Xiong Wen (David) Lou

Constructing Hierarchical Spheres from Large Ultrathin Anatase TiO2 Nanosheets with Nearly 100% Exposed (001) Facets for Fast Reversible Lithium Storage

Synthesis of nanocrystals with exposed high-energy facets is a well-known challenge in many fields of science and technology. The higher reactivity of these facets simultaneously makes them desirable catalysts for sluggish chemical reactions and leads to their small populations in an equilibrated crystal. Using anatase TiO(2) as an example, we demonstrate a facile approach for creating high-surface-area stable nanosheets comprising nearly 100% exposed (001) facets. Our approach relies on spontaneous assembly of the nanosheets into three-dimensional hierarchical spheres, which stabilizes them from collapse. We show that the high surface density of exposed TiO(2) (001) facets leads to fast lithium insertion/deinsertion processes in batteries that mimic features seen in high-power electrochemical capacitors.

Nanostructured metal oxide-based materials as advanced anodes for lithium-ion batteries.

The search for new electrode materials for lithium-ion batteries (LIBs) has been an important way to satisfy the ever-growing demands for better performance with higher energy/power densities, improved safety and longer cycle life. Nanostructured metal oxides exhibit good electrochemical properties, and they are regarded as promising anode materials for high-performance LIBs. In this feature article, we will focus on three different categories of metal oxides with distinct lithium storage mechanisms: tin dioxide (SnO(2)), which utilizes alloying/dealloying processes to reversibly store/release lithium ions during charge/discharge; titanium dioxide (TiO(2)), where lithium ions are inserted/deinserted into/out of the TiO(2) crystal framework; and transition metal oxides including iron oxide and cobalt oxide, which react with lithium ions via an unusual conversion reaction. For all three systems, we will emphasize that creating nanomaterials with unique structures could effectively improve the lithium storage properties of these metal oxides. We will also highlight that the lithium storage capability can be further enhanced through designing advanced nanocomposite materials containing metal oxides and other carbonaceous supports. By providing such a rather systematic survey, we aim to stress the importance of proper nanostructuring and advanced compositing that would result in improved physicochemical properties of metal oxides, thus making them promising negative electrodes for next-generation LIBs.

Formation of Fe2O3 microboxes with hierarchical shell structures from metal-organic frameworks and their lithium storage properties.

Fe(2)O(3) microboxes with hierarchically structured shells have been synthesized simply by annealing Prussian blue (PB) microcubes. By utilizing simultaneous oxidative decomposition of PB microcubes and crystal growth of iron oxide shells, we have demonstrated a scalable synthesis of anisotropic hollow structures with various shell architectures. When evaluated as an anode material for lithium ion batteries, the Fe(2)O(3) microboxes with a well-defined hollow structure and hierarchical shell manifested high specific capacity (~950 mA h g(-1) at 200 mA g(-1)) and excellent cycling performance.

Quasiemulsion-Templated Formation of α-Fe2O3 Hollow Spheres with Enhanced Lithium Storage Properties

α-Fe(2)O(3) hollow spheres with sheet-like subunits are synthesized by a facile quasiemulsion-templated method. Glycerol is dispersed in water to form oil-in-water quasiemulsion microdroplets, which serve as soft templates for the deposition of the α-Fe(2)O(3) shell. When tested as anode materials for lithium-ion batteries, these α-Fe(2)O(3) hollow spheres manifest greatly enhanced Li storage properties.

Assembling carbon-coated α-Fe2O3 hollow nanohorns on the CNT backbone for superior lithium storage capability

Novel hierarchical nanostructures composed of carbon coated α-Fe2O3 hollow nanohorns on carbon nanotube (CNT) backbones have been constructed by direct growth and thermal transformation of β-FeOOH nanospindles on CNTs, followed by carbon nanocoating. When evaluated as a potential anode material for lithium-ion batteries, such hierarchical structures exhibit superior lithium storage capabilities by virtue of their advantageous structural features.

Nitrogen-containing microporous carbon nanospheres with improved capacitive properties

We report the largely improved electrochemical capacitance of polypyrrole-derived microporous carbon nanospheres (MCNs, 80–100 nm in diameter) containing nitrogen functional groups. We have investigated the electrochemical properties of precursor polypyrrole nanospheres (PNs, with a high N/C ratio and low surface area) and as-derived carbon nanospheres (CNs, with a moderate N/C ratio and low surface area) prepared by carbonizing PNs at different temperatures, and MCNs (with a low N/C ratio and high surface area) obtained by chemical activation of CNs. The samples are thoroughly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), nitrogen sorption, elemental analysis, and X-ray photoelectron spectroscopy (XPS). It is found that MCNs with a high surface area and N-doping species exhibit much better capacitive performance compared to the PNs and CNs, and commercial carbon blacks (XC-72 and BP2000) as well. The MCN sample gives a reversible specific capacitance of ∼240 F g−1 for 3000 cycles in aqueous media as a result of combined advantages of high electrochemical activity of doped heteroatoms (N and O) and accessible well-developed porosity, demonstrating the promising use in high-energy-density supercapacitors.

Single-crystalline NiCo2O4 nanoneedle arrays grown on conductive substrates as binder-free electrodes for high-performance supercapacitors

In this work, we have successfully grown single-crystalline nanoneedle arrays of NiCo2O4 on conductive substrates such as Ni foam and Ti foil through a simple solution method together with a post-annealing treatment. Remarkably, the NiCo2O4–Ni foam binder-free electrode exhibits greatly improved electrochemical performance with very high capacitance and excellent cycling stability.

Growth of ultrathin mesoporous Co3O4 nanosheet arrays on Ni foam for high-performance electrochemical capacitors

An advanced electrode for high-performance electrochemical capacitors has been designed by growing ultrathin mesoporous Co3O4 nanosheet arrays on the Ni foam support. This unique 3D electrode manifests exceptional supercapacitive performance with ultrahigh specific capacitance at high current densities and excellent cycling stability.

Porous molybdenum carbide nano-octahedrons synthesized via confined carburization in metal-organic frameworks for efficient hydrogen production

Electrochemical water splitting has been considered as a promising approach to produce clean and sustainable hydrogen fuel. However, the lack of high-performance and low-cost electrocatalysts for hydrogen evolution reaction hinders the large-scale application. As a new class of porous materials with tunable structure and composition, metal-organic frameworks have been considered as promising candidates to synthesize various functional materials. Here we demonstrate a metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbides based on the confined carburization in metal-organic frameworks matrix. Starting from a compound consisting of copper-based metal-organic frameworks host and molybdenum-based polyoxometalates guest, mesoporous molybdenum carbide nano-octahedrons composed of ultrafine nanocrystallites are successfully prepared as a proof of concept, which exhibit remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions. The present study provides some guidelines for the design and synthesis of nanostructured electrocatalysts.

Double-shelled CoMn2O4 hollow microcubes as high-capacity anodes for lithium-ion batteries

IO N Hollow micro-/nanostructures with controlled size, shape, composition, and internal structure have attracted intense interest in recent years, mainly due to their promising use in many applications such as nanoreactors, drug delivery, gas sensors, and energy storage and conversion.[1–3] More recently, efforts have been dedicated to the rational design of complex hollow structures, such as multishelled hollow structures and yolkshell structures,[4–6] as these complex structures are expected to offer more handles to tailor the properties for different applications such as drug delivery,[7,8] photocatalysis,[9–11] dye sensitized solar cells,[12] gas sensors,[13,14] lithium-ion batteries (LIBs).[15–19] A general approach for the fabrication of multishelled hollow structures involves the employment of sacrificial templates, either hard ones, such as monodispersed polymer,[20] silica,[21,22] carbon,[14] and metal oxide nanoparticles,[23] or soft ones, such as micelles.[18,24] For example, Yang et al.[20] prepared double-shelled metal oxides by templating against commercially available hollow latex spheres; Lou et al.[21,22] reported the fabrication of double-shelled SnO2 hollow spheres and “nanococoons” based on shell-by-shell deposition of SnO2 on spherical and nonspherical silica; Lai et al.[14] fabricated multishelled Fe2O3 hollow spheres with controlled shell numbers by employing carbonaceous microspheres as sacrificial templates; Xu et al.[24] reported the synthesis of multishelled Cu2O hollow spheres via a multilamellar-micelle templating route. However, in most cases, the resulting hollow structures are spherical in shape and the materials are simple binary oxides. The number of reports on multishelled nonspherical hollow structures is significantly limited due to the paucity of nonspherical templates and difficulty in forming uniform coatings, especially multilayered coatings, around high-curvature surfaces.[21,23] Herein, we report the synthesis of double-shelled CoMn2O4 hollow microcubes via a facile co-precipitation and annealing