Hai-Tao Fang

Comparison of the rate capability of nanostructured amorphous and anatase TiO 2 for lithium insertion using anodic TiO 2 nanotube arrays

Nanostructured amorphous and anatase TiO2 are both considered as high rate Li-insertion/extraction electrode materials. To clarify which phase is more desirable for lithium ion batteries with both high power and high density, we compare the electrochemical properties of anatase and amorphous TiO2 by using anodic TiO2 nanotube arrays (ATNTAs) as electrodes. With the same morphological features, the rate capacity of nanostructured amorphous TiO2 is higher than that of nanostructured anatase TiO2 due to the higher Li-diffusion coefficient of amorphous TiO2 as proved by the electrochemical impedance spectra of an amorphous and an anatase ATNTA electrode. The electrochemical impedance spectra also prove that the electronic conductivity of amorphous TiO2 is lower than that of anatase TiO2. These results are helpful in the structural and componential design of all TiO2 mesoporous structures as anode material in lithium ion batteries. Moreover, all the advantages of the amorphous ATNTA electrode including high rate capacity, desirable cycling performance and the simplicity of its fabrication process indicate that amorphous ATNTA is potentially useful as the anode for lithium ion batteries with both high power and high energy density.

Amorphous TiO 2 nanotube arrays for low-temperature oxygen sensors

Titania nanotube arrays (TNTA) were synthesized on a titanium substrate using anodic oxidation in an electrolyte containing ammonium fluoride and evaluated for low-temperature oxygen sensing. Their sensing properties were tested at different temperatures (50, 100, 150, 200, 250 and 300 °C) when exposed to various oxygen concentrations. The as-prepared TNTA are amorphous and exhibit much higher carrier concentration than that of annealed TNTA. Such amorphous TNTA show much higher sensitivity than that of annealed TNTA, SrTiO(3) and Ga(2)O(3) sensors. This sample demonstrates the lowest detectable oxygen concentration of 200 ppm, excellent recovery and good linear correlation at 100 °C. These results indicate that TNTA are indeed very attractive oxygen-sensing materials.

Lamellar MoSe2 nanosheets embedded with MoO2 nanoparticles: novel hybrid nanostructures promoted excellent performances for lithium ion batteries

A carbon-free nanocomposite consisting of MoO2 nanoparticles embedded between MoSe2 nanosheets, named MoO2@MoSe2, has been synthesized and demonstrated excellent electrochemical properties for lithium ion batteries. In such a composite, MoSe2 nanosheets provide a flexible substrate for MoO2 nanoparticles; while MoO2 nanoparticles act as spacers to retain the desired active surface to electrolyte and also introduce metallic conduction. In addition, the heterojunctions at the interface between MoSe2 and MoO2 introduce a self-built electric field to promote the lithiation/delithiation process. As a result, such lamellar composite has a long cycling stability with a reversible capacity of 520.4 mA h g-1 at a current density of 2000 mA g-1 after 400 cycles and excellent rate performance, which are attributed to the synergistic combination of the two components in nanoscale.

Free-standing hybrid film of less defective graphene coated with mesoporous TiO2 for flexible lithium ion batteries with fast charging/discharging capabilities

Benefiting from extremely high conductivity, graphene sheets (GS) with very low defect density are preferable to reduced graphene oxide sheets for constructing the free-standing hybrid electrodes of flexible electrochemical energy storage devices. However, due to the hydrophobic nature and deficiency of nucleation sites, how to uniformly and intimately anchor electrochemically active materials onto less defective GS is a challenge. Herein, a free-standing and mechanically flexible hybrid film with two-layer structure, mesoporous TiO2 anchored less defective GS hybrid (mTiO2-GS) upper-layer and graphene under-layer, denoted as mTiO2-GS/G, is fabricated. The hydrolysis of a Ti glycolate aqueous sol solution were applied to form mTiO2. The decoration of less defective GS with sodium lignosulfonate (SLS) surfactant is crucial for anchoring TiO2 nanoparticles (NPs). The aromatic rings of SLS favor a non-destructive functionalization of GS through the π-π stacking interaction. The sulfonic acid groups and hydroxyl groups of SLS, respectively, greatly improve the dispersity of GS in water and trigger the nucleation of TiO2 through the oxolation in the hydrolysis of Ti glycolate sol solution. The following characteristics of free-standing mTiO2-GS/G electrode benefit the fast charging/discharging capabilities: highly conductive graphene framework, ultra-small NPs (~5.0 nm) in mTiO2 anchored, high specific surface area (202.5 m2 g−1), abundant mesopores (0.32 cm3 g−1), intimate interfacial interaction between mTiO2 and GS, robust contact between the mTiO2-GS upper-layer and an under-layer of bare graphene as the current collector. In coin half-cells, the mTiO2-GS/G electrode delivers a capacity of 130 mA h g−1 at 50 C, and 71 mA h g−1 at 100 C, and it also exhibits excellent cycle stability up to 10 000 cycles under 10 C, with a degradation rate of 0.0033% per cycle. When packed in flexible cells, the mTiO2-GS/G electrode maintains fast charging/discharging capabilities regardless of being flat or bent. Furthermore, because of the high durability of mTiO2-GS/G electrode, repeated deformations do not cause extra capacity degradation.

Erratum: X-ray Absorption Spectroscopic Characterization of the Synthesis Process: Revealing the Interactions in Cetyltrimethylammonium Bromide-Modified Sulfur-Graphene Oxide Nanocomposites (Journal of Physical Chemistry C (2016) 120:19 (10111-10117) DOI: 10.1021/acs.jpcc.6b00751)

Correction to “X-ray Absorption Spectroscopic Characterization of the Synthesis Process: Revealing the Interactions in Cetyltrimethylammonium Bromide-Modified Sulfur−Graphene Oxide Nanocomposites” Yifan Ye, Ayako Kawase, Min-Kyu Song, Bingmei Feng, Yi-Sheng Liu, Matthew A. Marcus, Jun Feng, Haitao Fang, Elton J. Cairns, Junfa Zhu, and Jinghua Guo* One sentence should be included in the “Acknowledgement” section: “We thank Richard Celestre for his technical support of the experiment performed on BL5.3.1 at the ALS.”