Weishan Li

Synthesis of Size-Tunable Anatase TiO2 Nanospindles and Their Assembly into Anatase@Titanium Oxynitride/Titanium Nitride−Graphene Nanocomposites for Rechargeable Lithium Ion Batteries with High Cycling Performance

This paper embarks upon three levels of undertaking ranging from nanomaterials synthesis to assembly and functionalization. First, we have prepared size-tunable anatase TiO(2) nanospindles via a hydrothermal process by using tubular titanates as self-sacrificing precursors. Second, we have densely dispersed the TiO(2) nanospindles onto functional graphene oxides (GO) via a spontaneous self-assembly process. After annealing of the TiO(2)/GO hybrid nanocomposite in an NH(3) gas flow, the TiO(2) surface was effectively nitridated and the GO was reduced to graphene sheets (GS) in order to further fortify the electronic functionality of the nanocomposite. Third, the anatase@oxynitride/titanium nitride-GS (TiO(2)@TiO(x)N(y)/TiN-GS) hybrid nanocomposite was studied as an anode material for lithium-ion batteries (LIBs), showing excellent rate capability and cycling performance compared to the pure TiO(2) nanospindles. Our systematic studies have revealed that the TiO(2)@TiO(x)N(y)/TiN-GS nanocomposites with graphene nanosheets covered with the TiO(2)@TiO(x)N(y)/TiN nanospindles on both sides provide a promising solution to the problems of poor electron transport and severe aggregation of TiO(2) nanoparticles by enhancing both electron transport through the conductive matrix and Li-ion accessibility to the active material from the liquid electrolyte. More generally, the size-tunable TiO(2) nanospindles with their unique (101) outer surface planes provide an archetype for the in depth investigation of their surface-specific and size-dependent physicochemical properties.

A novel nanostructured spinel ZnCo2O4 electrode material: morphology conserved transformation from a hexagonal shaped nanodisk precursor and application in lithium ion batteries

In this paper, we report a successful synthesis of porous ZnCo2O4 nanoflakes by a morphology-conserved and pyrolysis-induced transformation of novel hexagonally shaped, highly ordered, and inorganic–organic–inorganic layered hybrid nanodisks. It is shown that the hexagonal hybrid nanodisks are constructed from organic molecule (ethylene glycol)-directed assembly of inorganic bilayers. The assembly mechanism has been established by a number of structural and spectroscopic techniques. The porous ZnCo2O4 nanoflakes have also been tested as a lithium ion battery electrode, showing high capacity and high cyclability.

Density functional theory study of the role of anions on the oxidative decomposition reaction of propylene carbonate.

The oxidative decomposition mechanism of the lithium battery electrolyte solvent propylene carbonate (PC) with and without PF(6)(-) and ClO(4)(-) anions has been investigated using the density functional theory at the B3LYP/6-311++G(d) level. Calculations were performed in the gas phase (dielectric constant ε = 1) and employing the polarized continuum model with a dielectric constant ε = 20.5 to implicitly account for solvent effects. It has been found that the presence of PF(6)(-) and ClO(4)(-) anions significantly reduces PC oxidation stability, stabilizes the PC-anion oxidation decomposition products, and changes the order of the oxidation decomposition paths. The primary oxidative decomposition products of PC-PF(6)(-) and PC-ClO(4)(-) were CO(2) and acetone radical. Formation of HF and PF(5) was observed upon the initial step of PC-PF(6)(-) oxidation while HClO(4) formed during initial oxidation of PC-ClO(4)(-). The products from the less likely reaction paths included propanal, a polymer with fluorine and fluoro-alkanols for PC-PF(6)(-) decomposition, while acetic acid, carboxylic acid anhydrides, and Cl(-) were found among the decomposition products of PC-ClO(4)(-). The decomposition pathways with the lowest barrier for the oxidized PC-PF(6)(-) and PC-ClO(4)(-) complexes did not result in the incorporation of the fluorine from PF(6)(-) or ClO(4)(-) into the most probable reaction products despite anions and HF being involved in the decomposition mechanism; however, the pathway with the second lowest barrier for the PC-PF(6)(-) oxidative ring-opening resulted in a formation of fluoro-organic compounds, suggesting that these toxic compounds could form at elevated temperatures under oxidizing conditions.

Polyaniline/mesoporous tungsten trioxide composite as anode electrocatalyst for high-performance microbial fuel cells

A composite, polyaniline (PANI)/mesoporous tungsten trioxide (m-WO(3)), was developed as a platinum-free and biocompatible anodic electrocatalyst of microbial fuel cells (MFCs). The m-WO(3) was synthesized by a replicating route and PANI was loaded on the m-WO(3) through the chemical oxidation of aniline. The composite was characterized by using X-ray diffraction, Fourier transform infrared spectrum, field emission scanning electron microscopy, and transmission electron microscopy. The activity of the composite as the anode electrocatalyst of MFC based on Escherichia coli (E. coli) was investigated with cyclic voltammetry, chronoamperometry, and cell discharge test. It is found that the composite exhibits a unique electrocatalytic activity. The maximum power density is 0.98 W m(-2) for MFC using the composite electrocatalyst, while only 0.76 W m(-2) and 0.48 W m(-2) for the MFC using individual m-WO(3) and PANI electrocatalyst, respectively. The improved electrocatalytic activity of the composite can be ascribed to the combination of m-WO(3) and PANI. The m-WO(3) has good biocompatibility and PANI has good electrical conductivity. Most importantly, the combination of m-WO(3) and PANI improves the electrochemical activity of PANI for proton insertion and de-insertion.

Nano-molybdenum carbide/carbon nanotubes composite as bifunctional anode catalyst for high-performance Escherichia coli-based microbial fuel cell.

A novel electrode, carbon felt-supported nano-molybdenum carbide (Mo2C)/carbon nanotubes (CNTs) composite, was developed as platinum-free anode of high performance microbial fuel cell (MFC). The Mo2C/CNTs composite was synthesized by using the microwave-assisted method with Mo(CO)6 as a single source precursor and characterized by using X-ray diffraction and transmission electron microscopy. The activity of the composite as anode electrocatalyst of MFC based on Escherichia coli (E. coli) was investigated with cyclic voltammetry, chronoamperometry, and cell discharge test. It is found that the carbon felt electrode with 16.7 wt% Mo Mo2C/CNTs composite exhibits a comparable electrocatalytic activity to that with 20 wt% platinum as anode electrocatalyst. The superior performance of the developed platinum-free electrode can be ascribed to the bifunctional electrocatalysis of Mo2C/CNTs for the conversion of organic substrates into electricity through bacteria. The composite facilitates the formation of biofilm, which is necessary for the electron transfer via c-type cytochrome and nanowires. On the other hand, the composite exhibits the electrocatalytic activity towards the oxidation of hydrogen, which is the common metabolite of E. coli.

Layered Lithium-Rich Oxide Nanoparticles Doped with Spinel Phase: Acidic Sucrose-Assistant Synthesis and Excellent Performance as Cathode of Lithium Ion Battery.

Nanolayered lithium-rich oxide doped with spinel phase is synthesized by acidic sucrose-assistant sol-gel combustion and evaluated as the cathode of a high-energy-density lithium ion battery. Physical characterizations indicate that the as-synthesized oxide (LR-SN) is composed of uniform and separated nanoparticles of about 200 nm, which are doped with about 7% spinel phase, compared to the large aggregated ones of the product (LR) synthesized under the same condition but without any assistance. Charge/discharge demonstrates that LR-SN exhibits excellent rate capability and cyclic stability: delivering an average discharge capacity of 246 mAh g(-1) at 0.2 C (1C = 250 mA g(-1)) and earning a capacity retention of 92% after 100 cycles at 4 C in the lithium anode-based half cell, compared to the 227 mA g(-1) and the 63% of LR, respectively. Even in the graphite anode-based full cell, LR-SN still delivers a capacity of as high as 253 mAh g(-1) at 0.1 C, corresponding to a specific energy density of 801 Wh kg(-1), which are the best among those that have been reported in the literature. The separated nanoparticles of the LR-SN provide large sites for charge transfer, while the spinel phase doped in the nanoparticles facilitates lithium ion diffusion and maintains the stability of the layered structure during cycling.

Nanoconic TiO2 hollow spheres: novel buffers architectured for high-capacity anode materials

An attempt has been carried out here to use nanoconic TiO2 hollow spheres as buffers to accommodate the volume expansion of high-capacity materials. Based on the TiO2 hollow spheres, we tailor-designed a novel composite, in which the high Li+-transport dynamics of titanate hollow spheres (TiO2) and the high capacity of tin oxide (SnO2) were intimately integrated into a hierarchical architecture of nanocones, while the unique spatial arrangement of the SnO2 component in the nano-cavities effectively accommodates the volume change during lithiation/de-lithiation, hence rendering the composite stable cycling life. Electrochemical tests revealed favorable performances of the composite SnO2–TiO2 nanocones in terms of enhanced lithium storage capacity, stable cycle life and improved rate performance compared with each material components.

Synthesis, crystal structures and properties of Ln(III)–Cu(I)–Na(I) and Ln(III)–Ag(I) heterometallic coordination polymers

Nine 3D heterometallic coordination polymers, namely [NaLn2Cu6I5(IN)6(ox)(H2O)4]·H2O [Ln = La (1), Eu (2), Gd (3), Tb (4), HIN = isonicotinic acid, ox = oxalate], [Ln2Ag4(IN)5(ox)2(NO3)(H2O)2]·3H2O [Ln = Dy (5), (6) Ho], [LnAg(IN)2(ox)]·H2O [Ln = La (7), Pr (8), Tm (9)] have been successfully synthesized under hydrothermal conditions. Compounds 1–4 exhibit same unusual 3D pillared-layer heterometallic coordination frameworks that are built up by the Ln-ox-Na layers, 2D inorganic [(Cu6I5)+]n layers and IN ligands. Compounds 5 and 6 represent 3D coordination frameworks that are constructed from rare Ln(III)-ox-IN chains and Ag(I)-IN-ox layers. 3D coordination networks of compounds 7–9 are built up from 2D Ln(III)-IN-ox layers and Ag(I)-IN-ox subunits. Furthermore, the magnetic properties of compounds 5 and 6 and the luminescence properties of compounds 2, 4 and 5 have been investigated.

Morphology‐Conserved Transformations of Metal‐Based Precursors to Hierarchically Porous Micro‐/Nanostructures for Electrochemical Energy Conversion and Storage

To meet future market demand, developing new structured materials for electrochemical energy conversion and storage systems is essential. Hierarchically porous micro-/nanostructures are favorable for designing such high-performance materials because of their unique features, including: i) the prevention of nanosized particle agglomeration and minimization of interfacial contact resistance, ii) more active sites and shorter ionic diffusion lengths because of their size compared with their large-size counterparts, iii) convenient electrolyte ingress and accommodation of large volume changes, and iv) enhanced light-scattering capability. Here, hierarchically porous micro-/nanostructures produced by morphology-conserved transformations of metal-based precursors are summarized, and their applications as electrodes and/or catalysts in rechargeable batteries, supercapacitors, and solar cells are discussed. Finally, research and development challenges relating to hierarchically porous micro-/nanostructures that must be overcome to increase their utilization in renewable energy applications are outlined.

Photochemistry-Based Method for the Fabrication of SnO2 Monolayer Ordered Porous Films with Size-Tunable Surface Pores for Direct Application in Resistive-Type Gas Sensor

A new photochemistry-based method was introduced for fabricating SnO2 monolayer ordered porous films with size-tunable surface pores on ceramic tubes used for gas sensors. The growth of the spherical pore walls was controlled by two times irradiation of the ultraviolet light using polystyrene microsphere two-dimensional colloidal crystal as a template. The surface pore size of the final obtained porous films was well tuned by changing the second irradiation time rather than replacing the template microspheres. The monolayer ordered porous films on the tubes were directly used, for the first time, as gas sensors. The sensitivity of the sensor depended on the surface pore size and was carefully analyzed by ethanol gas detection. The sensor also exhibited short response-recovery time and long-term stability at lower than 300 °C in practical applications. Therefore, this study opens up a kind of construction method for gas sensors, provides a new strategy for controlling the surface pore size of the monolayer ordered porous film, and introduces a new type of sensitivity-controllable gas sensor.