves their physical stability. A preliminary application of these core-shell nanocapsules for hemoglobin (Hb) delivery is described. Through the H-bonding interaction between the hydroxyl groups on nanosilicas and the amino nitrogens of Hb, Hb-SiO(2) nanocomplexes in which the saturated adsorption amount of Hb on SiO(2) is 0.47 g g(-1) are coated with lipids to generate core-shell Hb-SiO(2)@liposome nanocapsules with mean diameters of 60-500 nm and Hb encapsulation efficiency of 48.4-87.9%. Hb-SiO(2)@liposome supramolecular nanovehicles create a mode of delivery that stabilizes the encapsulated Hb and achieves long-lasting release, thereby improving the efficacy of the drug. Compared with liposome-encapsulated Hb and Hb-loaded SiO(2) particles, such core-shell nanovehicles show substantially enhanced release performance of Hb in vitro. This finding opens up a new window of liposome-based formulations as drug delivery nanovehicles for widespread pharmaceutical applications.

A novel liposome-encapsulated hemoglobin/silica nanoparticle as an oxygen carrier

A novel liposome-encapsulated hemoglobin/silica nanoparticle (LEHSN) was fabricated by a water-in-oil-in-water (W/O/W) double emulsion approach. Bovine hemoglobin (Hb) was first adsorbed onto the surfaces of silica nanoparticles (SNs), and then the complex of Hb/SNs was encapsulated by liposome to form LEHSN which has a core-shell supramolecular structure. On the one hand, liposomes built a cell membrane-like environment for the controlled release of Hb. On the other hand, SNs which act as rigid core provide a supported framework for lecithin membrane, and enhance the stability of liposomes. In comparison with liposome-encapsulated Hb (LEH), LEHSN shows substantially enhanced stability and improved release property of Hb in vitro. This study highlights the potential of the novel LEHSN as an oxygen carrier for pharmaceutical applications.

Nanocarbon‐Based Materials for Flexible All‐Solid‐State Supercapacitors

Because of the rapid development of flexible electronics, it is important to develop high-performance flexible energy-storage devices, such as supercapacitors and metal-ion batteries. Compared with metal-ion batteries, supercapacitors exhibit higher power density, longer cycling life, and excellent safety, and they can be easily fabricated into all-solid-state devices by using polymer gel electrolytes. All-solid-state supercapacitors (ASSSCs) have the advantages of being lightweight and flexible, thus showing great potential to be used as power sources for flexible portable electronics. Because of their high specific surface area and excellent electrical and mechanical properties, nanocarbon materials (such as carbon nanotubes, graphene, carbon nanofibers, and so on) have been widely used as efficient electrode materials for flexible ASSSCs, and great achievements have been obtained. Here, the recent advances in flexible ASSSCs are summarized, from design strategies to fabrication techniques for nanocarbon electrodes and devices. Current challenges and future perspectives are also discussed.

A general strategy to synthesize high-level N-doped porous carbons via Schiff-base chemistry for supercapacitors

Recently, the synthesis of porous carbon-based materials, especially those with unique geometry, narrow pore size distribution, large surface area and high nitrogen content, has been highly attractive for widespread applications, but remains a great challenge. Herein, we demonstrate a novel strategy for highly efficient synthesis of high-level N-doped microporous carbon spheres (N-MCSs) based on a very simple Schiff-base reaction of 3,3′-diaminobenzidine and p-phthalaldehyde in ethanol solvent without any catalyst or tedious procedure, followed by a common one-step carbonization–activation process. The N-MCSs exhibit a spherical morphology, regular micropores, high surface areas and high nitrogen contents (up to 8.71 at%). N-MCSs used as supercapacitor electrodes deliver high gravimetric capacitance, good rate capability and cycling stability. More importantly, the synthetic approach can be extended to other Schiff-base systems such as p-phthalaldehyde and p-phenylenediamine or ethylenediamine to fabricate porous carbon-based materials with high nitrogen species, tunable morphology and pore structure. The general strategy presented in this study opens up a new window for heteroatom doping, geometry and structure control, and highlights the great potential of well-developed carbon-based materials for extensive applications.