Porous Anatase-TiO2(B) Dual-Phase Nanorods Prepared from in Situ Pyrolysis of a Single Molecule Precursor Offer High Performance Lithium-Ion Storage

Construction of TiO2(B)/Anatase Heterophase Junctions via a Water-Induced Phase Transformation Strategy for Enhanced Photocatalytic Hydrogen Production

The development of facile and green solution-phase routes toward the fabrication of TiO₂-based heterophase junctions with a delicate control of phase and structure is a challenging task. Herein, we report a simple and convenient method to controllably fabricate TiO₂(B)/anatase heterophase junctions, which was successfully realized by utilizing the ideal great solvent of water to treat the presynthesized TiO₂(B) nanosheet precursor at a low temperature of 80 °C. On the basis of phase structure transformation and morphology evolution data, the formation of these TiO₂(B)/anatase heterophase junctions was reasonably explained by a novel water-induced TiO₂(B) → anatase phase transformation mechanism. Benefiting from the desirable structural and photoelectronic advantages of more exposed active sites, enhanced light absorbance, and promoted separation of photogenerated electron-hole pairs, the thus-transformed TiO₂(B)/anatase heterophase junctions exhibit fascinating photocatalytic performance in water splitting. Specifically, with the help of Pt as a cocatalyst and methanol as a sacrificial agent, the H₂ production rate of optimized TiO₂(B)/anatase heterophase junction reaches 6.92 mmol·g^-1·h^-1, which is almost 7.1 and 2.1 times higher than those of the pristine TiO₂(B) nanosheets and the final anatase nanocrystals. More interestingly, the TiO₂(B)/anatase heterophase junction also delivers prominent activity toward pure water splitting to simultaneously produce H₂ and H₂O₂, with evolution rates of up to 1.10 and 0.55 mmol·g^-1·h^-1, respectively. Our work may advance the facile green solvent-mediated synthesis of metal oxide-based heterophase junctions for applications in energy- and environmental-related areas.

Nitrogen-doped TiO2(B) nanobelts enabling enhancement of electronic conductivity and efficiency of lithium-ion storage

To enhance the intrinsic electrical conductivities of TiO₂(B) nanobelts, nitrogen(N)-doped TiO₂(B) nanobelts (N-TNB) were prepared in this study by a facile and cost-effective hydrothermal method using urea as the nitrogen source with TiO₂ (P25) nanoparticles. x-ray photoelectron spectroscopy confirmed that the N-atoms preferentially occupied up to ∼0.516 atom% in the interstitial sites of the N-TNB and the maximum concentration of substituted-N bonds in the N-TNB was ∼0.154 atom%, thereby the total concentration of doped nitrogen elements of ∼0.67 atom% improved the high intrinsic electrical conductivity and ionic diffusivity of the TiO₂(B) nanobelts. The as-prepared N-TNB electrode delivered the highest specific capacity of 133.9 mAh g^-1 in the first cycle, with an exceptional cyclic capacity retention at an ultrafast current rate of 1000 mA g^-1; this is not less than 51% after 500 cycles and represents an excellent rate capability of ∼37 mAh g^-1 at an ultra-high rate of 40 C. These values are among the best ever reported on comparison of the delivered highest discharge capacity of N-TNB at 1000 mA g^-1 and high-rate capabilities of its Li⁺ ion storage with the literature data for N-TNB (∼231.5 mAh g^-1 at a very low current density of 16.75 mA g^-1, ∼0.1 C) of similar materials used in sodium-ion batteries. This implies the potential feasibility of these N-TNB as high-capacity anode materials for next-generation, high-energy-density, electrochemical energy-storage devices.

Watermelon-like TiO2 nanoparticle (P25)@microporous amorphous carbon sphere with excellent rate capability and cycling performance for lithium-ion batteries

To overcome the inferior rate capability and cycling performance of TiO₂ nanomaterials as an anode material of lithium-ion batteries, we encapsulate TiO₂ nanoparticles (P25) in carbon spheres through a facile pyrrole polymerization and carbonization. Material characterization demonstrates TiO₂ nanoparticles are uniformly embedded in microporous amorphous carbon spheres, forming a watermelon-like structure. P25@C exhibits excellent high rate capability with average discharge capacity of 496, 416, 297, 240, 180, 99, 49 and 25 mAh g^-1 at current rate of 0.5C, 1C, 5C, 10C, 20C, 50C, 100C and 200C, which shows superior long-term cycling performance with discharge capacity of 106.9 mAh g^-1 at 20C after 5000 cycles. The capacity loss rate is only 0.008% per cycle. The outstanding lithium storage performance is ascribed to the watermelon-like composite structure, which remarkably improves electronic conductivity and structure stability of TiO₂ nanoparticles. More importantly, the agglomeration of TiO₂ nanoparticles is eliminated, and the entire surface of every TiO₂ nanoparticle participates in the electrochemical reaction, which brings about an intense capacitive Li storage effect and leads to the high specific capacity and excellent rate capability of P25@C. This is confirmed through qualitative and quantitative analysis of the contributions from surface capacitive storage and bulk intercalation storage to the total capacity of the composite.