Xiang Peng

Mesoporous TiO2 Nanocrystals/Graphene as an Efficient Sulfur Host Material for High-Performance Lithium–Sulfur Batteries

Rechargeable lithium-sulfur (Li-S) batteries are promising in high-energy storage due to the large specific energy density of about 2600 W h kg(-1). However, the low conductivity of sulfur and discharge products as well as polysulfide-shuttle effect between the cathode and anode hamper applications of Li-S batteries. Herein, we describe a novel and efficient S host material consisting of mesoporous TiO2 nanocrystals (NCs) fabricated in situ on reduced graphene oxide (rGO) for Li-S batteries. The TiO2@rGO hybrid can be loaded with 72 wt % sulfur. The strong chemisorption ability of the TiO2 NCs toward polysulfide combined with high electrical conductivity of rGO effectively localize the soluble polysulfide species within the cathode and facilitate electron and Li ions transport to/from the cathode materials. The sulfur-incorporated TiO2@rGO hybrid (S/TiO2@rGO) shows large capacities of 1116 and 917 mA h g(-1) at the current densities of 0.2 and 1 C (1 C = 1675 mA g(-1)) after 100 cycles, respectively. When the current density is increased 20 times from 0.2 to 4 C, 60% capacity is retained, thereby demonstrating good cycling stability and rate capability. The synergistic effects of TiO2 NCs toward effective chemisorption of polysulfides and conductive rGO with high electron mobility make a promising application of S/TiO2@rGO hybrid in high-performance Li-S batteries.

Multilayered paper-like electrodes composed of alternating stacked mesoporous Mo2N nanobelts and reduced graphene oxide for flexible all-solid-state supercapacitors

Flexible all-solid-state supercapacitors (SCs) have great potential in flexible and wearable electronics due to their safety, flexibility, high power density, and portability. The energy storage properties of SCs are determined mainly by their composition and conductivity as well as the configuration of the integrated electrode material. Herein, a freestanding multilayered film electrode consisting of alternating stacked mesoporous Mo2N nanobelts and rGO nanosheets (MMNNBs/rGO) is described. The electrode has a high mass loading of 95.6 wt% of the Mo2N active material and boasts high areal capacitances of 142 and 98 mF cm−2 at current densities of 1 and 150 mA cm−2, respectively. All-solid-state SCs fabricated by sandwiching two thin and flexible freestanding MMNNBs/rGO hybrid electrodes with a poly (vinyl alcohol) (PVA)/H3PO4/silicotungstic acid (SiWA) gel electrolyte show a high volumetric capacitance of 15.4 F cm−3 as well as energy and power densities of 1.05 mW h cm−3 and 0.035 W cm−3 at a current density of 0.1 A cm−3 based on the volume of the entire cell. After 4000 charging–discharging cycles, the flexible SC retains 85.7% initial capacitance, thus exhibiting good cycling stability. This study provides a versatile method for the fabrication of flexible and high-performance ceramic-based nanohybrid films for SCs, and has immense potential in flexible and wearable electronics.

Antibacterial effects of titanium embedded with silver nanoparticles based on electron-transfer-induced reactive oxygen species

Although titanium embedded with silver nanoparticles (Ag-NPs@Ti) are suitable for biomedical implants because of the good cytocompatibility and antibacterial characteristics, the exact antibacterial mechanism is not well understood. In the present work, the antibacterial mechanisms of Ag-NPs@Ti prepared by plasma immersion ion implantation (PIII) are explored in details. The antibacterial effects of the Ag-NPs depend on the conductivity of the substrate revealing the importance of electron transfer in the antibacterial process. In addition, electron transfer between the Ag-NPs and titanium substrate produces bursts of reactive oxygen species (ROS) in both the bacteria cells and culture medium. ROS leads to bacteria death by inducing intracellular oxidation, membrane potential variation, and cellular contents release and the antibacterial ability of Ag-NPs@Ti is inhibited appreciably after adding ROS scavengers. Even though ROS signals are detected from osteoblasts cultured on Ag-NPs@Ti, the cell compatibility is not impaired. This electron-transfer-based antibacterial process which produces ROS provides insights into the design of biomaterials with both antibacterial properties and cytocompatibility.

Mitigation of Corrosion on Magnesium Alloy by Predesigned Surface Corrosion.

Rapid corrosion of magnesium alloys is undesirable in structural and biomedical applications and a general way to control corrosion is to form a surface barrier layer isolating the bulk materials from the external environment. Herein, based on the insights gained from the anticorrosion behavior of corrosion products, a special way to mitigate aqueous corrosion is described. The concept is based on pre-corrosion by a hydrothermal treatment of Al-enriched Mg alloys in water. A uniform surface composed of an inner compact layer and top Mg-Al layered double hydroxide (LDH) microsheet is produced on a large area using a one-step process and excellent corrosion resistance is achieved in saline solutions. Moreover, inspired by the super-hydrophobic phenomenon in nature such as the lotus leaves effect, the orientation of the top microsheet layer is tailored by adjusting the hydrothermal temperature, time, and pH to produce a water-repellent surface after modification with fluorinated silane. As a result of the trapped air pockets in the microstructure, the super-hydrophobic surface with the Cassie state shows better corrosion resistance in the immersion tests. The results reveal an economical and environmentally friendly means to control and use the pre-corrosion products on magnesium alloys.

Crumpled N-doped carbon nanotubes encapsulated with peapod-like Ge nanoparticles for high-rate and long-life Li-ion battery anodes

Germanium (Ge) is a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical specific capacity of 1620 mA h g−1. However, the large volume change during Li alloying/dealloying causes cracking and pulverization of the Ge anodes leading to rapid fading of the capacity. Herein, we report a novel peapod-like Ge/N-doped carbon (Ge/CNx) as a high-performance anode material for LIBs, in which isolated Ge nanoparticles are incorporated into crumpled CNx nanotubes. The peapod-like Ge/CNx not only provides enough voids to accommodate the volume expansion of pea-like Ge NPs during the Li–Ge alloy reactions, but also offers a continuous conducting framework for electron transport and accessible nanoporous channels for fast diffusion and transport of Li+ ions. This 0D-in-1D peapod-like Ge/CNx nanomaterial possesses a stable discharge capacity of 1080 mA h g−1 over 1200 cycles at a 0.5C rate (1C = 1600 mA g−1) and 62.3% capacity retention when the current density is increased 16 times from 0.5 to 8C, enabling promising applications in high-performance LIBs.

Elucidating the Intercalation Pseudocapacitance Mechanism of MoS2–Carbon Monolayer Interoverlapped Superstructure: Toward High-Performance Sodium-Ion-Based Hybrid Supercapacitor

Two-dimensional (2D) layered materials have shown great promise for electrochemical energy storage applications. However, they are usually limited by the sluggish kinetics and poor cycling stability. Interface modification on 2D layered materials provides an effective way for increasing the active sites, improving the electronic conductivity, and enhancing the structure stability so that it can potentially solve the major issues on fabricating energy storage devices with high performance. Herein, we synthesize a novel MoS2-carbon (MoS2-C) monolayer interoverlapped superstructure via a facile interface-modification route. This interlayer overlapped structure is demonstrated to have a wide sodium-ion intercalation/deintercalation voltage range of 0.4-3.0 V and the typical pseudocapacitive characteristics in fast kinetics, high reversibility, and robust structural stability, thus displaying a large reversible capacity, a high rate capability, and an improved cyclability. A full cell of sodium-ion hybrid supercapacitor based on this MoS2-C hybrid architecture can operate up to 3.8 V and deliver a high energy density of 111.4 Wh kg-1 and a high power density exceeding 12 000 W kg-1. Furthermore, a long cycle life of 10 000 cycles with over 77.3% of capacitance retention can be achieved.

Large and porous carbon sheets derived from water hyacinth for high-performance supercapacitors

To elevate the properties of carbon based electrical double-layer capacitors (EDLCs), sheet-like carbon with high porosity is desirable due to enhanced electron transport efficiency and good electrolyte accessibility. In this paper, large porous carbon sheets are fabricated via an acid treatment, pyrolytic carbonization, and alkali activation of water hyacinth (WH) biomass. The WH-derived carbon sheets with a large uniform area have a large specific surface of 1308 m2 g−1 and desirable pore volume of 0.84 cm3 g−1, resulting from the template of the original thin cell walls and large intercellular space, which deliver a high specific capacitance of 273 F g−1 at a current density of 1 A g−1, excellent capacity retention of 75% when the current density is increased from 1 to 50 A g−1, and superior cyclic stability over 10 000 cycles in 6 M KOH. The specific capacitance of the assembled symmetric capacitor based on the large and porous carbon sheets reaches a remarkable 81.5 F g−1 and an energy density of 7.24 W h kg−1 can be achieved at a current density of 1 A g−1. These outstanding electrochemical properties suggest that the WH-derived porous carbon sheets have commercial potential in high-performance supercapacitors and the simple and economical process utilizing the WH waste biomass is environmentally friendly.

Robust Electrodes Based on Coaxial TiC/C–MnO2 Core/Shell Nanofiber Arrays with Excellent Cycling Stability for High-Performance Supercapacitors

A coaxial electrode structure composed of manganese oxide-decorated TiC/C core/shell nanofiber arrays is produced hydrothermally in a KMnO4 solution. The pristine TiC/C core/shell structure prepared on the Ti alloy substrate provides the self-sacrificing carbon shell and highly conductive TiC core, thus greatly simplifying the fabrication process without requiring an additional reduction source and conductive additive. The as-prepared electrode exhibits a high specific capacitance of 645 F g(-1) at a discharging current density of 1 A g(-1) attributable to the highly conductive TiC/C and amorphous MnO2 shell with fast ion diffusion. In the charging/discharging cycling test, the as-prepared electrode shows high stability and 99% capacity retention after 5000 cycles. Although the thermal treatment conducted on the as-prepared electrode decreases the initial capacitance, the electrode undergoes capacitance recovery through structural transformation from the crystalline cluster to layered birnessite type MnO2 nanosheets as a result of dissolution and further electrodeposition in the cycling. 96.5% of the initial capacitance is retained after 1000 cycles at high charging/discharging current density of 25 A g(-1). This study demonstrates a novel scaffold to construct MnO2 based SCs with high specific capacitance as well as excellent mechanical and cycling stability boding well for future design of high-performance MnO2-based SCs.

In situ fabrication of Ni nanoparticles on N-doped TiO2 nanowire arrays by nitridation of NiTiO3 for highly sensitive and enzyme-free glucose sensing

A novel and simple strategy for the in situ fabrication of the microstructure composed of nickel (Ni) nanoparticles on nitrogen-doped TiO2 nanowire arrays (Ni NPs/TiOxNy NWAs) by nitridation of NiTiO3 nanowire arrays is designed and described. During nitridation, Ni is separated from NiTiO3 and aggregates uniformly on the surface. The reshaped composite that is supported by the compact structure and interface of the formed NPs and remaining highly conductive TiOxNy NW forms a robust electrode in highly sensitive and selective non-enzymatic glucose sensing. The materials exhibit outstanding electrocatalytic activity for glucose oxidation boasting a sensitivity of 421 μA mM-1 cm-2, a low detection limit of 0.39 μM, as well as high selectivity against interfering species such as ascorbic acid (AA), uric acid (UA) and dopamine (DA).

General fabrication of mesoporous Nb2O5 nanobelts for lithium ion battery anodes

Mesoporous Nb2O5 nanobelts (NBs) have been synthesized by sequential thermal treatment of solid Nb2O5 NBs in NH3 and air, which exhibit better crystallinity and a larger specific area (29.76 m2 g−1) than that of solid Nb2O5 NBs (8.86 m2 g−1) and exhibit a high capacity and good rate capability.