Da Deng

Green energy storage materials: Nanostructured TiO2 and Sn-based anodes for lithium-ion batteries

It is expected that the market dominance of lithium-ion batteries will continue for at least another decade as there are currently no competing alternatives with the versatility of lithium-ion batteries for powering mobile and portable devices; and for buffering the fluctuating supply of intermittent energy sources such as wind and solar. While the pursuit of higher energy density and higher power density materials constitute the bulk of current interest, there is increasing interest in durable active battery materials that can be produced with minimum environmental impact. It is with these considerations that TiO2- and Sn-based anode materials are most interesting candidates for fulfilling future green energy storage materials. This review will focus on the recent developments of nanostructured TiO2 and Sn-based anode materials, including rutile, anatase, TiO2 (B), and coated TiO2, and pristine SnO2, and SnO2/C, Sn(M)/C composites.

Thermal formation of mesoporous single-crystal Co3O4 nano-needles and their lithium storage properties

In this work, we report the simple solid-state formation of mesoporous Co3O4 nano-needles with a 3D single-crystalline framework. The synthesis is based on controlled thermal oxidative decomposition and re-crystallization of precursor β-Co(OH)2 nano-needles. Importantly, after thermal treatment, the needle-like morphology can be completely preserved, despite the fact that there is a large volume contraction accompanying the process: β-Co(OH)2 → Co3O4. Because of the intrinsic crystal contraction, a highly mesoporous structure with high specific surface area has been simultaneously created. The textual properties can be easily tailored by varying the annealing temperature between 200–400 °C. Interestingly, thermal re-crystallization at higher temperatures leads to the formation of a perfect 3D single-crystalline framework. Thus derived mesoporous Co3O4 nano-needles serve as a good model system for the study of lithium storage properties. The optimized sample manifests very low initial irreversible loss (21%), ultrahigh capacity, and excellent cycling performance. For example, a reversible capacity of 1079 mA h g−1 can be maintained after 50 cycles. The superior electrochemical performance and ease of synthesis may suggest their practical use in lithium-ion batteries.

Reversible Storage of Lithium in a Rambutan‐Like Tin–Carbon Electrode

Fruity electrodes: A simple bottom-up self-assembly method was used to fabricate rambutan-like tin-carbon (Sn@C) nanoarchitecture (see scheme, green Sn) to improve the reversible storage of lithium in tin. The mechanism of the growth of the pear-like hairs is explored.

Hydrophobic Meshes for Oil Spill Recovery Devices

Widespread use of petrochemicals often leads to accidental releases in aquatic environments, occasionally with disastrous results. We have developed a hydrophobic and oleophilic mesh that separates oil from water continuously in situ via capillary action, providing a means of recovering spilt oil from surface waters. Steel mesh is dip-coated in a xylene solution of low-density polyethylene, creating a hydrophobic surface with tunable roughness and opening size. The hydrophobic mesh allows oil to pass through the openings while preventing the concomitant passage of water. A bench-top prototype demonstrated the efficacy of such an oil recovery device and allowed us to quantify the factors governing the ability of the mesh to separate oil and water. Preliminary data analysis suggested that the oleophilic openings behave somewhat like capillary tubes: the oil flux is inversely proportional to oil viscosity, and directly proportional to the size of the mesh openings. An unpinned meniscus model was found to predict the water intrusion pressure successfully, which increased as the opening size decreased. The trade-off between water intrusion and oil flow rate suggests an optimal pore size for given oil properties and sea conditions.

Synthesis and characterization of one-dimensional flat ZnO nanotower arrays as high-efficiency adsorbents for the photocatalytic remediation of water pollutants.

We report on facile fabrication of 1-D flat ZnO nanotower arrays on various substrates, including a metal, a semiconductor and an insulator. The nanotowers have a unique flat basal section near the substrate and taper in stages to wire-like at the tip. Electron microscopy and X-ray photoelectron spectroscopy are used to characterize these new nanostructures, revealing that their morphologies are significantly influenced by reaction temperature. A qualitative formation mechanism is proposed based on the experimental observations. A proof-of-concept demonstration shows that the ZnO nanotower arrays are highly effective at adsorbing and subsequently photo-remediating a model pollutant (Eosin B) from water. These observations could promote new applications of photocatalytic adsorbents for wastewater treatment utilizing oxide semiconductor nanostructures.

Linker-free 3D assembly of nanocrystals with tunable unit size for reversible lithium ion storage

A simple and scalable procedure combining hydrothermal synthesis with post-synthesis calcination was developed to produce a linker-free, thermally stable, mesoscale 3D ordered assembly of spinel-type ZnCo(2)O(4) nanocrystals. The mesoscale assembly with distinctively sharp edges was formed by close-packing the ZnCo(2)O(4) nanocrystal building blocks with a unit size changeable by the synthesis temperature. A self-templating mechanism based on the topotactic transformation of an oxalato-bridged precursor coordination compound was proposed for the assembly. The packaging of crystalline ZnCo(2)O(4) nanoparticles, an active lithium ion storage compound, into a dense organized structure is an effective way to increase the volumetric capacity of ZnCo(2)O(4) nanoparticles for reversible lithium ion storage. The highly ordered 3D assembly of ZnCo(2)O(4) demonstrated excellent reversible lithium ion storage properties and a specific capacity (∼800 mAh g(-1)) much higher than that of carbon (typically ∼ 350 mAh g(-1)).

Direct fabrication of double-rough chestnut-like multifunctional Sn@C composites on copper foil: lotus effect and lithium ion storage properties

This paper reports the fabrication of a new, double-rough chestnut-like Sn@C composite in the form of mesospheres with nanohairs directly on a copper surface by a simple and scalable procedure. The hierarchical order in the nanostructure and the composition of the nanocomposite impart at least two functional properties: the lotus effect and reversible storage of lithium ions. The nanohairs of carbon nanotube-encapsulated metallic tin; and the underlying core of carbon-tin mesospheres with rough exterior; give rise to nanoscale and mesoscale roughness not unlike the double-rough surface of a lotus leave (nanohairs on microbumps). Subsequently the modified copper surface is superhydrophobic just like the lotus leaves. On the other hand the ability to directly deposit lithium-active storage compounds (Sn, C) on a current conductor (Cu) has also resulted in an electrode immediately usable as a lithium ion battery anode without additional processing. Indeed electrochemical measurements have shown quite satisfying properties for lithium ion battery applications.

Hollow Cocoon-Like Hematite Mesoparticles of Nanoparticle Aggregates: Structural Evolution and Superior Performances in Lithium Ion Batteries

We report the facile, fast, and template-free preparation of hollow α-Fe2O3 with unique cocoon-like structure by a one-pot hydrothermal method without any surfactants in a short reaction time of 3 h only. In contrast, typical hydrothermal methods to prepare inorganic hollow structures require 24 h or a few days. Templates and/or surfactants are typically used. The hollow α-Fe2O3 nanococoon was thoroughly characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Ex situ analysis of a series of samples prepared at different reaction times clearly revealed the structural evolution and possible formation mechanism. Superior electrochemical performance in terms of cyclability, specific capacity, and high rate was achieved, which could be attributed to its unique hollow cocoon-like structure. Structural stability was revealed by analyzing the samples after 120 charge-discharge cycles. The unusual structural stability of the hollow α-Fe2O3 nanococoons after 120 cycles, which is rarely observed for transition metal oxides of particle aggregates, will guarantee further research investigation. Experimental evidence further demonstrated that hollow nanococoons exceed solid nanococoons in reversible lithium-ion storage.

Wet-Chemical Synthesis of Phase-Pure FeOF Nanorods as High-Capacity Cathodes for Sodium-Ion Batteries†

It is challenging to prepare phase-pure FeOF by wet-chemical methods. Furthermore, nanostructured FeOF has never been reported. In this study, hierarchical FeOF nanorods were synthesized through a facile, one-step, wet-chemical method by the use of just FeF3⋅3H2O and an alcohol. It was possible to significantly control the FeOF nanostructure by the selection of alcohols with an appropriate molecular structure. A mechanism for the formation of the nanorods is proposed. An impressive high specific capacity of approximately 250 mAh g(-1) and excellent cycling and rate performances were demonstrated for sodium storage. The hierarchical FeOF nanorods are promising high-capacity cathodes for SIBs.

Bio-inspired synthesis of α-Ni(OH)2 nanobristles on various substrates and their applications

It is still a challenging task to develop simple methods for facile synthesis of α-Ni(OH)2 nanostructures on substrates under mild conditions without using expensive instruments. Here, α-Ni(OH)2 nanobristles were synthesized on various substrates under mild conditions via a bio-inspired method using a simple Nafion diaphragm-assisted system. By growing the unique networks of α-Ni(OH)2 nanobristles on a piece of glass, a double-rough surface, with structures at both the nanoscale and microscale, was achieved, showing interesting roughness-induced superhydrophobicity in air (water contact angle 156°) and superoleophobicity in water (oil contact angle 161°). Additionally, α-Ni(OH)2 nanobristles could be formed directly on Ni foam and used as integrated and binder-free electrodes for application in supercapacitors. The unique structure with a large exposed surface enables the electrodes to demonstrate an impressive capacity of 2090 F g−1 at a current of 2 A g−1. The α-Ni(OH)2 supercapacitor exhibits a relatively good long cycling performance, attributed to its network like structure and good stability. The method and ideas outlined in the paper, based on diaphragm-assisted systems, could be employed, in principle, for the synthesis of other functional materials or precursors under mild conditions.