Hydrogenated TiO2 Nanotube Arrays Research Articles

Activation of Osmium by the Surface Effects of Hydrogenated TiO2 Nanotube Arrays for Enhanced Hydrogen Evolution Reaction Performance.

Efficient cathodes for the hydrogen evolution reaction (HER) in acidic water electrolysis rely on the use of expensive platinum group metals (PGMs). However, to achieve economically viable operation, both the content of PGMs must be reduced and their intrinsically strong H adsorption mitigated. Herein, we show that the surface effects of hydrogenated TiO2 nanotube (TNT) arrays can make osmium, a so far less-explored PGM, a highly active HER electrocatalyst. These defect-rich TiO2 nanostructures provide an interactive scaffold for the galvanic deposition of Os particles with modulated adsorption properties. Through systematic investigations, we identify the synthesis conditions (OsCl3 concentration/temperature/reaction time) that yield a progressive improvement in Os deposition rate and mass loading, thereby decreasing the HER overpotential. At the same time, the Os particles deposited by this procedure remain mainly sub-nanometric and entirely cover the inner tube walls. An optimally balanced Os@TNT composite prepared at 3 mM/55 °C/30 min exhibits a record low overpotential (η) of 61 mV at a current density of 100 mA cm-2, a high mass activity of 20.8 A mgOs-1 at 80 mV, and a stable performance in an acidic medium. Density functional theory calculations indicate the existence of strong interactions between the hydrogenated TiO2 surface and small Os clusters, which may weaken the Os-H* binding strength and thus boost the intrinsic HER activity of Os centers. The results presented in this study offer new directions for the fabrication of cost-effective PGM-based catalysts and a better understanding of the synergistic electronic interactions at the PGM|TiO2 interface.

Enhancement and stabilization of isolated hydroxyl groups via the construction of coordinatively unsaturated sites on surface and subsurface of hydrogenated TiO2 nanotube arrays for photocatalytic complete mineralization of toluene

Hydroxyl groups on the photocatalyst surface provide adsorption sites and starting species to form hydroxyl radicals, and are thus considered as the most important species for the photocatalytic degradation of toluene. However, the complete mineralization of toluene over TiO2 photocatalysts is still challenging because of insufficient and unstable hydroxyl groups. Here, a hydrogenated TiO2 nanotube array mesh (H-TiO2) was fabricated. H-TiO2 capable of trapping light and serving high surface areas for active sites exhibited a toluene mineralization conversion of 100%. It was found that surface distortion and oxygen vacancies ensured the chemical dissociative adsorption of water to generate sufficient isolated hydroxyls on the surface and subsurface and benefited the regeneration in long-term operations. This study may provide an efficient TiO2-based photocatalyst for the removal of volatile organic compounds for air purification and give comprehensive understandings of the photocatalyst surface modification and theoretical guidance for designing hydroxyl-demanding photocatalysts.

Graphite carbon nitride coupled S-doped hydrogenated TiO2 nanotube arrays with improved photoelectrochemical performance

With the goal of improving the photoelectrochemical performances of titanium dioxide nanotube arrays (TiO2 NTAs), graphitic carbon nitride (g-C3N4)/S-doped hydrogenated TiO2 NTAs (g-C3N4/H-S-TiO2 NTAs) nanocomposite were fabricated by a feasible method. Photoelectrochemical tests showed that the photoelectric conversion efficiency of g-C3N4/H-S-TiO2 NTAs4 was up to 1.47%, which is about 5.44 times than that of TiO2 NTAs. The g-C3N4/H-S-TiO2 NTAs4 exhibited higher transient photocurrent density (1.64 mA/cm2) with good stability than TiO2 NTAs (0.29 mA/cm2). Furthermore, g-C3N4/H-S-TiO2 NTAs4 had a more negative open circuit potential and optimal photoelectric stability than other photoelectrodes. The possible photoelectric mechanism of g-C3N4/H-S-TiO2 NTAs was proposed. Photoelectrochemical characterizations demonstrated that hydrogenation, S-doping and the introduction of g-C3N4 have synergistic effects on the improvement of the photoelectrochemical performances of TiO2 NTAs.

Deposition of heterojunction of ZnO on hydrogenated TiO2 nanotube arrays by atomic layer deposition for enhanced photoelectrochemical water splitting

The heterojunction of ZnO was deposited on hydrogenated TiO2 nanotube arrays (H–TiO2) by atomic layer deposition (ALD) with various cycles. The ZnO was uniformly wrapped with the H–TiO2 samples and the thickness could be accurately controlled by the cycle numbers of ALD. The higher growth rate ~2.7 Å/cycle was obtained due to the surface amorphous layer, compared with the air-treated samples (A-TiO2), ~2.3 Å/cycle. When the cycle numbers increased to 200, nanowire arrays appeared. Interestingly, the absorption in the visible light region improved more significantly when ALD ZnO was employed for the H–TiO2 rather than the A-TiO2 samples. The H–TiO2 samples with 42 nm of ALD ZnO exhibited enhanced photoelectrochemical water splitting performances, compared with the A-TiO2 with 42 nm of ALD ZnO. This was related to the higher degree of the electronic band bending and improved photo-response in the UV and visible light region, resulting from the oxygen vacancies.

Effects of hydrogenated TiO2 nanotube arrays on protein adsorption and compatibility with osteoblast‐like cells

Effects of hydrogenated TiO2 nanotube arrays on protein adsorption and compatibility with osteoblast‐like cells

Effects of hydrogenated TiO2 nanotube arrays on protein adsorption and compatibility with osteoblast-like cells.

BackgroundModified titanium (Ti) substrates with titanium dioxide (TiO2) nanotubes have broad usage as implant surface treatments and as drug delivery systems.MethodsTo improve drug-loading capacity and accelerate bone integration with titanium, in this study, we hydrogenated anodized titanium dioxide nanotubes (TNTs) by a thermal treatment. Three groups were examined, namely: hydrogenated TNTs (H2-TNTs, test), unmodified TNTs (air-TNTs, control), and Ti substrates (Ti, control).ResultsOur results showed that oxygen vacancies were present in all the nanotubes. The quantity of -OH groups greatly increased after hydrogenation. Furthermore, the protein adsorption and loading capacity of the H2-TNTs were considerably enhanced as compared with the properties of the air-TNTs (P<0.05). Additionally, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to investigate the interactions of TNTs with proteins. During the protein-loading process, the H2-TNTs not only enabled rapid protein adsorption, but also decreased the rate of protein elution compared with that of the air-TNTs. We found that the H2-TNTs exhibited better biocompatibility than the air-TNT and Ti groups. Both cell adhesion activity and alkaline phosphatase activity were significantly improved toward MG-63 human osteoblast-like cells as compared with the control groups (P<0.05).ConclusionWe conclude that hydrogenated TNTs could greatly improve the loading capacity of bioactive molecules and MG-63 cell proliferation.

Deposition of Pd nanoparticles on the walls of cathodically hydrogenated TiO2 nanotube arrays via galvanic displacement: A novel route to produce exceptionally active and durable composite electrocatalysts for cost-effective hydrogen evolution

Noble metal-based materials are inevitable components of cathodes for the hydrogen evolution reaction (HER) in future water electrolysis systems for clean hydrogen fuel production. However, designing active and durable nanostructured catalysts with low amount of costly noble metals is still a great challenge. Herein, we show that Pd nanoparticles (NPs) can be synthesized on the highly developed surface of anodically grown TiO2 nanotube (TNT) arrays by applying a simple galvanic displacement strategy. In a two-step procedure, air-annealed TNT arrays are first cathodically protonated and then partially reoxidized by Pd(II) ions from a PdCl2 solution while providing a scaffold for the metallic Pd deposit. Structural and electrochemical characterizations reveal that the Pd content and the width of the Pd-populated zone of the tube walls are in correlation with the tube length. The Pd@TNT composites display remarkable HER activity in 1 M HClO4 delivering a current density of −10 mA cm−2 at an overpotential of −38 mV and a Tafel slope of only −13 mV/dec. More impressively, the mass and apparent activity of the Pd@TNTs is superior to even commercial Pt/C at higher current densities. The composites also show stable chronopotentiometric response over 25 h and a negligible HER overpotential increase after potential cycling tests. The exceptional performance of the Pd@TNT cathodes is assigned to the unique semiconducting properties of the three-dimensional, interactive TNT supporting structures that, on the one hand, provide abundance of Pd active sites with optimized atomic hydrogen binding energy for the cathodic HER, but on the other hand, prevent anodic degradation of the Pd catalyst.

Electrochemical hydrogenation of mixed-phase TiO2 nanotube arrays enables remarkably enhanced photoelectrochemical water splitting performance

We first report that photoelectrochemical (PEC) performance of electrochemically hydrogenated TiO2 nanotube arrays (TNTAs) as high-efficiency photoanodes for solar water splitting could be well tuned by designing and adjusting the phase structure and composition of TNTAs. Among various TNTAs annealed at different temperature ranging from 300 to 700 °C, well-crystallized single anatase (A) phase TNTAs-400 photoanode shows the best photoresponse properties and PEC performance due to the favorable crystallinity, grain size and tubular structures. After electrochemical hydrogenation (EH), anatase-rutile (A-R) mixed phase EH-TNTAs-600 photoanode exhibits the highest photoactivity and PEC performance for solar water splitting. Under simulated solar illumination, EH-TNTAs-600 achieves the best photoconversion efficiency of up to 1.52% and maximum H2 generation rate of 40.4 µmol h−1 cm−2, outstripping other EH-TNTAs photoanodes. Systematic studies reveal that the signigicantly enhanced PEC performance for A-R mixed phaes EH-TNTAs-600 photoanode could be attributed to the synergy of A-R mixed phases and intentionally introduced Ti3+ (oxygen vacancies) which enhances the photoactivity over both UV and visible-light regions, and boosts both charge separation and transfer efficiencies. These findings provide new insight and guidelines for the construction of highly efficient TiO2-based devices for the application of solar water splitting.

Fabrication and Electrochemical Properties of Hydrogenated TiO2 Nanotube Arrays

Nowadays, the requirement for energy and environment are a great challenge for our research society. Energy application and storage become the main issues. As a new energy-storage device with high power density, long cycle life and good application prospect, supercapacitors have attracted growing interest in recent years. The electrode materials for supercapacitors play an important role in the field of electrochemical capacitors. [1-5] In this paper, we report two easy and novel approaches to improve the conductivity of titanium dioxide nanotubes as electrochemical supercapacitor electrodes: first, increase the thickness of the TiO2 nanotube arrays (TNTAs), second, the synthesis of hydrogenated TiO2 NTAs. We fabricated TiO2 for 6 h,12 h and 16 h by anodization respectively(the thicknesses of each TNTAs are 4, 9, 40 micrometer when anodization time increases), and then hydrogenated each of them by electrochemical doping for 5s at the same condition. The H- TiO2 NTAs show great improvement of capacitance. For the 4 um H-TiO2, the hydrogenation improved the capacitance up to 7.83 mFcm-2 from CV calculation at a scan rate of 100mvs-1, which is 11 times higher than the capacitance obtained from TiO2 by air-annealed at the same condition. The largest capacitance we obtained is 25.14 mFcm-2 at a scan rate of 100 mvs-1 for 40 um H-TiO2.Hydrogenation produces reactive oxygen vacancies within the lattice by changing to which increase the host material by acting as a donor. The increase of the thickness provides longer tubular channel path and more active surface sites for ion diffusion and charge transfer. This work provide an suitable route for increasing the electrochemical capacitance of supercapacitors. Reference M. Salari, S.H. Aboutalebi, K. Konstantinov and H.K. Liu, Phys. Chem. Chem. Phys. 13, 5038–41 (2011).J. Wang, J. L. Polleux, J. Lim, B. J. Dunn, Phys. Chem., 111, 14925−14931 (2007).Z.K. Zheng, B.B. Huang, X.Y. Qin, X.Y. Zhang, Y. Dai and M.H. Whangbo, J. Mater. Chem. 21: 9079–87 (2011)X. Chen and S.S. Mao, Chem. Rev. 107, 2891–959(2007)X.H. Lu, G.M. Wang, T. Zhai, M.H. Yu, J.Y. Gan, Y.X. Tong and Y. Li Nano Lett., 12:1690–6 (2012) Figure 1

Design and synthesis of H-TiO2/MnO2 core–shell nanotube arrays with high capacitance and cycling stability for supercapacitors

Constructing hybrid electrodes with pseudocapacitive materials is an efficient strategy to realize high capacitance in supercapacitors for many high-energy applications ranging from portable electronics to consumer devices. However, as a typical pseudocapacitive electrode material, MnO2 usually suffers from poor electronic and ionic conductivities, which hinders the realization of their achievable pseudocapacitances. Comparing with conventional noble metals, cost-effective and robust hydrogenated TiO2 nanotube arrays are an excellent scaffold to support pseudocapacitive materials due to enhanced ion and electron delivery. Benefit from the structural and electronic advances, the well-designed H-TiO2/MnO2 NTAs supercapacitor exhibits specific capacitance as high as ~803 F g−1 at the scan rate of 5 mV s−1, reveals ~88% of the initial capacitance after 20000 cycles (only 0.0006% loss per cycle) and shows a high-rate capability. The well-performed designer could be a promising candidate for future power sources in a wide range of applications.

Investigation on IrO2 supported on hydrogenated TiO2 nanotube array as OER electro-catalyst for water electrolysis

IrO2 was electro-deposited on hydrogenated TiO2 nanotube arrays (TNTA) to form IrO2/H-TNTA for oxygen evolution reaction (OER). Hydrogenation by calcining in H2 atmosphere was conducted to improve the electric conductivity, which was owing to partially reduce of Ti4+ in TNTA. It was found that hydrogenated TiO2 can facilitate the electro-deposition of IrO2, and elevate the OER activity compared to that of non-calcined and air-calcined TNTA, which would be due to the improved conductivity of H-TNTA. IrO2/H-TNTA shows a five-fold higher activity than IrO2/air-TNTA with the same loading amount. The coverage of IrO2 on the surface of hydrogenated TNTA is crucial to the stability of catalyst and with the increased loading amount of IrO2, IrO2/H-TNTA shows much higher stability.

Hydrogenated TiO2 nanotube arrays with enhanced photoelectrochemical property for photocathodic protection under visible light

The hydrogenated TiO2 nanotube arrays (H-TiO2 NTs) were prepared by annealing anodized TiO2 NTs in hydrogen atmosphere, and then used as photoanodes for photocathodic protection of 304 stainless steel (304SS) under visible light and simulated solar light. The effects of hydrogenated temperature and time on the photoeletrochemical (PEC) performance of H-TiO2 NTs were studied in details. The PEC tests showed that the photocurrent density of H-TiO2 NTs was up to 270.8μA/cm2 and 1.20mA/cm2 under visible and simulated solar light with good stability, which is about 23 times and 4.5 times than that of pristine TiO2 NTs. Furthermore, photo-induced open circuit potential (OCP) and Tafel curves were measured to evaluate the photocathodic protection effect of H-TiO2 NTs. Salient visible light responses and sharp decline of the OCP made H-TiO2 NTs a promising photocathodic protection material and could be applied to protect the coupled 304 stainless steel from corrosion.

Preparation of Au/reduced graphene oxide/hydrogenated TiO2 nanotube arrays ternary composites for visible-light-driven photoelectrochemical water splitting

Visible-light-driven responsive Au/reduced graphene oxide/hydrogenated TiO2 nanotube arrays ternary composites (Au/RGO/H-TNTs) are constructed by electrophoretical deposition (EPD) of Au nanoparticles and graphene oxide sheets onto hydrogenated TiO2 nanotube arrays. Under visible light illumination (λ > 400 nm), the photoelectrochemical (PEC) current density and hydrogen evolution rate of Au/RGO/H-TNTs is 224 μA/cm2 and 45 μmol/cm2/h, which is much higher than that of pristine TNTs, H-TNTs and RGO/H-TNTs. The enhanced PEC activity of Au/RGO/H-TNTs ternary composites is attributed to (1) the outer layer of Au nanoparticles serves as photosensitizer for visible light harvesting due to the localized surface plasmon resonance effect, (2) the RGO middle layers act as excellent electron transporter which facilitating efficient separation of electron–hole pairs, and (3) the inner H-TNTs not only show certain visible light absorption due to its narrowed band gap, but also serve as electron collector and further transfer the electrons to counter electrode for hydrogen generation. The proposed PEC performance enhancement mechanism is further confirmed by electrochemical impedance spectroscopy and photoluminescence results.

Highly stable ternary tin–palladium–platinum catalysts supported on hydrogenated TiO2 nanotube arrays for fuel cells

Herein the Pt nanocrystals were synthesized by a high-pressure methanol reduction method onto the hydrogenated TiO2 nanotube arrays pre-treated by Sn/Pd. Then Sn/Pd/Pt ternary catalysts were fabricated by hydrogen treatment. The composite catalysts with a diameter of about 18 nm were located uniformly at the inner nanotubes. The novel catalyst combined with hydrogenated TiO2 nanotube arrays exhibits excellent electro-catalytic activity and high durability. The electrochemical performance of the catalysts after 18,000 potential cycles between 0 and 1.2 V vs. RHE could reach the maximum, and the electrochemical surface area of the catalyst at 18,000 cycles is about 136 m(2) g(-1)Pt+Pd, which is 1.3 folds than the commercial JM Pt/C (104 m(2) g(-1)Pt). Furthermore, there is little decrease in the electrochemical surface area for the catalyst after additional 7300 potential cycles (total 24,300 cycles). In a full cell testing, the fabricated novel electrode with extra-low Pt loading (0.043 mg cm(-2)) generated power as 1.21 kW g(-1)Pt when it is used as the cathode in a fuel cell.

Enhanced field emission from hydrogenated TiO2 nanotube arrays

The field emission (FE) properties of TiO2 nanotube arrays (TNAs) synthesized by anodization are dramatically improved after hydrogenation at various temperatures in a range of 400–550 °C. Compared with pristine TNAs, the turn-on fields of hydrogenated TNAs (H:TNAs) are significantly decreased from 18.23 to 1.75 V μm−1, and closely related to hydrogenation temperature. Importantly, the optimized sample of H:TNAs prepared at 550 °C shows excellent FE performances involving both a low turn-on field of 1.75 V μm−1, a high current density of 4.0 mA cm−2 at 4.50V μm−1, and a remarkable FE stability over 480 min. The substantially enhanced FE properties can be attributed to the combination of a typical tubular morphology, a reduced work function and the improved conductivity of H:TNAs.

Hydrogenated TiO2 Nanotube Arrays for Supercapacitors

We report a new and general strategy for improving the capacitive properties of TiO(2) materials for supercapacitors, involving the synthesis of hydrogenated TiO(2) nanotube arrays (NTAs). The hydrogenated TiO(2) (denoted as H-TiO(2)) were obtained by calcination of anodized TiO(2) NTAs in hydrogen atmosphere in a range of temperatures between 300 to 600 °C. The H-TiO(2) NTAs prepared at 400 °C yields the largest specific capacitance of 3.24 mF cm(-2) at a scan rate of 100 mV s(-1), which is 40 times higher than the capacitance obtained from air-annealed TiO(2) NTAs at the same conditions. Importantly, H-TiO(2) NTAs also show remarkable rate capability with 68% areal capacitance retained when the scan rate increase from 10 to 1000 mV s(-1), as well as outstanding long-term cycling stability with only 3.1% reduction of initial specific capacitance after 10,000 cycles. The prominent electrochemical capacitive properties of H-TiO(2) are attributed to the enhanced carrier density and increased density of hydroxyl group on TiO(2) surface, as a result of hydrogenation. Furthermore, we demonstrate that H-TiO(2) NTAs is a good scaffold to support MnO(2) nanoparticles. The capacitor electrodes made by electrochemical deposition of MnO(2) nanoparticles on H-TiO(2) NTAs achieve a remarkable specific capacitance of 912 F g(-1) at a scan rate of 10 mV s(-1) (based on the mass of MnO(2)). The ability to improve the capacitive properties of TiO(2) electrode materials should open up new opportunities for high-performance supercapacitors.