Electrochemical capacity retention of nearly X-ray amorphous nanostructured manganese oxide (nanoMnO2) synthesized by mixing directly KMnO4 with ethylene glycol under ambient conditions for ...supercapacitor studies is enhanced significantly. Although X-ray diffraction (XRD) pattern of nanoMnO2 shows poor crystallinity, it is found that by Mn K-edge X-ray absorption near edge structure (XANES) measurement that the nanoMnO2 obtained is locally arranged in a δ-MnO2-type layered structure composed of edge-shared network of MnO6 octahedra. Field emission scanning electron microscopy and XANES measurements show that nanoMnO2 contains nearly spherical shaped morphology with δ-MnO2 structure, and 1D nanorods of α-MnO2 type structure (powder XRD) in the annealed (600 °C) sample. Volumetric nitrogen adsorption−desorption isotherms, inductively coupled plasma analysis, and thermal analysis are carried out to obtain physicochemical properties such as surface area (230 m2 g−1), porosity of nanoMnO2 (secondary mesopores of diameter 14.5 nm), water content, composition, etc., which lead to the promising electrochemical properties as an electrode for supercapacitor. The nanoMnO2 shows a very high stability even after 1200 cycles with capacity retention of about 250 F g−1.
Aiming at enhancing the electrochromic properties of anodically colored NiO thin films, lithium doped NiO thin films were grown on FTO/glass substrates, by the pulsed laser deposition (PLD) method. ...Optimized conditions, namely a room temperature substrate under 10Pa oxygen pressure were used. Comparison with undoped NiO thin films indicates that lithium doping deteriorates NiO cubic phase (111) preferred orientation and also induces lattice disorder. The investigation of the electrochromic properties of Li–Ni–O thin films in aqueous liquid electrolyte, 1M KOH, on the one hand and in hydrophobic lithium conductive ionic liquid, 0.3M LiTFSI in BMITFSI, on the other hand, demonstrates an improvement in the electrochromic performances with lithium doping. Finally, electrochromic devices built on the association of WO3 and Li–Ni–O thin films and using the above quoted ionic liquid blended with PMMA as electrolyte are reported. Good electrochromic performances and neutral color are shown.
Natural molecular dye, anthocyanin, is described here as safe sensitizer for TiO2 particles in photo-degradation of organic contaminants in water. The dye is a promising replacement for the more ...costly and hazardous heavy metal based systems, such as CdS particles and Ru-compounds. TiO2/anthocyanin effectively catalyzed the photo-degradation of methyl orange contaminant under solar simulator radiation. The new TiO2/anthocyanin catalyst showed comparable efficiency to earlier systems, while avoiding their hazardous nature. When supported onto activated carbon (AC) particles, the resulting AC/TiO2/anthocyanin system showed enhanced efficiency and ease of recovery from the catalytic reaction mixture. The natural dye molecules showed the tendency to degrade under photo-degradation conditions, just like earlier hazardous sensitizers. However, complete mineralization of anthocyanin occurred leaving no traces of organic species in solution. Sensitizer degradation caused deactivation of the supported catalyst on recovery. Such a shortcoming was overcome by re-treatment of the recovered catalysts with fresh dye. Effects of different reaction parameters on the catalyst efficiency were studied. A mechanism, similar to earlier CdS-sensitized catalyst systems, is proposed for the TiO2/anthocyanin catalyst.
CdS thin films have been deposited onto FTO/glass substrates by two different techniques, electrochemical deposition (ECD) and chemical bath deposition (CBD). Feasibility of using these two film ...types in photoelectrochemical processes has been critically investigated here. The films were comparatively characterized by a number of techniques (solid state absorption spectra, solid state photoluminescence spectra, XRD and SEM). PEC characteristics of the electrodes, including current density–voltage (J–V) plots, conversion efficiency (η), stability and fill-factor (FF) were then studied. The results show that both systems involved nano-sized CdS particles living in coagulates. The ECD was thinner and more uniform than the CBD system. The CBD films were more effective in PEC processes than the ECD counterparts. Effect of annealing on characteristics of both electrode systems has been investigated. Annealing enhanced both film characteristics, but the CBD was affected to a higher extent, and the annealed CBD film was more effective than the ECD counterpart.
Display omitted Annealed CBD-prepared CdS films showed larger particle coagulates and higher stability under PEC conditions than the ECD counterparts.
► ECD technique yields thinner but more uniform CdS films than CBD. ► CdS films prepared by ECD were used in PEC processes for first time. ► CBD films of CdS are more effective in PEC processes than ECD counterparts.
Thin films of WO3 were prepared by surfactant assisted spray pyrolysis on F-doped SnO2 (FTO) conductive glass by using hexadecyltrimethylammonium bromide (HTAB) and polyethylene glycol (PEG400):HTAB ...as growth controlling agents. The surface tension of the spraying solutions was experimentally evaluated and was correlated with the deposition processes (nucleation and growth) of very smooth and homogenous films. The effect of the surfactant, alone and associated with PEG, on the structure (XRD), morphology (AFM), surface composition (XPS), FTIR and hydrophilicity (contact angle) were investigated and their influence on the electrochromic activity was discussed. Using surfactants and PEG, the coloration efficiency, transmission modulation and cycling stability of the WO3 thin films can be enhanced.
► WO3 thin films obtained by surfactant/polymer mediated spray pyrolysis. ► Solvation/interaction of WCl6 in/with surfactant changed solution properties. ► Film growth, crystallinity and topography influenced by solution composition. ► Film moisture sensitivity/wettability increased with surfactant content. ► Electrochromic activity of templated WO3 films tested in ionic liquid.
•Room Temperature Deposition of WO3 thin films on paper substrate.•UV irradiation of WO3 nano particles.•Electrochromic Performances in ionic liquid electrolyte.
Successful preparation of tungsten ...oxide thin films on paper substrate, using a novel room temperature deposition method involving the connection of tungsten oxide nanoparticles by UV-irradiation, is reported. WO3 thin films, prepared from synthesized monoclinic WO3 powder as compared to commercial ones, show higher electrochemical activity and good cycling stability in 0.3M trifluoromethanesulfonimide (HTFSI) in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI) ionic liquid electrolyte versus Pt as counter electrode. Electrochromic performances of complete devices using Prussian Blue (PB) as complementary counter electrode and 0.3M Lithium Bis(Trifluoromethanesulfonyl)Imide LiTFSI in BMITFSI plastified with polymethylmetacrylate (PMMA) membrane electrolyte are associated with a contrast in reflectance of 13%, from a yellow to a blue color.
Si doped zinc oxide (SZO, Si 3%) thin films are grown at low substrate temperature (
T≤150
°C) under oxygen atmosphere, using pulsed laser deposition (PLD). Si addition leads to film amorphization ...and higher densification. Hall effect measurements indicate a resistivity of 7.9×10
−4
Ω
cm for SZO thin films deposited at 100
°C under optimized 1.0
Pa oxygen pressure. This value is in good agreement with optical resistivity simulated from the transmittance spectra. XPS measurements suggest more than one oxygen environment, and a Si oxidation state lying in between 2 and 3 only. As a matter of fact, the values of both measured and simulated carrier numbers are smaller than the ones expected, assuming that all Si cations in the ZnO matrix are at the 4
+ oxidation state. Finally, the differences in the electrical and optical properties of SZO thin films deposited both on glass and PET substrates confirm the strong dependency of the electronic properties to the film crystallinity and stoichiometry in relationship with the substrate nature.
Display omitted
► Low temperature deposition of transparent and conductive ZnO:Si thin films. ► Confirmation of Hall effect measurements by modeling of the optical transmittance. ► XPS analysis of oxygen environment.
Mn K-edge X-ray absorption spectroscopic (XAS) analyses have been performed to probe the evolution of electronic and crystal structures of layered LiMnO2 upon chemical and electrochemical ...delithiation/relithiation. According to the X-ray absorption near-edge structure studies, it becomes clear that the trivalent manganese ion in LiMnO2 is significantly oxidized by acid treatment and is not fully recovered by subsequent lithiation reaction with n-BuLi. The extended X-ray absorption fine structure results presented here demonstrate that the local structure around manganese in LiMnO2 is changed from a layered α-NaFeO2-type structure to a spinel-like one upon chemical delithiation reaction. It is also found from the XAS analyses for the cycled LiMnO2 that the electrochemical charge−discharge process gives rise not only to the partial oxidation of manganese ion but also to the migration of Mn into the interlayer lithium site, resulting in the coexistence of the layered structure and the spinel one. Such results highlight the lattice instability of layered manganese oxide for the chemical and electrochemical extraction of lithium, which is responsible for the remarkable capacity fading and the formation of two plateaus at around the 3 and 4 V regions after the first electrochemical cycle. On the basis of the present experimental findings, we are now able to suggest that the electrochemical performance of layered LiMnO2 can be improved by blocking the Mn migration path through cationic substitution.
