scholarly journals Surface Morphology and Growth of Anodic Titania Nanotubes Films: Photoelectrochemical Water Splitting Studies

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Chin Wei Lai
Keyword(s):  
Oxide Layer ◽  
Water Splitting ◽  
Active Surface ◽  
Ammonium Fluoride ◽  
Photocurrent Density ◽  
Photon Absorption ◽  
Electrochemical Anodization ◽  
Nanoporous Structure ◽  
Active Surface Area ◽  
Surface Morphologies

Design and development of one-dimensional nanoarchitecture titania (TiO) assemblies have gained significant scientific interest, which have become the most studied material as they exhibit promising functional properties. In the present study, anodic TiO2films with different surface morphologies can be synthesized in an organic electrolyte of ethylene glycol (EG) by controlling an optimum content of ammonium fluoride (NH4F) using electrochemical anodization technique. Based on the results obtained, well-aligned and bundle-free TiO2nanotube arrays with diameter of 100 nm and length of 8 µm were successfully synthesized in EG electrolyte containing ≈5 wt% of NH4F for 1 h at 60 V. However, formation of nanoporous structure and compact oxide layer would be favored if the content of NH4F was less than 5 wt%. In the photoelectrochemical (PEC) water splitting studies, well-aligned TiO2nanotubular structure exhibited higher photocurrent density of ≈1 mA/cm2with photoconversion efficiency of ≈2% as compared to the nanoporous and compact oxide layer due to the higher active surface area for the photon absorption to generate more photo-induced electrons during photoexcitation stage.

Discovery of WO3/TiO2 Nanostructure Transformation by Controlling Content of NH4F to Enhance Photoelectrochemical Response

2012 ◽  
Vol 620 ◽  
pp. 173-178 ◽  
Author(s):  
Chin Wei Lai ◽  
Srimala Sreekantan
Keyword(s):  
Ammonium Fluoride ◽  
Anodic Oxide ◽  
Photocurrent Density ◽  
Electrochemical Anodization ◽  
Nanoporous Structure ◽  
Nanotubular Structure ◽  
Insufficient Amount ◽  
Photoelectrochemical Response ◽  
Anodization Process ◽  
Anodic Oxide Layer

We report on the effect of the tungsten (W) cathode in controlling the morphology and properties of titanium (Ti) anodic oxide layer via an electrochemical anodization process. The content of ammonium fluoride (NH4F) was varied in ethylene glycol (EG) electrolyte containing hydrogen peroxide (H2O2) in order to obtained the high ordered nanotubular structure. When amount of NH4F was upto 5 wt%, highly ordered WO3-TiO2nanotubes structure was observed. If insufficient amount of NH4F is applied, the nanoporous structure will be favored. Highly ordered WO3-TiO2nanotubes structure exhibited higher photocurrent density ( 0.9 mA/cm2) as compared to the WO3-TiO2nanoporous structure.

scholarly journals Ni/Si-Codoped TiO2 Nanostructure Photoanode for Enhanced Photoelectrochemical Water Splitting

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4102 ◽  
Author(s):  
Ting Li ◽  
Dongyan Ding
Keyword(s):  
Water Splitting ◽  
Annealing Temperature ◽  
Photocurrent Density ◽  
Electrochemical Anodization ◽  
Codoped Tio2 ◽  
Lower Charge ◽  
Si Doped ◽  
Tio2 Nanostructures ◽  
Tio2 Photoanode ◽  
Pec Water Splitting

We synthesized Ni/Si-codoped TiO2 nanostructures for photoelectrochemical (PEC) water splitting, by electrochemical anodization of Ti-1Ni-5Si alloy foils in ethylene glycol/glycerol solutions containing a small amount of water. The effects of annealing temperature on PEC properties of Ni/Si-codoped TiO2 photoanode were investigated. We found that the Ni/Si-codoped TiO2 photoanode annealed at 700 °C had an anatase-rutile mixed phase and exhibited the highest photocurrent density of 1.15 mA/cm2 at 0 V (vs. Ag/AgCl), corresponding to a photoconversion efficiency of 0.70%, which was superior to Ni-doped and Si-doped TiO2. This improvement in PEC water splitting could be attributed to the extended light absorption, faster charge transfer, possibly lower charge recombination, and longer lifetime.

scholarly journals Photocatalysis and Photoelectrochemical Properties of Tungsten Trioxide Nanostructured Films

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Chin Wei Lai
Keyword(s):  
Tungsten Trioxide ◽  
Critical Role ◽  
Solar Spectrum ◽  
Average Diameter ◽  
Active Surface ◽  
Sodium Sulphate ◽  
Electrochemical Anodization ◽  
Active Surface Area ◽  
Fluoride Ions ◽  
Nanotubular Structure

Tungsten trioxide (WO3) possesses a small band gap energy of 2.4–2.8 eV and is responsive to both ultraviolet and visible light irradiation including strong absorption of the solar spectrum and stable physicochemical properties. Thus, controlled growth of one-dimensional (1D) WO3nanotubular structures with desired length, diameter, and wall thickness has gained significant interest. In the present study, 1D WO3nanotubes were successfully synthesized via electrochemical anodization of tungsten (W) foil in an electrolyte composed of 1 M of sodium sulphate (Na2SO4) and ammonium fluoride (NH4F). The influence of NH4F content on the formation mechanism of anodic WO3nanotubular structure was investigated in detail. An optimization of fluoride ions played a critical role in controlling the chemical dissolution reaction in the interface of W/WO3. Based on the results obtained, a minimum of 0.7 wt% of NH4F content was required for completing transformation from W foil to WO3nanotubular structure with an average diameter of 85 nm and length of 250 nm within 15 min of anodization time. In this case, high aspect ratio of WO3nanotubular structure is preferred because larger active surface area will be provided for better photocatalytic and photoelectrochemical (PEC) reactions.

scholarly journals High-Index-Faceted Ni3S2 Branch Arrays as Bifunctional Electrocatalysts for Efficient Water Splitting

2019 ◽  
Vol 11 (1) ◽  
Author(s):  
Shengjue Deng ◽  
Kaili Zhang ◽  
Dong Xie ◽  
Yan Zhang ◽  
Yongqi Zhang ◽  
...  
Keyword(s):  
Water Splitting ◽  
Active Sites ◽  
Large Scale ◽  
High Efficiency ◽  
Hydrogen Generation ◽  
Metal Sulfide ◽  
Value Added ◽  
Active Surface ◽  
High Index ◽  
Active Surface Area

Abstract For efficient electrolysis of water for hydrogen generation or other value-added chemicals, it is highly relevant to develop low-temperature synthesis of low-cost and high-efficiency metal sulfide electrocatalysts on a large scale. Herein, we construct a new core–branch array and binder-free electrode by growing Ni3S2 nanoflake branches on an atomic-layer-deposited (ALD) TiO2 skeleton. Through induced growth on the ALD-TiO2 backbone, cross-linked Ni3S2 nanoflake branches with exposed {$$\bar{2}10$$ 2 ¯ 10 } high-index facets are uniformly anchored to the preformed TiO2 core forming an integrated electrocatalyst. Such a core–branch array structure possesses large active surface area, uniform porous structure, and rich active sites of the exposed {$$\bar{2}10$$ 2 ¯ 10 } high-index facet in the Ni3S2 nanoflake. Accordingly, the TiO2@Ni3S2 core/branch arrays exhibit remarkable electrocatalytic activities in an alkaline medium, with lower overpotentials for both oxygen evolution reaction (220 mV at 10 mA cm−2) and hydrogen evolution reaction (112 mV at 10 mA cm−2), which are better than those of other Ni3S2 counterparts. Stable overall water splitting based on this bifunctional electrolyzer is also demonstrated.

scholarly journals Modification of One-Dimensional TiO2Nanotubes with CaO Dopants for High CO2Adsorption

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Chin Wei Lai
Keyword(s):  
Nitrate Solution ◽  
Calcium Nitrate ◽  
Active Surface ◽  
Electrochemical Anodization ◽  
Active Surface Area ◽  
X Ray Diffraction ◽  
One Dimensional ◽  
X Ray ◽  
Calcium Source ◽  
Field Emission Microscopy

One-dimensional calcium oxide (CaO-) based titanium dioxide (TiO2) nanotubes were successfully synthesized through a rapid electrochemical anodization and chemical wet impregnation techniques. In this study, calcium nitrate solution was used as a calcium source precursor. The reaction time and concentration of calcium source on the formation of CaO-TiO2nanotubes were investigated using field emission microscopy, energy dispersion X-ray spectroscopy, and X-ray diffraction. The adsorption capacity of CO2was determined by thermal gravimetric analyzer. A maximum of 4.45 mmol/g was achieved from the CaO-TiO2nanotubes (6.64 at% of Ca). The finding was attributed to the higher active surface area for CaO to adsorb more CO2gas and then formed CaCO3compound during cyclic carbonation-calcination reaction.

scholarly journals Anodic CaO-TiO2Nanotubes Composite Film for Low Temperature CO2Adsorption

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Chin Wei Lai
Keyword(s):  
Low Temperature ◽  
Composite Film ◽  
Adsorption Capacity ◽  
Surface Area ◽  
Anodic Oxidation ◽  
Active Surface ◽  
Optimum Concentration ◽  
Electrochemical Anodization ◽  
Active Surface Area ◽  
One Dimensional

A novel one-dimensional anodic CaO-TiO2nanotubes composite film was prepared using a rapid-anodic oxidation electrochemical anodization technique for low temperature CO2absorption application. This study aims to determine the optimum concentration of Ca(NO3)2·4H2O used as the CaO precursor for loading CaO species on TiO2nanotubes. In this study, an optimum content of CaO on TiO2nanotubes (0.15 at% of Ca element) could enhance the CO2adsorption capacity up to 2.45 mmol/g at 400°C. This behavior was attributed to the large active surface area of CaO species were covered on the surface of TiO2nanotubes. The conversion of CaO into CaCO3could be achieved effectively for CO2absorption during the carbonate looping process.

scholarly journals Noble metal-free two dimensional carbon-based electrocatalysts for water splitting

BMC Materials ◽  
2019 ◽  
Vol 1 (1) ◽  
Author(s):  
Muhammad Adnan Younis ◽  
Siliu Lyu ◽  
Qidong Zhao ◽  
Chaojun Lei ◽  
Peiling Zhang ◽  
...  
Keyword(s):  
Water Splitting ◽  
Noble Metal ◽  
Noble Metals ◽  
Active Surface ◽  
Active Surface Area ◽  
Two Dimensional ◽  
Structure Property ◽  
Metal Free ◽  
Electrochemical Water Splitting ◽  
Carbon Based

AbstractNoble metal materials are widely employed as benchmark electrocatalysts to achieve electrochemical water splitting which comprises of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, the high cost and scarcity limit the wide ranging commercial applications of noble metal-based catalysts. Development of noble metal-free two dimensional (2D) carbon-based materials can not only reduce the consumption of noble metals, but also create materials with the characteristics of high active surface area, abundance, easy functionalization, and chemical stability, which may carve a way to promising electrochemical water splitting. In this review, noble metal-free 2D carbon-based electrocatalysts, including heteroatom (B, S, N, P, F, and O) doped graphene, 2D porous carbons modified with heteroatoms and/or transition metals, and 2D carbon-based hybrids are introduced as cost-effective alternatives to the noble metal-based electrocatalysts with comparable efficiencies to conduct HER, OER, and overall water splitting. This review emphasizes on current development in synthetic strategies and structure–property relationships of noble metal-free 2D carbon-based electrocatalysts, together with major challenges and perspectives of noble metal-free 2D carbon-based electrocatalysts for further electrochemical applications.

scholarly journals Single Step Formation of C-TiO2Nanotubes: Influence of Applied Voltage and Their Photocatalytic Activity under Solar Illumination

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Chin Wei Lai ◽  
Srimala Sreekantan
Keyword(s):  
Photocatalytic Activity ◽  
Applied Voltage ◽  
Active Surface ◽  
Ammonium Fluoride ◽  
Single Step ◽  
Electrochemical Anodization ◽  
Nanotube Arrays ◽  
Surface Areas ◽  
High Uniformity ◽  
Anodization Process

Self-aligned and high-uniformity carbon (C)- titania (TiO2) nanotube arrays were successfully formed via single step anodization of titanium (Ti) foil at 30 V for 1 h in a bath composed of ethylene glycol (EG), ammonium fluoride (NH4F), and hydrogen peroxide (H2O2). It was well established that applied voltage played an important role in controlling field-assisted oxidation and field-assisted dissolution during electrochemical anodization process. Therefore, the influences of applied voltage on the formation of C-TiO2nanotube arrays were discussed. It was found that a minimal applied voltage of 30 V was required to form the self-aligned and high-uniformity C-TiO2nanotube arrays with diameter of ~75 nm and length of ~2 μm. The samples synthesized using different applied voltages were then subjected to heat treatment for the conversion of amorphous phase to crystalline phase. The photocatalytic activity evaluation of C-TiO2samples was made under degradation of organic dye (methyl orange (MO) solution). The results revealed that controlled nanoarchitecture C-TiO2photocatalyst led to a significant enhancement in photocatalytic activity due to the creation of more specific active surface areas for incident photons absorption from the solar illumination.

Tenacious Mass Transfer Limitations Drive Catalytic Selectivity during Electrochemical Carbon Dioxide Reduction

2019 ◽  
Author(s):  
Kailun Yang ◽  
Recep Kas ◽  
Wilson A. Smith
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Catalyst Layer ◽  
Active Surface ◽  
Active Surface Area ◽  
High Concentration ◽  
Copper Electrodes ◽  
Surface Enhanced ◽  
Local Current

<p>This study evaluated the performance of the commonly used strong buffer electrolytes, i.e. phosphate buffers, during CO<sub>2</sub> electroreduction in neutral pH conditions by using in-situ surface enhanced infrared absorption spectroscopy (SEIRAS). Unfortunately, the buffers break down a lot faster than anticipated which has serious implications on many studies in the literature such as selectivity and kinetic analysis of the electrocatalysts. Increasing electrolyte concentration, surprisingly, did not extend the potential window of the phosphate buffers due to dramatic increase in hydrogen evolution reaction. Even high concentration phosphate buffers (1 M) break down within the potentials (-1 V vs RHE) where hydrocarbons are formed on copper electrodes. We have extended the discussion to high surface area electrodes by evaluating electrodes composed of copper nanowires. We would like highlight that it is not possible to cope with high local current densities on these high surface area electrodes by using high buffer capacity solutions and the CO<sub>2</sub> electrocatalysts are needed to be evaluated by casting thin nanoparticle films onto inert substrates as commonly employed in fuel cell reactions and up to now scarcely employed in CO<sub>2</sub> electroreduction. In addition, we underscore that normalization of the electrocatalytic activity to the electrochemical active surface area is not the ultimate solution due to concentration gradient along the catalyst layer.This will “underestimate” the activity of high surface electrocatalyst and the degree of underestimation will depend on the thickness, porosity and morphology of the catalyst layer. </p> <p> </p>

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