Triple electrode photogalvanic cell with energy storage capability

A photogalvanic cell includes a glass substrate with a transparent electrode which receives irradiating light energy. A second electrode is positioned in spaced relationship from the first electrode and has a thin film of charge storing tungsten oxide deposited thereon. Spaced from both the transparent electrode and the tungsten oxide thin film is a counterelectrode. An electrolyte having TiO.sub.2 powder mixed therein forms a photoactive site at the surface of the transparent electrode. By physically separating the tungsten oxide thin film from the transparent electrode, more light irradiates the TiO.sub.2 thereby increasing the photoconversion of the cell.

FIELD OF THE INVENTION 
The present invention relates to photogalvanic cells utilizing an aqueous 
electrolyte and more particularly to such a cell that is also capable of 
storing charge. 
BRIEF DESCRIPTION OF THE PRIOR ART 
In copending U.S. patent application Ser. No. 582,344, filed May 30, 1978, 
now U.S. Pat. No. 4,085,257, a photogalvanic cell is disclosed which has 
charge storing capability. The cell has a face against which impinging 
light strikes, the face including a thin film of charge storing tungsten 
oxide which contacts the contained electrolyte across the entire surface 
of the thin film. In the electrolyte it is the TiO.sub.2 which is 
primarily responsible for the conversion of light to electrical energy. 
Although the device disclosed in the copending application operates 
satisfactorily, it suffers from a disadvantage. This is due to the fact 
that the tungsten oxide will assume a color in response to light 
irradiation. The colored tungsten oxide acts as a filter which absorbs 
visible light energy which could otherwise irradiate the TiO.sub.2 
resulting in a greater energy conversion efficiency when the electrolyte 
is sensitized to visible light. 
BRIEF DESCRIPTION OF THE PRESENT INVENTION 
The present invention is an improvement over the structure set forth in the 
previously mentioned copending application. Whereas the device in the 
referenced application includes an electrode upon which a charge storing 
thin film of tungsten oxide is deposited and which further serves as the 
electrode for the photoactive TiO.sub.2 in the electrolyte, the present 
invention is designed to utilize separate electrodes for the charge 
storage layer and the photoactive TiO.sub.2. As a result of this 
separation, the aforementioned light filter problem is avoided because 
irradiating light is permitted to impinge onto the TiO.sub.2 directly 
rather than through the tungsten oxide material. In one embodiment of the 
present invention, the TiO.sub.2 is not utilized as a suspended powder in 
the electrolyte but is rather present in the form of a thin film. The 
present design permits the charge storage layer of tungsten oxide and the 
thin film TiO.sub.2 to be of different physical form. For example, the 
TiO.sub.2 may be a thin film while the tungsten oxide may be a sintered 
body which has distinct advantages as to energy conversion and operating 
characteristics.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the figures, and more particularly FIG. 1 thereof, a glass 
substrate 10 supports a light transparent thin film conductive electrode 
12 made from a material such as SnO.sub.2. The combination of the glass 
and deposited electrode is commercially available and is known as Nesa 
glass. A non-conductive substrate 14 is positioned in spaced relationship 
to the thin film electrode 12 and may be fabricated from a suitable 
support material such as plastic or glass. A circumferential wall 16 
encloses the interior of the cell, the wall being made from most any 
suitable inert sealing insulating material such as epoxy. A thin film 
electrode 18 is deposited upon the substrate 14 and extends toward the 
thin film electrode 12. A layer 20 of charge storing material such as 
tungsten oxide is deposited as a film upon the electrode 18 by 
conventional techniques such as evaporation, sputtering or chemical vapor 
deposition. The purpose of the layer 20 is to store charge after an 
irradiating source is removed. A counterelectrode 22 is also deposited on 
the substrate 14 in spaced relation to the electrode 18. The 
counterelectrode may be made from a suitable material such as carbon or 
platinized carbon which is deposited by coating or silk screening. 
A void created in the interior of the cell is filled with an electrolyte 23 
including a suspending agent, such as glycerine, a photoactive material 
such as TiO.sub.2 powder, and a solution of acid, typically sulfuric acid. 
This electrolyte was referred to as a charge compensation layer in the 
previously mentioned copending application. Preferably, the TiO.sub.2 is 
in the anatase form although the rutile form is satisfactory. 
In order to make the electrolyte 23 sensitive to visible light, an agent 
must be added to the electrolyte. In a preferred embodiment of the 
invention, this may be done by incorporating a dye system such as an 
N-methylphenazine dye system. Physically, this is accomplished by adding a 
material such as N-methylphenazine methosulfate which is commercially 
available from a source such as Eastman Kodak Company, and is available in 
powdered form. The utilization of such a dye system is discussed in a 
copending patent application Ser. No. 740,875 filed November 11, 1976, 
entitled "N-Methylphenazine Photogalvanic Cell" by Schoen-nan Chen and 
assigned to the same assignee as this present application. Of course, the 
invention is not limited by the specific mentioned dye system. Rather it 
is only necessary that an appropriate sensitizing material be added to the 
electrolyte which will sensitize the TiO.sub.2 to visible light which is 
ordinarily only sensitive to ultraviolet light. If a different photoactive 
material were used, which was sensitive to visible light, a sensitizing 
material would, of course, not be necessary. 
Leads 24, 26 and 28 are respectively connected to the electrode 12, the 
electrode 18, and the counterelectrode 22. These leads permit electrical 
energy to be drawn from the cell in response to irradiation, and after 
irradiation is removed due to the advantageous storage capability of the 
cell. 
In operation of the device, a light to electrical energy conversion occurs 
at the photoactive site or interface between the electrolyte 23 and the 
electrode 12. Stored charge is derived from the tungsten oxide thin film 
20 through the electrode 18. 
From the above description of the first embodiment, it will be noted that 
the design is conceived so that there is an absence of the charge storage 
layer 20 from the photoactive site. As a result, maximum photoconversion 
is made possible since the charge storage layer does not filter the 
irradiating light as it passes into the cell. 
It is also possible to modify the cell so that the charge storage layer 20 
appears as a ring in overlying relation with the wall 16. Of course, in 
such an event the charge storage layer must still make contact with an 
electrode since material such as tungsten oxide cannot always effectively 
function as a conductor. 
In operation of the device, a selector switch (not shown) may be connected 
to the wires 24, 26 and 28. This would permit the electrode 12 and 
counterelectrode 22 to be connected across a load (not shown) for 
utilization of photoconverted electrical energy during irradiation. 
Likewise, a jumper could be connected between electrodes 12 and 18 to 
achieve charge storage during irradiation of the cell. Alternately, the 
electrode 18 and counterelectrode 22 may be connected across an external 
load to discharge the charged electrical energy, particularly when the 
irradiating source of light is removed. 
FIG. 2 illustrates an alternate embodiment of the invention which 
essentially shows a different geometric configuration for the various 
components of the cell. 
A substrate 30 made from glass has a thin film electrode 32 deposited 
thereon, which may be the material doped SnO.sub.2. A thin film of 
photoactive material, such as TiO.sub.2 is shown at 34 to be deposited on 
the electrode 32. In this alternate embodiment, the electrolyte shown at 
33 remains an aqueous acidic medium but does not contain the TiO.sub.2 
pigment as was the case in connection with the first embodiment. Rather, 
the TiO.sub.2 is deposited as a thin film at 34. A separate thin film 
electrode 36 which may be of the same material as electrode 32 is also 
deposited on the glass substrate 30. The electrodes 32 and 36 may be 
formed on Nesa glass whose conductive transparent thin film has been 
etched to electrically isolate the two separate electrodes 32 and 36. A 
charge storage layer 38, of suitable material such as tungsten oxide, is 
deposited on the electrode 36. Whereas the thin film 34 forms a 
photoactive site with the electrolyte 33 along the interface between film 
34 and electrolyte 33, the charge storage layer 38 of tungsten oxide 
primarily stores charge which makes electricity available from the cell 
after irradiating light ceases. 
As previously mentioned in connection with the embodiment of FIG. 1, a 
sensitizing agent must be added to the electrolyte so that the TiO.sub.2 
becomes sensitive to visible light. As previously mentioned, an 
N-methylphenazine dye system may be used although this is not a limitation 
on the invention. Rather, other materials may be added to the electrolyte 
which will sensitize the TiO.sub.2 to visible light and render the cell 
absorptive to visible light. 
An insulating substrate 40 is positioned in spaced registry with the glass 
substrate 30. In the case of the substrate 40, a plastic or glass material 
may be utilized. The substrate 40 is used as a supporting member for a 
counterelectrode 42, which is coated or silk screened onto the substrate 
40. The counterelectrode 42 may be fabricated from carbon or platinized 
carbon. As to the electrolyte 33, the inclusion of glycerine to the 
aqueous acidic medium is no longer necessary for suspending the TiO.sub.2 
which is present in the first embodiment but not in this embodiment. 
Leads 46, 48 and 50 are connected to the electrodes/counterelectrodes 32, 
42 and 36, respectively. Electrode 32 and counterelectrode 42 are 
connected to a load when photoconverted energy is to be used during 
irradiation. In order to achieve charge storage during irradiation, a 
jumper conductor is connected between electrode 32 and electrode 36. 
Electrode 36 and counterelectrode 42 would be connected in circuit to a 
load when the stored charge is to be discharged to an external load. 
Although the load and an appropriate switch is not illustrated, it is not, 
per se, a part of the present invention but would be in the nature of a 
conventional selector switch well known to those skilled in the art. 
In order to properly seal the cell illustrated in FIG. 2 as well as 
insulate the various electrodes and counterelectrode from each other, an 
appropriate insulating wall 44 exists which is fabricated from a suitable 
inert insulating material such as epoxy. In the case of both embodiments, 
the counterelectrode may typically be 1 mm thick while the TiO.sub.2 film 
34 in the embodiment of FIG. 2 is typically 2,000 Angstroms, and the 
tungsten oxide film 38 of FIG. 2 is typically 5,000 Angstroms thick. 
It should be understood that the invention is not limited to the exact 
details of construction shown and described herein for obvious 
modifications will occur to persons skilled in the art.