Stock material or miscellaneous articles – Composite
Reexamination Certificate
1997-06-03
2001-02-27
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Composite
C428S131000, C428S457000, C428S901000, C428S918000, C428S917000, C428S912200, C359S265000, C359S267000, C359S269000, C359S270000, C359S271000, C359S266000, C359S274000
Reexamination Certificate
active
06194072
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an electrochromic unit having an electrochemical cell with at least two electrodes, an ion conductor located between the electrodes and an electrochromic material.
BACKGROUND OF THE INVENTION
The hitherto known electrochromic units are electrochromic windows with transparent systems, which can be coloured in any desired manner. They are intended to absorb incident electromagnetic radiation, preferably visible tight. They are e.g. used in the car sector, where they are employed in the form of dimmable rear-view mirrors. For this purpose the electrochromic windows have an electrochromic cell with two electrodes and an electrolyte located between them, the electrodes being in each case applied to a suitable carrier and at least one carrier and one electrode are transparent. The electrochromic material is applied to the transparent electrode between the electrode and the electrolyte. Glass normally forms the transparent carrier and is then coated with the transparent electrode. The electrochromic material is usually in the form of transition metal oxides, e.g. tungsten oxide. Such a window with tungsten oxide as the inorganic, electrochromic material is used in window construction, where the tungsten oxide is introduced between two window panes and is used for darkening the entire pane for reducing insolation. The electrolyte is always an ion conductor and is located between the electrochromic material, e.g. tungsten oxide, and the second electrode positioned parallel to the first. As a result of this arrangement (transparent carrier/first, transport electrode/electrochromic material/electrolyte/second electrode/carrier), it is ensured that the electrolyte and electrochromic material are always in intimate contact with one another, so that in the case of a current flow a material exchange can take place between them. As a result of an applied voltage, charges are injected into the electrochromic material, which gives rise to the desired colour change. However, it is disadvantageous that several minutes are always needed for the colouring or decolourizing of the window.
Apart from metal oxides, electrically conductive polymers are used as electrochromic materials. Here again charges are injected into the polymer by a current flow between the electrodes and give rise to a colour change. The transparent electrode is usually constituted by indium tin oxide to which the electrochromic polymer is applied. As ion conductors acidic electrolytes are needed, which is followed by the second electrode, which is usually also transparent. However, each windows have an inadequate long-term stability, because the acidic electrolytes act corrosively with respect to the transparent electrode. With time the latter gradually loses its electrical conductivity, so that the electrochromic material can no longer be activated. The electrochromic window can consequently no longer fulfil its function over a period time.
The problem of the invention is to provide an electrochromic unit of the aforementioned type, in which there is no need for a transparent carrier or a transparent electrode and which in the case of rapid switching times is characterized by a high long-term stability.
SUMMARY OF THE INVENTION
According to the invention the set problem is solved by an electrochromic unit of the aforementioned type, which is characterized in that the ion conductor is a proton exchange membrane and is the carrier for electrodes bilaterally applied thereto, that the electrodes are metal electrodes and that the electrochromic material is located on the membrane-remote side of an electrode carrying it. This electrochromic unit according to the invention is characterized in that, compared with an electrochromic window, it has a completely novel construction, in which the electrochromic polymer is located outside the electrochromic cell of electrodes and proton exchange membrane. As the electrochromic material is flow on the outside, there is no need for a transparent carrier or electrodes. This novel electrochromic system is based on the proton exchange membrane, which serves both as a carrier for the electrodes or electrical contacts and as a solid ion conductor allowing a charge transfer between the two electrodes. There is also no need for a further, separate carrier for the electrodes, as in the prior art. As the electrodes no longer need be transparent, there is a considerable increase in the number of possible electrode materials. It is correspondingly possible to use electrodes with a higher corrosion resistance than is the case with the hitherto available transparent electrode materials, such as e.g. indium tin oxide. Correspondingly the novel electrochromic unit according to the invention has a high long-term stability.
In preferred manner, the proton exchange membrane is constructed in the form of a solid film or foil. Due to the fact that on the film are now applied the electrodes and on an electrode the electrochromic polymer, it is possible to create a flexible, pliable electrochromic system. This makes possible wider fields of application than was possible with the known electrochromic windows, which were rigid and inflexible due to the carrier materials. The proton exchange membrane preferably comprises a fluorine polymer, to whose side chains are applied sulphonic acid groups. Such a membrane is obtainable under the trade name Nafion. However, it is also possible to use a membrane of any other suitable material. The membrane layer thickness is max 100 &mgr;m and is preferably 10 &mgr;m thick or less.
The electrodes, which no longer need be transparent, are preferably made from metal, such as gold or platinum. These metals have a much higher corrosion resistance than the hitherto available transparent electrode materials and can be bilaterally applied to the proton exchange membrane in the form of electric contacts. The application of the electrodes or electric contacts to the ion-conducting layer or PEM preferably takes place by deposition from the gas phase. It is alternatively possible to electrically contact one side of the proton exchange membrane by simply pressing on a metal net or lattice or a metal-coated net. However, this alternative procedure is only possible for the counterelectrode. Through deposition from the gas phase it is now possible to apply the metal coating forming the electrodes in such a thin manner that the metal coating appears optically transparent, but still permits electrical conduction. It is in particular possible in this way to ensure that the metal electrode is continuously, areal electrically conductive, whilst being permeable for the protons migrating between the electrochromic polymer and membrane. Without such an ion migration, in this case a proton migration, between the solid electrolyte and the electrochromic polymer through the metal electrode no colour change would be possible. It has been found that the requirements concerning proton permeability, as well as the continuous, areal electrical conductivity are fulfilled by a metal electrode with a minimum thickness of a few nanometers. The electric contacts or metal coating preferably have a thickness of at least 5 nm. As a function of the intended use, this thickness can be varied up to 30 nm.
The electrochromic polymer is preferably polyaniline or a derivative thereof. In the ease of polyaniline or its derivatives as the electrochromic material, it is possible to obtain different colours and consequently a different absorption behaviour at different wavelengths, particularly in the visible range of the spectrum. With such materials a transparent state can also be achieved. With polyaniline derivatives the different colours, etc. are brought about by the side chains on the polymer skeleton, because they have different absorption characteristics as a function of the chemical structure of the side chains. Consequently the absorption wavelengths can be displaced. In addition, polyaniline and its derivatives have a high long-term stability and are far batter than oth
Dörflinger Ulrike
Hambitzer Gunther
Schmidt Clemens
Stassen Ingo
Antonelli, Terry Stout & Kraus, LLP.
Fraunhofer-Gesellschaft zur Forderung der ange-wandten Forschung
Watkins III William P.
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