Photoelectrochemical cell and electrolyte for this cell

Details Photoelectrochemical cell and electrolyte for this cell Photoelectrochemical cell and electrolyte for this cell

1996-06-28

1998-03-17

Weisstuch, Aaron

Chemistry: electrical current producing apparatus, product, and

Deferred action type

Responsive to light

429188, 429194, 429198, 429199, 429203, H01M 630, H01M 604

Patent

active

057284873

DESCRIPTION:

BRIEF SUMMARY
The invention concerns a regenerative photoelectrochemical cell comprising a photoanode consisting of at least one semi-conductive metal oxide layer on a conductive substrate, a counter-electrode and an electrolyte positioned between these electrodes, at least one of these electrodes being transparent or translucent, and the said electrolyte including an oxidation-reduction system consisting of at least one electrochemically active salt and at least one molecule designed to form an oxidation-reduction system with the anion or cation of the said salt.
In particular, the invention concerns a cell of this type in which the said semi-conductive metal oxide layer is polycrystalline, especially a cell in which this layer consists of nanocrystalline titanium dioxide TiO.sub.2, sensitized by at least one chromophoric substance, the surface of the photoanode in contact with the electrolyte being porous, with a porosity factor of preferably at least 20.
The term "nanocrystalline" means that the semi-conductive metal oxide, in this case titanium oxide, is in polycrystalline form with a granulometry of the order of several nanometers, for example 10 to 50 nanometers.
The "porosity factor" is defined as the ratio of the photoelectrochemically active surface of the photoanode to the surface area of the substrate covered by the layer(s) of semi-conductive metal oxide.
Cells of this type are already known, especially that described in U.S. Pat. No. 4,927,721 and that described in international patent application WO 91/16719.
To date, liquid electrolytes have been used in this type of cell, comprising a solution with an oxidation-reduction system consisting of a mixture of at least one salt with a melting point higher than room temperature with at least one molecule corresponding to the anion of this salt, in a solvent or mixture of solvents, such as at least one polar organic solvent with a high dielectric constant, or in a high acidity aqueous medium.
For example, the oxidation-reduction system can consist of a solution of 0,5 M tetrapropylammonium iodide and 40 mM iodine and the solvent is a mixture of ethylene carbonate and acetonitrile.
It was found that regenerative photoelectrochemical cells using an electrolyte of the type mentioned above are likely to prove disadvantageous with regard to the nature and properties of such an electrolyte, with the following disadvantages in particular:
Due to the volatility of the solvents likely to be used for the electrolyte, if the electrolytic compartment is not perfectly leaktight, the solvent may evaporate thus preventing the cell from operating ("dead battery").
If the cell is operating at a temperature below room temperature, for example of the order of -10.degree. C. to -30.degree. C., the salt may precipitate in the form of a crystalline solid, which is manifested by an appreciable reduction in the performance of the cell at that temperature.
A progressive reduction in performance of the cell may also be found at a given constant temperature, such as room temperature, due to instability of the electrolyte, attributable to the breakdown of the solvents used or to spurious chemical reactions between the redox system constituents and the solvents.
Finally, if the solvent contains propylene or ethylene carbonate, substances may form in a gaseous state, such as carbon dioxide, again due to breakdown of the solvent or secondary reactions between this and the redox system elements, resulting not only in loss of performance of the cell but a risk of it exploding as well.
The present invention is in general designed to eliminate these disadvantages and more particularly improve the stability of the performance of the cell in the course of time, and as a function of operating temperature.
To this effect, the cell as per the invention is characterised in that the said electrochemically active salt has a melting point below room temperature or forms at least one phase with a melting point below room temperature, in presence of the second species of the said oxidation-reduction system.

REFERENCES:
K. Rajeshwar et al., Proceedings 16th ECEC, Aug. 1981, pp. 779-782.

Affiliated with

Also associated with

Rating

Photoelectrochemical cell and electrolyte for this cell does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Photoelectrochemical cell and electrolyte for this cell, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photoelectrochemical cell and electrolyte for this cell will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-956098