Oxide Nanotubes on Ti−Ru Alloys: Strongly Enhanced and Stable Photoelectrochemical Activity for Water Splitting (original) (raw)
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MRS Proceedings, 2011
The present work reports the synthesis of self-organized strontium-doped titania nanotubes arrays as a potential material for photocatalytic water splitting. Electrochemical anodization process was used to grow such material under various electrochemical conditions. The effect of dopant concentration on the morphology and photoelectrochemical properties of the material was investigated. The microstructure, morphology and composition of as-prepared and heat treated nanotubes were characterized by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The results showed that increasing the dopant concentration up to its solubility limit results in higher photoelectrochemical activity. A preliminary proof of concept of the photocatalytic activity of the fabricated material was estimated in terms of the use of such material as a photoanode for photoelectrochemical water splitting.
TiO2 Nanotubes for Photoelectrocatalytic Water Splitting: an Innovative Cell Design
2014
Photocatalytic properties of titanium dioxide make it an extremely useful material in the field of renewable energy. Here we describe an electrochemical cell with an innovative design in which the anode consists of an array of highly ordered TiO 2 nanotubes on porous nickel. Such a combination of materials renders this system able to work both in dark and under solar light exposure, thus opening new perspectives for industrial-scale applications.
Nature Publishing Group, 2018
Nowadays, increasing awareness of environment and fossil fuels protection stimulates intensive research on clean and renewable sources of energy. Production of hydrogen from water through solar-driven splitting reactions is one of the most promising approaches in the field of photoelectrochemistry (PEC). In this work we have fabricated well-aligned, highly-ordered, smooth-mouth TiO 2 nanotube arrays (TNAs) in a two-step anodization process of titanium foil, which were then used as photoelectrodes for PEC water splitting. It demonstrates for the first time correspondence between non-linear component characteristics of multiscale rough surface and crystalline structure of annealed TNAs measured at various fabrication stages and their photoelectrochemical response. The as-anodized TNAs with isotropic surface (deduced from AFM and SEM images) and largest figure of merit (according to their PEC performance) were annealed at 450 °C in air. Scale-invariant descriptors of the surface structure of the deposits involved: fractal dimension, corner frequency, roughness, size of nanostructures and their dominant habits. Moreover, X-ray diffraction data processed using the Rietveld method confirmed coexistence of various oxides, for example: TiO 2 in the form of anatase, TiO and Ti 3 O 5 phases in the TNAs under study pointing that previous well-established mechanisms of the TNA growth were to certain degree incomplete. Photoelectrochemical (PEC) water splitting is one of the most favorable approaches for H 2 production as a clean energy vector of the future. Since the work by Fujishima and Honda in 1972 1 , increasing research has been carried out towards this issue using electrodes made of various materials, e.g. semiconductors. Unfortunately, their practical application has encountered a number of technical complications. Among the metal oxides that has been taken into consideration, titanium dioxide (TiO 2) is found to be promising in PEC water splitting 2-9 due to its appropriate band-gap structure, superior chemical and optical stability and low cost. In particular, TiO 2 nanotube arrays prepared in anodization processes have numerous advantages over TiO 2 nanoparticle films resulting from facile preparation procedure, high surface-to-volume ratio for contact with the electrolyte, large light harvesting efficiency improved by light scattering into tubular morphology, and high electron mobility induced by their unidirectional channel 10,11. Some strategies such as doping or semiconductor heterocoupling were used for modification of TiO 2 nanotube arrays to be activated under visible light 12-14 .
International Journal of Hydrogen Energy, 2012
Sonication assisted anodization of titanium in a fluorinated ethylene glycol and water electrolyte using Ti itself as a cathode is investigated. The prepared anodic film has a highly ordered nanotube-array surface architecture. The resulting TiO 2 nanotubes at potential 20e40 V have various diameters (30e100 nm), tube length (3e12 mm) and wall thicknesses (6e15 nm). The tube diameter and wall thickness are increased with the anodization time while the overall length of the nanotube arrays is controlled by the duration of the anodization time. In addition, apart from the anodization time, formation of nanotubes is governed by the distance and supplied voltages between the two electrodes, for a given electrolyte. The crystal structure and surface morphology of the annealed anodic films are investigated by XRD and SEM, respectively. The corresponding photoelectrochemical water splitting efficiency (PCE) was calculated under UV light. Our results show a very high PCE under UV (315e400 nm, 100 mW/cm 2) irradiation. The maximum value of PCE for hydrogen generation obtained was 29% which is one of the best results reported in literature [1].
There are currently immense needs to optimize low-cost materials, such as TiO2, so they can efficiently split water photoelectrochemically into hydrogen and oxygen, thus providing a clean energy fuel. To this end, the nature of the crystalline phase and the dimension of the photocatalyst are of crucial significance. In this study, films of 7 μm long titania nanotube arrays were fabricated via anodization of titanium foil in formamide electrolytes containing NH4F and H3PO4. Upon annealing the as-anodized nanotubes, the anatase-to-rutile phase transformation was found to start at 550 °C, which is about 120 °C above the temperature observed for the 500 nm long nanotube films, with the nanotube films remaining stable up to 580 °C. Analysis of the variation of crystallite size with annealing temperature along with XPS analysis of the films was used to investigate the reason behind this observation. UV−vis measurements showed that the absorption edges of the annealed samples were red shifted from that of the as-anodized sample. The stabilization of the anatase phase up to 550 °C, while keeping the tubular structure in place, is very significant as anatase is the most photoactive polymorph of titania. Besides, the 7 μm long nanotubular structure provides a large surface medium for light utilization through scattering. Used as photoanodes to photoelectrochemically split water, the 580 °C crystallized nanotube arrays showed a three-electrode photoconversion efficiency of 10% under UV illumination (100 mW/cm2, 320−400 nm, 1 M KOH).
A significant enhancement in the photoconversion efficiency of anodically grown titania nanotube array photoanodes is observed when crystallized using an infrared annealing process. This infrared (IR) annealing treatment is performed over relatively short periods, 5-15 min, over the temperature range 300-600 degrees C with the anatase crystallite size increasing with annealing temperature and duration. Used as photoanodes to photoelectrochemically split water, the 15 min, 600 degrees C IR crystallized nanotube arrays show a three-electrode photoconversion efficiency of 13.13% under UV illumination (100 mW/cm(2) 320-400 nm, 1 M KOH). A reduction in the carrier trap states and an increased charge carrier transport due to reduction of the barrier layer thickness are believed responsible for the significant conversion efficiency seen with the IR annealed samples
Aminated TiO2 nanotubes as a photoelectrochemical water splitting photoanode
Catalysis Today, 2016
The present work reports on the enhancement of TiO 2 nanotubes photoelectrochemical water splitting rate by decorating the nanostructure with an amine layer in a hydrothermal process using diethylenetriamine (DETA). The aminate coated TiO 2 tubes show a stable improvement of the photoresponse in both UV and visible light spectrum and under hydrothermal conditions, 4-fold increase of the photoelectrochemical water splitting rate is observed. From intensity modulated photocurrent spectroscopy (IMPS) measurements significantly faster electron transport times are observed indicating a surface passivating effect of the Ndecoration.
TiO2 photoanodes for electrically enhanced water splitting
International Journal of …, 2010
Photoelectrochemical properties of self-organized TiO 2 nanotubes formed by electrochemical anodization of titanium sheets and their working mechanism are investigated. Formation and growth of self-organized nanotubes were carried out by Titanium anodization in acid electrolyte containing fluorides. Annealing of the samples was performed in order to increase the crystallinity of the material. Also some results obtained with samples annealed in Nitrogen atmosphere are presented. Electrochemical Impedance Spectroscopy was used to give an interpretation of the main charge transfer processes that occur at the nanotube/electrolyte interphase. The use of glycerol as hole scavenger was considered in order to improve the photoelectrochemical performance of the samples.
Topics in Catalysis, 2014
Highly ordered nitrogen-doped titanium dioxide (N-doped TiO 2) nanotube array films with enhanced photo-electrochemical water splitting efficiency (PCE) for hydrogen generation were fabricated by electrochemical anodization, followed by annealing in a nitrogen atmosphere. Morphology, structure and composition of the N-doped TiO 2 nanotube array films were investigated by FE-SEM, XPS, UV-Vis and XRD. The effect of annealing temperature, heating rate and annealing time on the morphology, structure, and photo-electrochemical property of the N-doped TiO 2 nanotube array films were investigated. A design of experiments method was applied in order to minimize the number of experiments and obtain a statistical model for this system. From the modelling results, optimum values for the influential factors were obtained in order to achieve the maximum PCE. The optimized experiment resulted in 7.42 % PCE which was within 95 % confidence interval of the predicted value by the model.