CA1288155C - Electrochromic window with metal grid counter electrode - Google Patents
Electrochromic window with metal grid counter electrodeInfo
- Publication number
- CA1288155C CA1288155C CA000568847A CA568847A CA1288155C CA 1288155 C CA1288155 C CA 1288155C CA 000568847 A CA000568847 A CA 000568847A CA 568847 A CA568847 A CA 568847A CA 1288155 C CA1288155 C CA 1288155C
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- CA
- Canada
- Prior art keywords
- article according
- electrochromic
- oxide
- metal
- film
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/15—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on an electrochromic effect
- G02F1/153—Constructional details
- G02F1/155—Electrodes
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/15—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on an electrochromic effect
- G02F1/153—Constructional details
- G02F1/155—Electrodes
- G02F2001/1555—Counter electrode
Abstract
Abstract of the Disclosure An electrochromic transparency comprising an electrochromic film and an ion-conductive layer disposed between a pair of electrodes is disclosed wherein the optical properties and electrochromic efficiency are improved by means of a metal grid electrode.
Description
~ 2~
ELECTROCHROMIC WINDOW WITH
METAL GRID COUNTER ELECTRODE
Background This invention relates generally to the art of electrochromic cells, and more particularly to the art of transparent electrochromic windows.
Electrochromic devices have been proposed for use in alpha-numeric display panels in items such as digital watches, calculators and the like. The electrochromic image formed by the application of an appropriate voltage to an electrochromic cell persists for a useful period after the activating voltage is discontinued, generally until it is erased by application of an appropriate voltage of reversed polarity.
U.S. Patent No. 3,521,941 to Deb et al discloses an electro-optical device having variable optical density useful in data dlsplay comprising a pair of transparent electrodes, and a film of transition metal compound and a current carrier permeable insulator disposed between the electrodes, the device exhibiting alternate coloration and bleaching at ambient temperature by control of the polarity of an applied electric field.
U.S. Patent No. 4,088,392 to Meyers discloses an electro-optical device comprising a pair of electrodes, and a film of a transition metal compound and a liquid electrolyte disposed between the electrodes, the device exhibiting coloration and bleaching thereof by control of the polarity of an applied electric field.
U.S. Patent No. 4,088,395 to Giglia discloses a method for forming a counter-electrode in a variable light modulating device of the electrochromic type. The counter-electrode is a paper composition of fibrous pulp and carbon.
1~88~
U.S. Patent No. 4,116,545 to Reddy discloses an electrochromic variable light modulating device including an improved ion conducting layer comprising a polymeric composition containing polyethylene sulfonic acid, a pigment and water. One of the electrodes comprises a glass substrate with an electroconductive layer of tin oxide over which is deposited an electrochromic tungsten oxide film. The second electrode is a paper electrode comprising a web of filament permeated with carbon, and is compression bonded to tin oxide coated glass.
U.S. Patent No. 4,174,152 to Giglia et al discloses electrochromic devices wherein the polymeric electrolyte material is a hydrophilic copolymer of a selected acrylate or methacrylate monomer and a selected acid group containing monomer, e.g. 2-acrylamido-2-methylpropanesulfonic acid.
U.S. Patent No. 4,335,938 to Giglia discloses electrochromic devices having a layer of tungsten oxide in contact with a layer of organic electrolyte resin comprising a hydrophilic layer of homopolymer of poly(2-acrylamldo-2-methylpropanesulfonic acid) with electrode means for changlng electrochromic properties of the devlce. A conventional electrochromic device is described as having a transparent electrochromic electrode comprising a glass substrate with a conductive tin oxide layer and an electrochromic, e.g. tungsten oxide, film; a pigmented, ion-conducting medium layer comprising a self-supporting layer of ion-conductive polymer having a pigment dispersed therein; and an opaque counter electrode such as carbon paper.
U.S. Patent No. 4,361,385 to Huang et al discloses electrochromic devices having a layer of electrochromic tungsten oxide in contact with a polymeric electrolyte wherein the stability and speed of the device are improved by using a copolymer of 2-acrylamido-2-~1 288155 methylpropanesulfonic acid and vinyl sulfonic acid as the polymerelectrolyte. An electrochromic film on an electrode is prepared by evaporation of an amorphous film of tungsten oxide onto a glass substrate coated with conductive tin oxide. The polymer mixture is cast, dried and hydrated in contact with the electrochromic film, and then a second electrode consisting of paper-carbon is pressed against the polymer layer with a second tin oxide coated glass plate backing the carbon-paper electrode.
U.S. Patent No. 4,375,318 to Giglia et al discloses electrochromic devices having a layer of electrochromic material, e.g.
tungsten oxide, in contact with a layer of organic electrolyte resin, with electrode means for changing electrochromic properties of the devices by electric field means. The electrolyte layer comprises a hydrophilic layer of homopolymer of poly(2-acrylamido-2-methylpropanesulfonic acid) with an organic humectant. An electrochromic device is prepared by thermal evaporation of an electrochromic tungsten oxide film onto an electroconductive tln oxide coated glass substrate. A pigmented resin solutlon is coated over the tungsten oxide and dried to form an ion-conductive polymer film which is hydrated to enhance ionic conductivity. An electrically conductive paper counter-electrode is pressed against the polymer with a graphite coated stainless steel plate.
U.S. Patent No. 4,478,991 to Huang et al discloses electrochromic devices having a layer of electrochromic material, e.g.
tungsten oxide, in contact with a polymeric electrolyte layer, the stability and speed of the device being improved by using a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and vinyl sulfonic acid as the polymer electrolyte. An electrochromic film on an electrode is prepared by evaporation of an amorphous film of tungsten oxide onto a glass ~1 288~55 substrate coated with conductive tin oxide. The polymer mixture is cast over the electrochromic film, dried to form a solid film and hydrated to enhance ion conductivity. A second electrode consisting of a paper-carbon structure is pressed against the polymer layer using a conductive tin oxide coated glass plate backing the paper counter electrode.
U. S. Patent No. 4,645,308 to Tracy et al discloses a solid-state transition metal oxide device comprising a plurality of layers including an electrochromic oxide layer and anode and cathode contacts.
Coloration is actuated within the electrochromic oxide layer by appllcation of a predetermined potential and the coloration action is adapted to sweep across the length of the electrochromic oxide layer.
Summary of the Invention The present invention provides an electrochromic cell which is transparent, and which darkens and bleaches completely at an applied electrical potential of less than 1.0 volt, positive and negative respectlvely. The present invention accomplishes the objective by means of a conductive metallic mesh counter electrode which allows transparency while insuring uniform rapid charge distribution over a large surface area and participating in a balancing half-cell reaction at a sufficient low potential to prevent electrolysis of water and concurrent gas evolution which occur at a higher voltage in the absence of the metal grid.
Description of the Drawings Figure 1 illustrates a metal grid useful as an electrode member in accordance with the present invention.
Figure 2 illustrates the transmittance at 550 nanometers of an electrochromic transparency in accordance with the present invention as a function of time over the course of darkening and bleaching cycles.
~ Z8815~
Description of the Preferred Embodiments Conventlonal electrochromic cells comprise a thin film of a persistent electrochromic material, i.e. a material responsive to the application of an electric field of a given polarity to change from a high-transmittance, non-absorbing state to a lower-transmittance, absorbing or reflecting state and remaining in the lower-transmittance state after the electric field is discontinued, preferably until an electric field of reversed polarity is applied to return the material to the high-transmittance state. The electrochromic film is in ion-conductive contact, preferably direct physical contact, with a layer of ion-conductive material. The ion-conductive material may be solid, liquid or gel, but is preferably a polymer layer. The electrochromic film and ion-conductive layers are disposed between two electrodes.
As a voltage is applied across the two electrodes, lons are conducted through the ion-conducting layer. When the electrode adjacent to the electrochromic film is the cathode, application of an electric field causes darkening of the film. Reversing the polarity causes reversal of the electrochromic properties, and the film reverts to its high transmittance state. Typically, the electrochromic film, preferably tungsten oxide, is deposited on a glass substrate coated with an electroconductive film such as tin oxide to form one electrode. The counter electrode of the prior art has typically been a carbon-paper structure backed by a similar tin oxide coated glass substrate or a metal plate.
While this conventional electrochromic device structure might be acceptable for data displays in items such as digital watches, it is not suitable for large transparent articles such as windows. While the opaque carbon-paper counter electrode may be replaced with a thin conductive film such as tin oxide, indium oxide or gold, these thin film electrodes encounter lateral electrical resistance which decreases the speed and uniformity of charge distribution as the surface area of the device increases. More importantly, in electric fields of about 1 volt, half-cell reactions which result in the evolution of gas from the electrolysis of water occur at the counter electrode, depending on the polarity, as follows:
Electrode Reaction Standard Potential . . _ Cathode 2H20 + 2e~ - H2 + 20H- -0.828 volts Anode 2H O 4H+ + 0 4 ~ -1.229 volts The hydrogen and oxygen gases produced by these reactions form bubbles which impair the optical properties of an electrochromic cell for use as a window.
The present invention involves the use of a metal mesh as the counter electrode, allowing transparency while providing uniform rapid charge distribution over a large surface area and participating in a balancing half-cell reaction at a lower potential which prevents electrolysis of water and concurrent gas evolution which would otherwise occur according to the following reactions, wherein x is typically up to about 0.5:
COLORATION
+
I e W03 + xe + xH - H W03 2H O 4H+ + O + 4 ~
1288~55 BLEACHING
-x 3 3 xH 2H O 1 2e~ ~ H + 20~-In accordance with the present invention, instead of the hydrolysis of water at the counter electrode, pictured on the right above, the balancing half-cell react$on in response to the electrochromic transition of tungsten oxide is the oxidation or reduction of the metal of the metal grid counter electrode which does not produce gas which can form bubbles and decrease the optical quality of the device.
In a preferred embodiment of the present invention, the electrochromic cell is a transparent laminate comprising two glass substrates. One electrode of the cell comprises one of the glass substrates coated with an electroconductive film, preferably tin oxide having a resistivlty of about 25 ohms per square or less. The electrochromic film, preferably tungsten oxide, is deposited over the conductive film, preferably by evaporation or sputtering to a preferred thickness of about 1000 to 4000 Angstroms. The second glass substrate is preferably uncoated glass. To form the counter electrode, a metal grid is disposed adjacen~ to the second glass substrate. A preferred metal for the grid is copper. For optimum optical properties, the copper grid preferably has line widths on the order of 0.0025 inch (about 0.0635 millimeter) and line spacing of about 20 lines per inch (about 8 lines per 1288~S5 centimeter). The metal grid pattern may be square or rectangular, but is preferably a pattern of interconnected circles for optimum optical properties as disclosed ln U.S. Patent 4,772,760. Preferred metal grids are produced by electroforming as disclosed in Canadian Serial No. 565,189. The electrochromic film/conductive film coated glass plate and the uncoated glass plate with ad~acent metal grid counter electrode are preferably spaced about 0.030 inch (about 0.76 millimeter) apart. Disposed in this space is an ion-conductive material, preferably an ion-conductive polymer as known in the art. Preferred ion-conductive polymers include homopolymers of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and copolymers of AMPS with vinyl sulfonic acid. Preferably, the metal grid counter electrode i8 embedded in the ion-conductive polymer at the interface of the polymer and the uncoated glass substrate. Electrical connections to the electrochromic film are preferably made by means of a bus bar, while connections to the metal grid counter electrode are preferably made directly.
The cell voltage in accordance with the present invention is sufficiently low 80 that the following electrolysis reactions of water, with concurrent evolution of gas which can form bubbles, do not occur:
Electrode Reaction Standard Potential Anode 2H 0 4H+ 0 4 ~ -1.229 volts Cathode 2H20 ~ 2e - H + 20H- -0.828 volt Instead, the metal grid counter electrode participates in balancing half-cell reactions at lower absolute potentials. For a copper grid counter electrode, the following balancing half-cell reactions occur instead:
~28815S
Electrode ReactionStandard Potential Anode Cu - Cu + e -0.521 volt Cù - Cu + e -0.153 volt Cathode Cu + e - Cu 0.153 volt Cu + e - Cu 0.521 volt The present invention will be further understood from the description of a specific example which follows.
EXAMPLE I
A transparent electrochromic cell is prepared using two glass cell members. One glass substrate is clear 3 millimeter thick float glass. The other is 5 millimeter thick float glass coated with a tin oxide film having a resistivity of 25 ohms per square. The conductive tln oxide glass member functions as an electrode, with a silver frit bus bar applied about the periphery. An electrochromic tungsten oxide film, ~03-yH20, wherein y represents the extent of hydration, is deposited over the conductive tin oxide film by resistive evaporation at an initial vacuum chamber pressure of about 4 x l0 Torr. The electrochromic tungsten oxide film is deposited to a thickness of about 4000 Angstroms.
The electrochromic film/conductive film coated glass member is positioned parallel with the uncoated glass member at a spacing of 0.030 inch (about 0.76 millimeter) utilizing a butyl rubber spacer. Into this sealed cell construction is cast a polymerization reaction mixture comprising 2-acrylamido-2-methylpropanesulfonic acid, water and organic solvent, which is cured to form an ion-conductive polymer film. Imbedded in the polymer, ~djacent to the uncoated glass substrate surface, is an electroformed copper square grid with 0.0025 inch lines at 20 lines per inch spacing, as illustrated in Figure 1, which functions as a counter electrode. The electrochromic cell thus formed has a luminous transmittance of about 70 percent at a wavelength of 550 nanometèrs. When an electric current is applied across the cell at a superficial current density of about 0.12 milliamps per square centimeter, the electrochromic film darkens to 20 percent transmittance in about 2 minutes. When the polarity is reversed, the electrochromic film returns to its initial transmittance in about 2 minutes as illustrated in Figure 2.
The above example is offered only to illustrate the present invention. While the above example utilizes a tungsten oxide electrochromic film, any electrochromic material may be employed, such as transition metal oxides, transition metal sulfides, transition metal oxysulfides, transition metal halides, selenides, tellurides, chromates, molybdates, tungstates, vanadates, niobates, tantalates, titanates, stannates, etc., especially oxides, sulfides and stannates of metals of Groups IV-B, V-B and VI-B, and oxides and sulfides of Lanthanide Series metals, particularly, in addition to tungsten oxide, molybdenum oxide, titanium oxide, vanadium oxide, niobium oxide, cerium oxide, copper stannate, cobalt tungstate and various metal molybdates, titanates and niobates.
Other electrochromic materials which reverse by short-circuiting or are effective only at elevated temperatures may also be employed. The ion-conductive layer may be chosen to be permeable to ions other than hydrogen, such as lithium. The metal mesh counter electrode may comprise nickel or other metals or alloys as well as the preferred copper. The metal mesh counter electrode may be coated with another material in order to provide a particularly desired balancing half-cell reaction, i.e. at a potential lower than that of the electrolysis of water, e.g. nickel coated with tungsten oxide or niobium oxide. While electroforming is a preferred lZ881S5 method for producing the counter electrode, any method which produces a grid with acceptable optical properties may be employed. The electrode in contact with the electrochromic material may also be in the form of a metal mesh, in which case the grid patterns of the two electrodes may be designed to complement each other or to provide particular optical properties. The substrate members of electrochromic cellæ may be any suitably transparent material. The scope of the present invention is defined by the following claims.
ELECTROCHROMIC WINDOW WITH
METAL GRID COUNTER ELECTRODE
Background This invention relates generally to the art of electrochromic cells, and more particularly to the art of transparent electrochromic windows.
Electrochromic devices have been proposed for use in alpha-numeric display panels in items such as digital watches, calculators and the like. The electrochromic image formed by the application of an appropriate voltage to an electrochromic cell persists for a useful period after the activating voltage is discontinued, generally until it is erased by application of an appropriate voltage of reversed polarity.
U.S. Patent No. 3,521,941 to Deb et al discloses an electro-optical device having variable optical density useful in data dlsplay comprising a pair of transparent electrodes, and a film of transition metal compound and a current carrier permeable insulator disposed between the electrodes, the device exhibiting alternate coloration and bleaching at ambient temperature by control of the polarity of an applied electric field.
U.S. Patent No. 4,088,392 to Meyers discloses an electro-optical device comprising a pair of electrodes, and a film of a transition metal compound and a liquid electrolyte disposed between the electrodes, the device exhibiting coloration and bleaching thereof by control of the polarity of an applied electric field.
U.S. Patent No. 4,088,395 to Giglia discloses a method for forming a counter-electrode in a variable light modulating device of the electrochromic type. The counter-electrode is a paper composition of fibrous pulp and carbon.
1~88~
U.S. Patent No. 4,116,545 to Reddy discloses an electrochromic variable light modulating device including an improved ion conducting layer comprising a polymeric composition containing polyethylene sulfonic acid, a pigment and water. One of the electrodes comprises a glass substrate with an electroconductive layer of tin oxide over which is deposited an electrochromic tungsten oxide film. The second electrode is a paper electrode comprising a web of filament permeated with carbon, and is compression bonded to tin oxide coated glass.
U.S. Patent No. 4,174,152 to Giglia et al discloses electrochromic devices wherein the polymeric electrolyte material is a hydrophilic copolymer of a selected acrylate or methacrylate monomer and a selected acid group containing monomer, e.g. 2-acrylamido-2-methylpropanesulfonic acid.
U.S. Patent No. 4,335,938 to Giglia discloses electrochromic devices having a layer of tungsten oxide in contact with a layer of organic electrolyte resin comprising a hydrophilic layer of homopolymer of poly(2-acrylamldo-2-methylpropanesulfonic acid) with electrode means for changlng electrochromic properties of the devlce. A conventional electrochromic device is described as having a transparent electrochromic electrode comprising a glass substrate with a conductive tin oxide layer and an electrochromic, e.g. tungsten oxide, film; a pigmented, ion-conducting medium layer comprising a self-supporting layer of ion-conductive polymer having a pigment dispersed therein; and an opaque counter electrode such as carbon paper.
U.S. Patent No. 4,361,385 to Huang et al discloses electrochromic devices having a layer of electrochromic tungsten oxide in contact with a polymeric electrolyte wherein the stability and speed of the device are improved by using a copolymer of 2-acrylamido-2-~1 288155 methylpropanesulfonic acid and vinyl sulfonic acid as the polymerelectrolyte. An electrochromic film on an electrode is prepared by evaporation of an amorphous film of tungsten oxide onto a glass substrate coated with conductive tin oxide. The polymer mixture is cast, dried and hydrated in contact with the electrochromic film, and then a second electrode consisting of paper-carbon is pressed against the polymer layer with a second tin oxide coated glass plate backing the carbon-paper electrode.
U.S. Patent No. 4,375,318 to Giglia et al discloses electrochromic devices having a layer of electrochromic material, e.g.
tungsten oxide, in contact with a layer of organic electrolyte resin, with electrode means for changing electrochromic properties of the devices by electric field means. The electrolyte layer comprises a hydrophilic layer of homopolymer of poly(2-acrylamido-2-methylpropanesulfonic acid) with an organic humectant. An electrochromic device is prepared by thermal evaporation of an electrochromic tungsten oxide film onto an electroconductive tln oxide coated glass substrate. A pigmented resin solutlon is coated over the tungsten oxide and dried to form an ion-conductive polymer film which is hydrated to enhance ionic conductivity. An electrically conductive paper counter-electrode is pressed against the polymer with a graphite coated stainless steel plate.
U.S. Patent No. 4,478,991 to Huang et al discloses electrochromic devices having a layer of electrochromic material, e.g.
tungsten oxide, in contact with a polymeric electrolyte layer, the stability and speed of the device being improved by using a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and vinyl sulfonic acid as the polymer electrolyte. An electrochromic film on an electrode is prepared by evaporation of an amorphous film of tungsten oxide onto a glass ~1 288~55 substrate coated with conductive tin oxide. The polymer mixture is cast over the electrochromic film, dried to form a solid film and hydrated to enhance ion conductivity. A second electrode consisting of a paper-carbon structure is pressed against the polymer layer using a conductive tin oxide coated glass plate backing the paper counter electrode.
U. S. Patent No. 4,645,308 to Tracy et al discloses a solid-state transition metal oxide device comprising a plurality of layers including an electrochromic oxide layer and anode and cathode contacts.
Coloration is actuated within the electrochromic oxide layer by appllcation of a predetermined potential and the coloration action is adapted to sweep across the length of the electrochromic oxide layer.
Summary of the Invention The present invention provides an electrochromic cell which is transparent, and which darkens and bleaches completely at an applied electrical potential of less than 1.0 volt, positive and negative respectlvely. The present invention accomplishes the objective by means of a conductive metallic mesh counter electrode which allows transparency while insuring uniform rapid charge distribution over a large surface area and participating in a balancing half-cell reaction at a sufficient low potential to prevent electrolysis of water and concurrent gas evolution which occur at a higher voltage in the absence of the metal grid.
Description of the Drawings Figure 1 illustrates a metal grid useful as an electrode member in accordance with the present invention.
Figure 2 illustrates the transmittance at 550 nanometers of an electrochromic transparency in accordance with the present invention as a function of time over the course of darkening and bleaching cycles.
~ Z8815~
Description of the Preferred Embodiments Conventlonal electrochromic cells comprise a thin film of a persistent electrochromic material, i.e. a material responsive to the application of an electric field of a given polarity to change from a high-transmittance, non-absorbing state to a lower-transmittance, absorbing or reflecting state and remaining in the lower-transmittance state after the electric field is discontinued, preferably until an electric field of reversed polarity is applied to return the material to the high-transmittance state. The electrochromic film is in ion-conductive contact, preferably direct physical contact, with a layer of ion-conductive material. The ion-conductive material may be solid, liquid or gel, but is preferably a polymer layer. The electrochromic film and ion-conductive layers are disposed between two electrodes.
As a voltage is applied across the two electrodes, lons are conducted through the ion-conducting layer. When the electrode adjacent to the electrochromic film is the cathode, application of an electric field causes darkening of the film. Reversing the polarity causes reversal of the electrochromic properties, and the film reverts to its high transmittance state. Typically, the electrochromic film, preferably tungsten oxide, is deposited on a glass substrate coated with an electroconductive film such as tin oxide to form one electrode. The counter electrode of the prior art has typically been a carbon-paper structure backed by a similar tin oxide coated glass substrate or a metal plate.
While this conventional electrochromic device structure might be acceptable for data displays in items such as digital watches, it is not suitable for large transparent articles such as windows. While the opaque carbon-paper counter electrode may be replaced with a thin conductive film such as tin oxide, indium oxide or gold, these thin film electrodes encounter lateral electrical resistance which decreases the speed and uniformity of charge distribution as the surface area of the device increases. More importantly, in electric fields of about 1 volt, half-cell reactions which result in the evolution of gas from the electrolysis of water occur at the counter electrode, depending on the polarity, as follows:
Electrode Reaction Standard Potential . . _ Cathode 2H20 + 2e~ - H2 + 20H- -0.828 volts Anode 2H O 4H+ + 0 4 ~ -1.229 volts The hydrogen and oxygen gases produced by these reactions form bubbles which impair the optical properties of an electrochromic cell for use as a window.
The present invention involves the use of a metal mesh as the counter electrode, allowing transparency while providing uniform rapid charge distribution over a large surface area and participating in a balancing half-cell reaction at a lower potential which prevents electrolysis of water and concurrent gas evolution which would otherwise occur according to the following reactions, wherein x is typically up to about 0.5:
COLORATION
+
I e W03 + xe + xH - H W03 2H O 4H+ + O + 4 ~
1288~55 BLEACHING
-x 3 3 xH 2H O 1 2e~ ~ H + 20~-In accordance with the present invention, instead of the hydrolysis of water at the counter electrode, pictured on the right above, the balancing half-cell react$on in response to the electrochromic transition of tungsten oxide is the oxidation or reduction of the metal of the metal grid counter electrode which does not produce gas which can form bubbles and decrease the optical quality of the device.
In a preferred embodiment of the present invention, the electrochromic cell is a transparent laminate comprising two glass substrates. One electrode of the cell comprises one of the glass substrates coated with an electroconductive film, preferably tin oxide having a resistivlty of about 25 ohms per square or less. The electrochromic film, preferably tungsten oxide, is deposited over the conductive film, preferably by evaporation or sputtering to a preferred thickness of about 1000 to 4000 Angstroms. The second glass substrate is preferably uncoated glass. To form the counter electrode, a metal grid is disposed adjacen~ to the second glass substrate. A preferred metal for the grid is copper. For optimum optical properties, the copper grid preferably has line widths on the order of 0.0025 inch (about 0.0635 millimeter) and line spacing of about 20 lines per inch (about 8 lines per 1288~S5 centimeter). The metal grid pattern may be square or rectangular, but is preferably a pattern of interconnected circles for optimum optical properties as disclosed ln U.S. Patent 4,772,760. Preferred metal grids are produced by electroforming as disclosed in Canadian Serial No. 565,189. The electrochromic film/conductive film coated glass plate and the uncoated glass plate with ad~acent metal grid counter electrode are preferably spaced about 0.030 inch (about 0.76 millimeter) apart. Disposed in this space is an ion-conductive material, preferably an ion-conductive polymer as known in the art. Preferred ion-conductive polymers include homopolymers of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and copolymers of AMPS with vinyl sulfonic acid. Preferably, the metal grid counter electrode i8 embedded in the ion-conductive polymer at the interface of the polymer and the uncoated glass substrate. Electrical connections to the electrochromic film are preferably made by means of a bus bar, while connections to the metal grid counter electrode are preferably made directly.
The cell voltage in accordance with the present invention is sufficiently low 80 that the following electrolysis reactions of water, with concurrent evolution of gas which can form bubbles, do not occur:
Electrode Reaction Standard Potential Anode 2H 0 4H+ 0 4 ~ -1.229 volts Cathode 2H20 ~ 2e - H + 20H- -0.828 volt Instead, the metal grid counter electrode participates in balancing half-cell reactions at lower absolute potentials. For a copper grid counter electrode, the following balancing half-cell reactions occur instead:
~28815S
Electrode ReactionStandard Potential Anode Cu - Cu + e -0.521 volt Cù - Cu + e -0.153 volt Cathode Cu + e - Cu 0.153 volt Cu + e - Cu 0.521 volt The present invention will be further understood from the description of a specific example which follows.
EXAMPLE I
A transparent electrochromic cell is prepared using two glass cell members. One glass substrate is clear 3 millimeter thick float glass. The other is 5 millimeter thick float glass coated with a tin oxide film having a resistivity of 25 ohms per square. The conductive tln oxide glass member functions as an electrode, with a silver frit bus bar applied about the periphery. An electrochromic tungsten oxide film, ~03-yH20, wherein y represents the extent of hydration, is deposited over the conductive tin oxide film by resistive evaporation at an initial vacuum chamber pressure of about 4 x l0 Torr. The electrochromic tungsten oxide film is deposited to a thickness of about 4000 Angstroms.
The electrochromic film/conductive film coated glass member is positioned parallel with the uncoated glass member at a spacing of 0.030 inch (about 0.76 millimeter) utilizing a butyl rubber spacer. Into this sealed cell construction is cast a polymerization reaction mixture comprising 2-acrylamido-2-methylpropanesulfonic acid, water and organic solvent, which is cured to form an ion-conductive polymer film. Imbedded in the polymer, ~djacent to the uncoated glass substrate surface, is an electroformed copper square grid with 0.0025 inch lines at 20 lines per inch spacing, as illustrated in Figure 1, which functions as a counter electrode. The electrochromic cell thus formed has a luminous transmittance of about 70 percent at a wavelength of 550 nanometèrs. When an electric current is applied across the cell at a superficial current density of about 0.12 milliamps per square centimeter, the electrochromic film darkens to 20 percent transmittance in about 2 minutes. When the polarity is reversed, the electrochromic film returns to its initial transmittance in about 2 minutes as illustrated in Figure 2.
The above example is offered only to illustrate the present invention. While the above example utilizes a tungsten oxide electrochromic film, any electrochromic material may be employed, such as transition metal oxides, transition metal sulfides, transition metal oxysulfides, transition metal halides, selenides, tellurides, chromates, molybdates, tungstates, vanadates, niobates, tantalates, titanates, stannates, etc., especially oxides, sulfides and stannates of metals of Groups IV-B, V-B and VI-B, and oxides and sulfides of Lanthanide Series metals, particularly, in addition to tungsten oxide, molybdenum oxide, titanium oxide, vanadium oxide, niobium oxide, cerium oxide, copper stannate, cobalt tungstate and various metal molybdates, titanates and niobates.
Other electrochromic materials which reverse by short-circuiting or are effective only at elevated temperatures may also be employed. The ion-conductive layer may be chosen to be permeable to ions other than hydrogen, such as lithium. The metal mesh counter electrode may comprise nickel or other metals or alloys as well as the preferred copper. The metal mesh counter electrode may be coated with another material in order to provide a particularly desired balancing half-cell reaction, i.e. at a potential lower than that of the electrolysis of water, e.g. nickel coated with tungsten oxide or niobium oxide. While electroforming is a preferred lZ881S5 method for producing the counter electrode, any method which produces a grid with acceptable optical properties may be employed. The electrode in contact with the electrochromic material may also be in the form of a metal mesh, in which case the grid patterns of the two electrodes may be designed to complement each other or to provide particular optical properties. The substrate members of electrochromic cellæ may be any suitably transparent material. The scope of the present invention is defined by the following claims.
Claims (20)
1. An article of manufacture having variable transmittance in response to an electric field comprising:
a. a transparent substrate;
b. an electroconductive electrode member;
c. a transparent electrochromic film in contact with said electroconductive electrode member;
d. an ion-conductive layer in contact with said electrochromic film; and e. a metal grid counter electrode in contact with said ion-conductive layer said metal capable of balancing half cell reactions at lower absolute potentials than the electrolysis reactions of water.
a. a transparent substrate;
b. an electroconductive electrode member;
c. a transparent electrochromic film in contact with said electroconductive electrode member;
d. an ion-conductive layer in contact with said electrochromic film; and e. a metal grid counter electrode in contact with said ion-conductive layer said metal capable of balancing half cell reactions at lower absolute potentials than the electrolysis reactions of water.
2. An article according to claim 1, wherein said transparent substrate is glass.
3. An article according to claim 1, wherein said electroconductive electrode member is a transparent film.
4. An article according to claim 3, wherein said film comprises a conductive material selected from the group consisting of metals and metal oxides.
5. An article according to claim 4, wherein said film comprises a conductive metal oxide selected from the group consisting of indium oxide, tin oxide and mixtures thereof.
6. An article according to claim 1, wherein said electroconductive electrode member is a metal grid.
7. An article according to claim 1, wherein said transparent electrochromic film comprises an electrochromic material selected from the group consisting of transition metal oxides, transition metal sulfides, transition metal oxysulfides, transition metal halides, selenides, tellurides, chromates, molybdates, tungstates, vanadates, niobates, tantalates, titanates and stannates.
8. An article according to claim 7, wherein said electrochromic material is selected from the group consisting of tungsten oxide, molybdenum oxide, titanium oxide, vanadium oxide, niobium oxide, cerium oxide, copper stannate and cobalt tungstate.
9. An article according to claim 8, wherein said electrochromic film comprises tungsten oxide at a thickness of 1000 to 4000 Angstroms.
10. An article according to claim 1, wherein said ion-conductive layer comprises a polymer.
11. An article according to claim 10, wherein said metal grid counter electrode is embedded in said polymer layer.
12. An article according to claim 1, wherein said metal grid comprises a metal selected from the group consisting of nickel and copper.
13. An article according to claim 12, wherein said metal grid comprises copper.
14. An article according to claim 1, wherein said metal grid is an electroformed grid.
15. An article according to claim 1, further comprising a second transparent substrate adjacent to said metal grid counter electrode.
16. An article according to claim 15, wherein said second transparent substrate is glass.
17. An article according to claim 16, wherein said metal grid counter electrode is adjacent to said second transparent substrate.
18. An article of manufacture having variable transmittance in response to an electric field comprising:
a. a transparent glass substrate;
b. an electroconductive electrode member deposited on said substrate;
c. a transparent electrochromic tungsten oxide film in contact with said electroconductive electrode member;
d. an ion-conductive polymer layer in contact with said electrochromic film; and e. a copper grid counter electrode in contact with said ion-conductive polymer layer.
a. a transparent glass substrate;
b. an electroconductive electrode member deposited on said substrate;
c. a transparent electrochromic tungsten oxide film in contact with said electroconductive electrode member;
d. an ion-conductive polymer layer in contact with said electrochromic film; and e. a copper grid counter electrode in contact with said ion-conductive polymer layer.
19. An article of manufacture having variable transmittance in response to an electric field comprising:
a. a transparent substrate;
b. an electroconductive electrode member;
c. a transparent electrochromic film in contact with said electroconductive electrode member;
d. an ion-conductive layer in contact with said electrochromic film; and e. a metal grid counter electrode in contact with said ion-conductive layer wherein said metal grid is coated with a material which undergoes a half-cell reaction at a potential lower than that of the electrolysis of water.
a. a transparent substrate;
b. an electroconductive electrode member;
c. a transparent electrochromic film in contact with said electroconductive electrode member;
d. an ion-conductive layer in contact with said electrochromic film; and e. a metal grid counter electrode in contact with said ion-conductive layer wherein said metal grid is coated with a material which undergoes a half-cell reaction at a potential lower than that of the electrolysis of water.
20. An article according to claim 19, wherein said material is selected from the group consisting of tungsten oxide and niobium oxide.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60,543 | 1987-06-10 | ||
| US07/060,543 US4768865A (en) | 1987-06-10 | 1987-06-10 | Electrochromic window with metal grid counter electrode |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1288155C true CA1288155C (en) | 1991-08-27 |
Family
ID=22030155
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000568847A Expired - Lifetime CA1288155C (en) | 1987-06-10 | 1988-06-07 | Electrochromic window with metal grid counter electrode |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4768865A (en) |
| EP (1) | EP0294756B1 (en) |
| JP (2) | JPS6478238A (en) |
| AU (1) | AU588507B2 (en) |
| BR (1) | BR8802785A (en) |
| CA (1) | CA1288155C (en) |
| DE (1) | DE3851011T2 (en) |
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| EP0400797A3 (en) * | 1989-05-30 | 1991-10-02 | Ford Motor Company Limited | Electrochromic device |
| AU615622B2 (en) * | 1989-09-13 | 1991-10-03 | Ppg Industries, Inc. | Electrochromic window with polymer layer |
| US5066111A (en) * | 1989-09-13 | 1991-11-19 | Ppg Industries, Inc. | Electrochromic window with integrated bus bars |
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| WO1991014198A1 (en) * | 1990-03-06 | 1991-09-19 | The Dow Chemical Company | Electrochromic device |
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| CA2056937C (en) * | 1990-12-26 | 1996-12-10 | Kuo-Chuan Ho | Solid-state electrochromic device with proton-conducting polymer electrolyte |
| US5161048A (en) * | 1990-12-26 | 1992-11-03 | Ppg Industries, Inc. | Electrochromic window with metal grid counter electrode and acidic polyelectrolyte |
| US5293546A (en) * | 1991-04-17 | 1994-03-08 | Martin Marietta Corporation | Oxide coated metal grid electrode structure in display devices |
| EP0526995A3 (en) * | 1991-07-18 | 1993-12-15 | Ford Motor Co | An electrochromic material |
| FR2689655A1 (en) * | 1992-04-02 | 1993-10-08 | Thomson Csf | Electrochromic-electrolyte cell for coating large surfaces e.g. vehicle or building window variable absorption filter - has electrode which ensures even distribution of resistance from connection point of external power supply using conductive grid or layer having resistance values related to distance from point. |
| US5384653A (en) * | 1992-11-06 | 1995-01-24 | Midwest Research Institute | Stand-alone photovoltaic (PV) powered electrochromic window |
| WO1994016356A1 (en) * | 1993-01-05 | 1994-07-21 | Martin Marietta Corporation | Improved electrode for display devices |
| JP3315187B2 (en) * | 1993-03-30 | 2002-08-19 | 新日本石油株式会社 | Counter electrode for dimmer and dimmer |
| US5408353A (en) * | 1993-07-13 | 1995-04-18 | Ford Motor Company | Controllable transparency panel with solar load reduction |
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| DE19631420B4 (en) * | 1996-08-06 | 2004-03-04 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | glazing element |
| US5903382A (en) * | 1997-12-19 | 1999-05-11 | Rockwell International Corporation | Electrodeposition cell with high light transmission |
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| DE19804314A1 (en) * | 1998-02-04 | 1999-08-12 | Bayer Ag | Electrochromic display |
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| US6055089A (en) * | 1999-02-25 | 2000-04-25 | Minnesota Mining And Manufacturing Company | Photovoltaic powering and control system for electrochromic windows |
| US7009751B2 (en) * | 1999-05-14 | 2006-03-07 | Gentex Corporation | Electrochromic rearview mirror incorporating a third surface partially transmissive reflector |
| US7256923B2 (en) * | 2001-06-25 | 2007-08-14 | University Of Washington | Switchable window based on electrochromic polymers |
| US7450290B2 (en) * | 2001-06-25 | 2008-11-11 | University Of Washington | Electropolymerization of enhanced electrochromic (EC) polymer film |
| US6819367B1 (en) | 2001-10-19 | 2004-11-16 | Frank James Cava | Shade-free light control system and method |
| US7298541B2 (en) | 2002-06-25 | 2007-11-20 | University Of Washington | Green electrochromic (EC) material and device |
| US7808691B2 (en) * | 2002-06-25 | 2010-10-05 | University Of Washington | Green electrochromic materials |
| JP2007054742A (en) * | 2005-08-25 | 2007-03-08 | Niigata Univ | Hydrogen generating catalyst, hydrogen generating electrode, and manufacturing method thereof |
| US7874666B2 (en) | 2007-03-26 | 2011-01-25 | University Of Washington Through Its Center For Commercialization | Smart sunglasses, helmet faceshields and goggles based on electrochromic polymers |
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| US11745702B2 (en) | 2018-12-11 | 2023-09-05 | Ppg Industries Ohio, Inc. | Coating including electrically conductive lines directly on electrically conductive layer |
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-
1987
- 1987-06-10 US US07/060,543 patent/US4768865A/en not_active Expired - Fee Related
-
1988
- 1988-06-07 CA CA000568847A patent/CA1288155C/en not_active Expired - Lifetime
- 1988-06-07 DE DE3851011T patent/DE3851011T2/en not_active Expired - Fee Related
- 1988-06-07 EP EP88109044A patent/EP0294756B1/en not_active Expired - Lifetime
- 1988-06-08 BR BR8802785A patent/BR8802785A/en unknown
- 1988-06-09 JP JP63142740A patent/JPS6478238A/en active Pending
- 1988-06-09 AU AU17559/88A patent/AU588507B2/en not_active Ceased
-
1994
- 1994-02-14 JP JP000605U patent/JPH0676940U/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE3851011T2 (en) | 1995-03-09 |
| US4768865A (en) | 1988-09-06 |
| AU1755988A (en) | 1989-02-23 |
| DE3851011D1 (en) | 1994-09-15 |
| JPS6478238A (en) | 1989-03-23 |
| EP0294756A1 (en) | 1988-12-14 |
| EP0294756B1 (en) | 1994-08-10 |
| BR8802785A (en) | 1988-12-27 |
| AU588507B2 (en) | 1989-09-14 |
| JPH0676940U (en) | 1994-10-28 |
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