Tunable electrochemical properties of liquid phase deposited TiO2 films

Titanium dioxide (TiO₂) films on glassy carbon (GC) electrode surface were prepared by the liquid phase deposition (LPD) process for different deposition times. The morphological structure, interfacial property and electrocatalytic activity of as-prepared LPD TiO₂ films on GC surface were studied by field-emission scanning electron microscopy (FE-SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The FE-SEM observation showed that the deposition time controlled the morphology of film on GC surface. With increasing deposition time, TiO₂ formed nanoparticles at the initial 5-h stage and compact thick films after 20 h. Due to the semiconducting properties of TiO₂, the LPD films inhibited the electron transfer process of [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ on GC by increasing the redox reaction peak potential separation of CV curve and electron transfer resistance of EIS. The inhibition was increased with TiO₂ film thickness. Nevertheless, the onset reduction potential of maleic acid decreased with increasing LPD TiO₂ film thickness while the cathodic and anodic currents increased, demonstrating the useful electrocatalytic activity of LPD TiO₂ films.     

Microwave-assisted synthesis of Ag–TiO2/graphene composite for hydrogen production under visible light irradiation

Novel photocatalysts based on silver (Ag), TiO₂, and graphene were successfully synthesized by microwave-assisted hydrothermal method. The prepared photocatalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) specific surface area analysis, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The influence of silver loading and graphene incorporation on photocatalytic hydrogen (H₂) production of as-prepared samples was investigated in methanolic aqueous solution under visible light irradiation (λ≥420 nm). The results showed that Ag–TiO₂/graphene composite had appreciably enhanced photocatalytic H₂ production performance under visible light illumination compared to pure TiO₂, Ag–TiO₂ and TiO₂/graphene samples. The enhanced photocatalytic hydrogen production activity of Ag–TiO₂/graphene composite under visible light irradiation could be attributed to increased visible light absorption, reduced recombination of photogenerated charge carriers and high specific surface area. This novel study provides more insight for the development of novel visible light responsive TiO²⁻ graphene based photocatalysts for energy applications.     

Electrochemical impedance spectroscopy of the alkaline manganese dioxide electrode

Two-probe electrochemical impedance spectroscopy measurements were carried out on the electrolytic manganese dioxide electrode in concentrated KOH electrolytes under a variety of experimental conditions. These included varying the electrode thickness and compaction pressure, electrolyte content and concentration, degree of manganese dioxide reduction and the presence of TiO₂ (anatase) as an additive. The overall electrode impedance was found to decrease when thin electrodes, prepared under high compaction pressures, with an excess of electrolyte, were used. The impedance of the EMD/electrolyte interface was also minimized when 5.0 M KOH was used as the electrolyte. This correlates with a maximum in electrolyte conductivity. The electrode impedance also increased as the degree of EMD reduction was increased, as was expected. Under these experimental conditions the electrode impedance increased in the presence of TiO₂ (anatase), which has negative implications for its commercial use. This conclusion was reached despite the differences in experimental conditions between this work and in commercial applications. An equivalent circuit was also derived and used as an aid in interpreting the impedance data.     

Incorporation of plasma-functionalized carbon nanocapsules into a nanocrystalline TiO2 photoanode for use in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated using TiO₂ nanoparticles incorporating different amounts of plasma functionalized carbon nanocapsules (CNCs) as the photoanode. The functionalization was obtained by grafting maleic anhydride (MA) onto the walls of CNCs immediately after the in situ argon plasma treatment. Nanocrystalline semiconductor film electrodes were prepared by sintering TiO₂ with added MA-CNCs on a conducting glass substrate. Capacitance measurements obtained from electrochemical impedance spectroscopy (EIS) analysis in an aqueous electrolyte are fitted using the Mott–Schottky relationship and demonstrate the variation of flatband potential (V_fb) for the composite with MA-CNC content. The potential chronoamperometric and cyclic voltammetric data supports the argument that the increased V_fb minimizes the defect state for trapping/detrapping of electrons within the MA-CNC/TiO₂. As a result of higher film capacitance and electron accumulation, the MA-CNC/TiO₂ shows increased conversion efficiency and photocurrent density when used as the photoanode in DSSCs. EIS measurement further demonstrates that charge recombination at the interface of MA-CNC/TiO₂ and electrolyte is suppressed with increasing electron lifetime and is in good agreement with the photovoltaic performance. The amount of MA-CNCs added, however needs to be optimized due to the unavoidable issue of aggregation.     

Crystalline phase of TiO2 nanotube arrays on Ti–35Nb–4Zr alloy: Surface roughness,electrochemical behavior and cellular response

An investigation was made into the electrochemical, structural and biological properties of self-organized amorphous and anatase/rutile titanium dioxide (TiO₂) nanotubes deposited on Ti–35Nb–4Zr alloy through anodization-induced surface modification. The surface of as-anodized and heat-treated TiO₂ nanotubes was analyzed by field emission scanning electron microscopy (FE-SEM), revealing morphological parameters such as tube diameter, wall thickness and cross-sectional length. Glancing angle X-ray diffraction (GAXRD) was employed to identify the structural phases of titanium dioxide, while atomic force microscopy (AFM) was used to measure surface roughness associated with cell interaction properties. The electrochemical stability of TiO₂ was examined by electrochemical impedance spectroscopy (EIS) and the results obtained were correlated with the microstructural characterization. The in vitro bioactivity of as-anodized and crystallized TiO₂ nanotubes was also analyzed as a function of the presence of different TiO₂ polymorphic phases. The results indicated that anatase TiO₂ showed higher surface corrosion resistance and greater cell viability than amorphous TiO₂, confirming that TiO₂ nanotube crystallization plays an important role in the material's electrochemical behavior and biocompatibility.     

Highly visible light responsive metal loaded N/TiO2 nanoparticles for photocatalytic conversion of CO2 into methane

Photocatalytic reduction of carbon dioxide (CO₂) into valuable hydrocarbon such as methane (CH₄) using water as reducing agent is a good strategy for environment and energy applications. In this study, a facile and simple sol-gel method was employed for the synthesis of metal (Cu and Ag) loaded nanosized N/TiO₂ photocatalyst. The prepared photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, BET Surface area analyzer, X-ray photoelectron spectroscopy and UV–vis diffuses reflectance spectroscopy. The photocatalytic conversion of CO₂ into methane was carried out under visible light irradiation (λ≥420 nm) by prepared photocatalysts in order to evaluate the photocatalytic efficiency. The results demonstrate that Ag loaded N/TiO₂ showed enhanced photocatalytic performance for methane production from CO₂ compared to other Cu–N/TiO₂, N/TiO₂ and TiO₂ photocatalysts. The improvement in the photocatalytic activity could be attributed to high specific surface area, extended visible light absorption and suppressed recombination of electron – hole pair due to synergistic effects of silver and nitrogen in the Ag–N/TiO₂ photocatalyst. This study demonstrates that Ag–N/TiO₂ is a promising photocatalytic material for photocatalytic reduction of CO₂ into hydrocarbons under visible light irradiation.     

Sol-gel–mediated synthesis of TiO2 nanocrystals: Structural,optical, and electrochemical properties

Nanoparticles of titanium dioxide were prepared using the sol-gel method without any impurity. Rietveld refinement of XRD data confirmed the anatase phase of synthesized nanoparticles with space group I4_1/amd (141). XRD pattern revealed the crystalline nature of synthesized nanopowder. The average crystallite size of synthesized nanoparticles was calculated 7.5 nm. The electrochemical performance of synthesized TiO₂ nanopowder was investigated as working electrode. The electrochemical reaction was found diffusion-controlled as observed from cyclic voltammetry (CV) studies at different scan rates. The diffusion-controlled charge storage mechanism also confirmed by charge transfer resistance and Warburg impedance, as calculated from the EIS analysis. SEM micrograph showed the plate-like structure grown in cluster cloud of particles of synthesized TiO₂ nanocrystals. Absorbance and optical bandgap were obtained using UV-Vis spectra. De-convoluted PL spectra provided the emission pattern from the ultra-violet region to green region due to the presence of interstitial oxygen vacancies. The tune bandgap with EIS measurements of synthesized TiO₂ nanoparticles offers its potential application in energy storage devices and photovoltaic applications.     

Electrochemical immunoassay for human chorionic gonadotrophin based on Pt hollow nanospheres and silver/titanium dioxide nanocomposite matrix

BACKGROUND: A new electrochemical immunosensor for human chorionic gonadotropin (HCG) assay was developed based on Pt hollow nanospheres and silver/titanium dioxide nanocomposites. Silver nanoparticles were initially doped into TiO₂ and chitosan (Cs) colloids to form silver/titanium dioxide nanocomposites (Ag? TiO₂? Cs), which had good redox electrochemical activity and excellent film‐forming ability. Then, the free amino groups of chitosan were used to attach Pt hollow nanospheres for immobilization of human chorionic gonadotropin antibody (anti‐HCG) to construct an immunosensor. RESULTS: Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) confirmed consecutive growth of the multilayer films, and transmission electron microscopy (TEM) was used to describe the microstructure of nanoparticles. Optimal response of the immunosensor was obtained at pH 6.5 and 25 °C with an incubation time of 40 min. The immunosensor exhibited a linear range from 0.5 to 250 mIU mL^?1 HCG with a detection limit of 0.26 mIU mL^?1 at three times background noise. The selectivity, stability and repeatability of the immunosensor were satisfactory. CONCLUSION: The strategy showed low‐cost, high sensitivity, broad linear range and fast analytical time. It is expected that the immobilized technique and the detection methodology could be further developed for other proteins. Copyright © 2010 Society of Chemical Industry     

Electrochemical impedance spectroscopy study on silver coated metallic implants

This work presents the preparation of nano-structured silver coatings on TiAl₆V₄ and CoCrMo alloys by a pulse current technique and the study of time dependent electrochemical behaviour of silver coated metallic implants. EIS data as a function of immersion time in 0.9 wt% NaCl solution have been obtained to clarify the electrochemical processes occurring in the system. During early stage immersion (1–2 days), the impedance response shows near capacitive behaviour. As the time passes, the electrolyte gradually penetrates the silver coating and the sandblasted metallic implants. The silver comes into contact with the electrolyte and the conditions for galvanic corrosion are fulfilled. Due to the potential difference between silver coating and the metallic alloy, discrete anodic and cathodic areas are formed, which result in the release of silver, since the silver acts as an anode in galvanic cells. The cathode process is the reduction of the dissolved oxygen at the surface of the substrate. For antimicrobial applications of nanosilver coated TiAl₆V₄ and CoCrMo alloys, it is very important to maintain the continuous release silver ions. Degradation of silver coatings have been traced and confirmed by different methods such as SEM micrographs, EDX analysis, EIS measurements and solution analysis by ICP-MS methods.     

Preparation and photocatalytic activity of silver and TiO2 nanoparticles/montmorillonite composites

Ag–TiO₂/montmorillonite (Ag–TiO₂/MMT) was synthesized as photocatalyst using TiCl₄ hydrolysis to introduce nanosized TiO₂ into the interlayer space of the montmorillonite (MMT). Stable pillared TiO₂/MMT was obtained by calcination at 500 °C, then silver was loaded by reduction of silver nitrate. The physico–chemical properties of the photocatalyst were determined by X-ray diffraction (XRD), infrared spectroscopy (IR), atomic absorption spectrophotometer (AAS), nitrogen gas adsorption (BET method) and UV–Visible spectra. The photooxidation activity for methylene blue (M.B.) degradation was as follows: Ag–TiO₂/MMT > TiO₂/MMT > TiO₂(P25). Among them Ag–TiO₂/MMT had the highest photooxidation activity because of its larger specific surface caused by pillaring and loading of silver for improving its light absorption.     

Electrochemical properties of carbide-derived carbon electrodes in non-aqueous electrolytes based on different Li-salts

Electrochemical characteristics of carbide-derived micro/mesoporous carbon material C(TiC) (prepared from TiC) have been studied in 1 M LiClO₄, 0.5 M LiClO₄ + 0.5 M LiPF₆, and 1 M LiPF₆ electrolyte solutions in ethylene carbonate–dimethyl carbonate solvent mixture (1:1 by volume), by using cyclic voltammetry (CV), constant current charge/discharge and electrochemical impedance spectroscopy (EIS). Region of ideal polarizability, values of series capacitance and resistance, charge transfer resistance and capacitance, and other characteristics dependent on the electrolyte anion chemical composition have been established. The dependence of Li⁺ ion intercalation characteristics and solid electrolyte interface (SEI) formation on the salt anion composition have been established and discussed. It was found that the three electrolytes studied are comparatively weak candidates for long-lasting high energy and power density supercapacitors.     

Solid‐state synthesis and characterization of polyaniline/nano‐TiO2 composite

Polyaniline/nano‐TiO₂ composites with the content of nano‐TiO₂ varying from 6.2 wt % to 24.1 wt % were prepared by using solid‐state synthesis method at room temperature. The structure and morphology of the composites were characterized by the Fourier transform infrared (FTIR) spectra, ultraviolet‐visible (UV–vis) absorption spectra, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The electrochemical performances of the composites were investigated by galvanostatic charge–discharge measurement, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results from FTIR and UV–vis spectra showed that the composites displayed higher oxidation and doping degree than pure PANI. The XRD and morphological studies revealed that the inclusion of nano‐TiO₂ particles hampered the crystallization of PANI chains in composites, and the composites exhibited mixed particles from free PANI particles and the nano‐TiO₂ entrapped PANI particles. The galvanostatic charge–discharge measurements indicated that the PANI/nano‐TiO₂ composites had higher specific capacitances than PANI. The composite with 6.2 wt % TiO₂ had the highest specific capacitance among the composites. The further electrochemical tests on the composite electrode with 6.2 wt % TiO₂ showed that the composite displayed an ideal capacitive behavior and good rate ability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

LaCoO3-modified RuO2–TiO2/Ti electrode as an efficient electrocatalyst for oxygen evolution reaction

A RuO₂–TiO₂/Ti electrode modified with LaCoO₃ was successfully fabricated by thermal decomposition and its electrochemical properties were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and stability tests. In contrast with an unmodified RuO₂–TiO₂/Ti electrode, the LaCoO₃–RuO₂–TiO₂/Ti electrode displays a more uniform layer with smaller microparticles. This electrode also displays higher OER performance with lower overpotential (289 mV vs. 348 mV) at a current density of 10 mA cm⁻² and lower Tafel slope (87 mV dec⁻¹ vs. 104 mV dec⁻¹) than the unmodified RuO₂–TiO₂/Ti electrode. The modified LaCoO₃–RuO₂–TiO₂/Ti electrode possesses larger current density, higher specific voltammetric charge, and lower charge transfer resistance (R_ct) than the unmodified RuO₂–TiO₂/Ti electrode does in a KOH solution, according to CV and EIS studies. The LaCoO₃–RuO₂–TiO₂/Ti electrode is very stable. The results show that the modified LaCoO₃–RuO₂–TiO₂/Ti electrode presents higher electrocatalytic activity and good stability for OER.

Graphic abstract

     

Micro-Capacitor Behavior of Poly(3-Hexyl Thiophene)/Carbon Fiber/Electrolyte System and Equivalent Circuit Model

In this article, 3-Hexyl thiophene (3HTh) monomer was electrocoated on carbon fiber micro electrode (CFME) to study electrochemical impedance spectroscopic (EIS) analysis. Poly(3HTh)/CFME is characterized by Cyclic voltammetry (CV), Fourier transform infrared reflectance-attenuated total reflection spectroscopy (FTIR-ATR), Scanning electron microscopy-Energy Dispersive X-ray analysis (SEM-EDX), and electrochemical impedance spectroscopy (EIS). The effects of different monomer concentrations (0.5, 1.0 and 1.5 mM) on polymer were reported in 0.1 M tetraethyl ammonium tetrafluoroborate (TEABF₄)/acetonitrile (ACN) solution. The highest low frequency capacitance (C_LF = 1.394 mF cm^?2) was obtained for [3HTh]₀ = 0.5 mM. The equivalent circuit model of R(QR(CR)(RW))(CR) was examined for polymer/electrolyte system.     

Supercapacitive behavior of mesoporous carbon CMK-3 in calcium nitrate aqueous electrolyte

Calcium nitrate Ca(NO₃)₂ aqueous solution was found to be an effective aqueous electrolyte for a supercapacitor using ordered mesoporous carbon as the electrode materials. The supercapacitive behavior of ordered mesoporous carbon CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte was investigated utilizing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge measurements. CMK-3 electrode shows excellent supercapacitive behavior with wide voltage window, high specific gravimetric capacitance and satisfactory electrochemical stability in Ca(NO₃)₂ aqueous electrolyte. The specific gravimetric capacitance of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte reaches 210 F g^?1 at a current density of 1 A g^?1, which is higher than that in conventional aqueous electrolytes NaNO₃ and KOH solution about 40% and 54%, respectively. The high charge density of the electric double layer formed at the interface of the CMK-3 electrode and Ca(NO₃)₂ aqueous electrolyte and the pseudo-capacitive effect originating from the oxygen groups on the surface of CMK-3 were believed to respond for the excellent supercapacitive behavior of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte.     

Photocatalytic degradation of dairy effluent using AgTiO2 nanostructures/polyurethane nanofiber membrane

Dairy effluent (DE) is environmentally toxic and needs special attention. Photocatalytic degradation of DE was studied using novel polyurethane (PU)-based membranes. Typically, silver–titanium dioxide nanofibers (AgTiO₂ NFs) and silver–titanium dioxide nanoparticles (AgTiO₂ NPs) were individually incorporated in PU electrospun nanofibers to overcome the mandatory sophisticated separation of the nanocatalysts, which can create a secondary pollution, after the treatment process. These nanomembranes were characterized in SEM, TEM, XRD and UV studies. The polymeric electrospun nanofibers were smooth and continuous, with an average diameter of about 550 nm, and held their nanofibrous morphology even after more than 2 h of photocatalytic degradation of DE, due to the good stability of PU in the aqueous solutions, which indicates good imprisoning of the functional photocatalysts. The PU–AgTiO₂ NPs and PU–AgTiO₂ NFs were effective materials for degradation of DE, even after two successive cycles. PU–AgTiO₂ NPs and PU–AgTiO₂ NFs showed a maximum degradation of 75% and 95%, respectively after 2 h. The significant enhancement of degradation in the PU–Ag–TiO₂ NPs and PU–Ag–TiO₂ NFs is attributed to the photoactivity of Ag–TiO₂ material under visible light irradiation.     

Controllable preparation of Ti/TiO2-NTs/PbO2–CNTs–MnO2 layered composite materials with excellent electrocatalytic activity for the OER in acidic media

High oxygen evolution overpotential and low corrosion resistance are the main challenges for oxygen evolution materials in acidic media. In this study, a novel composite material, Ti/TiO₂-NTs/PbO₂–CNTs–MnO₂, with high oxygen evolution electrocatalytic activity was successfully prepared. First, TiO₂ nanotubes (TiO₂-NTs) were synthesized in situ on a Ti sheet via anodization and used as an intermediate layer. Subsequently, the adhesion and conductivity of the TiO₂-NTs layer were increased through additional anodization, annealing, and electrochemical reduction. Finally, PbO₂ was electrodeposited with a constant current in a lead acetate medium and doped with carbon nanotubes (CNTs) and MnO₂. The surface morphology, phase composition, and electrochemical performance of the composite materials were investigated. Notably, in an acidic electrolyte (150 g/L H₂SO₄), Ti/TiO₂-NTs/PbO₂–CNTs–MnO₂ exhibited good stability (30 h) and a low oxygen evolution overpotential of 410 mV at 50 mA/cm², which is almost equivalent to that of precious metals (RuO₂ and IrO₂) and 499 mV lower than that of the industrial Pb–0.76 wt% Ag alloy. The outstanding performance is mainly attributed to the high aspect ratio of the TiO₂-NT structure, synergistic effects of the active particles, and inherently good electrochemical properties of the active particles. Therefore, this study provides a new synthetic route for oxygen evolution materials in acidic media.     

碳纳米管/纳米TiO2-聚苯胺复合膜电极的制备及电化学性能

在含有0.2 mol·L^-1苯胺的0.5 mol·L^-1 H2SO4溶液中;采用循环伏安法（CV）;以扫描速度50 mV·s^-1;扫描电位为-0.1～0.9 V;在碳纳米管/纳米TiO₂（CNT/nanoTiO₂）膜电极上实现了苯胺的电化学聚合;通过CV法和电化学阻抗谱（EIS）并结合电子扫描显微镜和红外谱图对制备的碳纳米管/纳米TiO₂-聚苯胺（CNT/nanoTiO₂-PAn）复合膜电极的电化学性质和结构进行了表征;同时研究了复合膜电极对抗坏血酸（AH₂）的电催化性能;发现该复合膜电极对抗坏血酸的氧化具有较高的电催化活性。     

Optimization of the dye-sensitized solar cell performance by mechanical compression

In this study, the P25 titanium dioxide (TiO₂) nanoparticle (NP) thin film was coated on the fluorine-doped tin oxide (FTO) glass substrate by a doctor blade method. The film then compressed mechanically to be the photoanode of dye-sensitized solar cells (DSSCs). Various compression pressures on TiO₂ NP film were tested to optimize the performance of DSSCs. The mechanical compression reduces TiO₂ inter-particle distance improving the electron transport efficiency. The UV–vis spectrophotometer and electrochemical impedance spectroscopy (EIS) were employed to quantify the light-harvesting efficiency and the charge transport impedance at various interfaces in DSSC, respectively. The incident photon-to-current conversion efficiency was also monitored. The results show that when the DSSC fabricated by the TiO₂ NP thin film compressed at pressure of 279 kg/cm², the minimum resistance of 9.38 Ω at dye/TiO₂ NP/electrolyte interfaces, the maximum short-circuit photocurrent density of 15.11 mA/cm², and the photoelectric conversion efficiency of 5.94% were observed. Compared to the DSSC fabricated by the non-compression of TiO₂ NP thin film, the overall conversion efficiency is improved over 19.5%. The study proves that under suitable compression pressure the performance of DSSC can be optimized.     

Development and protection evaluation of two new,advanced ceramic composite thermal spray coatings,Al2O3–40TiO2 and Cr3C2–20NiCr on carbon steel petroleum oil piping

Carbon steel is the most commonly used material in the petroleum industry owing to its high performance and relatively low cost compared with highly alloyed materials. The corrosion resistance of carbon steel in aqueous solutions is dependent on the surface layer created on carbon steel. This layer often consists of siderite (FeCO₃) and cementite (Fe₃C), but it is neither compact nor dense. To improve the carbon steel surface resistance against corrosion and wear, a compact and dense layer can be deposited onto the surface by thermal spray coating. In this research, Al₂O₃–40TiO₂ and Cr₃C₂–20NiCr were deposited onto mechanical part surfaces by HVOF spray technique. The present study describes and compares the electrochemical behavior of carbon steel, Cr₃C₂–20NiCr and Al₂O₃–40TiO₂ in 3.5% NaCl using open-circuit potential measurement (OCP) and electrochemical impedance microscopy (EIS) for 36 days. The tribological and mechanical properties are also investigated using a tribometer (pin-on-disc). The results indicate that these chemical composition coatings facilitated significant anti-corrosion and anti-wear improvement. However, the samples coated with Al₂O₃–40TiO₂ exhibited the lowest corrosion rate. In terms of wear performance, both coated samples displayed similar behavior under different loads. Scanning electron microscopy (SEM) showed the distinctive microstructure of the HVOF-sprayed samples before and after corrosion and wear testing.