Hafnium-doped titania (Hf/Ti = 0.01; 0.03; 0.05) had been facilely synthesized via a template sol–gel method on carbon fibre. Physico-chemical properties of the as-synthesized materials were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, scanning transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry analysis and Brunauer–Emmett–Teller measurements. It was confirmed that Hf ⁴⁺ substitute in the Ti ⁴⁺ sites, forming Ti _{1– x} Hf _x O ₂ ( x = 0.01; 0.03; 0.05) solid solutions with an anatase crystal structure. The Ti _{1– x} Hf _x O ₂ materials are hollow microtubes (length of 10–100 µm, outer diameter of 1–5 µm) composed of nanoparticles (average size of 15–20 nm) with a surface area of 80–90 m ² g ^–1 and pore volume of 0.294–0.372 cm ³ g ^–1 . The effect of Hf ion incorporation on the electrochemical behaviour of anatase TiO ₂ in the Li-ion battery anode was investigated by galvanostatic charge/discharge and electrochemical impedance spectroscopy. It was established that Ti _0.95 Hf _0.05 O ₂ shows significantly higher reversibility (154.2 mAh g ^–1 ) after 35-fold cycling at a C /10 rate in comparison with undoped titania (55.9 mAh g ^–1 ). The better performance offered by Hf ⁴⁺ substitution of the Ti ⁴⁺ into anatase TiO ₂ mainly results from a more open crystal structure, which has been achieved via the difference in ionic radius values of Ti ⁴⁺ (0.604 Å) and Hf ⁴⁺ (0.71 Å). The obtained results are in good accord with those for anatase TiO ₂ doped with Zr ⁴⁺ (0.72 Å), published earlier. Furthermore, improved electrical conductivity of Hf-doped anatase TiO ₂ materials owing to charge redistribution in the lattice and enhanced interfacial lithium storage owing to increased surface area directly depending on the Hf/Ti atomic ratio have a beneficial effect on electrochemical properties.

Nickel- and zinc-doped TiO₂(B) nanobelts were synthesized using a hydrothermal technique. It was found that the incorporation of 5 at.% Ni into bronze TiO₂ expanded the unit cell by 4%. Furthermore, Ni dopant induced the 3d energy levels within TiO₂(B) band structure and oxygen defects, narrowing the band gap from 3.28 eV (undoped) to 2.70 eV. Oppositely, Zn entered restrictedly into TiO₂(B), but nonetheless, improves its electronic properties (E_g is narrowed to 3.21 eV). The conductivity of nickel- (2.24 × 10⁻⁸ S·cm⁻¹) and zinc-containing (3.29 × 10⁻⁹ S·cm⁻¹) TiO₂(B) exceeds that of unmodified TiO₂(B) (1.05 × 10⁻¹⁰ S·cm⁻¹). When tested for electrochemical storage, nickel-doped mesoporous TiO₂(B) nanobelts exhibited improved electrochemical performance. For lithium batteries, a reversible capacity of 173 mAh·g⁻¹ was reached after 100 cycles at the current load of 50 mA·g⁻¹, whereas, for unmodified and Zn-doped samples, around 140 and 151 mAh·g⁻¹ was obtained. Moreover, Ni doping enhanced the rate capability of TiO₂(B) nanobelts (104 mAh·g⁻¹ at a current density of 1.8 A·g⁻¹). In terms of sodium storage, nickel-doped TiO₂(B) nanobelts exhibited improved cycling with a stabilized reversible capacity of 97 mAh·g⁻¹ over 50 cycles at the current load of 35 mA·g⁻¹.

Nanostructured TiO2 and TiO2-ZrO2 (4 wt % ZrO2) in the anatase crystal modification have been synthesized through a template sol-gel route. Morphological and structural features of these compounds...