Electrochromic and colorimetric properties of nickel(II) oxide thin films prepared by aerosol-assisted chemical vapor deposition.

Aerosol-assisted chemical vapor deposition (AACVD) was used for the first time in the preparation of thin-film electrochromic nickel(II) oxide (NiO). The as-deposited films were cubic NiO, with an octahedral-like grain structure, and an optical band gap that decreased from 3.61 to 3.48 eV on increase in film thickness (in the range 500-1000 nm). On oxidative voltammetric cycling in aqueous KOH (0.1 mol dm(-3)) electrolyte, the morphology gradually changed to an open porous NiO structure. The electrochromic properties of the films were investigated as a function of film thickness, following 50, 100, and 500 conditioning oxidative voltammetric cycles in aqueous KOH (0.1 mol dm(-3)). Light modulation of the films increased with the number of conditioning cycles. The maximum coloration efficiency (CE) for the NiO (transmissive light green, the "bleached" state) to NiOOH (deep brown, the colored state) electrochromic process was found to be 56.3 cm(2) C(-1) (at 450 nm) for films prepared by AACVD for 15 min followed by 100 "bleached"-to-colored conditioning oxidative voltammetric cycles. Electrochromic response times were <10 s and generally longer for the coloration than the bleaching process. The films showed good stability when tested for up to 10 000 color/bleach cycles. Using the CIE (Commission Internationale de l'Eclairage) system of colorimetry the color stimuli of the electrochromic NiO films and the changes that take place on reversibly oxidatively switching to the NiOOH form were calculated from in situ visible spectra recorded under electrochemical control. Reversible changes in the hue and saturation occur on oxidation of the NiO (transmissive light green) form to the NiOOH (deep brown) form, as shown by the track of the CIE 1931 xy chromaticity coordinates. As the NiO film is oxidized, a sharp decrease in luminance was observed. CIELAB L*a*b* coordinates were also used to quantify the electrochromic color states. A combination of a low L* and positive a* and b* values quantified the perceived deep brown colored state.

Influence of the film thickness and morphology on the colorimetric properties of spray-coated electrochromic disubstituted 3,4-propylenedioxythiophene polymers.

Variation of the colorimetric properties as a function of the film thickness and morphology has been investigated for two spray-coated electrochromic disubstituted 3,4-propylenedioxythiophene polymers. Changes in the luminance, hue, and saturation have been tracked using CIE 1931 Lxy chromaticity coordinates, with CIELAB 1976 color space coordinates, L*, a*, and b*, being used to quantify the colors. For (precycled) neutral PProDOT-(Hx)(2) films, with an increase in the thickness, L* is seen to decrease, with a* and b* coordinates moving in positive and negative directions, respectively, with quantification of the pink/purple (magenta) color as the summation of red and blue. For all thicknesses, L* is comparable, pre- and postcycling, with a* decreasing (less red) and b* becoming more negative (more blue) and the film now appearing as purple in the neutral state. Color coordinates for the reverse (reduction) direction exhibited hysteresis in comparison with the initial oxidation, with the specific choice of perceived color values depending not only on the film thickness but also on both the potential applied and from which direction the potential is changed. Neutral PProDOT-(2-MeBu)(2) films appear blue/purple to the eye both as-deposited and after potential cycling to the transparent oxidized state. For the neutral, colored state, with an increase in the thickness, L* is seen to decrease, with a* and b* coordinates moving in positive and negative directions, respectively. For PProDOT-(2-MeBu)(2) films, the a* coordinates are lower positive values and the b* coordinates are higher negative values, thus quantifying the high dominance of the blue color in the blue/purple films compared to the pink/purple PProDOT-(Hx)(2) films. As for the PProDOT-(Hx)(2) films, the tracks of the color coordinates show that the specific choice of perceived color values depends on the film thickness. Unlike the PProDOT-(Hx)(2) films, hysteresis is absent in the oxidation/reduction track of the x-y coordinates for the PProDOT-(2-MeBu)(2) films, although slight hysteresis is present in the luminance. Characterization of the film morphologies through atomic force microscopy reveals a much rougher, higher surface area morphology for the PProDOT-(2-MeBu)(2) films versus the PProDOT-(Hx)(2) films. The branched repeat unit in the PProDOT-(2-MeBu)(2) films provides a structure that allows ions to ingress/egress more effectively, thus removing hysteresis from the optical response.

Fingerprint and inkjet-trace imaging using disulfur dinitride.

Exposure of fingerprints to S(2)N(2) vapour results in the prints being visually imaged by polymeric (SN)(x) on an unprecedented range of media; in addition, the polymer forms in response to the interaction of S(2)N(2) with traces of inkjet inks, for example the minute amounts left by the contact between printed paper and an envelope.

Electrooxidation and Determination of Dopamine Using a Nafion®-Cobalt Hexacyanoferrate Film Modified Electrode.

The electrocatalysis of dopamine has been studied using a cobalt hexacyanoferrate film (CoHCFe)-modified glassy carbon electrode. Using a rotating disk CoHCFe-modified electrode, the reaction rate constant for dopamine was found to be 3.5 × 105 cm³ mol-1 s-1 at a concentration of 5.0 × 10-5 mol L-1. When a Nafion® film is applied to the CoHCFe-modified electrode surface a high selectivity for the determination of dopamine over ascorbic acid was obtained. The analytical curve for dopamine presented linear dependence over the concentration range from 1.2 × 10-5 to 5.0 × 10-4 mol L-1 with a slope of 23.5 mA mol-1 L and a linear correlation coefficient of 0.999. The detection limit of this method was 8.9 × 10-6 mol L-1 and the relative standard deviation for five measurements of 2.5 × 10-4 mol L-1 dopamine was 0.58%.

Rapid polymerisation of S2N2 within Na-ZSM-5 channels.

Reaction of S(2)N(2) vapour with Na-ZSM-5 results in rapid polymerisation and inclusion of the resulting (SN)(x) within the zeolite channels.

Spectroelectrochemical responses of thin-film conducting copolymers prepared electrochemically from mixtures of 3,4-ethylenedioxythiophene and 2,2'-bithiophene.

Here we have studied the electrocopolymerisation of binary mixtures of functionalised thiophenes in varying compositions and determined independently for each copolymer the spectroelectrochemical responses and the composition of the material using X-ray photoelectron spectroscopy. We have observed strong correlations between the composition of the copolymer material and the composition of the binary solution from which the polymer was grown. In addition, we have shown that the spectroelectrochemical properties of the copolymers indicate the presence of random copolymer material where the lambda(Max) values of the neutral, undoped, polymer scales with composition but also suggest that there may be small amounts of block copolymer or phase-separated mixtures of the homopolymer components.

Electrochemical properties of core-shell TiC-TiO2 nanoparticle films immobilized at ITO electrode surfaces.

Titanium carbide (TiC) nanoparticles are readily deposited onto tin-doped indium oxide (ITO) electrodes in the form of thin porous films. The nanoparticle deposits are electrically highly conducting and electrochemically active. In aqueous media (at pH 7) and at applied potentials positive of 0.3 V vs. SCE partial anodic surface oxidation and formation (at least in part) of novel core-shell TiC-TiO2 nanoparticles is observed. Significant thermal oxidation of TiC nanoparticles by heating in air occurs at a temperature of 250 degrees C and leads first to core-shell TiC-TiO2 nanoparticles, next at ca. 350 degrees C to TiO2 (anatase), and finally at temperatures higher than 750 degrees C to TiO2 (rutile). Electrochemically and thermally partially oxidized TiC nanoparticles still remain very active and for some redox systems electrocatalytically active. Scanning and transmission electron microscopy (SEM and TEM), temperature dependent XRD, quartz crystal microbalance, and voltammetric measurements are reported. The electrocatalytic properties of the core-shell TiC-TiO2 nanoparticulate films are surveyed for the oxidation of hydroquinone, ascorbic acid, and dopamine in aqueous buffer media. In TiC-TiO2 core-shell nanoparticle films TiO2 surface reactivity can be combined with TiC conductivity.

Dynamic in situ electrochemical neutron reflectivity measurements.

We report the first dynamic in situ electrochemical neutron reflectivity (NR) measurements on electroactive films. By using a boxcar integration strategy within a cyclic voltammetric experiment, it is possible to acquire neutron reflectivity data associated with narrow, defined windows of potential. Accumulation of data from repetitive cycles allows one to build up potential- (time-) resolved profiles. The effective time resolution is now on the order of seconds, as compared to ca. 1 h using conventional methodology, making in situ NR a practical technique for dynamic electrochemical studies. Illustrative data for polyvinylferrocene films reveal hysteresis in (de)swelling, incomplete desolvation upon reduction, and transient salt retention, all of which respond to time-scale variations.

Liquid / liquid ion-transfer processes at the dioctylphosphoric acid (N,N-didodecyl-N',N'-diethylphenylenediamine) / water (electrolyte) interface at graphite and mesoporous TiO2 substrates.

Biphasic electrode systems are studied for the case of the oxidation of the water-insoluble liquid N,N-didodecyl-N',N'-diethylphenylenediamine (DDPD) neat and dissolved in bis(2-ethylhexyl) phosphate (HDOP) and immersed in aqueous electrolyte media. The oxidation process in the absence of HDOP is accompanied by transfer of the anion (perchlorate or phosphate) from the water into the organic phase. However, in the presence of HDOP, oxidation is accompanied by proton exchange instead. This electrochemically driven proton exchange process occurs over a wide pH range. Organic microdroplet deposits of DDPD in HDOP at basal plane pyrolytic graphite electrodes are studied by voltammetric techniques and compared in their behavior to organic microphase deposits in mesoporous TiO2 thin films. The mesoporous TiO2 thin film acts as a host for the organic liquid and provides an alternative biphasic electrode system compared to the random microdroplet/graphite system. Two types of mesoporous TiO2 thin-film electrodes, (i) a 300-400-nm film on ITO and (ii) a 300-400-nm film on ITO sputter-coated with a 20-nm porous gold layer, are investigated.

New electrochromic materials.

A number of inorganic and organic materials exhibit redox states (reduced and/or oxidised forms) with distinct UV-Visible (electronic) absorption bands. When electrochemical switching of these redox states gives rise to different colours (i.e. new or different visible region bands), the material is described as being electrochromic. By virtue of their numerous applications, both of academic and commercial interest, electrochromic materials are currently attracting a great deal of interest. This review provides an introduction to the major classes of electrochromic materials, namely transition metal oxides, Prussian blue systems, viologens, conducting polymers, transition metal and lanthanide coordination complexes and metallopolymers, and metal phthalocyanines. Examples of some new materials and of prototype and commercial electrochromic devices are cited.