This review highlights different strategies and techniques for introducing and detecting oxygen vacancies in titanium oxide-based nanomaterials.

Here, we report the synthesis of TiO 2 /BiFeO 3 nano-heterostructure (NH) arrays by anchoring BiFeO 3 (BFO) nanoparticles on TiO 2 nanotube surface and investigate their pseudocapacitive and photo-electrochemical properties considering their applications in green energy fields. The unique TiO 2 /BFO NHs have been demonstrated both as energy conversion and storage material. Capacitive behavior of the NHs has found to be significantly higher than the pristine TiO 2 NTs which is mainly due to the anchoring of redox active BFO nanoparticles.Specific capacitance of about 440 F g -1 has been achieved for this NHs at a current density of 1.1 Ag -1 with ~ 80% capacity retention at a current density of 2.5 A g -1 . The NHs also exhibit high energy and power performance (energy density of 46.5 Wh kg -1 and power density of 1.2 kW kg -1 at a current density of 2.5 Ag -1 ) with moderate cycling stability (92 % capacity retention after 1200 cycles). Photo-electrochemical investigation reveals that the photo current density of the NHs is almost 480% higher than the corresponding dark current and it shows significantly improved photo switching performance as compared to pure TiO 2 nanotubes which has been demonstrated based the interfacial type-II band alignment between TiO 2 and BFO.INTRODUCTION. Intensive research attention has been focused on the energy storage and conversion from the renewable and clean energy sources in order to deal with the ever-increasing energy consumption and environmental issues. 1, 2 Recently, hybrid supercapacitors (SCs) having high energy and high power density, which can bridge the gap between rechargeable battery and ordinary dielectric capacitor, are being considered to be one of the pioneers in the field of alternative energy storage systems in lieu of the conventional rechargeable battery and fuel-cell to quench the energy-thirst of the battery powered electronic gadgets, hybrid vehicles, mechatronic systems and medical instruments. 3, 4 Among SCs, the pseudocapacitors have gained remarkable attention because of their high theoretical specific capacitance, high energy and power density and long life cycle associated with Faradaic redox reactions compared to the electrical double-layer capacitors (EDLCs). 5-8 Being inspired by the high pseudocapacitance of various transition metal oxides such as MnO 2 , Fe 2 O 3 , NiO, Co 3 O 4 , NiCo 2 O 4 and V 2 O 5 , they have been studied extensively as promising candidates for SC electrodes which are also economical, environment friendly, abundant in nature and can be fabricated using easy, cost-effective routes.suitable band gap of BFO to absorb visible light efficiently and also the type II heterojunction formation due to the interface engineering which helps the generation/separation of free charge carriers (electron-hole pairs) allowing unidirectional current flow. This study indicates that the arrays of TiO 2 /BFO nano-heterostructure with enhanced capacitive and photo-electrochemical performance holds potential for applications in both renewable en...

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Origin of unexpected defect engineered room-temperature ferromagnetism observed in tin-doped indium oxide (ITO) nanostructures (Nanowires, Nano-combs) and nanocrystalline thin films fabricated by pulsed laser deposition has been investigated. It is found that the ITO nanostructures prepared under argon environment exhibit strongest ferromagnetic signature as compared to that nanocrystalline thin films grown at oxygen. The evidence of singly ionized oxygen vacancy (V0+) defects, obtained from various spectroscopic measurements, suggests that such V0+ defects are mainly responsible for the intrinsic ferromagnetic ordering. The exchange interaction of the defects provides extensive opportunity to tune the room-temperature d0 ferromagnetism and optical properties of ITOs.

This article demonstrates comprehensive studies on different visible-light driven photoelectrochemical and photocatalytic aspects of a hydrothermally synthesized n-type HTiO (HTO) nanowire mesh and its carbon and nitrogen functionalized counterparts, namely C-HTO and N-HTO. It was found that the presence of various defect states within the band gap of HTO, C-HTO and N-HTO nanowires, make them photoactive under visible-light. The photo-conversion efficiencies of HTO, C-HTO, and N-HTO nanowire electrodes are about 0.066, 0.129, and 0.076%, respectively, at around 1 V vs. Ag/AgCl. Carbon functionalization of HTO nanowires has been found to be most beneficial in increasing the charge carrier density, resulting in the highest current density, high photo conversion efficiency, remarkable photoelectrochemical water splitting performance and enhanced photocatalytic activity. The photocurrent density of the C-HTO NWs was found to be 0.0562 mA cm at 1 V vs. Ag/AgCl, which is almost two times that of the pristine HTO NWs (0.029 mA cm). Although nitrogen functionalization increases the charge carrier density of the HTO nanowires, nitrogen incorporation produces lots of recombination centres in the nanowires, which are found to play a detrimental role in the photoelectrochemical and photocatalytic performance of N-HTO nanowires, limiting the expected performance. Therefore, the present study demonstrates a suitable surface engineering technique for nanostructures to maximize the utilization of green solar light.

This work demonstrates a strategic nanoengineering design of a TiO2 nanorod (NR)-based photoanode. Here, the doping of Sb in TiO2 NRs along with co-integration of plasmonic gold nanoparticles and an amorphous lanthanum-cobalt double hydroxide (LaCo­(OH) x ) oxygen evolution catalyst (OEC) is found to improve visible-light absorption, rapid electron–hole pair separation, fast electron transportation, and the surface photocatalytic reaction of the photoanode, resulting in the ameliorated water oxidation performance. The Sb-doped TiO2 NRs exhibit a reduced band gap, improved photoconductivity, and an excellent photocurrent density (1.03 mA·cm–2 at 1.23 V vs reversible hydrogen electrode (RHE)). The anchoring of Au nanoparticles on Sb-TiO2 NRs significantly improves visible-light absorption and the photocurrent density because of the localized surface plasmon resonance effect. Herein, LaCo­(OH) x is demonstrated as a photo-electrocatalyst and incorporated with a TiO2 NR-based photoanode for the first time. Integration of a suitable amount of the LaCo­(OH) x OEC with Au/Sb-TiO2 NRs significantly improves photocarrier separation, photogenerated charge transportation, and the surface photo-electrocatalytic reaction and reduces the charge transfer resistance, delivering above 10 mA/cm2 photocurrent density at 2.06 V vs RHE and resulting in the enhanced photoelectrochemical (PEC) activity and photostability for water oxidation. The LaCo­(OH) x -electrodeposited Au/Sb-TiO2 NR sample exhibits a hydrogen production rate of 21.4 μmol·cm–2·h–1 at the counter electrode under illumination. This work demonstrates a strategic design of a TiO2-based photoanode integrating doping with plasmonic nanostructures and cocatalysts for solar fuel production through water splitting.

The poor visible light absorption, defect-mediated charge carrier recombination, slow water oxidation kinetics, and charge transportation limit the performance of TiO2 photoelectrodes for water oxidation. In order to tackle these issues, here a one-dimensional photoanode is designed by electrodepositing a p-ZnCo2O4 nanolayer on n-TiO2 nanotubes surface and finally electrochemically coupling the TiO2/ZnCo2O4 surface with an ultrathin layer of the cobalt phosphate (Co-Pi) catalyst nanoparticles. These typical TiO2/ZnCo2O4@Co-Pi nanoheterostructures exhibit a remarkably enhanced visible light driven photoelectrochemical property with applied bias photoconversion efficiency (ABPE) ∼ 3% at 0.2 V vs NHE. The TiO2/ZnCo2O4@Co-Pi nanoheterostructures also show enhanced visible light absorption with large photocurrent density ∼440% higher than that of the TiO2 nanotubes electrode at 1.2 V vs Ag/AgCl and significantly low onset potential for water oxidation. Studies on the transient photocurrent and flat-band potential demonstrate the remarkable improvement in the photogenerated charge carrier separation or reduced recombination because of the favorable band alignment at the heterointerface. The Co-Pi catalyst further boosts the water oxidation reaction by reducing electron–hole pair recombination through the suppression of the surface trap states. Moreover, Co-Pi also serves as a hole-acceptor layer, improving the charge-transfer kinetics for an enhanced photoelectrochemical performance.