Μm Thick TiO2 Research Articles

Increasing the wear resistance of hip prostheses components using micro-nanostructured thin layers

Evaluation of micro-nanostructured thin layers applicability for increasing the lifetime of rehabilitation systems, mainly hip prostheses, is the aim of the present research. This because, the final objective of the complete project is to improve the quality of human prostheses using micro-nanostructured thin layers. In order to realize these researches, 0.5, 1, and 1.5 µm thick thin layers of TiN and TiO2, were deposited on substrates made of materials currently used for hip prostheses – M30NW steel and CoCr – using physical deposition methods, respectively Cathodic Arc (CA), Direct Current (DC) sputtering and High-Power Impulse Magnetron Sputtering (HiPIMS). After tribological and nanoindentation tests, the 1.5 μm thick TiN and TiO2 thin layers deposited on the steel and CoCr substrates using the DC sputtering method presented superior mechanical properties. Functional characterization of a total hip prosthesis, that have had components coated with these thin layers presented an increased resistance to fatigue wear. After comparative analysis, the main conclusion of the realized researches was that TiN layers with a thickness of 1.5 μm have an increased resistance to fatigue wear in comparison with TiO2 layers, when both are deposited by DC sputtering on M30NW steel and CoCr substrates. It was observed that 1.5 μm thick TiN layers ensures a prolongation by 15% of the lifetime of femoral heads compared to those uncoated.

Farklı Kalınlıklarda Üretilen TiO2 İnce Filmlerinin Boya Duyarlı Güneş Pili Performansına Etkisi

Dye-sensitized solar cells (DSSC) are known as 3rd generation solar cells. One of the most important parameters affecting the performance of DSSCs is the thin film thickness that forms the photoanode layer. In this study, we examined how 38, 60 and 76 µm thick TiO2 thin films change dye-sensitized solar cell performance. The highest efficiency (4.73%) was seen in the solar cell with 38 µm thin film thickness. In addition, the mineralogical and morphological analyses of the produced TiO2 nanopowders were performed with X-ray diffraction (XRD) and Scanning electron microscopy (SEM). XRD analyses showed that TiO2 was in the anatase crystal phase. SEM photographs confirmed the formation of microspheres in close contact with each other.

Enhancing the photocatalytic properties of doped TiO2 nanowires grown by seed-assisted thermal oxidation

In the present paper, an investigation of the structural, optical, and photo-catalytical properties of TiO2 nanowires (NWs) was conducted. The NWs were synthesized on a Si substrate by thermal oxidation of a thick (4 µm) Ti film covered by a thin (∼ 5 nm) Au film. The annealing process at 750 °C produced a 1.7 μm thick NWs TiO2 layer over a 3 μm thick TiO2 film. Characterization techniques show that TiO2 NWs are in rutile phase and have gold nanoparticles on top. Fe-doped TiO2 NWs were synthesized to increase photoactivity in the visible range. The doping was performed using an unusual strategy, that is, implanting Fe+ ions into the Ti layers before the growth of the TiO2 NWs. The defectiveness introduced by the ion implantation is avoided and precise control of the doping is achieved. The photocatalytic properties were studied by following the degradation of methylene blue. In order to increase the photo-degradation rate under UV light of undoped NWs, two different strategies have been followed: 1) deposition of Pt nanoparticles on the front or on the rear side of the samples, and 2) thermal annealing in a reductive environment. A three-fold activity enhancement is obtained and discussed. Photocatalytic activity in the visible range was also measured for the Fe-doped samples, showing good activity, which was further improved by using the same strategies implemented under UV irradiation.

ZnO hierarchical structures as sacrificial inclusions for enhanced performance under full sun and indoor light in bifacial dye sensitized solar cells

We have already demonstrated a facile strategy for improving light scattering in bifacial dye sensitized solar cells (DSSCs) through fugitive inclusions of ZnO micro-flowers leading to enhanced photovoltaic performance without adversely affecting the transparency (Sasidharan et al., 2020). In the present work, we were able to further ameliorate the light scattering properties by employing micron sized ZnO hierarchical structures (fibril and sheet like aggregates) as sacrificial inclusions. ZnO hierarchical structures being deposited over TiO2 active layer were selectively etched off, leaving behind imprints over the TiO2 layer, which act as scattering centers to enhance the photocurrent of DSSCs owing to the increased light absorption. The present strategy extends the possibility to improve the performance of DSSCs under both one sun (100 mW/cm2) as well as indoor/ambient light conditions without compromising transparency to larger extend. By employing this strategy on a 6 µm thick TiO2 photoanode and implementing it in a DSSC using N719 sensitizer and iodide/triiodie electrolyte, power conversion efficiency of 15.5% could be achieved under indoor illumination (1000 lx) from a compact fluorescent lamp. A detailed study of the charge transfer dynamics at various interfaces were carried out using a range of electrical and optical perturbation techniques.

Electrocatalytic activity of nanoparticulate TiO2 coated onto Ta-doped IrO2/Ti substrates: Effects of the TiO2 overlayer thickness

The trade-off between short-term efficiency and long-term durability in electrocatalysis has always been a tough choice. This study examines the electrocatalytic activity of double-layered oxide electrodes comprising a ~1 μm-thick Ta-IrO2 underlayer (coated on a Ti plate) and ~3.5 μm- and 5.5 μm-thick nanoparticulate TiO2 overlayers (TEC-1 and TEC-2, respectively) in NaClO4 and NaCl solutions as non-active and active supporting electrolytes, respectively. The physicochemical features of both TEC samples, including the crystalline pattern, elemental states, morphology, and electrochemically active surface area, are very similar, except for the TiO2 overlayer thickness. The TEC-1 electrode shows ~54% lower electrode/electrolyte interfacial charge-transfer resistances than those of TEC-2. In the bulk electrolysis for the decomposition of ammonia, the current density with the TEC-1 electrode is two-fold larger than that with TEC-2 under the same potential, due to the relatively low interfacial charge transfer with TEC-1. Electron spin resonance spectroscopic analysis reveals that OH and O2−/HOO are the primary reactive oxygen species responsible for the ammonia decomposition in NaClO4. In the NaCl electrolyte, reactive chlorine species (i.e., free chlorines) decompose ammonia with significantly faster kinetics compared to the case with the reactive oxygen species. Regardless of the electrolyte type, TEC-1 is always more active than TEC-2. However, prolonged bulk electrolysis tests over 300 h show that TEC-2 is more durable than TEC-1, maintaining its electrocatalytic activity and faradaic efficiency. The effect of the TiO2 overlayer thickness on the efficiency and durability of the electrodes is discussed in detail.

10 μm-thick MoO3-coated TiO2 nanotubes as a volume expansion regulated binder-free anode for lithium ion batteries

In this study, 10μm-thick TiO2 nanotube arrays (TNAs) coated with a MoO3 layer were prepared by electrochemical oxidation on titanium foil followed by successive cyclic voltammetric deposition, aiming at the fabrication of a thick binder-free anode with high capacity and good cycling stability for lithium ion batteries (LIBs). Through the evaluation of the electrochemical performance of electrodes prepared under various conditions, the electrode obtained at a precursor concentration of 5mM showed the best electrochemical performance, exhibiting high reversible capacity and enhanced cycling stability. With the structural advantage and intrinsic characteristics of TNAs, the large volume expansion of MoO3 is successfully accommodated, resulting in 97% retention at a rate of 5 C over 500 cycles and 91% retention even at a high rate of 25 C.

Design and Synthesis of Novel NIR Dyes with Phosphonic Acid Derivative Anchoring Groups Aiming Towards Stable Dye-Sensitized Solar Cells

Introduction: The solar energy is a promising solution to the sustainable energy supply and the relevant environmental concerns. Production of the traditional solar cells is expensive and this poses difficulty for the mass-level implementation of this kind of solar cells. So, there has been a lot of effort and interest to propose cost-effective and efficient solar cells, where dye-sensitized solar cells (DSSCs) are one of the potential candidates. DSSCs have emerged due to their good photo conversion efficiency (PCE) beyond 12 % in spite of photon harvesting window mainly in the visible region (400-700 nm). Dyes are the “Heart” of the solar cells and anchoring group present in it not only controls the overall PCE but also stability of photo anode, which ultimately controls the stability of DSSCs. Amongst various anchoring groups, phosphonic acid has been widely reported to give improved stability to the DSSCs as compared to their most commonly used carboxylic acid anchoring group counterparts. Owing to huge possibilities of molecular structures, quantum chemical (QC) calculations have emerged as one of the potential tools for the prediction of their energetics and spectral behavior. The goal of this research is to propose and develop of novel near infrared (NIR) dyes bearing phosphonic acid groups having the capability of improved stability as well as PCE focusing on Donor-Acceptor-Donor framework bearing squaraine dyes. Experimental: In this work, a series of unsymmetrical squaraine (SQ) dyes such as SQ-143, SQ-148, SQ-151, SQ-157, SQ-159 bearing different phosphonic acid anchoring groups with the molecular structure as shown in the Fig. 1 were logically designed and subjected to QC calculations using 6-311G/DFT/B3PW91 and PCM model using ethanol solvent to judge their suitability as sensitizer before the synthesis. Some of the suitable dyes having favorable energetics have been synthesized by multistep synthetic route. Structural characterization and confirmation have been done by 1H NMR and Fab Mass techniques followed by their Photophysical characterizations in 5 µM ethanolic solution for electronic absorption spectral behavior. Adsorption behavior of these dyes on the mesoporous TiO2 has been investigated by adsorbing the respective dyes from their 0.1 mM solution in ethanol. Photovoltaic characterization was also performed after fabricating DSSCs based on 10-12 µm thick mesoporous TiO2 with adsorbed dyes from their 0.2 mM solution as photo anode, catalytic amount of Pt coated conductive glass as counter electrode and I-/I3 - as redox electrolyte. Results and Discussion: After the successful synthesis and structural characterizations, SQ dyes under investigation were subjected to their photophysical characterizations. It can be clearly seen from the solution as well as solid-state absorption spectra shown in the Fig. 1 that due to extended p-conjugation in SQ-148 and SQ-157, exhibit bathochromically shifted absorption maxima as compared to their SQ-143 and SQ-151 dye counterparts. At the same time, in spite of having two free –OH groups in the dyes SQ-148 and SQ-143, former exhibited less extent of the dye aggregation. A swift dye adsorption in combination with reduced aggregated species are highly desired for commercial applications. Investigation pertaining to the dye adsorption behavior on the TiO2 reveals the trend of SQ-143>SQ-148>SQ-157>SQ-151 suggesting that less aggregation tends to the relatively higher rate of dye adsorption. This can be attributed to the swift diffusion of the dye molecules in the nanopores of the mesoporous TiO2 during the dye adsorption process. Stability of the adsorbed dyes on the mesoporous TiO2 is another important parameter responsible to impart the stability to the DSSCs. This was conducted by investigating the dye binding strength based on dye desorption studies. Apart from their synthesis and photophysical characterizations, dyes were also used as sensitizer to fabricate the DSSCs and implication of the nature anchoring groups on photon harvesting and overall PCE was also investigated. Results on the photovoltaic performance revealed that newly designed dye SQ-159 makes a good compromise imparting improved stability as well as PCE amongst the dyes under investigation. Acknowledgement: SSP would like to express sincere thanks to the Japan Society for Promotion of Science for the financial support by Grant-in-Aid for scientific research (C) [Grant No.-18K05300] to carry out the research Figure 1

Nanoscale Perovskite‐Sensitized Solar Cell Revisited: Dye‐Cell or Perovskite‐Cell?

A general and straightforward way of preparing few‐nanometer‐sized well‐separated MAPbIxBr3−x (MA=methylammonium) perovskite photosensitizers on the surface of an approximately 1 μm thick mesoporous TiO2 photoanode was suggested through a two‐step sequential deposition of low‐concentrated lead halides (0.10–0.30 m PbI2 or PbBr2) and methylammonium iodide/bromide (MAI/MABr). When those nanoscale MAPbIxBr3−x perovskites were incorporated as a photosensitizer in typical solid‐state dye‐sensitized solar cells (ss‐DSSCs), it could be verified clearly by the capacitance analysis that nano‐particulate MAPbI3 perovskites play the same role as that of a typical dye sensitizer (MK‐2 molecule) although their size, composition, and structure are different.

Transparent Platinum Counter Electrode Prepared by Polyol Reduction for Bifacial, Dye-Sensitized Solar Cells.

Pt catalytic nanoparticles on F-doped SnO2/glass substrates were prepared by polyol reduction below 200 °C. The polyol reduction resulted in better transparency of the counter electrode and high power-conversion efficiency (PCE) of the resultant dye-sensitized solar cells (DSSCs) compared to conventional thermal reduction. The PCEs of the DSSCs with 5 μm-thick TiO2 photoanodes were 6.55% and 5.01% under front and back illumination conditions, respectively. The back/front efficiency ratio is very promising for efficient bifacial DSSCs.

Blue-colored dyes featuring a diketopyrrolopyrrole spacer for translucent dye-sensitized solar cells

We report the facile synthesis of blue-colored dyes featuring a diketopyrrolopyrrole (DPP) spacer with dimethylamine and bis(4-dibuotxylphenyl)-phenyl-amine as donor residues (CSD-08 and CSD-09), their spectroscopic, electrochemical and colorific properties, and their application to translucent dye-sensitized solar cells (DSSCs). In the DSSCs fabricated with 5 μm-thick TiO2 photoanodes, CSD-08 and CSD-09 yield power-conversion-efficiencies of 3.43% and 3.62%, respectively, under simulated one sun illumination.

Metal-Free Organic Chromophores Featuring an Ethynyl-Thienothiophene Linker with an n-Hexyl Chain for Translucent Dye-Sensitized Solar Cells.

We report the simple synthesis of two organic chromophores featuring an ethynyl-thienothiophene linker with an n-hexyl chain (CSD-03 and CSD-04), their optical and electrochemical properties, and their use as photosensitizers in dye-sensitized solar cells (DSSCs). Our theoretical and experimental studies show that adding the second thienothiophene allows for narrowing the bandgap of the molecule and thus ensuring more light harvesting in the visible region. The efficiencies of both CSD-03 (5.46 ± 0.03%) and CSD-04 (5.20 ± 0.03%) are comparable to that of N719 (5.92 ± 0.01%) in translucent DSSCs fabricated with 5 μm-thick TiO2 photoanodes.

Laser irradiation synthesis and photocatalytic properties of TiO2-SiO2 hybrid thin films

In this study, we introduce a noble method for the fabrication of highly crystalline hybrid TiO2-SiO2 thin films using laser irradiation under ambient conditions. Upon light absorption at the interface between TiO2 sol-gel film and Si wafer during the laser irradiation process, the TiO2 gel film coated on the Si wafer is transformed into anatase TiO2 film, and the surface of underlying Si wafer is oxidized to a 20.63 μm thick SiO2 film composed of nano-spheres with average diameter of 24.12 nm. The photocatalytic characteristics of the TiO2-SiO2 hybrid film on methylene blue and its discriminated morphologies are compared with those of a TiO2 film fabricated by conventional thermal annealing. The TiO2-SiO2 hybrid film shows enhanced super-hydrophilicity and superior photocatalytic characteristics, while thermally annealed 0.16 μm thick TiO2 films exhibit hydrophobic and low photocatalytic properties. The laser assisting process is promising for the fabrication of highly crystalline TiO2-SiO2 hybrid film with super-hydrophilic and photocatalytic characteristics.

Laser Sintering of TiO2 Films for Flexible Dye-Sensitized Solar Cells

In this study, laser sintering of TiO2 nanoparticle films on plastic substrates was conducted in order to improve the incident photon-to-electron conversion efficiency (IPCE) of flexible dye-sensitized solar cells (DSCs). Lasers with different wavelengths (355 nm and 1064 nm) were used to process the TiO2 electrodes. With an optimized processing parameter combination, the 1064 nm laser can sinter 13 μm thick TiO2 films uniformly, but the uniform sintering cannot be achieved by the 355nm ultraviolet (UV) laser, since the films possess a high absorption ratio at 355 nm. The experimental results demonstrate that the near-infrared laser sintering can enhance the electrical connection between TiO2 nanoparticles without destroying the flexible plastic substrate, reduce the transmission impedance of electrons and increase the absorption rate of incident light. Furthermore, the charge collection efficiency, fill factor, and short-circuit current have all been improved to some extent, and the solar conversion efficiency increased from 4.6% to 5.7%, with an efficiency enhancement reaching 23.9%.

Impact of ionizing radiation doses on nanocrystalline TiO2 layer in DSSC’s photoanode film

Abstract In dye-sensitized solar cell (DSSC) properties of nanocrystalline oxide layer of photoanode may changes when exposed to ionization radiation environment which may leads to change the cell performance. In this study, 10 µm thick TiO2 (Degussa-P25) was deposited as a photoanode film on microscopic glass slide with the doctor-blade coating. The deposited film was subjected to different gamma (γ) radiation doses (0–20 kGy) to study the effect of ionizing radiation on morphological, structural, optical and compositional characteristics of the film. At 10 kGy dose, dislocation density (DD), strain, crystallites per unit surface area (CPSA), specific surface area (SSA) of anatase phase (1 0 1) of the film were decreased abruptly, conversely, crystal size and morphology index (MI) were increased at the same radiation dose slowly. UV-Vis-NIR spectroscopy results showed that in irradiated photoanode film the light transmittance and absorption depth were decreased, whereas, absorption and absorption coefficient were increased beyond the visible wavelength. The optical band gap of the irradiated film was increased by 12.5% when the gamma radiation dose increased from 0 kGy to 20 kGy. Thus, the irradiation induced changes in physio-chemical properties of nanocrystalline photoanode film may affect the DSSC cell performance.

Optimized reduction of graphite oxide for highly exfoliated silver nanoparticles anchored graphene sheets for dye sensitized solar cell applications

In the present work, we have synthesized graphene sheets by optimizing reduction of graphite oxide (GO) by hydrazine hydrate (N2H4·xH2O) reducing agent and anchored them with silver nanoparticles (Ag NPs). Morphological and spectroscopic studies confirmed the formation of highly exfoliated graphene sheets separated by Ag NPs with improved C/O ratio. The highly electrocatalytic and exfoliated network of graphene sheets/Ag nanocoatings uniformly adhered to FTO substrate has been utilized as platinum (Pt) free counter electrode (CE) in dye sensitized solar cells (DSSC). Fabricated DSSC with only 2.7 μm thick TiO2 photoanode exhibited photo conversion efficiency (η = 3.44%) and short circuit current density (Jsc = 7.03 mA cm−2) comparable to DSSC containing Pt-CE without any loss of open circuit voltage (Voc = 0.71 V) and fill factor (FF = 0.68).

11% efficiency solid-state dye-sensitized solar cells with copper(II/I) hole transport materials

Solid-state dye-sensitized solar cells currently suffer from issues such as inadequate nanopore filling, low conductivity and crystallization of hole-transport materials infiltrated in the mesoscopic TiO2 scaffolds, leading to low performances. Here we report a record 11% stable solid-state dye-sensitized solar cell under standard air mass 1.5 global using a hole-transport material composed of a blend of [Cu (4,4′,6,6′-tetramethyl-2,2′-bipyridine)2](bis(trifluoromethylsulfonyl)imide)2 and [Cu (4,4′,6,6′-tetramethyl-2,2′-bipyridine)2](bis(trifluoromethylsulfonyl)imide). The amorphous Cu(II/I) conductors that conduct holes by rapid hopping infiltrated in a 6.5 μm-thick mesoscopic TiO2 scaffold are crucial for achieving such high efficiency. Using time-resolved laser photolysis, we determine the time constants for electron injection from the photoexcited sensitizers Y123 into the TiO2 and regeneration of the Y123 by Cu(I) to be 25 ps and 3.2 μs, respectively. Our work will foster the development of low-cost solid-state photovoltaic based on transition metal complexes as hole conductors.

Improving the mass transport of copper-complex redox mediators in dye-sensitized solar cells by reducing the inter-electrode distance.

In this work, we study the influence of the distance between electrodes on the performance of dye-sensitized solar cells based on TiO2 using the organic dye LEG4 and a Cu(dmp)2 redox couple (dmp = dimethyl phenantroline). The solar cells are characterized by a large open circuit voltage of up to 1.03 V, and an efficiency of 8.2% has been achieved for a 5.3 μm thick TiO2 film using an epoxy resin-based sealed cell configuration with a minimal separation between electrodes. Transient short-circuit photocurrent measurements up to an intensity of 3 Suns show a significant decay in photocurrent after an initial peak current upon switching on the light for larger distance, resulting in a lower steady state photocurrent. For the smaller distance cells, the steady state photocurrent is linear with light intensity up to 2 Suns. Charge extraction measurements under short-circuit conditions show that reducing the distance between electrodes increases the electron collection efficiency and thus, the attainable photocurrent. Recombination losses increase with larger electrode separation distance and higher light intensity due to mass transport limitation of the redox mediator. Electrochemical impedance measurements confirm the effect of electrode distance on the redox couple transport, showing an additional loop with increasing distance. For the configuration where the TiO2 film is in very close proximity to the PEDOT-covered counter electrode, inductive behavior is observed at low frequencies. The inductive behavior disappears with the incorporation of an insulating porous ZrO2 layer. The equivalent circuit for the solar cell has been expanded to include this effect.

Long-term corrosion tests of Ti3SiC2 and Ti2AlC in oxygen containing LBE at temperatures up to 700 °C

Two MAX-phase materials, Ti3SiC and Ti2AlC, were tested at 550 °C, 650 °C and 700 °C up to 10 000 h in LBE (lead-bismuth-eutectic) containing of 10−6 and 10−8 wt% oxygen. It was found that secondary phases have a strong influence on corrosion effects. Ti3SiC showed a surface disintegration at 550°C/10−6 wt% oxygen after longer exposure, while a 4–7 μm thick TiO2 layer with Pb-Bi inclusions was detected on Ti2AlC. However, Ti3SiC is protected by a double layered oxide with an outer part of TiO2 and a mixed inner layer of SiO2 and TiO2 at the higher temperatures. Ti2AlC formed a TiO2 surface layer containing Al2O3. Some defects could be observed on the Ti3SiC surface in LBE containing 10−8 wt% oxygen at 550 °C and 650 °C. The secondary phases between the Ti3SiC grains showed strong oxidation at 700 °C. Due to the high Al solubility in LBE, Ti2AlC experienced strong dissolution attack after longer exposure times at 650 and 700 °C.

Anodic Ag/TiO2 nanotube array formation in NaOH/fluoride/ethylene glycol electrolyte as a photoanode for dye-sensitized solar cells

Self-organized, 23 μm-thick anodic TiO2 nanotube (TNT) arrays were formed in sodium hydroxide/fluoride/ethylene glycol (EG) electrolyte at 60 V for 60 min. The presence of sodium hydroxide (NaOH) in the fluoride/EG electrolyte accelerates the formation of the TiO2 nanotube arrays. The anodic film was then decorated with silver nanoparticles (Ag NPs) by the photodeposition process and used as a photoanode in a rear-side-illuminated dye-sensitized solar cell. The Ag NPs decorated TNT arrays, with the former having diameters of 10–30 nm formed from 0.2 M of Ag-precursor solution and exhibiting the highest photoconversion efficiency (η) of 3.7% and a short-circuit current density of 12.2 mA cm−2 compared to η = 3% and short-circuit current density of 9.1 mA cm−2 for a sample without Ag NPs. The increase in η is thought to be due to the surface plasmon resonance and excess electrons from the nanoparticles.

Fabrication and characterization of TiO2 nanotube arrays on Ti membrane enlarged by anodic oxidation

Abstract TiO2 nanotube arrays have attracted a great deal of attention as photocatalytic and photoelectrode materials due to their large surface area, low cost and easy fabrication. Highly ordered TiO2 nanotube arrays for the photoelectrodes in dye-sensitized solar cells have been fabricated from Ti foil. However, the TiO2 nanotube arrays from Ti foil were not effective for the photocatalytic materials, because it had only one plane for the photocatalytic reaction. We have fabricated the TiO2 nanotube arrays from macroporous Ti metal membrane by anodic oxidation and tried to scale it up. Various factors were controlled to obtain the optimal microstructure of the TiO2 nanotube arrays on the surface of macroporous Ti metallic membrane. Microstructure and phase were studied by SEM and XRD, respectively. Temperature was a very important factor in anodic oxidation of large surface area. 10 μm thick TiO2 nanotube arrays on Ti metallic membrane having a large surface area were fabricated and some factors for scaling-up were discussed.