Solvothermal synthesis of g-C3N4 and ZnO nanoparticles on TiO2 nanotube as photoanode in DSSC

In this research, the dye-sensitized solar cells (DSSCs) were fabricated by using g-C₃N₄ and ZnO modified TiO₂nanotube (TNT) arrays as photoanodes. The TNT arrays were synthesized by the anodizing method. G-C₃N₄ and ZnO modified TNTs were synthesized via a solvothermal method in which ethylene glycol served as a solvent. The short circuit current (I_SC) and open-circuit voltage (V_OC) of DSSCs based on ZnO + g-C₃N₄modified TNTs photoanode considerably increased from 9.25 mA/cm⁻²to 14.68 mA/cm⁻², and from 0.707 mV to 0.695 mV, respectively, resulting in a135% increase in the efficiency compared with the pure TNT arrays photoanode. However, the DSSC fabricated with g-C₃N₄ TNT did not show much improvement in the conversion efficiency compared with the pure TNT arrays photoanode, implying more effective processes of the carrier production and transport between ZnO, g-C₃N₄ and TNTs. Also, the electrochemical impedance spectroscopy (EIS) and open-circuit voltage decay (OCVD) analyses showed that ZnO + g-C₃N₄ can promote the electron collecting rate, suppress he electron recombination and extend the electron lifetime.     

水热法制备TiO2纳米晶胶体及其在DSSC电池中的应用

采用钛酸异丙酯作前驱体,利用水热法制备了TiO2纳米溶胶溶液。以此制备了染料敏化太阳能电池的光阳极并组装电池。对产物采用激光粒度仪（HPPS）、X射线衍射（XRD）、扫描电镜（SEM）等进行表征。XRD显示了TiO2纳米颗粒为纯锐钛矿结构,SEM观察薄膜电极呈多孔结构。表征电池的光电化学性能,所制备的TiO2纳米晶薄膜的光电转换效率达到3．03％。     

Carbon membrane bridged ZnSe and TiO2 nanotube arrays: Fabrication and promising application in photoelectrochemical water splitting

In this work, a cascade structure among ZnSe, carbon membrane and TiO₂ NTAs was constructed precisely. This carbon membrane bridged ZnSe and TiO₂ composite exhibits excellent H₂ evolution activity, the H₂ evolution rate of ZnSe/C/TiO₂ NTAs (866.76 μmol/cm²) is about 6.95 times higher than that of pure TiO₂ NTAs (124.64 μmol/cm²) after 200 min irradiation. The introduction of carbon membrane can greatly facilitate the electron transfer from ZnSe to TiO₂, ZnSe/C/TiO₂ ternary composite exhibits the highest transient photocurrent density (1.05 mA/cm²) and the lowest impedance (677.6 Ω) among all the samples. Besides, the contact between TiO₂ and electrolyte is improved after introducing carbon membrane, therefore C/TiO₂ NTAs shows more positive flat band potential of (1.86 V) compared with TiO₂ NTAs (0.50 V). It is also found that pure carbon powder can achieve H₂ production under visible light irradiation, its sensitization effect can further improve photocurrent density of the composite under 500 nm light radiation, the electrons produced in carbon film can inject into TiO₂, and holes from TiO₂ can quickly transfer to carbon film, leading to excellent H₂ evolution efficiency.     

Synthesis of TiO2 nanoparticles at low hydrothermal temperature and its performance for DSSC sensitized using natural dye extracted from Melastoma malabathricum L. seeds

Efficiency of a dye‐sensitized solar cell (DSSC) device depends on its semiconductor layer and the sensitizing dye to absorb the light. This work seeks to obtain the best solvent for the natural dye extraction from Melastoma malabathricum L. seeds. The extracted dye is used as sensitizer on TiO₂ nanoparticles produced via hydrothermal but optimized at relatively low temperature. Infrared characterization of the extracted dyes showed differences in functional groups using different solvents, whereas ultraviolet visible examination of the dyes showed differences in intensity along the spectrum ranges of 600 to 400 nm with maximum absorption around 550 to 500 nm. Thermal analysis revealed that the natural dye should be stable around room temperature. Analysis on the synthesized TiO₂ nanoparticles showed that the average crystallite size reported in the previous work is consistent with crystallite sizes observed in the transmission electron microscope images. Photoactivity examination showed that the DSSC sensitized using natural dye extracted with ethanol containing 20% distilled water on TiO₂ synthesized at 150°C has an efficiency of 5.7%, whereas the one on commercial TiO₂ P25 Degussa has an efficiency of 3.0%. The DSSC device sensitized using commercial dye on TiO₂ synthesized at 150°C has an efficiency of 4.4%, whereas the one on TiO₂ P25 Degussa has an efficiency of 4.0%. This result is promising for further development of the DSSC device using TiO₂ nanoparticles synthesized at low hydrothermal temperature and sensitized with the natural dye.     

Synthesis and characterisation of Cu - Doped TiO2 nanoparticles for DSSC and photocatalytic applications

In the present work, copper-doped TiO₂ nanoparticles were synthesized via sol-gel technique with different molar concentration of copper precursor (0.025 M-CT-1, 0.05 M-CT-2, 0.1 M-CT-3 and 0.2 M-CT-4). The effect of copper doping on the structural, morphological, compositional, optical and electrical properties of TiO₂ was systematically analyzed for its better suitability as photoanode in Dye-Sensitized Solar Cells (DSSC) and photocatalyst in dye degradation. From structural analysis, all the synthesized samples show anatase phase with a tetragonal crystal system. The broadening and shift in the peaks of the synthesized samples show the successful incorporation of Cu ions into TiO₂ lattices. All the synthesized samples exhibit spherical shape morphology with slight agglomeration. EDS analysis exhibit the purity of the synthesized nanoparticles with the presence of only Ti, O, and Cu. UV-DRS analysis reveals the decrease in reflectance of the TiO₂ with increasing the Cu concentration. The bandgap values of the Cu–TiO₂ decreased from 2.66 to 2.40 eV with the increase of copper concentration. From PL analysis, the peak observed at 380.20, 469.56 and 535.24 nm corresponds to the band-band PL emission, free excitons, and oxygen vacancies, respectively. Further, we have fabricated DSSC using Cu-doped TiO₂ as a photoanode without treatment of any scattering layer and we have obtained the maximum efficiency of 3.90% for 0.1 M Cu–TiO₂ (CT-3). Similarly, the maximum degradation efficiency of 97.12% was obtained against rhodamine-B dye with the highest regression coefficient (R² = 0.9957) and lesser half-life degradation time (t_1/2 = 47.1428 min) for CT-3. This higher efficiency was not reported elsewhere using Cu-dopant concentrations. From these observations, it was concluded that 0.1 M concentration of Cu was the optimum dopant concentration with TiO₂ which was suitable for DSSC and photocatalytic applications.     

Performance of TiO2 nanoparticles synthesized by microwave and solvothermal methods as photoanode in dye-sensitized solar cells (DSSC)

In this work, a direct comparison of the properties of the TiO₂ nanoparticles prepared by microwave and solvothermal methods were carried out and its performance as photoanode in dye-sensitized solar cells (DSSC) was analyzed. Though previously some works exist on the preparation of TiO₂ nanoparticles by solvothermal or microwave methods, they could not be compared directly as the experiment conditions such as choice of solvent, precursors and reaction temperatures were not virtually same. Herein, TiO₂ nanoparticles were synthesized by microwave and solvothermal methods using the same initial precursors and properties of the prepared nanoparticles were compared. From the X-ray diffraction pattern and Raman analysis, the prepared nanoparticles in both the cases were found to be of anatase phase. Optical properties and its carrier lifetime were studied using UV–Vis absorption, photoluminescence (PL) analysis and PL lifetime studies, respectively. Further, its morphology analyzed using scanning electron microscope (SEM) and transmission electron microscope (TEM) images, and SAED (selected area electron diffraction) patterns reveals the polycrystalline nature of the prepared nanoparticles. The surface area and the pore size distribution were studied using BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda) analysis, which revealed its mesoporous nature and uniform pore distribution. The chemical states of the prepared nanoparticles were further characterized using X-ray photoelectron spectroscopy. The DSSC was fabricated using the prepared TiO₂ nanoparticles as photoanodes. Further, the power conversion efficiency and the electron transport properties were analyzed.     

Preparations of different ZnO nanostructures on TiO2 nanotube via electrochemical method and its application in hydrogen production

In the present study, zinc oxide doped titanium dioxide nanotubes (ZnO/TiO₂-NTs) were designed by using electrochemical deposition method. Titanium dioxide nanotubes (TiO₂-NTs) were fabricated by anodization method. Nanostructured ZnO was deposited with various deposition times on TiO₂-NTs. The morphological, structural, optoelectronic properties of ZnO/TiO₂-NTs were examined in detail. The morphological and structural characterization of obtained electrodes was investigated with help of field emission scanning electron microscopy and X-ray diffraction. ZnO nanostructures with three different morphologies were obtained from nanotowers to nanoleafs. XRD results depicted that ZnO nanostructures have the high crystallinity with hexagonal wurtzite structure. The measurements of the contact angle were utilized to determine the wetting behavior of the obtained surface of materials. Electrochemical impedance spectroscopy measurement was used in 1 M KOH to investigate electrocatalytic behavior of the obtained materials towards hydrogen evolution reaction. Flat band potentials, as well as charge carrier densities, were determined by using Mott-Schottky analysis. The charge carrier densities were calculated as 1.06 × 10¹⁹ and 1.66 × 10²⁰ cm⁻³ for TiO₂-NTs and 30-ZnO/TiO₂-NTs, respectively. The energy consumption and energy efficiency were determined for hydrogen evolution on ZnO/TiO₂-NTs electrodes.     

Optimization and characterization of TiO2-based solar cell design using diverse plant pigments

The design of electrochemical solar cells (SCs), including those composed of biological pigments is an actively developing direction of obtaining alternative energy. SCs were studied under different temperatures, light intensities and spectral conditions. Furthermore, to understand processes occurring in the SCs, investigations characterizing the efficiency and stability with regard to environmental factors are also required. For this aim, novel instrumentation for the investigation of environmental effects on photocurrent generated by SCs has been designed and constructed. The system can be a model, which reflects conditions required for effective and stable functioning of the solar cells. Preliminary results are shown for two types of solar cells with two photosensitizers: thylakoid membrane preparations and anthocyanin-enriched raspberry extracts. It was shown that electrogenic activity decreased by a half at 40 °C and returned back to the initial value under gradual cooling. Maximum current obtained from the thylakoid-based SC was 0.46 μA, while maximum current generated by the anthocyanin-based SC was 1.75 μA. The goal of this investigation is to find new ways to increase efficiency and stability of bio-based SCs. In future, this measuring system can be used for investigation of solar cells based on long-wave forms of chlorophylls (Chls d and f) and components of the photosynthetic apparatus comprising these chlorophylls.     

Fabrication and characterization of Ni modified TiO2 electrode as anode material for direct methanol fuel cell

Highly ordered porous titanium dioxide nanotube (TiO₂-NT) surfaces were prepared with anodization method to obtain a larger specific surface area that plays a very important role in methanol oxidation. In this regard, optimum conditions such as various anodization voltages and times were determined. The largest surface area of TiO₂ occurred at anodization voltage and time of 60 V and 2 h, respectively. After obtaining the high specific surface area, very small amounts of Nickel (Ni) nanoparticles were deposited on TiO₂-NT surface and their behaviors of methanol electro-oxidation were investigated by Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) methods. Characterizations of the TiO₂-NT and Ni modified electrodes are exerted by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The average tube length and diameter are 36.32 μm and 93.6 nm according to SEM images. XRD results indicated the tetragonal structured anatase of TiO₂ and Ni (111) and (200). While methanol oxidation peak does not observe on TiO₂-NT surface, behaviors of methanol oxidation depend on the Ni content on TiO₂-NT surface. Oxidation response increases by the increasing amount of Ni nano-particles in the deposits. High surface coverage (Γ) with 3.87 × 10⁻⁹ mol cm⁻² and very low activation energy (E_a) with 11.0 kJ/mol are measured on Ni modified TiO₂-NT with the highest Ni content. Charge transfer resistance either reduced or provided long stability and durability with the deposition of Ni on TiO₂-NT. This may associate that TiO₂-NTs with the large surface areas may play a significant role in the methanol oxidation efficiency. Modification of TiO₂-NT surface with Ni particles is an effective plan for high-performance electrocatalysis. Besides, the strong electronic interaction between Ni and TiO₂ may facilitate the adsorption of methanol through the bi-functional mechanism on the electrode surface.     

Transformation of TiO2 nanoparticles to nanotubes by simple solvothermal route and its performance as dye-sensitized solar cell (DSSC) photoanode

Titania nanotubes were synthesized by simple solvothermal method using quasi crystalline TiO₂ nanoparticles as the starting material without using autoclave. In the presence of concentrated NaOH (sodium hydroxide), TiO₂ nanoparticles were transformed into nanotubes. The complete transformation of nanoparticles to nanotubes was witnessed using Field Emission Scanning Electron Microscopy (FESEM) and High-resolution transmission electron microscopy (HRTEM) images and further, the materials were found to be polycrystalline in nature. From the X-ray diffraction pattern and Raman analysis, the TiO₂ nanoparticles were found to exhibit the anatase phase and the nanotubes were found to exhibit the titanate phase. The surface area and pore size distribution were analysed using BET (Brunauer–Emmett–Teller) and BJH (Barrett–Joyner–Halenda) analysis. The surface area of the nanotubes was found to be higher compared to the initial nanoparticles and bimodal type pore distributions were observed from the BJH study. The bandgap and defect emissions of the nanotubes and nanoparticles were analysed using UV–Vis absorption and photoluminescence (PL) analysis. The chemical states of the prepared nanoparticles were further characterized using X-ray photoelectron spectroscopy. The Dye-sensitized solar cells (DSSC) were fabricated using the prepared TiO₂ nanostructures as photoanodes and their power conversion efficiencies were analysed.     

A review on highly ordered,vertically oriented TiO2 nanotube arrays: Fabrication,material properties,and solar energy applications

We review the fabrication, properties, and solar energy applications of highly ordered TiO₂ nanotube arrays made by anodic oxidation of titanium in fluoride-based electrolytes. The material architecture has proven to be of great interest for use in water photoelectrolysis, photocatalysis, heterojunction solar cells, and gas sensing. We examine the ability to fabricate nanotube arrays of different shape (cylindrical, tapered), pore size, length, and wall thickness by varying anodization parameters including electrolyte concentration, pH, voltage, and bath temperature, with fabrication and crystallization variables discussed in reference to a nanotube array growth model. We review efforts to lower the band gap of the titania nanotubes by anionic doping. Measured optical properties are compared with computational electromagnetic simulations obtained using finite difference time domain (FDTD). The article concludes by examining various practical applications of the remarkable material architecture, including its use for water photoelectrolysis, and in heterojucntion dye-sensitized solar cells.     

Photocatalytic activity of TiO2 nanotube layers coated with Ag and Pt

Abstract

Abstract

Thin films of anatase TiO₂ nanotube arrays (TiO₂ NTs) were prepared in this study. Pt and Ag were coated on the TiO₂ NTs films, which intend to increase the photocatalytic activity under ultraviolet-visible (UV-vis) irradiation. The phase and structure of the films were investigated by X-ray diffraction and scanning electron microscopy. Photocatalytic activity was tested by UV-vis absorption spectroscopy and showed that UV-vis light absorption of the films was remarkably improved by coated Ag and Pt by 72% and 183% respectively. The photocatalytic activities of the films towards degraded methyl orange and HCHO were compared and were all found to follow the sequence Pt/TiO₂ NTs>Ag/TiO₂ NTs>TiO₂ NTs. It was also found that the kinetics of HCHO photocatalytic degradation by the films fits the first order reaction model better and has higher efficiency than that of the methyl orange photocatalytic degradation by the same films.     

Photoelectrochemical performance of TiO2 nanotube arrays modified with Ni2P Co-catalyst

Solar-driven water splitting to produce hydrogen is an important solution to the problem of energy shortage and environmental pollution. The photolysis of water to produce hydrogen requires highly efficient and stable photocatalysts, and the anode used as catalyst for oxygen evolution is a bottleneck in this process. In this paper, the a-TNTAs/Ni₂P composite photo-anode was constructed by electrodeposition to anchor the Ni₂P co-catalyst for oxygen evolution at the active site of TiO₂ nanotube arrays (TNTAs). The a-TNTAs/Ni₂P delivered excellent oxygen evolution at a photocurrent density of 1.058 mA cm^-2, an improvement of 2.78 times, 13.2 times, and 15.8 times over a-TNTAs, TNTAs/Ni₂P, and TNTAs photo-anodes, respectively. The Mott-Schottky curve showed that Ni₂P as co-catalyst for oxygen evolution accelerated the rates of separation and transfer of the photogenerated electrons. This research provides a simple and efficient method to promote the OER performance of optical semiconductors.     

TiO2 beads as photocatalyst and photoelectrode for dye‐sensitized solar cells synthesized by a microwave‐assisted hydrothermal method

In this study, a two‐step process involving a sol–gel and microwave‐assisted hydrothermal (MH) techniques has been used to synthesize a novel TiO₂ structure, namely, TiO₂ mesoporous beads. Various hydrothermal synthesis parameters were investigated to study their effects on the resulting beads. It was found that within the processing conditions used, the TiO₂ beads have similar sizes (~325 nm) and contain uniform‐sized anatase TiO₂ nanoparticles (<10 nm), which are single crystals. Crystalline TiO₂ beads are obtained in as short as 15 min at a low temperature of only 140 °C without any post‐process calcination. Less surface oxygen vacancies was obtained at a higher MH temperature. Compare to the commercial P‐25 TiO₂ powders and conventional hydrothermal synthesized TiO₂ beads, MH synthesized TiO₂ beads exhibit much higher values of specific surface areas, pore volumes, and porosities. The use of TiO₂ beads as photocatalyst and photoelectrode for dye‐sensitized solar cells has also been investigated. Copyright © 2015 John Wiley & Sons, Ltd.     

One-step synthesis LiMn2O4 cathode by a hydrothermal method

Spinel LiMn₂O₄ powders have been successfully synthesized by a hydrothermal method directly, which is no any pretreatment and following treatment in the process. The structure and morphology of the powders were studied in detail by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA). The data reveal that the products have well-defined stable spinel structure, and the particles show distinctive crystal faces with 50–300 nm in particle sizes. The electrochemical characteristics of the spinel materials are measured in the coin-type cells in a potential range of 3.2–4.35 V versus Li/Li⁺. The as-synthesized LiMn₂O₄ delivers reversible capacity of about 121 mAh g⁻¹ at a current density of 1/10 C. Cycled the cell to 40 cycles, the capacity remains at about 111 mAh g⁻¹ at 1/2 C.     

Fabrication of dye-sensitized solar cells by transplanting highly ordered TiO2 nanotube arrays

Highly ordered TiO₂ nanotube arrays fabricated by anodization are very attractive to dye-sensitized solar cells (DSCs) due to their superior charge percolation and slower charge recombination. However, the efficiency of TiO₂-nanotube-based DSCs is 6.89%, which is still lower than that of TiO₂-nanoparticle-based DSCs. We have suggested the transplanting the highly ordered TiO₂ nanotube arrays to FTO glass to improve the performance of TiO₂-nanotube-based DSCs. DSCs based on transplanted TiO₂ nanotube arrays and TiO₂ nanoparticles were fabricated by same process and materials to exclude the unexpected factors. In TiO₂ thickness of ca. 15 μm, the efficiency of 2.91% in front-side illuminated DSCs based on TiO₂ nanotube arrays was higher than those in back-side illuminated DSCs based on TiO₂ nanotube arrays and in front-side illuminated DSCs based on TiO₂ nanoparticle. Front-side illuminated DSCs based on TiO₂ nanotube arrays having various thicknesses were successfully fabricated. The efficiency in DSCs having 20.0 μm thick TiO₂ nanotube arrays was improved to 5.36% by TiCl₄ treatment.     

Preparation of TiO2 nanofibers,porous nanotubes,RGO/TiO2 composite by electrospinning and hydrothermal synthesis and their applications in improving the electrochemical hydrogen storage properties of Co2B material

Co₂B hydrogen storage material was prepared via a high temperature solid phase process. The TiO₂ nanofibers (TiO₂–NF) and TiO₂ porous nanotubes (TiO₂-NT) with different size, structure and morphology were fabricated by electrospinning and hydrothermal synthesis. In order to improve the conductivity, the reduced graphene oxide/TiO₂ nanotubes composite (RGO/TiO₂-NT) was synthesized by an alkaline hydrothermal process. The three-dimensional porous TiO₂ nanotubes were attached to the two-dimensional RGO and formed a uniform dispersion. For the purpose of improving the electrochemical performance of Co₂B, composites of Co₂B doped with TiO₂–NF, TiO₂-NT and RGO/TiO₂-NT were manufactured by ball milling. Ultimately, all the composite electrodes showed higher discharge capacities than ordinary Co₂B. Among them, Co₂B modified with RGO/TiO₂-NT exhibited the highest discharge capacity (691.4 mAh/g). TiO₂-NT with large specific surface area and unique tubular porous structure can offer sufficient electrochemical active sites to anchor hydrogen and improve the electrocatalytic activity of Co₂B, meanwhile, the RGO component in RGO/TiO₂-NT with excellent electrical conduction can further provide fast channels for charger transfer during the charging/discharging processes. Moreover, the corrosion resistance, HRD and kinetics performance of Co₂B were also enhanced after doping of TiO₂–NF, TiO₂-NT and RGO/TiO₂-NT.     

Efficient hydrogen evolution activity of 1T-MoS2/Si-doped TiO2 nanotube hybrids

Catalytic hydrogen evolution is promising process used for production of clean fuel hydrogen and attracting many attentions. In this work, the synthesis and hydrogen evolution catalytic activity of MoS₂/TiO₂ nanotubes and MoS₂/Si-doped TiO₂ NTs hybrids were studied. The MoS₂ in the hybrids exhibited 1T structure with high conductivity and catalytic activity for hydrogen evolution reaction. MoS₂ decoration provided high light absorbance for the hybrids and highly efficient interface-induced effect between the nanotubes and MoS₂. Thus, the hybrids showed photocatalytic and electrocatalytic activities remarkably greater than the nanotubes. Moreover, the Si-doping resulted in the increase in specific surface area and hydrophilicity and so further enhanced the catalytic activity.     

A new method to evaluate the feasibility of a dye in DSSC application

Search for better photo sensitizers has always been a challenge in the field of dye sensitized solar cell (DSSC). This paper suggests a new method to identify a good dye for DSSC through the evaluation of energy levels of dye–TiO₂ complex. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the complex are evaluated using cyclic voltammetry (CV) and spectroscopic technique. These energy levels have been used to predict the performance of the solar cell even without fabricating a cell. The authenticity of this method is also revalidated through the correlation of efficiency of practical cell. Copyright © 2017 John Wiley & Sons, Ltd.     

Preparation of spinel LiMn2O4 by supercritical hydrothermal method with heat-treatment

利用超临界水热结合后续煅烧处理的方法制备了锂离子电池正极材料LiMn₂O₄,并详细讨论了超临界水热反应过程中反应压力、反应温度和后续处理煅烧温度对LiMn₂O₄材料晶型、颗粒形貌和电化学性能的影响。实验结果表明,LiMn₂O₄材料在400 ℃、30 MPa下反应15 min,后续经过700 ℃煅烧3 h得到的样品具有结晶度良好、颗粒分布均匀等优点。LiMn₂O₄材料制备的扣式电池表现出优异的电化学性能,0.1 C倍率下初始放电比容量为125 mA·h/g;1 C下循环50周同样表现出良好的电化学性能。