César O. Avellaneda

Thin films of V2O5/MoO3 and their applications in electrochromism

Pure and doped vanadium pentoxide (V2O5, V2O5/MoO3) thin films were prepared by sol-gel method and dip coating technique. Furthermore, they were characterized by chronocoulometry, cyclic voltammetry (CV), UV-Vis, atomic force microscopy (AFM), X-ray diffraction (XRD), and perfilometry. The best results were obtained with V2O5/MoO3 5xa0mol% film, which showed highest ion storage capacity of ~92xa0mCxa0cm−2 when compared to other films. Moreover, thisxa0film showed optical modulation of 40% at 633xa0nm after coloration and bleaching for 60xa0s. XRD patterns revealed that the film has orthorhombic crystalline structure; AFM and perfilometry confirmed roughness and thickness of 4.38 and 554xa0nm, respectively.

Li+ ions diffusion coefficient in V2O5:MoO3 Sol-Gel films

ABSTRACT Present work shows results of Li+ ions insertion and extraction from vanadium pentoxide doped with 5 mol% of molybdenum trioxide (V2O5:MoO3) thin films. The characterizations were performed by cyclic voltammetry (CV), potentiostatic intermittent titration technique (PITT), and electrochemical impedance spectroscopy (EIS). The obtained results revealed Li+ diffusional behavior for anodic and cathodic processes, and it was found that Li+ diffusion coefficient (D) values obtained from CV, PITT, and EIS varied from 10−10 to 10−12 cm2 s−1. Finally, a diffusion of Li+ process was modeled by solving Fick equation with constant D in plane sheet geometry.

Influence of Li+:V2O5 doping on Nb2O5 thin films electrochemical performance

ABSTRACT Aiming to improve electrochromic properties of niobium pentoxide (Nb2O5) there were synthesized new, doped with lithium trifluoromethane sulfonate salt (LiCF3SO3), and vanadium pentoxide (Nb2O5:Li+:V2O5) thin films. A study of these films focused on influence of doping on the electrochromic performance of these films. It was observed that Nb2O5:Li+:V2O5 presents a reversible and fast insertion/extraction kinetics. A maximum charge density for three layers film was −36.0 mC cm−2, and it corresponded to spectral transmission change of ΔT = 66%, i.e., variation from 80 to 20% from transparent to colored states.

Electrochemical, UV–Vis, and microscopical characteristics of sol–gel CeO 2 :V 2 O 5 thin film

Cerium dioxide (CeO2) and cerium dioxide doped with vanadium pentoxide (CeO2:V2O5) were synthesized from sol–gel precursors and deposited by spin coating on a conductive glass substrate (FTO). The films with different concentration of dopant and number of deposited layers were studied throughout cyclic voltammetry (CV), chronoamperometry/chronocoulometry, atomic force microscopy (AFM), scanning electron microscopy (SEM), and UV–Vis spectroscopy. The best value of charge density of 18.9xa0mCxa0cm−2 was obtained for CeO2 doped with 15xa0mol% of V2O5 film. The chemical diffusion coefficient of lithium ions into CeO2 was 1.73u2009×u200910−12 and CeO2:V2O5 15xa0mol% 6.75u2009×u200910−13xa0cm2xa0s−1. This film presented 79% of transparency in UV–Vis and 5% color change under ±u20091.3xa0V of applied potentials. Structural analyses revealed its homogeneous surface and the root mean-squared roughness (RMS) value of 9.42xa0nm. Based on the obtained results, CeO2 doped with 15xa0mol% V2O5 film is a promising thin coating for the use in electrochromic devices as a passive counter-electrode.

Ecologically friendly xanthan gum-PVA matrix for solid polymeric electrolytes

Two water-soluble and biodegradable polymers: xanthan gum (XG) and poly(vinyl alcohol) (PVA) were used to synthesize ecologically friendly solid polymer electrolyte (SPE) matrices. While XG is a natural polymer, PVA is a synthetic one, but both are colorless and form transparent membranes. To obtain ionic conductivity properties, the samples were doped with acetic acid and characterized by electrochemical impedance spectroscopy (EIS), X-ray diffraction, UV-Vis spectroscopy, and tensile test. The best results of ionic conductivity of 1.97xa0×xa010−4 and 7.41xa0×xa010−4xa0S/cm at room temperature and 80xa0°C, respectively, were obtained for the sample containing 55xa0wt% of acetic acid. Moreover, this electrolyte was found to be predominantly amorphous with transmittance in the visible region of 80% and absorbance values below 0.5 between 240 and 375xa0nm. Tensile test of this sample, applied up to 18xa0N of maximum force, resulted in strain of 2322% and Young’s modulus of 0.02xa0MPa. The obtained results showed that these new eco-friendly materials are promising for use as electrolytes in electrochemical devices.

Influence of molybdenum trioxide thin film thickness on its electrochemical properties

ABSTRACT Molybdenium trioxide (MoO3) thin films of one to ten coatings were obtained. The X-ray diffractograms of the xerogels revealed the formation of α-orthorhombic phase of MoO3 with index plane of 020 and crystallite size of 45 nm. The electrochemical reversibility upon Li+ intercalation/deintercalation was confirmed by cyclic voltammetry, and the best anodic (Qa = 25 mC cm−2) and cathodic charge (Qc = 25.5 mC cm−2) ratio of 0.98 was obtained for the nine-layered film. This film changed 43% of its transmittance between blue and transparent states. SEM evidenced a grain structured film surface and 376 nm thickness of nine-layered MoO3 film, and the Atomic Force Microscopy (AFM) showed a dense morphology with roughness of 54 nm.