Efficient photocatalytic activity of water oxidation over WO3/BiVO4 composite under visible light irradiation

A coupled WO₃/BiVO₄ thin film has been deposited on FTO substrate by a spin coating method from precursor solutions. The composite films were characterized by AFM, SEM, XPS and XRD techniques. The incident photon to current efficiency (IPCE) of BiVO₄ electrode was increased by 10 times when a WO₃ film was layered between the BiVO₄ layer and the FTO substrate. The enhanced performance of WO₃/BiVO₄ composite film electrode is mainly ascribed to the effective electron-hole separations at the semiconductor heterojunction. A schematic mechanism of charge transfer was proposed to explain the photocurrent enhancement for the WO₃/BiVO₄ electrode surface.     

Enhanced solid-state electrogenerated chemiluminescence of Au/CdS nanocomposite and its sensing to H2O2

Au nanoparticles (AuNPs) are good quenchers once they closely contact with luminophore. Here we reported a simple approach to obtain enhanced electrogenerated chemiluminescence (ECL) behavior based on Au/CdS nanocomposite films by adjusting the amount of AuNPs in the nanocomposite. The maximum enhancement factor of about 4 was obtained at an indium tin oxide (ITO) electrode in the presence of co-reactant H₂O₂. The mechanism of this enhancement was discussed in detail. The strong ECL emission from Au/CdS nanocomposites film was exploited to determine H₂O₂. The resulting ECL biosensors showed a linear response to the concentration of H₂O₂ ranging from 1.0 × 10⁻⁸ to 6.6 × 10⁻⁴ mol L⁻¹ with a detection limit of 5 nmol L⁻¹ (S/N = 3) and good stability and reproducibility.     

Preparation of micro-dot electrodes of LiCoO2 and Li4Ti5O12 for lithium micro-batteries

Fabrications of micro-dot electrodes of LiCoO₂ and Li₄Ti₅O₁₂ on Au substrates were demonstrated using a sol-gel process combined with a micro-injection technology. A typical size of prepared dots was about 100 μm in diameter, and the dot population on the substrate was 2400 dots cm⁻². The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were characterized with scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and cyclic voltammetry. The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were evaluated in an organic electrolyte as cathode and anode for lithium micro-battery, respectively. The LiCoO₂ micro-dot electrode exhibited reversible electrochemical behavior in a potential range from 3.8 to 4.2 V versus Li/Li⁺, and the Li₄Ti₅O₁₂ micro-dot electrode showed sharp redox peaks at 1.5 V.     

Enhanced inactivation of E. coli bacteria using immobilized porous TiO2 photoelectrocatalysis

Immobilized TiO₂ nanotube electrodes with high surface areas were grown via electrochemical anodization in aqueous solution containing fluoride ions for photocatalysis applications. The photoelectrochemical properties of the grown immobilized TiO₂ film were studied by potentiodynamic measurements (linear sweep voltammetry), in addition to the calculation of the photocurrent response. The nanotube electrode properties were compared to mesoporous TiO₂ electrodes grown by anodization in sulfuric acid at high potentials (above the microsparking potential) and to 1 g/l P-25 TiO₂ powder. Photocatalyst films were evaluated by high resolution SEM and XRD for surface and crystallographic characterization. Finally, photoelectrocatalytic application of TiO₂ was studied via inactivation of E. coli. The use of the high surface area TiO₂ nanotubes resulted in a high photocurrent and an extremely rapid E. coli inactivation rate of ∼10⁶ CFU/ml bacteria within 10 min. The immobilized nanotube system is proven to be the most potent electrode for water purification.     

Investigation of hydrogen transport through Mm(Ni3.6Co0.7Mn0.4Al0.3)1.12 and Zr0.65Ti0.35Ni1.2V0.4Mn0.4 hydride electrodes by analysis of anodic current transient

Hydrogen transport through such metal-hydride electrodes as Mm(Ni_3.6Co_0.7Mn_0.4Al_0.3)_1.12 and Zr_0.65Ti_0.35Ni_1.2V_0.4Mn_0.4 was investigated in 6 M KOH solution by using potentiostatic current transient technique. From the shape of the anodic current transient and the dependence of the initial current density on the discharging potential, the boundary conditions at the electrode surface were established during hydrogen extraction from the as-annealed and as-surface-treated electrodes. Especially, it was experimentally confirmed that the diffusion-limited boundary condition is no longer valid at the electrode surface during hydrogen transport in case hydrogen diffusion is coupled with either the interfacial charge transfer reaction or the hydrogen transfer reaction between adsorbed state on the electrode surface and absorbed state at the electrode sub-surface. From the transition behaviour of the boundary condition, it was further recognised that the boundary condition at the electrode surface during hydrogen transport is not fixed at the specific electrode/electrolyte system by itself, but it is rather simultaneously determined even at any electrode/electrolyte system by the potential step and the nature of the electrode surface, depending upon e.g. the presence or absence of the surface oxide scales.     

Cycling-induced stress in lithium ion negative electrodes: LiAl/LiFePO4 and Li4Ti5O12/LiFePO4 cells

In this work, we examined the electrochemical behaviour of lithium ion batteries containing lithium iron phosphate as the positive electrode and systems based on Li-Al or Li-Ti-O as the negative electrode. These two systems differ in their potential versus the redox couple Li⁺/Li and in their morphological changes upon lithium insertion/deinsertion. Under relatively slow charge/discharge regimes, the lithium-aluminium alloys were found to deliver energies as high as 438 Wh kg⁻¹ but could withstand only a few cycles before crumbling, which precludes their use as negative electrodes. Negative electrodes consisting solely of aluminium performed even worse. However, an electrode made from a material with zero-strain associated to lithium introduction/removal such as a lithium titanate spinel exhibited good performance that was slightly dependent on the current rate used. The Li₄Ti₅O₁₂/LiFePO₄ cell provided capacities as high as 150 mAh g⁻¹ under C-rate in the 100th cycle.     

Li diffusion in LiNi0.5Mn0.5O2 thin film electrodes prepared by pulsed laser deposition

Kinetic and transport parameters of Li ion during its extraction/insertion into thin film LiNi_0.5Mn_0.5O₂ free of binder and conductive additive were provided in this work. LiNi_0.5Mn_0.5O₂ thin film electrodes were grown on Au substrates by pulsed laser deposition (PLD) and post-annealed. The annealed films exhibit a pure layered phase with a high degree of crystallinity. Surface morphology and thin film thickness were investigated by field emission scanning electron microscopy (FESEM). The charge/discharge behavior and rate capability of the thin film electrodes were investigated on Li/LiNi_0.5Mn_0.5O₂ cells at different current densities. The kinetics of Li diffusion in these thin film electrodes were investigated by cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). CV was measured between 2.5 and 4.5 V at different scan rates from 0.1 to 2 mV/s. The apparent chemical diffusion coefficients of Li in the thin film electrode were calculated to be 3.13 × 10⁻¹³ cm²/s for Li intercalation and 7.44 × 10⁻¹⁴ cm²/s for Li deintercalation. The chemical diffusion coefficients of Li in the thin film electrode were determined to be in the range of 10⁻¹²-10⁻¹⁶ cm²/s at different cell potentials by GITT. It is found that the Li diffusivity is highly dependent on the cell potential.     

Study of the reactions taking place at the ‘GaAs electrode/SiMo12O40 solution’ interface

The electrochemical response of GaAs, n- and p- type, in the presence of a Keggin-type heteropolyanion—SiMo₁₂O₄₀⁴⁻—has been studied in order to determine the reactions which take place at the GaAs/SiMo₁₂O₄₀⁴⁻ solution interface. The behavior of the GaAs electrodes, in the dark and under illumination, allowed us to determine the nature of the semiconductor carriers involved in the charge transfer. All the charge transfers occur via the GaAs valence band (VB). At open circuit potential, the SiMo₁₂O₄₀⁴⁻ ions are reduced at the GaAs surface which therefore undergoes an anodic dissolution process. Under polarization, when the reduction current is maximum, no GaAs oxidation reaction takes place. The SiMo₁₂O₄₀⁴⁻ reduction current densities are the same at a platinum electrode and at a GaAs electrode. These observations imply that at a GaAs/SiMo₁₂O₄₀⁴⁻ solution interface, under electroless conditions, the GaAs anodic dissolution occurs via a purely electrochemical process, by consumption of the holes injected during SiMo₁₂O₄₀⁴⁻ reduction.     

Effect of particle dispersion on high rate performance of nano-sized Li4Ti5O12 anode

Nano-sized Li₄Ti₅O₁₂ powders with high dispersivity were fabricated by a sol-gel process using P123 as surfactant, which exhibited much better high rate performance towards Li⁺ insertion/extraction as compared to the densely aggregated Li₄Ti₅O₁₂ particles although the primary grain sizes of both samples were almost the same. The Li₄Ti₅O₁₂ electrode prepared from the well-dispersed nanopowders can preserve 88.6% of the capacity at 0.1 A g⁻¹ when being cycled at 1 A g⁻¹, which is obviously higher than that of the densely aggregated sample, in which only 30% capacity can be retained. By improving the dispersivity, the specific surface area of the Li₄Ti₅O₁₂ nanoparticles, hence the electrode-electrolyte contact area was increased; meanwhile, more homogeneous mixing of the active materials with carbon black was achieved. All these factors might have resulted in the better high rate performance.     

Electrochemical investigation of LiNi0.5Mn1.5O4 thin film intercalation electrodes

This work provides kinetic and transport parameters of Li-ion during its extraction/insertion into thin film LiNi_0.5Mn_1.5O₄ free of binder and conductive additive. Thin films of LiNi_0.5Mn_1.5O₄ (0.2 μm thick) were prepared on electronically conductive gold substrate utilizing the electrostatic spray deposition technique. High purity LiNi_0.5Mn_1.5O₄ thin film electrodes were observed with cyclic voltammetry, to exhibit very sharp peaks, high reversibility, and absence of the 4 V signal related to the Mn³⁺/Mn⁴⁺ redox couple. The electrode subjected to 100 CV cycles of charge/discharge delivered a capacity of 155 mAh g⁻¹ on the first cycle and sustained a good cycling behavior while retaining 91% of the initial capacity after 50 cycles. Kinetics and mass-transport of Li-ion extraction at LiNi_0.5Mn_1.5O₄ thin film electrode were investigated by means of electrochemical impedance spectroscopy. The apparent chemical diffusion coefficient (D_app) value determined from EIS measurements changed depending on the electrode potential in the range of 10⁻¹⁰-10⁻¹² cm² s⁻¹. The D_app profile shows two minimums at the potential values close to the peak potentials of the corresponding cyclic voltammogram.     

CdS quantum-dot-sensitized Zn2SnO4 solar cell

The ternary oxide zinc stannate (Zn₂SnO₄) nanoparticles are first used as the electrode materials for the quantum dot sensitized solar cells. CdS quantum dots are utilized to sensitize Zn₂SnO₄ electrode via a chemical bath deposition technique. The covering of ZnS layer, the kinds of conducting substrates and the thickness of film are optimized to improve the cell performance. The optimal film thickness is found to be 6.4 μm, and the electrode prepared at sixth CBD cycle exhibits a highest efficiency of 0.228% under the illumination of 1 sun (AM1.5, 100 mW cm⁻²).     

Synthesis and electrochemical properties of CeO2 nanoparticle modified TiO2 nanotube arrays

In this paper, a cerium dioxide (CeO₂) modified titanium dioxide (TiO₂) nanotube array film was fabricated by electrodeposition of CeO₂ nanoparticles onto an anodized TiO₂ nanotube array. The structural investigation by X-ray diffraction, scanning electron microscopy and transmission electron microscopy indicated that the CeO₂ nanoparticles grew uniformly on the walls of the TiO₂ nanotubes. The composite was composed of cubic-phase CeO₂ crystallites and anatase-phase TiO₂ after annealing at 450 °C. The cyclic voltammetry and chronoamperometric charge/discharge measurement results indicated that the CeO₂ modification obviously increased the charge storage capacity of the TiO₂ nanotubes. The charge transfer process at the surface, that is, the pseudocapacitance, was the dominate mechanism of the charge storage in CeO₂-modified TiO₂ nanotubes. The greater number of surface active sites resulting from uniform application of the CeO₂ nanoparticles to the well-aligned TiO₂ nanotubes contributed to the enhancement of the charge storage density.     

Properties of sol-gel SnO2/TiO2 electrodes and their photoelectrocatalytic activities under UV and visible light illumination

A visible light active binary SnO₂-TiO₂ composite was successfully prepared by a sol-gel method and deposited on Ti sheet as a photoanode to degrade orange II dye. Titanium and SnO₂ can promote the development of rutile phase of TiO₂ and inhibit the formation of anatase phase of TiO₂. Formation of SnO₂ crystalline is insignificant even when the calcination temperature increases to 700 °C. Heterogenized interface between SnO₂ and TiO₂ inhibits growth of TiO₂ linkage and leads to the particle-filled surface morphology of SnO₂-containing films. The carbonaceous, Ti-O-C bonds and Ti³⁺ species are likely to account for the photoabsorption and photoelectrocatalytic (PEC) activity under visible light illumination. The electrode with 30% SnO₂ exhibits higher photocurrent when compared with those in the region of 0-50%. The 600 °C-calcined SnO₂-TiO₂ electrode indicates higher activity when compared with those at 400, 500, 700 and 800 °C. PEC degradation of orange II follows the Langmuir-Hinshelwood model and takes place much effectively in a solution of pH 3.0 than those in pH 7.0 and pH 11.0.     

Electrochemical stability of thin film LiMn2O4 cathode in organic electrolyte solutions with different compositions at 55 °C

A survey of the electrochemical stability of electrostatic spray deposited thin film of LiMn₂O₄ was performed in LiClO₄-EC-PC, LiBF₄-EC-PC, and LiPF₆-EC-PC solutions at 55 °C. The solution resistance, the surface film resistance, and the charge-transfer resistance were all found to depend on the electrolyte composition. Among the LiX-salts studied, the lowest charge transfer-resistance, and surface layer resistance were obtained in LiBF₄-EC-PC solution. There is no major influence of the electrolyte solution compositions upon lithium ion transport in the LiMn₂O₄ bulk at 55 °C. The diffusion coefficient of lithium in the solid phase varied within 10⁻¹⁰-10⁻⁸ cm² s⁻¹ in the three solutions. In general, it seems that in LiBF₄ solutions, the surface chemistry is the most stable in the three solutions examined, and hence the electrode impedance in LiBF₄ solutions was the lowest. In LiPF₆ solutions, HF seems to play an important role, and thus, the electrode impedance is relatively high due to the precipitation of surface LiF.     

Electrochemical performance of the carbon coated Li3V2(PO4)3 cathode material synthesized by a sol-gel method

A carbon coated Li₃V₂(PO₄)₃ cathode material for lithium ion batteries was synthesized by a sol-gel method using V₂O₅, H₂O₂, NH₄H₂PO₄, LiOH and citric acid as starting materials, and its physicochemical properties were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscope (TEM), and electrochemical methods. The sample prepared displays a monoclinic structure with a space group of P2₁/n, and its surface is covered with a rough and porous carbon layer. In the voltage range of 3.0-4.3 V, the Li₃V₂(PO₄)₃ electrode displays a large reversible capacity, good rate capability and excellent cyclic stability at both 25 and 55 °C. The largest reversible capacity of 130 mAh g⁻¹ was obtained at 0.1C and 55 °C, nearly equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹). It was found that the increase in total carbon content can improve the discharge performance of the Li₃V₂(PO₄)₃ electrode. In the voltage range of 3.0-4.8 V, the extraction and reinsertion of the third lithium ion in the carbon coated Li₃V₂(PO₄)₃ host are almost reversible, exhibiting a reversible capacity of 177 mAh g⁻¹ and good cyclic performance. The reasons for the excellent electrochemical performance of the carbon coated Li₃V₂(PO₄)₃ cathode material were also discussed.     

Effect of synthesis condition on the structural and electrochemical properties of Li[Ni1/3Mn1/3Co1/3]O2 prepared by the metal acetates decomposition method

In order to get homogeneous layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ as a lithium insertion positive electrode material, we applied the metal acetates decomposition method. The oxide compounds were calcined at various temperatures, which results in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni_1/3Mn_1/3Co_1/3]O₂ powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry and SEM. XRD experiment revealed that the layered Li[Ni_1/3Mn_1/3Co_1/3]O₂ material can be best synthesized at temperature of 800 °C. In that synthesized temperature, the sample showed high discharge capacity of 190 mAh g⁻¹ as well as stable cycling performance at a current density of 0.2 mA cm⁻² in the voltage range 2.3-4.6 V. The reversible capacity after 100 cycles is more than 190 mAh g⁻¹ at room temperature.     

Mn3O4 nanoparticles embedded into graphene nanosheets: Preparation, characterization, and electrochemical properties for supercapacitors

Mn₃O₄/graphene nanocomposites were synthesized by mixing graphene suspension in ethylene glycol with MnO₂ organosol, followed by subsequent ultrasonication processing and heat treatment. The as-prepared product consists of nanosized Mn₃O₄ particles homogeneously distributed on graphene nanosheets, which has been confirmed by field emission scanning electron microscopy and transmission electron microscopy analysis. Atomic force microscope analysis further identified the distribution of dense Mn₃O₄ nanoparticles on graphene nanosheets. When used as electrode materials in supercapacitors, Mn₃O₄/graphene nanocomposites exhibited a high specific capacitance of 175 F g⁻¹ in 1 M Na₂SO₄ electrolyte and 256 F g⁻¹ in 6 M KOH electrolyte, respectively. The enhanced supercapacitance of Mn₃O₄/graphene nanocomposites could be ascribed to both electrochemical contributions of Mn₃O₄ nanoparticles, functional groups attached to graphene nanosheets, and significantly increased specific surface area.     

Enhanced performance of a dye-sensitized solar cell with a modified poly(3,4-ethylenedioxythiophene)/TiO2/FTO counter electrode

ClO₄⁻-poly(3,4-ethylenedioxythiophene)/TiO₂/FTO (ClO₄⁻-PEDOT/TiO₂/FTO) counter electrode (CE) in dye-sensitized solar cells (DSSCs) is fabricated by using an electrochemical deposition method. Comparing with the DSSCs with ClO₄⁻-PEDOT/FTO counter electrode, the photocurrent-voltage (I-V) measurement reveals that the photocurrent conversion efficiency (η), fill factor (FF) and short-circuit current density (J_SC) of DSSCs with a ClO₄⁻-PEDOT/TiO₂/FTO CE increase. The enhanced performances of the DSSCs are attributed to the higher J_SC arising from the increase of active surface area of ClO₄⁻-PEDOT/TiO₂/FTO CE. Electrochemical impedance spectra (EIS) also indicate that the charge-transfer resistance on the ClO₄⁻-PEDOT/electrolyte interface decreases. Cyclic voltammetry results indicate that the ClO₄⁻-PEDOT/TiO₂/FTO electrode shows higher activity towards I₃⁻/I⁻ redox reaction than that of ClO₄⁻-PEDOT/FTO electrode.     

Controllable synthesis of CaTi2O4(OH)2 nanoflakes by a facile template-free process and its properties

Serrated leaf-like CaTi₂O₄(OH)₂ nanoflake crystals were synthesized via a template-free and surfactant-free hydrothermal process. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The growth process for CaTi₂O₄(OH)₂ nanoflakes was dominated by a crystallization–dissolution–recrystallization growth mechanism. BET analysis showed that CaTi₂O₄(OH)₂ nanoflakes had mesoporous structure with an average pore size of 8.7 nm, and a large surface area of 88.4 m² g⁻¹. Cyclic voltammetry and galvanostatic charge–discharge tests revealed that the electrode synthesized from CaTi₂O₄(OH)₂ nanoflakes reached specific capacitances of 162 F g⁻¹ at the discharge current of 2 mA cm⁻², and also exhibited excellent electrochemical stability.     

Low-temperature synthesis of Bi2Fe4O9 nanoparticles via a hydrothermal method

Bi₂Fe₄O₉ (BFO) nanoparticles were successfully synthesized by a hydrothermal method at a temperature as low as 100 °C. The as-prepared powders, characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM) and physical property measurement system (PPMS), exhibited a pure BFO phase about 100 nm size with uniform sheet-like shape and exhibited an AF order at room temperature. It was found that high alkali concentration and alkali ion Na⁺ played a key role in the formation of BFO nanoparticles at a low temperature of 100 °C.