Metal treatment – Process of modifying or maintaining internal physical... – Treating loose metal powder – particle or flake
Patent
1998-03-24
2000-02-15
Wyszomierski, George
Metal treatment
Process of modifying or maintaining internal physical...
Treating loose metal powder, particle or flake
75369, 148537, 148678, 427125, 4273833, 429 41, 429 44, 502101, 502339, H01M 492
Patent
active
060248076
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for manufacturing an electrode for an electrochemical device which comprises two electrodes, having corresponding electrochemically active surfaces arranged in mutual facing relationship and separated by a layer of an electrolyte comprising a solution of an electron transfer mediator, consisting of a redox system iodine (I.sub.2)/iodide (I.sup.-), in a solvent, said process comprising the step of depositing metallic platinum onto an electrically conductive substrate.
A variety of such electrochemical device are already known and widely used, e.g. in the form of photoelectrochemical energy conversion apparatus utilizing a iodine/iodide redox couple as mediator, as well as of sensor devices or other iodine/iodide mediated electrochemical devices involving electrochromism, charge or energy storage or energy conversion, such as fuel cells.
The invention is, more particularly, useful for manufacturing a cathode for a photovoltaic cell of the type disclosed in International Patent Application WO 91/16719 (Gratzel et al.).
In this photovoltaic cell, at least one of said electrodes has a visible light transmittance of at least 60% and said electrode is the cathode, the other electrode of the cell consisting in a photoanode comprising a high surface area semiconducting titanium dioxide active layer, which is in contact with the electrolyte and which is preferably coated with a layer of a photosensitizer such as a transition metal complex.
The iodine/iodide redox couple mediates the transfer of electrons from the external circuit required for the regeneration of the oxidized state of the photosensitizer after electron injection into the active layer of semiconducting titanium dioxide.
During the mediator regenerative cycle, the oxidized species, namely iodine or triiodide, must be converted back, i.e. reduced, to iodide, according to the reactions 3I.sub.2 +2e.sup.- .fwdarw.2I.sub.3.sup.- and I.sub.3.sup.- +2e.sup.- .fwdarw.3I.sup.-, at minimum energy loss, on the cathode.
The cathode of the above-mentioned photovoltaic cell is preferably constituted by a transparent support plate made of a conductive material, such as an electric conducting glass, coated with a layer of electric conducting tin oxide or indium-tin oxide which is, in turn, coated with metallic platinum.
Optionally, the metallic platinum coating may be applied directly onto the surface of a support plate made of electric conducting glass.
Different methods are known for applying the metallic platinum coating onto the surface of the support plate, in particular a method of electrochemical deposition.
The aim of providing the surface of the cathode which is in contact with the electrolyte with such metallic platinum coating is to improve the kinetic performance of said cathode, i.e. to increase the exchange current of the reaction of reduction of triiodide to iodide, by catalyzing tis reaction, so as to reduce the voltage consumption at the cathodic surface and consequently, increase the electrical power delivered by the photovoltaic cell for a given energy conversion efficiency of the photoanode.
However, the catalytic activity of the metallic platinum coatings, obtained by any of the know methods, on the reaction of reduction of triiodide to iodide is insufficient for allowing obtention of a substantial reduction of the voltage consumption at the cathodic surface.
Furthermore, this catalytic activity depends on the nature of the solvent used in the electrolyte. More particularly, the catalytic activity is lower in the case when such organic solvents as nitroethane, propylene carbonate, ethylene carbonate, n-methyl-pyrrolidone and n-methyl-oxazolidone are used than in the case when the solvent of the electrolyte is acetonitrile.
The present invention aims at improving the catalytic activity of the metallic platinum deposited on the substrate of the counterelectrode (i.e. the cathode) so as to obtain a high value of the catalytic activity on the reduction reaction of triiodide to iodide essentially independent of the n
REFERENCES:
patent: 4808493 (1989-02-01), Breault
patent: 5494704 (1996-02-01), Ackerman
patent: 5786026 (1998-07-01), Seko et al.
patent: 5879828 (1999-03-01), Debe et al.
patent: 5910378 (1999-06-01), Debe et al.
Scientific American, vol. 266, No. 1, Jan. 1992, "Curent Event-Bright Future for a Photovoltaic Cell", p. 117.
Nakato, Y., et al., "A New Approach to an Efficient . . . with Ultrafine Metal Islands", Japanese J. of Applied Physics, vol. 28, No. 2, Feb. 1989, pp. 261-2.
Gratzel Michael
Pappas Nicholas
Ecole Polutechnique Federale de Lausanne
Wyszomierski George
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