Chemistry: electrical current producing apparatus – product – and – Having earth feature
Patent
1993-11-12
1995-11-28
Skapars, Anthony
Chemistry: electrical current producing apparatus, product, and
Having earth feature
205241, 205255, 427437, 4274431, H01M 800, B05D 118
Patent
active
054706734
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novel electrochromic and electrocatalytic material supported on a substrate, to a process for the preparation of the said material, to its use in electrochromic applications, and to its use as an electrocatalyst, more especially in alcohol fuel cells, in the electrochemical determination of alcohol contents and in the electrochemical oxidation of gaseous mixtures, more especially gaseous mixtures including carbon monoxide, for example, reformed gases containing hydrogen, carbon dioxide and carbon monoxide.
2. Brief Description of Related Art
Tungsten trioxide is an electrochromic material which colours by a reduction process. For applications to displays and windows, tungsten trioxide has been considered as a potential competitor to liquid crystals. However, there have been certain problems hindering its widespread acceptance, a crucial one being relatively slow response time arising from the fact that tungsten trioxide has relatively high resistivity and overpotential for hydrogen oxidation and evolution.
The reaction for the colouration of a tungsten trioxide film to hydrogen tungsten bronze in an acidic medium is as follows: where 0<x.ltoreq.1.
The forward reaction is the colouring process and the backward reaction is the bleaching process. The colouring rate is limited by the diffusion rate of the hydrogen into the WO.sub.3 film to form the electronically conducting hydrogen tungsten bronze, as the initial reaction occurs at the interface of the conducting substrate and the film. If the highly resistive tungsten trioxide layer could be made more conductive, then this would have the effect of increasing the rate of colouration. One method of doing this is by the incorporation of catalysts into the film. It has previously been proposed to admix platinum black with tungsten trioxide powder, to bind the resulting mixture using a PTFE dispersion and to support the bonded mixture on a metallic screen. Use of such a Pt/WO.sub.3 mechanical admixture results in very active hydrogen evolution since the hydrogen evolution and oxidation overpotential on platinum is very low and the hydrogen formed readily diffuses into the tungsten trioxide lattice. The resulting hydrogen tungsten bronze will also participate in the electrochemical reaction, the so-called spill-over effect. Pt/WO.sub.3 mixtures, however, have the drawback that they rely on contacts between platinum particles and tungsten trioxide particles and not all of the platinum atoms can be utilised.
SUMMARY OF THE INVENTION
The present invention provides an electrochemical deposition process which comprises forming a solution of ions comprising at least one metal (A) capable of forming a hydrogen bronze and ions comprising at least one metal (B) from Group VIII of the periodic table, and causing electrochemical deposition from the said solution onto a cathodic substrate.
The electrodeposited material obtainable by the process of the invention has both electrochromic and electrocatalytic properties.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a, 1b and 1c show the typical cyclic voltammetry curves (in 0.5 mol/l sulphuric acid, +0.5 V to -0.5 V vs Standard Calomel Electrode, scan rate 50 mV/s) of, respectively, tungsten trioxide films, tungsten trioxide films doped with cobalt and films doped with nickel, deposited (at the various cathodic potentials shown on the Figures) on indium-tin-oxide-coated glass.
FIG. 2 shows a comparison to FIGS. 1a, 1b and 1c of their coloring currents at -0.45 and -0.5 V in 0.5 mol/l H.sub.2 SO.sub.4 aqueous solution.
FIGS. 3 to 6 show plots of the transient peak current vs. pulse potential in potential pulse experiments on tungsten trioxide films doped with cobalt or nickel obtained by the process of the invention.
FIG. 7 is a comparison to FIGS. 3-6, to compare the current efficiency of deposition.
FIG. 8 shows the cathodic peak current in cyclovoltammetry as a function of scan rate for film-coated gold electrodes made from deposition soluti
REFERENCES:
Journal of the Electrochemical Society, vol. 138, No. 9, Sep. 1991, P. K. Shen et al. "The Performance of Electrochemical Tungsten Trioxide Films Doped With Cobalt or Nickel", pp. 2778-2783.
Journal of Electrochemical Society pp. 874-875 Extended Abstracts (Aug. 1988).
Chemical Abstracts--The Performance of Electrochromic Tungsten Etc. (Aug. 1988).
Methanol Oxidation Characteristics of Rare Earth Tungsten etc. (Aug. 1988).
Shen Pei K.
Syed-Bokhari Jade
Tseung Alfred C. C.
Skapars Anthony
University of Essex
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