Hao Ge

Advanced Mesoporous Spinel Li4Ti5O12/rGO Composites with Increased Surface Lithium Storage Capability for High-Power Lithium-Ion Batteries

Spinel Li4Ti5O12 (LTO) and reduced graphene oxide (rGO) are attractive anode materials for lithium-ion batteries (LIBs) because of their unique electrochemical properties. Herein, we report a facile one-step hydrothermal method in preparation of a nanocomposite anode consisting of well-dispersed mesoporous LTO particles onto rGO. An important reaction step involves glucose as a novel linker agent and reducing agent during the synthesis. It was found to prevent the aggregation of LTO particles, and to yield mesoporous structures in nanocomposites. Moreover, GO is reduced to rGO by the hydroxyl groups on glucose during the hydrothermal process. When compared to previously reported LTO/graphene electrodes, the newly prepared LTO/rGO nanocomposite has mesoporous characteristics and provides additional surface lithium storage capability, superior to traditional LTO-based materials for LIBs. These unique properties lead to markedly improved electrochemical performance. In particular, the nanocomposite anode delivers an ultrahigh reversible capacity of 193 mA h g(-1) at 0.5 C and superior rate performance capable of retaining a capacity of 168 mA h g(-1) at 30 C between 1.0 and 2.5 V. Therefore, the newly prepared mesoporous LTO/rGO nanocomposite with increased surface lithium storage capability will provide a new opportunity to develop high-power anode materials for LIBs.

Synthesis of a tailored SrTiO3–TiO2 microspherical photocatalyst and its photogenerated charge properties

A series of SrTiO3–TiO2 microspheres with different porosities were prepared by a facile hydrothermal reaction method in the presence of Sr(OH)2 and titanium glycolate. The photogenerated charge separation and surface trapping process was studied by surface photovoltage (SPV) spectra and corresponding phase spectra. Compared with one-dimension nanowires, the SrTiO3–TiO2 microspheres show structural advantage in photocatalytic degradation under visible-light. The enhanced photocurrent of Rhodamine B (RhB) sensitized SrTiO3–TiO2 porous microspheres reveals that a photosensitization effect leads to the photodegradation process. According to the experimental results, these SrTiO3–TiO2 porous microspheres have great potential applications in photocatalytic decomposition or optoelectronic devices.

Influence of Surface States on the Evaluation of the Flat Band Potential of TiO2

Flat band potential (Vfb) is one of the most important physical parameters to study and understand semiconductor materials. However, the influence of surface states on the evaluating Vfb of titanium oxide (TiO2) and other semiconductor materials through a Mott-Schottky plot is ignored. Our study indicated that the influence of surface states should be introduced into the corresponding equivalent circuit even when the kinetic process did not occur. Ignoring the influence of surface states would lead to an underestimation of the space charge capacitance. Our paper would be beneficial for accurate determination of Vfb of semiconductor materials. We anticipate that this preliminary study will open new perspectives in understanding the semiconductor-electrolyte interface.

Direct electrochemistry of cholesterol oxidase and biosensing of cholesterol based on PSS/polymeric ionic liquid–graphene nanocomposite

A novel graphene nanocomposite, functionalized by polymeric ionic liquids (PILs) and poly(sodium-p-styrenesulfonate) (PSS), was successfully prepared and exhibited excellent conductivity, favourable biocompatibility and good film-forming properties as an electrode material. TEM showed that the nanocomposite possessed an individual nanosheet-like structure. Owing to the surface modification of graphene, PSS/PILs–GP can not only be well dispersed in aqueous solution, but also possesses a strong negative charge. Due to electrostatic interactions, positively charged cholesterol oxidase (ChOx) can be immobilized onto the surface of PSS/PILs–GP to form the ChOx/PSS/PILs–GP/GC electrode material. UV-vis and FT-IR spectroscopy were used to monitor the assembly process of the nanocomposite. Due to the conductivity and biocompatibility of PSS/PILs–GP, the immobilized ChOx exhibited enhanced direct electron transfer (DET) at a glassy carbon (GC) electrode. Furthermore, the ChOx/PSS/PILs–GP/GC electrode displayed excellent catalytic performance with a wide linear range of 10.5 × 10−6 to 10.4 × 10−3 mol L−1, and a low detection limit of 3.5 μmol L−1 for the detection of cholesterol.

Unique Li4Ti5O12/TiO2 multilayer arrays with advanced surface lithium storage capability

Nanostructured arrays grown on metal substrates have been attracting considerable attention as promising electrode materials for energy storage systems. Herein, unique Li4Ti5O12/TiO2 multilayer arrays (LTO/TiO2 MLAs) featuring advanced surface lithium storage capability are successfully synthesized for the first time via a facile substrate-free hydrothermal method with subsequent calcination. The proposed substrate-free growth mechanism of the LTO/TiO2 MLA is demonstrated in detail. Compared to previously reported LTO and LTO/TiO2 arrays grown on various substrates, a novel multilayer array structure and remarkable surface lithium storage capability have been clearly detected in our newly prepared LTO/TiO2 MLA. The unique framework of the LTO/TiO2 MLA can not only offer abundant grain boundaries and phase interfaces for increasing the number of Li+ storage sites but also provide rich and hierarchical channels to ensure more lithium ions and electrons rapidly diffuse and migrate, contributing to advanced surface lithium storage capability. The as-prepared LTO/TiO2 MLA exhibits great practical potential for further achieving both high-capacity and high-rate lithium storage, delivering an ultrahigh reversible capacity of 193 mA h g−1 at 0.5C and a superior rate capability of 148 mA h g−1 at 30C between 1.0 and 2.5 V. Our present work provides a facile yet scalable and substrate-free approach for the rational design and fabrication of multilayer arrays with superior electrochemical performance. We believe that the multilayer array structure with abundant active sites and diffusion channels will attract intense interest.

Study on the energy band structure and photoelectrochemical performances of spinel Li{sub 4}Ti{sub 5}O{sub 12}

Highlights: • Spinel Li{sub 4}Ti{sub 5}O{sub 12} possesses more positive potential of valence band and wider band gap than TiO{sub 2}. • Spinel Li{sub 4}Ti{sub 5}O{sub 12} displays typical n-type semiconductor characteristic and excellent UV-excitateded photocatalysis activity. • Our preliminary study will open new perspectives in investigation of other lithium-based compounds for new photocatalysts. - Abstract: Energy band structure, photoelectrochemical performances and photocatalysis activity of spinel Li{sub 4}Ti{sub 5}O{sub 12} are investigated for the first time in this paper. Li{sub 4}Ti{sub 5}O{sub 12} possesses more positive valence band potential and wider band gap than TiO{sub 2} due to its valence band consisting of Li{sub 1s} and Ti{sub 3d} orbitals mixed with O{sub 2p}. Li{sub 4}Ti{sub 5}O{sub 12} shows typical photocatalysis material characteristics and excellent photocatlytic activity under UV irradiation.