Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Removing metal
Reexamination Certificate
1999-12-16
2001-03-13
Teskin, Fred (Department: 1713)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Removing metal
C205S687000, C204S280000, C204S282000, C204S291000, C252S506000, C252S518100, C252S520300, C427S126500, C427S243000, C428S367000, C428S379000, C428S403000, C428S469000, C502S101000, C502S326000
Reexamination Certificate
active
06200457
ABSTRACT:
The present invention relates to an electroactivated material comprising fibres and a binder and additionally having an electrocatalytic agent in the form of particles comprising a precious metal oxide or in the form of particles comprising a support and a coating based on such an oxide.
The electroactivated material can be used especially as cathode component of an electrolysis cell and in particular of a call for the electrolysis of aqueous sodium chloride solutions.
Moreover, it relates to a composite material comprising the said material and to processes for the preparation of each of the two materials.
In recent years, the use of cathodes consisting of a metal surface on which is deposited a fibrous shoot and then optionally a diaphragm has spread in the field of the electrolysis of aqueous sodium chloride solutions. Such cathodes have a low overpotential with respect to the reaction for the production of hydrogen at the cathode and for this reason have made it possible to reduce energy consumption.
Moreover, it is-known to add electrocatalytic agents, such as nickel, for example, to the abovementioned sheet in order to increase further the behaviour thereof. These agents can be used in the form of a powder dispersed in the abovementioned fibrous sheet or alternatively in a for of a deposit on the said sheet, obtained, for example, by an electrochemical route
However, cathodes of this type do not have a very high resistance to poisoning, due to the nature of the electrocatalytic agents, and are therefore relatively rapidly deactivated.
The aim of the present invention is to propose an electroactivated material and a composite material comprising the latter, which can be used as cathode in a cell for the electrolysis of aqueous sodium chloride solutions, in which the resistance to poisoning and, consequently, the lifetime are increased.
The first subject of the present invention is therefore an electroactivated material comprising fibres, of which at least a part is electrically conducting, and a binder and additionally comprising an electrocatalytic agent consisting of particles formed of ruthenium, platinum, palladium or iridium oxide, or their mixture, or of one or several of the said oxides distributed at least partly over an electrically-conducting support.
A second subject of the invention consists of a composite material comprising (a) a material of high porosity and (b) the abovementioned electroactivated material.
A third subject of the invention consists of a composite material comprising, from one face towards the other: (a) a metal surface of high porosity, (b) the abovementioned electroactivated material and (c) a separator.
The invention also relates to a method for the preparation of an electroactivated material which consists in carrying out the following stages:
(a) an aqueous suspension comprising the fibres, the binder, the electrocatalytic agent and optionally adjuvants is prepared,
(b) a shoot in deposited by filtering the said suspension, under programmed vacuum, through a material of high porosity,
(c) the liquid in removed and the sheet thus formed is optionally dried,
(d) the shoot thus obtained is optionally sintered.
The final subject of the present invention in a method for the preparation of a composite material. This consists in carrying out the following stages:
(a) an aqueous suspension comprising the fibres, the binder, the electrocatalytic agent and optionally adjuvants is prepared,
(b) a shoot is deposited by filtering the said suspension, under programmed vacuum, through a material of high porosity,
(c) the liquid is removed and the shoot thus formed is optionally dried,
(d) the sheet thus obtained is optionally sintered,
(e) a dispersion, in water or in an aqueous sodium hydroxide solution, comprising fibres, a binder and optionally adjuvants is deposited on the said sheet by filtering under programmed vacuum,
(f) the liquid is removed and the diaphragm thus formed is optionally dried,
(g) the whole unit is sintered.
However, other advantages and characteristics of the invention will become more clearly apparent on reading the description and examples which will follow.
As was indicated above, the electrocatalytic agent which forms part of the composition of the electroactivated material according to the invention can be provided in the form of particles based on ruthenium, platinum, iridium or palladium oxide, these oxides being alone or as a mixture. The said agent can additionally be provided in the form of particles consisting of an electrically-conducting support comprising, for at least part of the said particles, a coating in the form of ruthenium, platinum, iridium or palladium oxide, these oxides being alone or as a mixture.
In the following, the abovementioned list will be denoted by the term precious metal(s). It is understood that the term precious metal will subsequently represent, without distinction, one or several of the abovementioned metals.
The combination of these two variants can, of course, be envisaged.
Mixture is understood to mean, first of all, particles comprising several oxides or alternatively particles, containing at least one oxide, mixed with other particles comprising at least one different oxide, or finally these two possibilities simultaneously. Such a definition is valid whether the oxides are found throughout the thickness of the particle or simply in the form of a coating.
The electrocatalytic agent according to the invention is preferably provided in the form of a coating on a support.
The support consists of a material which is electrically conducting and stable under the conditions of a subsequent application of the material (pH and temperature, especially).
More particularly, the latter is chosen from iron, cobalt, nickel, Raney iron, Raney cobalt, Raney nickel, the elements of columns IVA and VA of the periodic classification, carbon or graphite. Here and throughout the description, the comments relating to the table of the periodic-classification of the elements refer to that which appeared in the supplement to the Bulletin de la Société Chimique de Prance (No. 1, January 1966).
The support is preferably provided in the form of a powder.
More particularly, the particle size of the support is between 1 and 100 &mgr;m.
The specific surface of the said support is not greater than 1000 m
2
/g. More particularly, the specific surface varies between 5 and 500 m
2
/g.
The proportion by weight, between the coating and the support, varies between 0.5 and 50. It should be noted that proportions outside, and more particularly higher than, those indicated above can be envisaged. However, this does not introduce specific advantages for the behaviour of the electroactivated material, while needlessly increasing its cost.
The electrocatalytic agent according to the invention can additionally comprise additives chosen from iron, cobalt, nickel and/or their oxides.
The proportion of the said additives, with respect to the precious metal oxide (by weight), varies from 0 to 50%.
The electrocatalytic agent which forms part of the composition of the electroactivated material according to the invention can be distributed either uniformly within the said material or else be gathered together in a specific region of the latter, for example at the periphery.
However, according to a preferred implementational variant of the invention, the electrocatalytic agent is uniformly distributed throughout the body of the electroactivated material.
The amount of electrocatalytic agent in the material according to the invention represents 10 to 70% by weight, with respect to the combined fibres, binder and electrocatalytic agent.
In addition to this electrocatalytic agent, the material according to the invention comprises fibres, of which at least a part is electrically conducting.
These fibres are provided in the form of filaments, the diameter of which is generally less than 1 mm and preferably between 10
−5
and 0. 1 mm, and the length of which is greater than 0. 5 mm and preferably between 1 and 20 mm, the said materia
Durand Robert
Le Helloco Jean-Guy
Burns Doane Swecker & Mathis L.L.P.
Rhone-Poulenc Chimie
Teskin Fred
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