Dr. Liu's Main Page

Research

TiO₂ as lithium ion battery anodes

Lithium-ion batteries (LIBs) have been widely studied because of their wide range of applications from cell phones, laptops to hybrid automobiles. It’s a device that converts chemical energy to electrical energy, where high capacity, good cyclic stability and rate capability are preferred. Traditional anode materials of LIBs are based on carbonaceous materials, which have some drawbacks such as the excessive solid electrolyte interface (SEI) formed during charge/discharge processes, volume expansion upon Li insertion/extraction during prolonged cycling, especially at elevated temperatures (e.g. 60 °C). TiO₂ has many advantages when used as lithium ion battery electrodes, notably chemical stability, low price and non-toxicity. In our research, we fabricated various TiO₂ nanostructures via wet chemical processes without templates. By manipulating the reaction process and carrying out surface modification, we anticipate a suitable nanostructure of TiO₂, which has high reversible capacity and fine rate performance. In addition, it can also work under some harsh environment, e.g. high or low temperature.
Here are some experimental results of our work:

1. TiO₂ Nanosheet-based Spheres: We synthesize this specific structure via a two-step strategy without using any template. Hydrothermal treatment is employed in this process. By controlling the reaction temperature and time, well-dispersed nanosheet spheres can be obtained, which show favorable performance when used as anode materials in LIBs (~170 mAhg-1 at 1 C).

2. Mesoporous TiO₂ nanostructure: TiO2 nanospheres are used as the precursor in the hydrothermal processing. Mesoporous TiO₂ nanoparticle aggregates are obtained.

3. Hierarchical Macro-/Mesoporous TiO₂: This nanostructure of TiO₂ owns high specific surface area. It is synthesized via solution reaction without any template. After calcination at specific temperatures, it exhibits high charge/discharge capacity when used in LIBs.

4. Layered protonated TiO₂: Large-scale of layered TiO₂ powders is fabricated at room temperature. After surface modification, this nanostructure of TiO₂ also shows promising performance in the application of LIBs.

Metal oxides as non-enzymatic electrochemical biosensor electrodes:

The reliable, accurate and fast detection of hydrogen peroxide (H₂O₂) and glucose is of great significance, since H₂O₂ is a common oxidizing agent and an essential intermediate in biomedical, pharmaceutical, industrial and environmental fields and enzymatic reaction. Meanwhile, glucose is associated with the diabetes diagnosis, which is one of the major health afflictions worldwide. Among various techniques for  H₂O₂ and glucose detection, electrochemical method is most attractive due to its high sensitivity, simple operation, low cost, and the possibility for real-time detection. Conventional enzyme based electrochemical sensors have the advantages of high sensitivity and good selectivity. However, enzyme is critical about the environment, thus these sensors often suffer from unstable response as well as poor reproducibility. In recent years, metal oxide nanomaterials have received considerable attention for fabricating nonenzymatic sensors due to their high catalysis, low cost, and good stability. The performance of these sensors mainly depends on the modified nanomaterials. Therefore, it is greatly demanded to explore new nanomaterials systems for the fast and accurate detection of H₂O₂ and glucose.

In our research, copper oxide (along with nickel oxide) with various one-dimensional and hierarchical structures is used as non-enzymatic biosensor electrodes. Hydrothermal method is primarily used for fabricating various CuO nanostructures. Electrospinning and electrodeposition techniques may also involved in the long term. The purpose of this work is to obtain stable nanostructures with high specific surface area, which can provide high catalytic active sites for the absorption and electrochemical reaction of the analytes. Meanwhile, the hybrid nanocomposites will tried to be prepared because of their synergistic effect. Moreover, some other treatments that can help improving the biosensor electrodes’ sensitivity, selectivity and stability will also be carried out, such as ion doping, surface modification and phase structure control. Several analysis and measurement techniques will be used in this research. Surface morphologies and crystal structures will be characterized by SEM, TEM and XRD. Elemental existence and composition will be revealed by EDS, XPS and FTIR. Electrochemical measurements were carried out in a conventional three-electrode electroanalysis system controlled by electrochemical workstation. Electrochemical impedance spectroscopy (EIS) is used for studying the interfacial properties of surface-modified electrodes. The anti-interference study, repeatability and stability are also performed.

1. CuO from hydrothermal: at constant hydrothermal temperature and time, without using any surfactants, by changing the amount of reactant copper nitrite, the morphologies of the prepared samples changed from particle-like spheres to grass-like morphology (assembled from individual flower-like particles), and finally aggregate. All the three samples show well response to H₂O₂.

2. CuO from copper foil: Copper foil has also been used as raw materials to fabricate CuO nanostructures using hydrothermal process. The morphology of as-prepared sample is shown below. The electrochemical test shows that the sample possesses good electrocatalytic property.