TiO₂ and other titanium oxide-based nanomaterials have drawn immense attention from researchers in different scientific domains due to their fascinating multifunctional properties, relative abundance, environmental friendliness, and bio-compatibility. However, the physical and chemical properties of titanium oxide-based nanomaterials are found to be explicitly dependent on the presence of various crystal defects. Oxygen vacancies are the most common among them and have always been the subject of both theoretical and experimental research as they play a crucial role in tuning the inherent properties of titanium oxides. This review highlights different strategies for effectively introducing oxygen vacancies in titanium oxide-based nanomaterials, as well as a discussion on the positions of oxygen vacancies inside the TiO₂ band gap based on theoretical calculations. Additionally, a detailed review of different experimental techniques that are extensively used for identifying oxygen vacancies in TiO₂ nanostructures is also presented.

This study demonstrates a scheme to design and fabricate a novel 1D core/shell Ni/NiO nano-architecture electrode as a pseudocapacitor with significantly improved capacitive performance through hydrogenation. The specific capacitance of the as prepared 1D core/shell Ni/NiO nanoheterostructure (717 F g⁻¹ at a scan rate of 2 mV s⁻¹) is nearly 1635 F g⁻¹ after the hydrogenation. The improved pseudocapacitive properties of hydrogenated Ni/NiO nano-heterostructures are attributed to the incorporation of the hydroxyl groups on the NiO surface due to hydrogenation, where the metallic Ni nanowire core of this unique 1D core/shell heterostructure serves as the efficient channel for the fast electron conduction to the current collector. The H–Ni/NiO nanoheterostructures exhibit good rate capability (retaining nearly 60% of their initial charge) and good long-term cycling stability with an excellent specific energy and power density of 49.35 W h kg⁻¹ and 7.9 kW kg⁻¹, respectively, at a current density of 15.1 A g⁻¹. This study demonstrates that the H–Ni/NiO nano-heterostructure is very promising for next generation high-performance pseudocapacitors.

The mechanism of the visible-light driven photoelectrochemical properties of surface engineered H₂Ti₃O₇nanowires has been demonstrated.

The present article reports a facile method for preparing the vertically-aligned 1D arrays of a new type of type II n–n TiO₂/ZnO core/shell nano-heterostructures by growing the nano-shell of ZnO on the electrochemically fabricated TiO₂ nanotubes core for visible light driven photoelectrochemical applications. The strong interfacial interaction at the type II heterojunction leads to an effective interfacial charge separation and charge transport. The presence of various defects such as surface states, interface states and other defects in the nano-heterostructure enable it for improved visible light photoelectrochemical performance. The presence of such defects has also been confirmed by the UV-vis absorption, cathodoluminescence, and crystallographic studies. The TiO₂/ZnO core/shell nano-heterostructures exhibit strong green luminescence due to the defect transitions. The TiO₂/ZnO core/shell nano-heterostructures photo-electrode show significant enhancement of visible light absorption and it provides a photocurrent density of 0.7 mA cm⁻² at 1 V vs. Ag/AgCl, which is almost 2.7 times that of the TiO₂/ZnO core/shell nano-heterostructures under dark conditions. The electrochemical impedance spectroscopy results demonstrate that the substantially improved photoelectrochemical and photo-switching performance of the nano-heterostructures photoanode is because of the enhancement of interfacial charge transfer and the increase in the charge carrier density caused by the incorporation of the ZnO nano-shell on TiO₂ nanotube core.