A photogalvanic cell having a light transparent electrode and a spaced counterelectrode separated by an electrolyte. The electrolyte includes an n-methylphenazine dye system which not only contributes to the conversion of light to electrical energy but also is capable of storing electrical charge after light is removed.

FIELD OF THE INVENTION 
The present invention relates to photogalvanic cells and more particularly 
to a photogalvanic cell using a fluid dye system as an electrolyte. 
BRIEF DESCRIPTION OF THE PRIOR ART 
The use of a dye system in the electrolyte of a photogalvanic cell is well 
known. In an article appearing in the publication "Solar Energy", Volume 
17, pages 147-150, Pergamon Press, 1975 and entitled PHOTOGALVANIC CELLS 
by Clark and Eckert, the theory and structure for photogalvanic cells is 
presented, showing that they are electrochemical cells which are recharged 
with light. A description in the article of a photogalvanic cell is based 
on an iron-thionine dye system which demonstrates a relatively low power 
conversion efficiency for absorbed monochromatic light. It is pointed out 
in the article that the concept of the photogalvanic cell should not be 
confused with a photovoltaic cell as the fundamental operation of the two 
devices is entirely different. The photovoltaic cell relies on direct 
excitation of an electron by a photon to produce electricity while the 
photogalvanic cell relies on the excitation of a molecule by a photon 
which induces chemical reactions to render high energy products. These 
products can subsequently lose their energy electrochemically, as in an 
ordinary battery. These reactions are more generally known as reversible, 
endergonic photochemical processes or reactions which are pushed uphill 
with light. 
The particular photogalvanic cell which is disclosed in the aforementioned 
article relies on the iron-thionine endergonic system. The photochemical 
processes involved are reversible and not complicated by competing side 
reactions when extraneous oxidants and reductants are excluded. The 
electrolyte utilized is stated as being an aqueous-acid medium. 
The iron-thionine dye system which is utilized normally exists as a purple 
solution when not exposed to sunlight. However, when there is exposure to 
sunlight, the solution becomes colorless due to the formation of the 
leucothionine. The purple color reappears when the solution is taken out 
of sunlight in a matter of seconds. This operation can be performed 
repeatedly and demonstrates the reversibility of the system. 
With respect to specific materials used in the cell of the mentioned prior 
art, the concentrations of species in solutions depend on the solvent for 
maximum photogalvanic response but generally are in the range of 10.sup.-2 
M for ferrous ion, 10.sup.-3 to 10.sup.-5 M for ferric ion and thionine, 
and 10.sup.-1 to 10.sup.-3 M for hydrogen ion in aqueous and 
aqueous-organic solutions. 
The discussed prior art discloses the structure of an actual photogalvanic 
cell using the iron-thionine electrolyte system. The structure includes 
spaced electrodes comprising transparent Nesa glass and platinum sputtered 
on glass. Fluorinated hydrocarbon separators are used between the 
electrodes and are extremely thin to allow the electrolyte solution to be 
held between the two electrodes by capillary action. The device is sealed 
with any suitable inert material such as paraffin wax or polyethylene. 
Although the discussed prior art cell accomplishes power conversion, the 
efficiency of the cell is demonstrated to be quite low, in the nature of 
0.15 percent. It is recognized that one of the contributing problems for 
this low conversion efficiency is that the iron-thionine single dye system 
only absorbs a fraction of the available sunlight. At best, test results 
verify that thionine at best absorbs only 10 percent of the total 
spectrum. It is mentioned in the aforementioned article that the authors 
are investigating with other thionine-type dyes which absorb in other 
areas of the spectrum, the hope of the authors being to design a mixed dye 
system which will absorb more of the solar spectrum. 
In a copending application entitled DYE-TITANIUM DIOXIDE PHOTOGALVANIC CELL 
by Chen et al Ser. No. 740,876, filed Nov. 11, 1976, now U.S. Pat. No. 
4,080,488, a photogalvanic cell is disclosed which includes an electrode 
and counterelectrode that are physically separated by an aqueous 
electrolyte which contains the specific dye of the present invention 
dissolved in solution as well as TiO.sub.2 suspended therein, as a pigment 
powder, the cell relying principally upon the TiO.sub.2 for the actual 
conversion of light to electrical energy. 
The prior art includes photogalvanic cells relying upon a TiO.sub.2 
-electrolyte interface for constituting a photoactive site which converts 
irradiating light energy to electrical energy. In copending U.S. patent 
application Ser. No. 582,344, filed May 30, 1974, now U.S. Pat. No. 
4,085,257 there is brief mention of the possibility of using a dye system 
in a photogalvanic cell. This is mentioned on page 6, line 21, of the 
referenced copending application. Although the usefulness of the dye 
system in a photogalvanic cell was theorized, the application of specific 
dyes was not envisioned by that invention. 
In a published paper in Proceedings VIII International Conference on 
Photochemistry, Edmonton, Canada, August, 1975, by James R. Bolton 
entitled "Photochemical Storage of Solar Energy by the Dye Sensitized 
Photolysis of Water" use of the particular dye, relied upon by the present 
invention, is recognized. In FIG. 2, the embodiment disclosed by Bolton is 
illustrated. In the left-hand compartment, a dye D (which should be a good 
donor in the ground state) will be excited by light so that the excited 
state D* is able to reduce water to hydrogen leaving the oxidized dye 
D.sup.+. In the right-hand compartment, a dye A (which should be a good 
acceptor in the ground state) will be excited by light so that A* will be 
able to oxidize water to oxygen leaving the reduced dye A.sup.-. The two 
compartments are then coupled together electrochemically so that A.sup.- 
can spontaneously reduce D.sup.+ thus restoring the dyes to their 
original states. The dark reactions following the photochemical electron 
transfers may be rather complex and specific catalysts capable of storing 
electrochemical equivalents will be required. Bolton discovered a reaction 
which partially meets the requirements for the dye A. The dye is the 
N-methylphenazinium cation (NMP.sup.+). At wavelengths less than 500 nm 
NMP.sup.+ is able to photooxidize water yielding the reduced dye 
NMPH.sup.+ and .OH radicals. 
Although the Bolton concept recognized the particular dye utilized in the 
present invention, his structure was directed to a multi-compartment cell 
for achieving photolysis of water. 
BRIEF DESCRIPTION OF THE PRESENT INVENTION 
With respect to the iron-thionine cell, the present invention is directed 
to an alternate dye system for a photogalvanic cell having a structure 
similar to that of the prior art. However, an entirely different dye 
system is used in the electrolyte which achieves spectral sensitivity in 
the region ranging from 500 nm down to ultra-violet. This is in contrast 
to the iron-thionine photogalvanic cell which is not sensitive below 500 
nm. The present photogalvanic cell should exhibit a greater power 
conversion efficiency. A second distinct advantage of the present 
invention over the iron-thionine prior art relies upon the fact that the 
dye utilized in the present electrolyte, namely, N-methylphenazine, is 
capable of achieving charge storage in addition to energy conversion from 
light to electrical forms of energy.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, the photogalvanic cell of the present invention is 
seen to include a light transparent substrate material such as glass 10. A 
thin film or layer of conducting material is deposited onto the glass to 
function as electrode 12. In a preferred embodiment of the invention, the 
electrode 12 is fabricated from a transparent thin film conducting 
material such as SnO.sub.2. A prefabricated material including the glass 
and the electrode deposited thereon is commercially available and is known 
in the industry as Nesa glass. 
A counterelectrode 18 is positioned in spaced registry with electrode 12 
and may be fabricated from a disc of carbon or a platinized carbon member. 
In the event of the latter, the platinum may be deposited on the carbon 
material by conventional metalization techniques. 
The aqueous material between the electrode 12 and the counterelectrode 18 
is the electrolyte which includes the previously mentioned 
N-methylphenazine dye system. The electrolyte is an aqueous medium which 
includes a conventional acid, such as sulphuric acid. The aqueous medium 
has N-methylphenazine methosulfate added thereto, the latter being 
commercially available from a number of sources such as Eastman Kodak 
Company, and is available in powdered form. 
An annular wall 16 is transversely disposed between and connected to the 
electrode 12 and counterelectrode 18 and serves the purpose of sealing the 
electrolyte 14 within the device as well as supporting the internal cell 
components. The wall 16 may be fabricated from most any suitable inert and 
electrically insulative material such as epoxy or polyethylene. 
Wires 20 and 22 respectively are connected to the electrode 12 and 
counterelectrode 18. A load 24 is connected between these wires and draws 
current from the device when the latter is exposed to light. 
The transparent electrode 12 is a thin film semiconductor and upon 
irradiation by light shorter than 500 nm, the transparent electrode 
becomes negatively charged while the counterelectrode becomes positively 
charged. As a result, electric current will be drawn by load 24. 
It has been found that the particular dye system including the 
N-methylphenazinium ions permits the cell to also store electrical energy. 
Accordingly, the cell could be charged without an attached load and after 
irradiating energy ceases, a load may be connected across the cell for 
power. 
The stability of the present N-methylphenazine photogalvanic cell may be 
improved by adding to the electrolyte a suitable redox couple, such as 
Fe(II)-Fe(III). 
The suspected mechanism for the theoretical operation of the device is that 
the light excites the molecules of the dye to reach excited states. The 
excited molecules or their photoproducts eject electrons and these are 
collected by the electrodes or stored in the electrolyte for later use by 
a connected load. 
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.