Nb-doped TiO2 Research Articles

High efficient Perovskite solar cells base on Niobium Doped TiO2 as a Buffer Layer

Here, the effect of lightly Niobium doped TiO2 layer on the performance of perovskite solar cells has been studied by using solar cell capacitance simulator (SCAPS). N addition, the effects of Niobium concentration, buffer film thickness and operating temperature on the performance of the perovskite solar cell are investigated. For doping level of 3.0 mol% into the TiO2 layer, cell efficiency of 18.26% with Voc of 0.96 V, Jsc of 22.45 mA/ cm2 and FF of 84.25% has been achieved. Calculations show that thickness widening of Nb-doped TiO2 layer would decrease the efficiency and Voc of the cells. Increase in operating temperature from 300 k to 400 k would weaken the performance of the perovskite solar cell with both pure and Nb-doped TiO2 layers. However, the cell with Nb-doped TiO2 layer shows higher stability than the cell with pure TiO2 buffer at higher temperatures. The efficiency of the cell with pure and doped buffer layers decreased from 15.52% to 11.47% (with 26.09% reduction) and 18.26% to 14.07% (with 22.9% declination), respectively. Therefore, the cell with doped buffer layer shows better stability at higher operating temperatures

Optimum in the thermoelectric efficiency of nanostructured Nb-doped TiO2 ceramics: from polarons to Nb-Nb dimers.

Rutile is the most common and stable polymorph form of titanium oxide TiO2 at all temperatures. The doping of rutile TiO2 with a small amount of niobium is reknown for being responsible for a large increase of the electrical conductivity by several orders of magnitude, broadening its technological interest towards new emerging fields such as the thermoelectric conversion of waste heat. The electronic conduction has been found to be of a polaronic nature with strongly localized charges around the Ti3+ centers while, on the other side, the relatively high value of the thermal conductivity implies the existence of lattice heat carriers, i.e. phonons, with large mean free paths which makes the nanostructuration relevant for optimizing the thermoelectric efficiency. Here, the use of a high-pressure and high-temperature sintering technique has allowed to vary the grain size in rutile TiO2 pellets from 300 to 170 nm, leading to a significant reduction of the lattice thermal conductivity. The thermoelectric properties (electrical conductivity, Seebeck coefficient and thermal conductivity) of Nb-doped rutile nanostructured ceramics, namely NbxTi1-xO2 with x varying from 1 to 5%, are reported from room temperature to ∼900 K. With the incorporation of Nb, an optimum in the thermoelectric properties together with an anomaly on the tetragonal lattice constant c are observed for a concentration of ∼2.85%, which might be the fingerprint of the formation of short Nb dimers.

Surface chemistry and growth mechanism of highly oriented, single crystalline Nb-doped TiO2 nanorods

The effect of the Nb doping on morphological changes in TiO2 nanorods by hydrothermal growth and its enhanced carrier transport were investigated. The nanorod diameter, film thickness, nucleation density, and photocurrent are discussed.

Nb-doped TiO2 support with enhanced durability as a cathode for polymer electrolyte membrane fuel cells

Stability is one of the key requirements of electrocatalyst support materials for polymer electrolyte membrane fuel cells. To develop a highly stable Pt catalyst support material, in this work, we have synthesized Nb-doped TiO2 electrocatalyst supports. The amount of Nb dopant is measured using inductively coupled plasma mass spectrometry, while the characteristics of the as-prepared Nb-doped TiO2 supports are analyzed by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Durability experiments are conducted by high potential cycling using the as-prepared Pt/TiO2-Nbx materials; half-cell cyclic voltammetry and single-cell performance measurements reveal that Pt/TiO2-Nb4 shows superior durability and corrosion resistance with a degradation rate of only 20% while the performance of commercial Pt/C support decreased 55%.

Synthesis of Nb-doped TiO2films on rigid and flexible substrates at low temperature

In this work, an attempt has been made to compare the physical properties of conductive films of Nb-doped TiO2deposited on Kapton polyimide, glass and silicon substrates. Thin films were deposited by radio frequency sputtering at room temperature and subsequently characterized using X-ray diffraction, X-ray photoelectron spectroscopy, UV-VIS-NIR spectroscopy and Hall Effect measurement. Structurally, the films grown on the flexible substrate exhibit more strain and had inferior crystallinity (crystallite size [Formula: see text]13.8 nm) compared to the films deposited on glass and silicon substrates (crystallite size [Formula: see text]27 nm). The film on glass had a resistivity value around [Formula: see text] while the resistivity of the films grown on polyimide was found about five-fold higher. Furthermore, the films deposited on glass substrate showed optical transparency of [Formula: see text]80% in the visible range (400–750 nm). The inferior electrical transport properties of the films grown on polyimide were correlated with the poor crystallinity and cracks induced during the annealing process. Furthermore, various possible routes have been discussed to improve crystallinity and control cracks in the films.

Nb-doped TiO2 Thin Films Prepared through TiCl4 Treatment for Improvement of Their Carrier Transport Property

ABSTRACTNb-doped TiO2 thin-films were prepared on fluorine-doped tin oxide (FTO) coated glass directly with niobium ethoxide and TiCl4 in water under the acidic conditions with several concentrations of HCl at 70-90 °C for 45 minutes or 1 hour followed by rinsing with water and annealing at 100 °C for 1 hour. Thin films of 0-1% Nb-doped TiO2 with rutile phase on FTO were obtained, which were confirmed through X-ray diffraction analyses and measurements of energy dispersive X-ray spectroscopy (EDS). Scanning electron microscopy observations equipped with EDS revealed that higher growth temperature over 90 °C is required for doping of Nb. While higher concentration of HCl resulted in much amount of Nb-doping. Band gap of rutile TiO2 gradually reduced from 3.3 eV to 3.23 eV through Nb-doping from 0% to 1%, which were estimated from uv-vis absorption spectroscopic analyses. Hall effect measurements by taking van der Pauw method confirmed that 2.26 times increase of the carrier density and 1.78 times enhancement of the conductivity have been achieved in the case of 1% Nb-doping.

Synthesis and corrosion protection of Nb doped TiO2 nanopowders modified polyaniline coating on 316 stainless steel bipolar plates for proton-exchange membrane fuel cells

The Nb doped TiO2 nanopowders modified polyaniline (TNO-PANI) and polyaniline (PANI) coatings are electrodeposited galvanostatically on 316 stainless steel bipolar plates for proton-exchange membrane fuel cells in 0.5 M aniline and 1 M H2SO4 solution with and without Nb doped TiO2 (Nb-TiO2) nano-powders, respectively. Electrochemical measurements in 1 M H2SO4 solution indicate that the addition of Nb doped TiO2 (Nb-TiO2) powders can increase the corrosion potential and decrease the corrosion current density of the PANI coating. During the 20 days immersion, the TNO-PANI composite coating can protect the 316 stainless steel more effectively through its barrier effect and in-situ anodic passivation effect.

Effect of annealing temperature on structural and electrical properties of Al/Nb-doped TiO2 Schottky diodes on Pt–Si substrates

The Nb-doped TiO2 (NTO) thin films were deposited on Pt-coated Si substrates for fabrication of Al/NTO Schottky diodes using RF magnetron sputtering technique. The effects of annealing temperature on the microstructure, surface morphological and electrical properties are systematically investigated. X-ray diffraction pattern shows that the crystallinity of NTO thin films can be improved by adjusting the annealing temperature. The surface morphological analysis shows that the grain size and roughness can be affected by the annealing temperature. According to I–V characteristics, the ideal factor, barrier height and series resistance of Al/NTO Schottky diodes calculated by various methods are consistent well. The ideal factor and series resistance decrease with annealing temperature rising from 200 to 600 °C. When the NTO thin films are annealed at 600 °C, the Al/NTO Schottky diodes have good rectifying behaviors with an ideal factor of 4.97, a Schottky barrier height of 1.04 eV and a relatively low series resistance of 235 Ω. These results indicate that the prepared Al/NTO Schottky diodes have potential application prospects in rectifying devices.

Preparation of Nb-doped TiO2 nanopowder by liquid-feed spray pyrolysis followed by ammonia annealing for tunable visible-light absorption and inhibition of photocatalytic activity

Visible-light absorbing TiO2 with color tunability and negligible photocatalytic activity was developed by synthesizing Nb-doped TiO2 using liquid-feed flame spray pyrolysis (LF-FSP) followed by NH3 annealing. Nb-doped TiO2 nanopowders with selected Nb contents were synthesized by changing ratios of metalloorganic precursors. By using Ti and Nb precursors whose thermal decomposition behavior is very similar, the maximum Nb doping concentration was improved compared to Nb-doped TiO2 prepared by flame spray pyrolysis (FSP) in previous reports. As-synthesized Nb-doped TiO2 nanopowders were white regardless of the Nb content, while all became colored after NH3 annealing. In addition, the color of Nb-doped TiO2 after NH3 annealing varied from yellow to dark green depending on the Nb content. Light absorption characterization indicates that the color variation is attributable to the localized levels formed by interstitial N-doping and Nb-doping-induced Ti3+ formation resulting from reduction by H2, formed as a result of NH3 decomposition.

Titanium Oxide Nano-Particles as Supports of Cathode Catalysts for Polymer Electrolyte Fuel Cells

INTRODUCTION Development of carbon-free electro-conductive supports for oxygen reduction reaction (ORR) catalysts are required for a widespread of polymer electrolyte fuel cells (PEFCs) because carbon materials, which are used as a support in the present PEFCs, are easily oxidized at high potential [1]. Many conductive or semi-conductive oxides such as indium tin oxide (ITO) [2], TiOx [3], SnO2 [4] and so on have been studied as catalyst supports or as secondary supports to improve the performance of the cathodes of PEFCs. These metal oxides have shown promising effects on the catalytic activity for the ORR [5,6] and the durability [7,8] under the condition of PEFC cathode. Nb-doped TiO2 shows the high conductivity compared with pure TiO2, suggesting that Nb-doped TiO2 particles have great potential as carbon-free electro-conductive supports. EXPERIMENTAL Nb-doped TiO2 particles were prepared by hydrothermal method. First, titanium butoxide was mixed with niobium ethoxide with a desired Nb/Ti atomic ratio. Second, a deionized water of 30 mL was added to the mixture to obtain complex hydroxide. The precipitation and remained solution were moved into the reactor. Then, the reactor was heated at 180 oC, 20 h to proceed the hydrothermal reaction. Finally, the precipitate was obtained by filtration and dried under vacuum at 90 oC, 12 h and calcined at 380 oC, 3 h in air to remove the organic residue. The Nb-doped TiO2 particles was heated under pure hydrogen gas to further increase the conductivity. RESULTS Fig. 1 shows the XRD pattern of Nb-doped TiO2 prepared by hydrothermal treatment. According to the XRD pattern, the Nb-doped TiO2 was identified as the anatase phase. In addition, there were no niobium oxides peaks such as Nb2O5 or other niobium oxides, indicating that niobium was doped into TiO2 anatase successfully. In order to evaluate the durability of the Nb-doped TiO2, the accelerated durability tests (ADT) was done in 0.1 M HClO4 at 30 oC under N2 atmosphere in the potential range from 1.0 to 1.5 V vs. RHE with a scan rate of 500 mVs-1. After undergoing the 15000 cycles ADT, the mass loss of the support was less than 3%.

MPL/GDL-Supported Pt Electrocatalysts for PEFCs

Introduction Currently, Pt electrocatalysts supported on carbon black (Pt/C) are widely used in polymer electrolyte fuel cells (PEFCs). However, carbon corrosion can occur on the cathode side especially during start-stop cycles, leading to performance degradation of PEFCs (1). To solve this technological issue, we have developed SnO2 and TiO2 support materials dispersed on graphitized carbon materials acting as the conductive backbone, exhibiting high durability (2-4). Here in this study, we focus on non-carbon support such as Nb-doped TiO2 which is stable under both anode and cathode conditions. In addition, we prepared various electrocatalyst layers directly on the microporous layer (MPL) coated on the gas diffusion layer (GDL) to simplify membrane electrode assembly (MEA) structure and manufacturing processes. Non-carbon support was deposited on the MPL/GDL by using arc plasma deposition (APD), and Pt catalyst nanoparticles are then deposited on this porous substrate to prepare a “Pt/non-carbon support/MPL/GDL” structure, as schematically shown in Fig. 1. MEAs can be prepared just by heater-pressing this integrated structure with the polymer electrolyte membrane. Experimental By using APD, various non-carbon support materials were deposited on the MPL/GDL structure, and then Pt catalysts were deposited on it to prepare “Pt/non-carbon support/MPL/GDL” structures. Their microstructure was observed by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and transmission electron microscopy (TEM). Electrochemical measurements were performed with single cells. Their performance was measured and compared by varying preparation conditions such as voltage of APD or types of GDL used. Results and discussion Figure 2 shows a STEM image of the Pt/Ti(Nb)O2/MPL/GDL structure after 100 APD pulses for Ti(Nb)O2 support and 500 pulses for Pt catalyst by APD. Pt particles of a few nm in average diameter on the MPL/GDL were observed. Figure 3 shows I-V characteristics of MEAs with the Pt/Ti(Nb)O2/MPL/GDL structure, in which Pt was deposited on the MPL/GDL by 70, 100, and 150V of APD. I-V characteristics of an MEA with the standard Pt/C catalyst (Tanaka Kikinzoku, TEC10E20E) are also shown for comparison, with the common cathode Pt loading of 0.024 mgPt/cm2. For this considerably low Pt loading, higher cell performance was obtained in case Pt was deposited by 100V of APD. Further improvement in electrochemical performance is however needed to realize such catalyst-integrated MPL/GDL structures. Acknowledgment Financial support by the Center-of-Innovation program, JST Japan, is gratefully acknowledged.

Single-Crystalline Nb-Doped Rutile TiO2 Nanoparticles as Anode Materials for Na-Ion Batteries

Single-crystalline Nb-doped TiO2 particles were hydrothermally synthesized for Na-storage materials. Annealing in air changed the particle color from blue to white. The successful introduction of o...

Crystal-Plane Dependence of Nb-Doped Rutile TiO2 Single Crystals on Photoelectrochemical Water Splitting

The crystal-plane dependence of the photoelectrochemical (PEC) water-splitting property of rutile-structured Nb-doped TiO2 (TiO2:Nb) single-crystal substrates was investigated. Among the crystal planes, the (001) plane was a very promising surface for attaining good photocurrent. Under 1 sun illumination at 1.5 V vs. a reversible hydrogen electrode, the TiO2:Nb(001) single-crystal substrate showed the highest photocurrent (0.47 mA/cm2) among the investigated substrates. The doped Nb ions were segregated inward from the top surface, and the TiO2 ultrathin layer was formed at the surface of the crystal, resulting in the formation of a heterointerface between the TiO2 and the TiO2:Nb. The enhancement of the PEC properties of the TiO2:Nb(001) single-crystal substrate originated from favorable atomic configurations for water molecule absorption and facilitation of transport of photoexcited electron–hole pairs in the depletion layer formed around the heterointerface of TiO2 thin layers on the base crystal.

Microstructure of Candidate Conductive Buffer and Superconducting Layers in a Coated Conductor Using {100} <001> Textured Cu Tape

To develop a low-cost coated conductor, a new wire architecture using conductive buffer layers and a metal tape with high conductivity has been proposed. Nb-doped SrTiO 3 (Nb-STO) was chosen as the conductive buffer layer. A high JC of 2.5 MA/cm 2 at 77 K under a self-magnetic field was demonstrated using a Nb-STO buffer layer and a cube-textured Cu and stainless-steel laminate tape as a metal tape with high conductivity. Considering the industrial production of wires, it is preferable to have many suitable materials. Thus, Nb-doped TiO 2 (Nb-TiO 2 ) was examined as a new conductive buffer layer. However, it was found to be difficult to grow a well biaxially aligned YBCO layer on a single Nb-TiO 2 buffer. Therefore, in this paper, buffer layers combining both Nb-STO and Nb-TiO 2 were prepared and an YBCO layer was deposited on this buffer layer by PLD with the purpose of realizing a superior conductivity characteristic to that of the single Nb-STO buffer layer. It was found that the combined buffer layer has potential use as a conductive buffer layer. However, the process must be optimized to increase the benefit of adding Nb-TiO 2 to Nb-STO.

Investigation of Reduced Graphene Oxide and a Nb-Doped TiO2 Nanotube Hybrid Structure To Improve the Gas-Sensing Response and Selectivity

The precise detection of flammable and explosive gases and vapors remains an important issue because of the increasing demand for renewable energy sources and safety requirements in industrial processes. Metal oxides (TiO2, SnO2, ZnO, etc.) are very attractive materials for the manufacturing of chemical gas sensors. However, their gas selectivity issues and further improvement in the sensing response remain a significant challenge. The incorporation of metal oxides with two-dimensional (2D) graphene oxide (GO) is considered to be a promising approach to obtaining hybrid structures with improved gas-sensing performance. Herein, we report the development of GO and niobium-doped titanium dioxide nanotube (NT) hybrid structures with a tunable selectivity and sensing response against hydrogen gas, achieved by properly controlling the degree of reduction and concentration of GO. The effects of these parameters are systematically studied in terms of the response amplitude and selectivity. It was found that, compared to undoped titanium dioxide nanotubes, the hybrid material with an optimal concentration of reduced-GO and the introduction of niobium shows an increase in hydrogen response of about an order of magnitude and a simultaneous reduction of the response to possible interfering compounds such as carbon monoxide and acetone, thus providing enhanced selectivity. This research may provide an efficient way to enhance the chemical sensing performance of metal oxide nanomaterials.

Titanium Oxide Nano-Particles as Supports of Cathode Catalysts for Polymer Electrolyte Fuel Cells

Because of low durability of carbon support which is widely used as a matrix of cathode catalyst in polymer electrolyte fuel cells (PEFCs), a novel carbon-free support with high durability is needed. The conductive oxide is one of the promising candidates due to its high durability. Titanium oxide nano-particles were already applied to an alternative material of carbon, with they have high chemical stability in the acid electrolyte and high electronic conductivity. In this study, we prepared a Nb-doped TiO2 by hydrothermal method and it was reduced in a pure hydrogen atmosphere to obtain Nb-TiOx support. Comparing with a commercial Pt/C catalyst, the Pt/Nb-TiOx catalyst behaved higher durability after 5000 cycles of start-stop accelerated durability test.

Understanding the Oxygen Reduction Reaction Activity and Oxidative Stability of Pt Supported on Nb-Doped TiO2.

Commercial fuel cell electrocatalyst degradation results from carbon electrocatalyst support oxidation at high operating potential transients. Guided by density functional theory (DFT) calculations, Nb-doped TiO2 (NTO) was synthesized, which exhibits a unique combination of high surface area, high electrical conductivity, and high porosity. This catalyst retained 78 % of its initial electrochemically active surface area compared with 57.6 % retained by Pt/C following the DOE/FCCJ protocol for accelerated stability test. Strong metal-support interactions, which were predicted by DFT calculations and confirmed experimentally by X-ray photoelectron spectroscopy and kinetics measurements, resulted in 21 % higher oxygen reduction reaction mass activity (at 0.9 V vs. reversible hydrogen electrode) on Pt/NTO compared with commercial Pt/C. The ex situ activity and durability of Pt/NTO translated to a fuel cell. The rise in electrode ohmic resistance and non-electrode concentration overpotential indicate that improving the conductivity of NTO and optimizing the catalyst ink formulation are critical next steps in the development of Pt/NTO-catalyzed proton exchange membrane fuel cells.

Ionic liquid–assisted hydrothermal synthesis of Nb/TiO2 nanocomposites for efficient photocatalytic hydrogen production and photodecolorization of Rhodamine B under UV-visible and visible light illuminations

In this work, we reported synthesis of Nb/TiO2 nanoparticles (NPs) at 140°C in one day using an ionic liquid (IL)–assisted hydrothermal method using 1-butyl-2,3-dimethylimidazolium tetrafluoroborate as the IL and titanium (IV) isopropoxide and Niobium (V) Nitrate as precursors. Physicochemical properties of the obtained photocatalysts were investigated via thorough characterizations. The framework substitution of Nb in TiO2 NPs was established by X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area, electron paramagnetic resonance, and energy dispersive X-ray spectroscopy techniques. XRD and transmission electron microscopy image results confirmed the anatase phase and nanocrystalline nature of Nb/TiO2. The optical properties revealed an extended tailing of the absorption edge toward the visible region upon Nb heterojunction. The concentration of Nb in the TiO2 matrix has been fine-tuned to improve the hydrogen production and photodecolorization of Rhodamine B dye. The synergy between the Nb and TiO2 has an optimum for concentration of 0.3 wt% Nb-doped TiO2. The optimized product has produced promising hydrogen evolution of 1146 μmol g−1 under illumination with a visible light source in a water/ethanol system. The optimized product that has shown promising photocatalytic detoxification ability of the material toward Rhodamine B dye was explored. Nb/TiO2 NPs was extracted after 1st use, then washed twice, and was dried at 80°C for 2 h. The dried powder was again used to reuse as a catalyst to degrade the dye and photocatalytic hydrogen generation for almost 6 cycles, and from the recycle and reusability studies, it was clear that the prepared 0.3 wt% Nb/TiO2 photocatalyst showed good photostability.

The Effect of Nb-doped TiO2 Coating for Improving Stability of NiCrAl Alloy Foam

Nb-doped TiO2(NTO) coated NiCrAl alloy foam for hydrogen production is prepared using ultrasonic spray pyrolysis deposition(USPD) method. To optimize the size and distribution of NTO particles based on good physical and chemical stability, we synthesize particles by adjusting the weight ratio of the Nb precursor solution(5 wt%, 10 wt% and 15 wt%). The morphological, chemical bonding, and structural properties of the NTO coated NiCrAl alloy foam are investigated by X-ray diffraction(XRD), X-ray photo-electron spectroscopy(XPS), and Field-Emission Scanning Electron Microscopy(FESEM). As a result, the samples of controlled Nb weight ratio exhibit a common diffraction pattern at ~25.3°, corresponding to the(101) plane, and have chemical bonding(O-Nb=O) at 534 eV. The NTO particles with the optimum weight ratio of N (10 wt%) show a uniform distribution with a size of ~18.2-21.0 nm. In addition, they exhibit the highest corrosion resistance even in the electrochemical stability estimation. As a result, the introduction of NTO coated NiCrAl alloy foam by USPD improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the foam and the electrolyte. Thus, the optimized NTO coating can be proposed for excellent protection of NiCrAl alloy foam for hydrocarbon-based steam methane reforming(SMR).

Tantalum-Doped Titanium Oxide with Rutile Structure as a Novel Anode Material for Sodium-Ion Battery

We hydrothermally synthesized various-element-doped rutile TiO2 for Na-ion battery anodes. Sn- and In-doped TiO2 electrodes showed poor performances. In contrast, Ta- and Nb-doped TiO2 electrodes exhibited larger discharge capacities, which is attributed to an expanded diffusion path and improved electronic conductivity. Among them, the Ta-doped one delivered excellent cycling performance and better rate capability. A first-principles calculation revealed that Ta doping reduced electron charge density in rutile’s Na+-diffusion path because Ta5+ has larger effective nuclear charge to attract strongly outermost electron. Therefore, Na+ was not bound by electron to easily diffuse in TiO2 particle, which leading to the enhanced capacity.