Xi-Jie Lin

Controlled Formation of Metal@Al2O3 Yolk–Shell Nanostructures with Improved Thermal Stability

Yolk-shell structured nanomaterials have shown interesting potential in different areas due to their unique structural configurations. A successful construction of such a hybrid structure relies not only on the preparation of the core materials, but also on the capability to manipulate the outside wall. Typically, for Al2O3, it has been a tough issue in preparing it into a uniform nanoshell, making the use of Al2O3-based yolk-shell structures a challenging but long-awaited task. Here, in benefit of our success in the controlled formation of Al2O3 nanoshell, we demonstrated that yolk-shell structures with metal confined inside a hollow Al2O3 nanosphere could be successfully achieved. Different metals including Au, Pt, Pd have been demonstrated, forming a typical core@void@shell structure. We showed that the key parameters of the yolk-shell structure such as the shell thickness and the cavity size could be readily tuned. Due to the protection of a surrounding Al2O3 shell, the thermal stability of the interior metal nanoparticles could be substantially improved, resulting in promising performance for the catalytic CO oxidation as revealed by our preliminary test on Au@Al2O3.

General Synthetic Strategy for Hollow Hybrid Microspheres through a Progressive Inward Crystallization Process

Hollow hybrid microspheres have found great potential in different areas, such as drug delivery, nanoreactors, photonics, and lithium-ion batteries. Here, we report a simple and scalable approach to construct high-quality hollow hybrid microspheres through a previously unexplored growth mechanism. Starting from uniform solid microspheres with low crystallinity, we identified that a hollowing process can happen through the progressive inward crystallization process initiated on the particle surface: the gradual encroachment of the crystallization frontline toward the core leads to the depletion of the center and forms the central cavity. We showed that such a synthetic platform was versatile and can be applicable for a large variety of materials. By using the production of Li4Ti5O12-carbon hollow hybrid microspheres as an example, we demonstrated that high-performance anode materials could be achieved through synthesis and structure control. We expect that our findings offer new perspectives in different areas ranging from materials chemistry, energy storage devices, catalysis, to drug delivery.

Engineering Hollow Carbon Architecture for High-Performance K-Ion Battery Anode

K-ion batteries (KIBs) are now drawing increasing research interest as an inexpensive alternative to Li-ion batteries (LIBs). However, due to the large size of K+, stable electrode materials capable of sustaining the repeated K+ intercalation/deintercalation cycles are extremely deficient especially if a satisfactory reversible capacity is expected. Herein, we demonstrated that the structural engineering of carbon into a hollow interconnected architecture, a shape similar to the neuron-cell network, promised high conceptual and technological potential for a high-performance KIB anode. Using melamine-formaldehyde resin as the starting material, we identify an interesting glass blowing effect of this polymeric precursor during its carbonization, which features a skeleton-softening process followed by its spontaneous hollowing. When used as a KIB anode, the carbon scaffold with interconnected hollow channels can ensure a resilient structure for a stable potassiation/depotassiation process and deliver an extraordinary capacity (340 mAh g-1 at 0.1 C) together with a superior cycling stability (no obvious fading over 150 cycles at 0.5 C).

Controlling the Reaction of Nanoparticles for Hollow Metal Oxide Nanostructures

Hollow nanostructures of metal oxides have found broad applications in different fields. Here, we reported a facile and versatile synthetic protocol to prepare hollow metal oxide nanospheres by modulating the chemical properties in solid nanoparticles. Our synthesis design starts with the precipitation of urea-containing metal oxalate, which is soluble in water but exists as solid nanospheres in ethanol. A controlled particle hydrolysis is achieved through the heating-induced urea decomposition, which transforms the particle composition in an outside-to-inside style: The reaction starts from the surface and then proceeds inward to gradually form a water-insoluble shell of basic metal oxalate. Such a reaction-induced solubility difference inside nanospheres becomes highly efficient to create a hollow structure through a simple water wash process. A following high temperature treatment forms hollow nanospheres of different metal oxides with structural features suited to their applications. For example, a high performance anode for Li-ion intercalation pseudocapacitor was demonstrated with the hollow and mesoporous Nb2O5 nanospheres.

Controlled synthesis of hierarchically-structured MnCo 2 O 4 and its potential as a high performance anode material

To satisfy the upsurging demand for energy storage in modern society, anode materials which can deliver high capacity have been intensively researched for the next generation lithium ion batteries. Typically, the binary MnCo2O4 with a characteristic coupled metal cations showed promising potential due to its high theoretical capacity and low cost. Here, by means of a well-designed synthesis control, we demonstrated a scalable process to achieve a hierarchical structure of MnCo2O4, which existed as uniform microspheres with embedded mesopores, showing favorable structural characters for high performance during a fast charge/discharge process. Our synthesis highlighted the importance of sodium salicylate as an essential additive to control the precipitation of the two involved metal cations. It was proved that a dual role was played sodium salicylate which cannot only facilitate the formation of microspheric shape, but also act as an effective precursor for the creation of inner mesopores. We confirmed that the hierarchically-structured MnCo2O4 showed outstanding performance when it was tested as an anode material in lithium ion batteries as revealed by its extraordinary cycling stability and high rate capability.

The facile construction of a yolk–shell structured metal–TiO2 nanocomposite with potential for p-nitrophenol reduction

A yolk–shell structured metal–TiO2 nanocomposite was constructed using a facile and versatile method. Due to the dual functions of 3-aminophenol which worked as the template precursor and metal ion coordination agent, metal nanoparticles could disperse well, and the as-prepared yolk–shell Ag–TiO2 nanocomposite showed promising catalytic activity for the reduction of p-nitrophenol.

Facile synthesis of hollow Ti 2 Nb 10 O 29 microspheres for high-rate anode of Li-ion batteries

Titanium niobium oxides emerge as promising anode materials with potential for applications in lithium ion batteries with high safety and high energy density. However, the innate low electronic conductivity of such a composite oxide seriously limits its practical capacity, which becomes a serious concern especially when a high rate charge/discharge capability is expected. Here, using a modified template-assisted synthesis protocol, which features an in-situ entrapment of both titanium and niobium species during the formation of polymeric microsphere followed by a pyrolysis process, we succeed in preparing hollow microspheres of titanium niobium oxide with high efficiency in structural control. When used as an anode material, the structurally-controlled hollow sample delivers high reversible capacity (103.7 mA h g−1 at 50 C) and extraordinary cycling capability especially at high charge/discharge currents (164.7 mA h g−1 after 500 cycles at 10 C).

A facile template free synthesis of porous carbon nanospheres with high capacitive performance

Porous carbon nanospheres have been widely used in different fields such as electric devices, catalysts, and water treatment. Here we will introduce a template-free process for the preparation of porous carbon nanospheres starting from a direct 3-aminophenol formaldehyde polymerization in a mixed solution. We identify that the addition of different alcohols, particularly ethanol and n-butanol, is able to change the growth habit of the polymer nanospheres and introduce a favorable inner compositional homogeneity for the preparation of porous structure. After the carbonization of the polymer nanospheres, the obtained porous carbon exhibits promising electrochemical performance when used as electrode material in super capacitor.

Construction of Uniform Cobalt-Based Nanoshells and Its Potential for Improving Li-Ion Battery Performance

Surface cobalt doping is an effective and economic way to improve the electrochemical performance of cathode materials. Herein, by tuning the precipitation kinetics of Co2+, we demonstrate an aqueous-based protocol to grow uniform basic cobaltous carbonate coating layer onto different substrates, and the thickness of the coating layer can be adjusted precisely in nanometer accuracy. Accordingly, by sintering the cobalt-coated LiNi0.5Mn1.5O4 cathode materials, an epitaxial cobalt-doped surface layer will be formed, which will act as a protective layer without hindering charge transfer. Consequently, improved battery performance is obtained because of the suppression of interfacial degradation.