FR2805927A1 - Fuel cell production forms a polymer film on a reinforced carrier to take an electrode on one surface to be separated from the carrier when dry and set for a further electrode to be applied to the other film surface - Google Patents

Abstract

To form an assembly with at least one electrode (13) with an active surface, and a membrane (1) of a thermostable polymer, a solution of the thermostable polymer is bonded to a carrier to give a film of the solution which is dried by evaporation of the solvents. An electrode is placed on the film before it is completely dry, with the active electrode surface towards the film surface. The assembly is dried, and the electrode/membrane are detached from the substrate. The carrier is reinforced before the layer of thermostable polymer solution is applied, using glass fibers or a polymer. When the thermostable polymer solution layer is in place, a reinforcement is introduced within it by lamination. The assembly can be produced with two electrodes flanking a membrane, where the process is repeated after the electrode/membrane have been separated from the substrate for an additional electrode to be bonded to the other side of the membrane in the same sequence as for the first electrode. The film of thermostable polymer can be formed by impregnating the carrier with the solution, and electrodes are placed on both sides of the film. The thermostable polymer is an ion exchange polymer e.g. a proton conductive polymer.

Description

<B><U></U></U></B></B><U><U> - </ U></U></U></U><BR><BR><BR><U> MEMBRANE </ U><B> AND </ b> ELECTRODE <B></B><U> MEMBRANE </ U><B> - </ b> ELECTRODE <B><U> ASSEMBLIES </ U><U> SO <B> OBTAINED </ B></U><U> AND </ U><U> DEVICE <B> FROM </ The present invention relates to <B> A <B> A </ B></U><B><U> INCLUDING THESE ASSEMBLIES </ U></B><U></B> a process for preparing electrode assemblies <B> - </ B> membrane and electrode <B> - </ B> membrane <B> - </ B> electrode and assemblies thus obtained.

These <SEP> assemblies <SEP> are <SEP> more <SEP> precisely <SEP> of
<tb> assemblies <SEP> electrode <SEP><B> - <SEP> membrane <SEP><B> - </ B><SEP> electrode, <SEP> in
<tb> which <SEP><SEP> membranes <SEP> are <SEP> polymeric <SEP> membranes <SEP>,
<tb> ion exchange <SEP>, <SEP><SEP> such <SEP> assemblies <SEP> find <SEP> more
<tb> especially <SEP> their <SEP> application <SEP> in <SEP><SEP> Stacks <SEP><B> to </ B>
<tb> fuel, <SEP> including <SEP><SEP> batteries <SEP><B><SEP> fuel <SEP><B> to </ B><SEP> low
<tb> temperatures <SEP> running <SEP> usually <SEP> since <SEP> la
<tb> ambient <SEP> temperature, <SEP> up to <SEP> approximately <SEP><B> 1000C, <SEP> such <SEP> as
<tb> the <SEP> batteries <SEP><B><SEP> fuel <SEP><B><SEP> membrane <SEP> exchange <SEP> from
<tb> protons <SEP> running <SEP> or <SEP> with <SEP> the <SEP> couple <SEP> gaseous
<tb> (H2 / Oxygen <SEP> of <SEP> air), <SEP> Known <SEP> under <SEP><SEP><SEP> name <SEP> PEMFC, <SEP> is
<tb> with <SEP> the <SEP> pair <SEP> methanol / oxygen <SEP> of <SEP> air, <SEP> known <SEP> under <SEP>
<tb><SEP> name of <SEP> DMFC <SEP><B>(SEP> Direct <SEP> Methanol <SEP> Fuel <SEP> Cell <SEP><B>,</B><SEP> in
<tb> English).
<tb> In <SEP> consequence, <SEP> the invention <SEP> has <SEP> also
<tb> line <SEP><B> to <SEP> a <SEP> device <SEP> from <SEP> Stack <SEP><B> to </ B><SEP> fuel, <SEP> in
<tb> particular <SEP> of the <SEP> type <SEP><B> to </ B><SEP> electrolyte <SEP> solid, <SEP> comprising <SEP> at least one of said electrode assemblies <B> - < / B> membrane <B> - </ B> electrode.

The technical field of the invention can thus be defined as that of the batteries <B> to </ B> fuel, in particular batteries <B> to </ B> fuel type <B> to </ B> solid electrolyte .

The <B> to </ B> type solid polymer electrolyte fuel cells are particularly suitable for use in electric vehicles which are currently the subject of many development programs, in order to provide a solution <B> to <B> the pollution caused by vehicles <B> to </ B> engine.

The <B> to </ B> fuel <B> to the solid polymer electrolyte could, by acting as an electrochemical energy converter, associate a reservoir of energy with the <B> to </ B> embedded, for example hydrogen or alcohol, to overcome the problems, including recharge time and autonomy, related to the use of batteries in electric vehicles.

The schematic assembly of a fuel cell <B> to </ B>, allowing the production of electrical energy, is shown in part in the attached figure <B> 1.

The essential element of such a cell is an ion exchange membrane, specifically a proton exchange membrane, formed of a solid polymer electrolyte, more specifically a proton conductive polymer. <B> (1) </ B> this membrane serves <B> to </ B> separate the anode compartment (2), where occurs the oxidation of the fuel, such as hydrogen H2 (4), according to the diagram <B></B>

2H2 <SEP><B>-><SEP> 4H + <SEP><B> + </ B><SEP> 4e-, cathode compartment <B> (3), where </ B> the oxidant, such as the oxygen of the air 02 <B> (5) </ B> is reduced, according to the scheme <B>: </ B>

02 <SEP><B> + </ B><SEP> 4H + <SEP><B> + </ B><SEP> 4th <SEP><B>-></B><SEP> 2H20, with production of water <B> (6), </ B> while the anode and the cathode are connected by an external circuit <B> (10). </ B> The water thus produced circulates between the two compartments by electroosmosis and diffusion (arrows <B> 11, </ B> 12).

The <SEP> electrodes <SEP> volumic <SEP><B> (13), </ B>
<tb> electronic, <SEP>, <SEP> placed <SEP> of <SEP> part <SEP> and <SEP> of other
<tb> of <SEP> the <SEP> membrane, <SEP> include <SEP> usually <SEP> a <SEP> zone
<tb> active <SEP> (14) <SEP> and <SEP> a <SEP><SEP> broadcast <SEP><15> zone. <SEP> The <SEP> zone
<tb> active, <SEP> expected <SEP> typically <SEP> on <SEP> one <SEP> of <SEP><SEP> surfaces of
<tb> the electrode, <SEP> is <SEP> constituted <SEP> of a <SEP> Teflonated <SEP> porous <SEP> felt,
<tb> loaded <SEP> of <SEP> black <SEP> of <SEP> carbon <SEP> or <SEP> of porous <SEP> graphite <SEP>,
<tb> coated <SEP> with <SEP> metal <SEP> noble <SEP> finely <SEP> divided <SEP><B> (16) <SEP> (by
<tb> example, <SEP> under <SEP> form <SEP> of <SEP> grains), <SEP> such <SEP> as <SEP> the <SEP> platinum, <SEP> and
<tb> of a <SEP> thin <SEP> deposition <SEP> of <SEP> polymer <SEP> conductor <SEP> ionic, <SEP> of
<tb> structure <SEP> typically <SEP> similar <SEP><B><SEP> that <SEP> from <SEP> la
<tb> membrane. <SEP> The <SEP><SEP> Diffusional Area <SEP><B> (15) <SEP> is <SEP> as <SEP><B> to </ B><SEP> it,
<tb> made up <SEP> of a <SEP> porous <SEP> material, <SEP> by <SEP> example <SEP> of <SEP> same
<tb> Teflon coated <SEP> porous <SEP> felt, <SEP> charged <SEP> c # e <SEP> black <SEP> of <SEP> carbon, <SEP> or <SEP> of
<tb> same <SEP> graphite <SEP> porous, <SEP> rendered <SEP> hydrophobic <SEP> by the integration of a hydrophobic polymer, such as PTFE. The hydrophobic nature allows the evacuation of liquid water. The noble metal, such as platinum, located in the active zone, allows either to oxidize hydrogen or methanol <B> to </ B> the anode, or to reduce the oxygen <B> to </ B> the cathode.

The protons produced <B> at </ B> the anode, by oxidation, for example hydrogen, on the surface of noble metal grains, such as platinum, are transported <B> (9) </ B> through the membrane to the cathode where they recombine with the ions produced by the reduction, for example oxygen from the air to give water <B> (6). </ B>

The electrons thus produced <B> (17), </ B> make it possible to supply, for example, an electric motor <B> (18) </ B> placed in the external circuit <B> (10), < / B> with only by-product of the reaction, water.

The membrane and electrode assembly is a very thin assembly with a thickness of about one millimeter, called <B> </ B> assembly electrode <B> - </ B> membrane <B> - </ B> electrode (EME <B> </ B> and each electrode is fed from the back, for example <B> to </ B> using a fluted plate, through the gases.

The power densities obtained by this recombination and which are generally of the order of <B> 0.5 to </ B> 2 W / cm 2 <B>. </ B> in the case where one puts in of hydrogen and oxygen, require the combination of several of these voluminal-membrane-vplumic electrode structures to obtain, for example the <B> 50 </ B> kW required <B> to </ B > a standard electric vehicle. In other words, it is necessary to assemble a large number of these structures, whose elementary surfaces may be of the order of 2 × 20 × 20 cm to obtain the desired power, especially in the case where the battery <B> to < / B> fuel is implemented in an electric vehicle.

For this purpose, each assembly formed of two electrodes and a membrane, defining an elementary cell of the <B> to </ B> fuel cell, is thus disposed between two sealed plates <B> (7, 8) </ B> which, on the one hand, ensure the distribution of hydrogen on the anode side and, on the other hand, oxygen on the cathode side. These plates are called bipolar plates.

The ionic conductive membrane is generally an organic membrane containing ionic groups which, in the presence of water, allow the conduction of protons <B> (9) </ B> products <B> to </ B> the anode by oxidation hydrogen.

The thickness of this membrane is from a few tens <B> to </ B> a few hundred microns and results from a compromise between the mechanical strength and the ohmic drop. This membrane also allows the separation of gases. The chemical and electrochemical resistance of these membranes allows, in general, a battery operation over periods of greater than <B> <B> 1000 </ B> hours.

The polymer constituting the membrane must therefore fulfill a number of conditions relating <B> to </ B> its mechanical, physicochemical and electrical properties. The polymer must first be able to give thin films, from <B> 50 to 100 </ B> micrometers, dense, without defects. The mechanical properties, modulus of stress <B> at </ B> break, ductility, should make it compatible with assembly operations includingf for example, clamping between metal frames. The properties must be preserved by passing from the dry state <B> to the wet state.

The polymer must have good chemical stability with respect to hydrolysis and have good resistance <B> to </ B> reduction and <B> to </ B> oxidation up to 100 '> C. This stability is appreciated in terms of variation of ionic resistance, and in terms of variation of the mechanical properties.

The polymer must finally have a high ionic conductivity, this conductivity is provided by strong acid groups, such as phosphoric acid groups, but especially sulfonic groups connected to the polymer chain. As a result, these polymers will generally be defined by their equivalent weight, i.e., the weight of polymer in grams per acid equivalent.

<B> A </ B> As an example, the best systems currently developed are capable of providing a specific power of <B> 1 </ b> W.cm- #, ie a current density of 2 <B> A. </ B> CM-2 for <B> 0.5 </ B> Volts.

The currently used <B> plus </ B> polymers are sulfonated fluorinated thermoplastic copolymers whose linear main chain is perfluorinated and whose side chain carries a sulfonic acid group.

These thermoplastic copolymers are commercially available under the trade name of NAFIONO from the Du Pont Company, or ACIPLEX-So from the Asahi Chemical Company, others are experimental, produced by the DOW Company for the manufacture of the membrane called "XUS ". it has been seen that the electrochemical reactions, described by the operations mentioned above, involve protons coming from the membrane, electrons, the catalyst situated on one of the surfaces of the electrode and finally, the reducing agent, such as that the hydrogen, or the oxidant, such as oxygen from the air, these reactions occurring essentially <B> at </ B> the boundary or interface between the membrane and the electrode.

It is therefore clear that the performance of an electrode-membrane assembly and therefore of the <B> to </ B> fuel stack are closely related <B> to </ B> the quality of the <B> electrode interface - </ B> membrane, which basically depends on the probability of simultaneous presence in this area of the different species, mentioned above. The manufacturing process of assemblies or assemblies electrode <B> - </ B> membrane <B> - </ B> electrode has a decisive influence on the quality of the electrode interface <B> - </ B> membrane. The manufacture of electrode assemblies <B> - </ B> membrane <B> - </ B> electrode (EME) is not or very little described in the literature. Indeed, it is the <B> plus </ B> often of a know-how <B> to </ B> each laboratory or industrial involved in the manufacture of batteries <B> to </ B> fuel .

The EME manufacturing process, most often cited, consists of making the EME assemblies by hot passing of the electrodes vis-a-vis on the proton exchange membrane. said membrane having previously been separately prepared, generally by casting, and completely dried.

This technique is commonly used in the case of proton exchange membranes, most commonly used <B> at </ B> at present and <B> already </ B> mentioned above <B> at </ B> > know, NAFION type polymer membranes To manufacture the EME assemblies, the electrodes are pre-impregnated, for example, with a solution of NAFION <B> 0, </ B> and then pressed <B> to </ B > hot, between 1200 and 1500C, on both sides of the membrane. The thermoplastic nature of the NAFION and the impregnation of the electrodes, <B> to </ B> with the help of a polymer identical <B> to </ B> that which compose the membrane make it possible to obtain an excellent quality of the Membrane electrode interface, both from the point of view of mechanical properties, represented by excellent adhesion, than that of the exchange surface protons <B> - </ B> electrodes.

The electrochemical performance of fuel cells incorporating such assemblies is therefore satisfactory.

However, this product manufacturing EME sets has several major disadvantages <B>: </ B> in the first place, this process is difficult to industrialize and NAFION type polymers)) are extremely expensive. However, in the context of the development of fuel cells used for automobile traction, another essential problem, now well identified by the experts, is the cost of the membrane, the latter is with that of the bipolar plates the preponderant factor influencing the cost price of the <B> to </ B> fuel pile.

In <B> 1995, </ B> the cost of membranes produced or under development is in the range of <B> 3,000 to 3,500 </ B> F / M2 and it is estimated that this cost should be divided by <B> 10, </ B> or by 20, to assist <B> in </ B> an industrial development of fuel cells <B> to </ B> for the automotive industry.

With a view to lowering costs, sulfonated poly 1,4- (diphenyl-2,6) -phenyl ether on the main chain, polyethersulfones and polyetherketones were synthesized and tested without actually competing with the fluorinated membranes with respect to instant performance and durability. In order to provide membranes meeting the relative conditions, especially <B> to </ B> their mechanical, physicochemical and electrical properties, while having a manufacturing cost significantly lower than that, prohibitive perfluorinated membranes, described above New sulphonated polyimide polymers have been developed which are described in FR-A-2 748 485.

However, the method, described above, is not suitable for other types of membranes, that is to say membranes that are not a thermoplastic polymer such as NAFION. In particular, the process used in the case of membranes NAFION®) is absolutely not suitable for membranes which are composed of a polymer with a sulfonated <B> to </ B> heat-stable skeleton, among which include polyimides, polyethersulfones, polyetheretherketones, polybenzoxazoles, polybenzimidazoles, polyphenylenes and their derivatives, etc.

Indeed, such membranes have neither the thermoplastic nature nor the chemical structure of NAFION <B> 0 </ B> and therefore they have no affinity for the electrode impregnated with a solution of NAFION (D and the quality electrode interface <B> - </ B> membrane is poor.

In addition, in the case where the membrane is a thermostable polymer, the process involves the use of several compounds, <B> to </ B> namely a thermostable sulfonated polymer for the proton exchange membrane and a solution of NAFIONO for impregnation of the electrode.

In addition, the process is then a complex batch process comprising multiple steps, inter alia <B>: elaboration of the proton exchange membrane, impregnation of the electrodes, pressing, heating.

As a result, the performance and even the interest of such assemblies, involving a thermostable polymer membrane and a NAFION type polymer impregnated electrode are extremely limited from an industrial point of view.

If one wishes to preserve all the advantages of the membranes in thermostable sulfonated polymer especially in terms of cost, and overcome the drawbacks mentioned above by improving in particular the quality of the interface electrode <B> - </ B> membrane it has been envisaged, in the same way as for <B> 0 </ B> NAFION <B> polymer membranes, to impregnate the electrodes with a solution of the polymer that makes up the membrane in the case of heat-stable skeleton-containing polymers such as polyimides, polyethersulfones, polyetheretherketones, polybenzoxazoles, polybenzimidazoles, polyphenylenes and their derivatives, etc.

However, the mechanical rigidity of this family of polymers causes the appearance of high mechanical stress at the interfaces during the drying phase by evaporation of the solvent.

In addition, the lack of thermoplastic nature of these polymers does not allow to establish sufficient contact between the membrane and the impregnated electrodes. In this case, the electrochemical performances are not so high and are not reproducible from one operation to another. The quality of the interfaces is not sufficient to allow the proton conductor to be intimately in contact with the conductor / electronics and the catalyst <B> at the </ B> surface of the electrode. This type of assembly is likely to be sensitive to aging and to evolve rapidly as a function of time. Despite high temperature pressing, the electrode adhesion remains weak.

Finally, the multiple steps, <B> already </ B> indicated above, which mark out the realization of these assemblies constitute an obstacle <B> to </ B> the continuous manufacture. It is also known from US-A-5,242,764, an assembly method to avoid the use of a proton exchange membrane. This technique is based on the impregnation of the electrodes, using a large amount of a solution of NAFION <B>& 1 </ B> followed by <B> bonding to </ B>> hot two electrodes and impregnated. This technique is, again, only adapted to thermoplastic polymers of the NAFION <B> 0 </ B> type and makes it difficult to obtain a homoqene and azimuth impervious conductive polymer layer.

There <SEP> exists <SEP> so <SEP> a <SEP> need <SEP> for <SEP> a <SEP> process <SEP> of
<tb> manufacture, <SEP> of <SEP> preparation, <SEP> of assemblies <SEP> including
<tb> a <SEP> electrode <SEP> and <SEP> a <SEP> membrane <SEP> in <SEP> a <SEP> polymer
<tb> thermostable, <SEP> also <SEP> called <SEP> elementary <SEP> assemblies,
<tb> and <SEP> of assemblies <SEP> electrode <SEP><B> - <SEP> membrane <SEP><B> - </ B><SEP> electrode, <SEP> which
<tb> either <SEP> simple, <SEP> reliable, <SEP> reproducible, <SEP> and <SEP> safe <SEP><B>;<SEP> which <SEP> does not
<tb> present <SEP> that a <SEP> number <SEP> limited <SEP> of steps, <SEP> which <SEP> is <SEP> of a
<tb> limited <SEP> cost, <SEP> and <SEP> which <SEP> can <SEP> be <SEP> set <SEP> in <SEP>#penet<SEP> in
<tb> continuous, <SEP> this <SEP> process <SEP> presenting, <SEP> by <SEP> elsewhere, <SEP> all <SEP>
<tb> inherent <SEP> benefits <SEP><B><SEP><SEP>SEP> membranes <SEP> use in
<tb> thermostable polymers <SEP>. This method must also make it possible to obtain membrane electrode interfaces of excellent quality, without defects, with a very high cohesion of the membrane electrode bond. intimate contact of the catalyst with the membrane, these properties being stable over time and insensitive to aging.

The electrode <B> - </ B> electrode <B> - </ B> assemblies obtained must finally have excellent and perfectly reproducible electrochemical properties.

The object of the present invention is to provide a method for preparing an assembly comprising an electrode and at least one membrane made of a heat-stable polymer, more specifically a method for preparing a membrane electrode assembly. <B> - </ B> electrode, which responds, inter alia, <B> to </ B> all the needs indicated above.

The object of the present invention is still to provide a process for preparing an assembly comprising an electrode and a membrane made of a thermostable polymer, more precisely a <B> - </ B> electrode assembly. electrode membrane (EME) consisting of a membrane of a thermostable polymer and two electrodes, which does not have the disadvantages, defects, limitations and disadvantages of the processes of the prior art and which solves the problems posed by the processes of the prior art.

This and still further object is achieved according to the invention by a method of preparing an assembly comprising at least one electrode (preferably one) having an active face, and a membrane in one embodiment. thermostable polymer, in which the following steps are carried out: a) a solution of a heat-stable polymer is cast on a support so as to obtain a film of thermostable polymer solution; <B>;</B> then <B> b) </ B> the thermostable polymer solution film is partially dried by evaporation of the solvent from said solution <B>;</B> c) an electrode is deposited on the surface of said thermostable polymer solution film, being dried, before it is completely dry, the active face of the electrode facing <B> to said surface, so <B> to </ B> obtaining an assembly comprising a thermostable polymer membrane (formed by said partially dried polymer solution film) and said electrode <B></B>

<B> d) <SEP> on <SEP> dry <SEP> completely <SEP> said <SEP> assembly
<tb> got <SEP> when <SEP> of <SEP> step <SEP> c) <SEP><B>;</B><SEP> then
<tb> e) <SEP> on <SEP> takes off <SEP> the <SEP> assembly comprising
<tb> said <SEP> membrane <SEP> and <SEP> said <SEP> electrode <SEP> of the <SEP> substrate.
<tb> The <SEP> process <SEP> according to <SEP> the invention <SEP> allows <SEP> to
<tb> answer <SEP> to <SEP> needs <SEP> and <SEP> from <SEP> remedy <SEP> to <SEP> disadvantages
<tb> mentioned <SEP> above.
<tb> The <SEP> process <SEP> according to <SEP> the invention <SEP> is suitable <SEP> all
<tb> particularly <SEP> with <SEP> membranes <SEP> in <SEP> polymer <SEP> thermostable
<tb> of which <SEP> the <SEP> advantages, <SEP> inherent <SEP><B> to </ B><SEP> this <SEP> type <SEP> of <SEP> polymer, <SEP> is
<tb> echo <SEP> also <SEP> on <SEP> the <SEP> process <SEP> which <SEP><SEP> puts <SEP> into
<tb>#work.
<tb> The <SEP> process <SEP> according to <SEP> the invention <SEP> comprises <SEP> a
<tb><SEP> limited <SEP> number of steps, <SEP> simple, <SEP> easy <SEP><B> to </ B><SEP> perform <SEP> by

proven <SEP> means <SEP>, <SEP> it <SEP> is <SEP> reliable <SEP> and <SEP> reproducible,
<tb> achievable <SEP><B> at </ B><SEP> low <SEP> temperature, <SEP> without <SEP> consumption
<tb> energy <SEP> high, <SEP> only <SEP> request <SEP> a <SEP> duration
<tb> relatively <SEP> Limited, <SEP> and <SEP> imply <SEP> only <SEP> few <SEP> of <SEP> topics
<tb> first, <SEP> these <SEP> se <SEP> limiting <SEP> to <SEP> polymer, <SEP> to
<tb> solvent <SEP> and <SEP><B> to </ B><SEP> the electrode.
<tb> In <SEP> the opposite, <SEP><SEP> processes <SEP> of <SEP> art
<tb> earlier, <SEP> it <SEP> allows <SEP> a <SEP> manufacture <SEP> in <SEP> continuous <SEP> and <SEP><B> to </ B>
<tb> low <SEP> cost.

<SEP> way <SEP> fundamental, <SEP> according to <SEP> the invention,
<tb> assembly <SEP> electrode <SEP><B> - <SEP> membrane <SEP> is <SEP> performed <SEP> during
<tb> development <SEP> of <SEP> the <SEP> membrane <SEP> by <SEP> casting.
<tb> According to <SEP> the invention, <SEP> according to <SEP><B> to </ B><SEP> step
<tb> c) <SEP> of the <SEP> method, <SEP> on <SEP> simply <SEP> deposit the <SEP> electrode,
<tb> directly <SEP> and <SEP> without <SEP> other <SEP><SEP> operations (such <SEP> as
<tb> pressing <SEP> or <SEP> others, <SEP> like <SEP> in <SEP> earlier <SEP> art, <SEP> on <SEP> la
<tb> surface <SEP> of <SEP> the <SEP> membrane <SEP> at <SEP> course <SEP> of <SEP> drying <SEP> of <SEP> this one,
<tb> that is to say <SEP> that <SEP> the <SEP> membrane <SEP> is <SEP> then <SEP> constituted <SEP> of a
<tb> film <SEP> of <SEP> solution <SEP> of <SEP> polymer <SEP> thermostable <SEP> still <SEP> wet
<tb> and <SEP> no <SEP> completely <SEP> sec.
<tb> On <SEP> knows <SEP> that, <SEP> of <SEP> way <SEP> classic, <SEP> the
<tb> membrane <SEP> is <SEP> prepared <SEP> by <SEP> casting <SEP> of a <SEP> solution <SEP> of
<tb> polymer <SEP> on <SEP> a <SEP> substrate <SEP> or <SEP> support, <SEP> of <SEP> way <SEP><B> to </ B>
<tb> get <SEP> a <SEP> film <SEP> from <SEP> solution <SEP> from <SEP> polymer, <SEP> including <SEP> from
<tb> thermostable polymer <SEP>, <SEP> then <SEP> than <SEP> this <SEP> film <SEP> of <SEP> polymer <SEP> in
<tb> solution <SEP> is <SEP> then <SEP> dried <SEP> with <SEP> evaporation <SEP> total <SEP> of
<tb> solvent, <SEP> the extract <SEP> sec <SEP> obtained <SEP> constituting <SEP> the <SEP> membrane
<tb> such <SEP> as <SEP> the <SEP> membrane <SEP> exchange <SEP> of <SEP> protons.
<tb> In <SEP> the <SEP> processes <SEP> of <SEP> manufacturing
<tb> assemblies <SEP> electrode <SEP><B> - <SEP> membrane <SEP> and <SEP> assemblies <SEP><B> EME </ B>
<tb> of <SEP> the former <SEP> art, <SEP> such <SEP> as <SEP><SEP> processes <SEP> of <SEP> pressing <SEP><B> to </ B> hot, the assembly operation to <B> to </ B> achieve the assembly and <B> to </ B> establish a connection between the electrode (s) and the membrane is in any case carried out with a membrane whose development process has been driven <B> to </ B> its term and which is completely dry. It is therefore a completely, completely formed and dry membrane which is used in the processes of the prior art.

According to the invention, one goes <B> to </ B> against this approach, unanimously followed in the prior art, using, during the preparation of the assembly of a membrane during training , not yet fully formed, still wet and not completely dry. In the essential step c) of the process of the invention, during drying, and when the viscosity of the polymer film in solution has reached an optimum level, an electrode is carefully deposited <B> at </ B>. surface of the film.

A well-defined fraction of the polymer solution then impregnates the electrode, and <B> more </ B> precisely, the active layer located on the active face thereof which faces <B> at </ B> the surface of the polymer film in solution. This impregnation is simply under the action of the weight of the electrode in the still viscous polymer and no pressure is applied.

Thanks to the method of the invention and in particular because of the specific step c) that it comprises the interface elec tFode membrane is of excellent quality. It is totally surprising that an interface of such quality is obtained with thermostable polymer membranes <B>; </ B> such a result, which until now was only obtained for <B> 0 </ B> thermosplastic polymers type NAFION <B>, </ B> is achieved for the first time by implementing the method of the invention. It has been shown that the membrane electrode interface prepared by the method of the invention was perfectly smooth and flawless. The cohesion between the electrode and the membrane and the electrode is such that it is no longer possible to separate them, unlike the assemblies made by the methods of the prior art. This excellent adhesion is, among others, one of the fundamental effects and advantages brought about by the process of the invention, compared to prior art processes, such as pressing processes <B> to </ B > hot electrode or electrodes on the membrane.

It can be explained that, in the method of the invention the deposition operation according to step c) being carried out when the membrane is not yet completely formed <B> or </ B> dry, it means <B> more precisely that the substance that impregnates the electrode is composed of thermostable polymer, more especially proton conducting polymer, and a slight fraction of solvent. This makes it possible to drive the proton conductor evenly within the active layer of the electrode. The assembly thus obtained is then dried under precise conditions <B> at </ B> moderate temperature, generally from 700C <B> to </ B> 1500C, preferably <B> at </ B> a temperature of 1000C <B> to 1200C. An example of a suitable temperature is in particular close to 700C. This promotes the presence of proton conductive polymer in the vicinity of the electronic conductor and the catalyst contained in the electrode. In <B> dl </ B> other terms, thanks to <B> to </ B> the quality of the interfaces obtained by the method of the invention, there is a close contact between the membrane and the electrode (s) that is, the proton conductor is intimately in contact with the electronic conductor and the catalyst <B> at the surface of the electrode. It follows that the assemblies prepared by the process of the invention have very high and perfectly reproducible electrochemical properties and performances, that is to say, in particular, an evolution of the voltage as a function of the current density at the less similar to assemblies <B> </ B> any NAFION <B> 0. </ B> In order to further improve the mechanical properties of the assemblies according to the invention, we can <B> to </ B> the issue in step a) providing a reinforcement within the heat-stable polymer solution film, for example by rolling.

Or, for the same purpose, one can have a reinforcement on the support or substrate, before <B> to </ B> step a) of the method according to the invention.

The invention more specifically relates to a method for preparing an electrode assembly consisting of an electrode consisting of a thermostable polymer membrane and two electrodes. This method comprises, first of all, the production of a first electrode assembly <B> - </ B> membrane by the method previously described, then <B> to </ B> the outcome of step e) , we proceed <B> to </ B> the following step <B> f) </ B> <B>: </ B> we pour on the face of the assembly constituted by the membrane a solution of a thermostable polymer, so <B> to </ B> obtain a thermostable polymer solution film <B>; </ B> then the steps <B> b) to </ b> e) are substantially repeated. In other words, the electrode assembly <B> - </ B> membrane obtained <B> at </ B> after the step c) is then used as a substrate during a second casting operation , partial drying, deposition of a second electrode, and total drying.

The steps of this process will therefore be, in addition to the steps a), b), c), d), e) and f>, the following steps <B>: </ B>

<B> g) <SEP> on <SEP> dry <SEP> partially <SEP> said <SEP> film <SEP> of
<tb> solution <SEP> of <SEP> polymer <SEP> thermostable <SEP> by <SEP> evaporation <SEP> of
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<tb> h). The advantages and effects provided by this process are those already described, in particular the assemblies have higher mechanical, electrochemical (voltage evolution as a function of current density), etc. properties. assemblies obtained by the method of the prior art.

According to a variant of the process of the invention, called <B> </ B> impregnation <B> </ B> method as opposed to <B> </ B> <B> coating method, </ B> describes in the foregoing, an electrode <B> - </ B> electrode <B> - </ B> electrode assembly is prepared by the following steps: <b>: </ b> a) a reinforcement is impregnated with a solution of thermostable polymer, so as to obtain a film of heat-stable and self-supporting thermostable polymer solution; then, the said film is partially dried; a solution of thermostable polymer reinforced and self-supported, by evaporation of the solvent of said solution; <b> c) an electrode is deposited on each of the faces of said thermostable polymer solution film, being dried, before it is totally dry, the active face of each of the electrodes facing <B> to </ B> each of the surfaces of said film <B>; </ B> <B> d) </ B> the assembly is completely dried obtained during the step c).

According to a particularly advantageous characteristic of the process of the invention, whether it is the coating method <B> or </ B> of the impregnation method, it can be carried out continuously, which is not the case of the processes of the prior art.

The invention also relates to assemblies comprising at least one membrane and at least one electrode, as well as the electrode <B> - </ B> electrode <B> - </ B> assemblies that can be obtained by the method -above. We have seen that these assemblies, as such and because of the excellent and surprising quality of their interface and the mechanical properties (adhesion, etc.) and electrochemical (evolution of the voltage as a function of the current density) which as a result, inherently possessed properties differentiating them from prior art assemblies and rendering them superior to these.

The invention further relates to a fuel cell device comprising at least one electrode electrode assembly obtained by the process according to the invention. the invention. In the same way, the batteries possess, as such, excellent and surprising properties, due as well to the properties of the thermostable membranes as to the properties of the EME assemblies, the properties resulting directly from the implementation of the process of the invention.

The invention will now be described in more detail with reference to the accompanying drawings, in which: <B>: </ B> <B> - </ B> <B> 1 </ B> schematically represents a fuel cell comprising several elementary cells with an electrode electrode assembly, as well as bipolar plates <B>; </ B> FIG. 2 is an image obtained by scanning electron microscopy of a membrane electrode interface obtained by the process of the invention with a membrane of sulfonated polyimide. The scale is <B> 10 </ B> <B> <B> - <B> 3 </ B> is an image obtained by electron microscopy <B> at </ B> scanning a membrane interface <B> - </ B> membrane obtained by a method of the prior art with a membrane of sulfonated polyimide. The scale is <B> 10 </ B> pm.

More specifically, the process according to the invention, in its variant, called <B> </ B> coating <B>, </ B> first comprises the preparation of a solution, in a solvent, a thermostable polymer.

The thermostable polymer may be any known polymer. The method according to the invention adapts to all the polymers capable of giving membranes by casting. By thermostable is generally meant a polymer whose glass transition temperature (case of amorphous polymers) or melting (case of semi-crystalline polymers) is greater <B> than </ B> the degradation temperature of the polymer.

Preferably, the polymer is an ion exchange polymer, more preferably a proton conductive polymer, such as a sulfonated polymer, but a polymer carrying phosphate functions or the like may also be suitable. Suitable polymers include, for example, sulphonated polyimides, sulphonated polyethersulfones, sulphonated polystyrenes and their sulphonated derivatives, sulphonated polyetheretherketones and their sulphonated derivatives, and sulphonated polybenzoxazoles. sulphonated polybenzimidazoles, sulphonated polyparaphenylenes and their sulphonated derivatives.

Particularly preferred polymers are the sulfonated polyimides described in FR-A-2 748 incorporated herein by reference, especially for the parts of this document describing these polymers. .

dans lesquelles<B>:</B> <B>-</B> x est un nombre réel, de préférence supérieur ou égal <B>à</B> 4, de préférence encore de 4<B>à 15 ;</B> et <B>- y</B> est un nombre réel, de préférence supérieur ou égal <B>à 5,</B> de préférence encore de<B>5 à 10 ;</B> <B>-</B> et les groupes<B>Ci</B> et<B>C2</B> peuvent être identiques ou différents et représentent chacun un groupe tétravalent comprenant au moins un cycle aromatique carboné, éventuellement substitué, ayant de<B>6 à 10</B> atomes de carbone et/ou un hétérocycle<B>à</B> caractère aromatique, éventuellement substitué, ayant de<B>5 à 10</B> atomes et comprenant un ou plusieurs hétéroatomes choisis parmi <B><I>S, N</I></B> et<B>0 ; Cl</B> et<B>C2</B> formant chacun, avec les groupes imides voisins, des cycles<B>à 5</B> ou<B>6</B> atomes, <B>-</B> les groupes Ar, et Ar2 peuvent être identiques ou différents et représentent chacun un groupe divalent comprenant au moins un cycle aromatique carboné, éventuellement substitué, ayant de<B>6 à 10</B> atomes de carbone et/ou un hétérocycle<B>à</B> caractère aromatique, éventuellement substitué, ayant de<B>5 à 10</B> atomes et comprenant un ou plusieurs hétéroatomes choisi parmi<B>S,</B> <B>N</B> et<B>0</B> au moins un desdits cycles aromatiques carbonés et/ou hétérocycle de Ar2 étant, en outre, substitué par au moins un groupe acide sulfonique. Other polymers of sulfonated polyimide type are the sulfonated block polyimides formed by the blocks or sequences represented by the following formulas (I) and (Iy) <B>: </ B>

in which: x is a real number, preferably greater than or equal to 4, more preferably 4 to 15; </ B> and <B> - y </ B> is a real number, preferably greater than or equal to <B> to 5, </ B> more preferably <B> 5 to 10; </ B></B></B></B>B> - </ B> and the <B> Ci </ B> and <B> C2 </ B> groups may be identical or different and each represents a tetravalent group comprising at least one optionally substituted carbon aromatic ring having of <B> 6 to 10 </ B> carbon atoms and / or a heterocyclic <B> to </ B> aromatic character, optionally substituted, having from <B> 5 to 10 </ B> atoms and comprising one or a plurality of heteroatoms selected from S, N, and B; Cl </ B> and <B> C2 </ B> each forming, with neighboring imide groups, <B> to 5 </ B> or <B> 6 </ B> atoms, <B> - < The groups Ar 1 and Ar 2 may be identical or different and each represents a divalent group comprising at least one optionally substituted carbon aromatic ring having from <B> 6 to 10 </ B> carbon atoms and / or a heterocycle <B> to </ B> aromatic character, optionally substituted, having from <B> 5 to 10 </ B> atoms and comprising one or more heteroatoms selected from <B> S, </ B><B> N < And at least one of said aromatic carbon and / or heterocycle rings of Ar 2 being further substituted with at least one sulfonic acid group.

dans laquelle<B>Ci, C2,</B> Ar, et Ar2, x et<B>y</B> ont la signification<B>déjà</B> donnée ci-dessus, z est un nombre, de préférence de<B>1 à 10,</B> de préférence encore de 2<B>à 6,</B> et OÙ chacun des groupes R, et R2 représente NH2, ou un groupe de formule<B>:</B>

<B>OÙ C3</B> est un groupe divalent comprenant au moins un cycle aromatique carboné, éventuellement substitué, ayant de<B>6 à 10</B> atomes de carbone et/ou un hétérocycle <B>à</B> caractère aromatique, éventuellement substitué, ayant de<B>5 à 10</B> atomes et comprenant un ou plusieurs hétéroatomes choisis parmi<B><I>S, N</I></B> et<B>0, C3</B> formant avec le groupe imide voisin un cycle<B>à 5</B> ou<B>6</B> atomes. Such sulfonated polyimides may <B> satisfy the following general formula (I) <B>: </ B>

where <B> Ci, C2, </ b> Ar, and Ar2, x and <b> y </ B> have the meaning <B> already </ B> given above, z is a number, preferably from 1 to 10, more preferably from 2 to 6, and where each of R, and R 2 represents NH 2, or a group of formula <B>: / B>

<B> wherein C3 </ B> is a divalent group comprising at least one optionally substituted carbon aromatic ring having from <B> 6 to 10 </ B> carbon atoms and / or a heterocycle <B> to </ B> aromatic character, optionally substituted, having from <B> 5 to 10 </ B> atoms and comprising one or more heteroatoms selected from <B><I> S, N </ I></B> and <B> 0, C3 </ B> forming with the neighboring imide group a cycle <B> to 5 </ B> or <B> 6 </ B> atoms.

Such polymers are for the most part readily available commercially and at a low cost.

The thermostable polymer must also be soluble in the solvent of the solution, this solvent can be easily chosen by the skilled person depending on the polymer used.

The solvent is generally an organic solvent which is chosen, for example, from polar aprotic solvents, such as dimethylformamide (DMF), dimethylacetamide (DMAC), N-methylpyrrolidone (NMP) <B>, </ B> alone or in mixing with, for example, aromatic solvents, such as xylene or glycol ether solvents.

The solvent may also be a phenolic solvent, ie it is selected, for example, from phenol, phenols substituted by one or more halogens <B> (Cl, </ B> I, Br , F), cresols (o-, m- and p-cresol), halogen-substituted cresols (Cl, I, Br, F) and mixtures thereof.

The concentration, the viscosity and the temperature of the polymer solution are adjusted in order to allow the production of a homogeneous film by the coating system. <B> A </ B> As an example, this casting system, is preferably chosen from the so-called systems <B> </ B> Hand Coater <B> </ B> or manual applicators.

The concentration, the viscosity, and the temperature of the applied polymer solution depend on the nature of the latter, but suitable ranges will be, for example, from <B> 30 to 100 </ B> g / l, for the concentration , <B> 1 to 10 </ B> Pa.s, for the viscosity, and <B> 80 to 130 ° C </ B> for the temperature of the solution applied by casting (in the case of a sulfonated polyimide polymer).

This solution of polymer cast on a support or substrate that can be both flexible and rigid. <B> A </ B> as a suitable material for the substrate or support, there may be mentioned <B>: </ B> glass, aluminum, polyester, etc. The shape of this substrate or support generally corresponds to that of the membrane and the final assembly that it is desired to prepare. This substrate is usually plane.

It is furthermore preferable that the substrate or support be perfectly clean during casting. The result of casting, a generally planar film of heat-stable polymer solution on the surface of the substrate or support, is obtained at <B> </ B>. B> wet <B>, </ B> that is to say rich in solvent and comprising substantially all the solvent present in the solution used for casting. The thickness of the wet film is variable, it is generally calibrated <B> to </ B> a thickness of <B> 500 to <B> 5000 </ B> pm, for example <B> to 3000 </ B> pm.

the polymer solution film is then partially dried by evaporation of the solvent from said solution. For this purpose, the substrate or support is generally maintained at a temperature of 40 ° C to 150 ° C, for example 120 ° C. C, </ B> to cause rapid evaporation of the solvent. Such a temperature can be achieved by placing the substrate or support provided with the polymer solution film in an oven.

The drying is a partial drying, i.e. the polymer solution film still contains solvent, generally the solvent fraction still present is <B> 5 to <B>% < Of the amount of solvent initially present.

In other words, the drying is stopped after a variable period, typically from <B> 60 to </ B> 120 minutes, when the viscosity of the polymer film has reached a high enough level to support the electrode. . This viscosity can be easily determined by those skilled in the art, but is generally from 20 to 30 Pa.s.

The electrode is thus deposited on the surface of said thermostable polymer solution film being dried, before it is completely dry, the active face of the electrode facing said surface. The electrode is a commercially available conventional electrode of the type commonly used in fuel cells and has already been described above. Such an electrode, generally flat, and with a thickness of <B> 100 to 500 </ b> pm, generally comprises a so-called active face containing the catalyst, for example platinum carbon, it is this active face which is deposited gently on the surface of the wet film of thermostable polymer solution.

This slowly infiltrates the active layer, for example the platinum-carbon layer <B> to the </ B> surface of the electrode and thus forms a membrane assembly (still wet) <B> - </ B> electrode .

In the next step, the drying of the membrane electrode assembly obtained is continued for a variable duration of <B> 30 to 60 </ B> minutes <B> to </ B>. temperature of <B> 70 to 150 ° C, for example <B> 120 ° C, </ B> in order to remove all remaining residual solvent and form the final assembly. In fact, it is during this stage that is actually formed the <B> </ B> membrane <B>. </ B> Finally, in a final step, the electrode assembly <B> - </ B > membrane is detached from the support or substrate.

The thickness of such an assembly is <B> 100 </ B> <B> to 500 Pm. When it is desired to carry out a complete assembly of electrode <B> - </ B> - </ B> - </ B> electrode by the coating method according to the invention, one starts, first of all, by preparing a first assembly, according to <B> to </ B> the description given above. The membrane electrode assembly thus obtained is then used as a substrate to make a second electrode assembly membrane, that is to say a new one. wet film of thermostable polymer solution is poured on the membrane of the first elementary assembly. This is usually the same solution of the same polymer as cast to make the first assembly. Then, during the drying of this wet film, a second electrode, generally similar to the first, is carefully deposited under the conditions already mentioned above. Again, it is the active side of the electrode which is deposited on the surface of the wet film.

the complete drying is then carried out under the same conditions as those described for the preparation of the first elementary assembly.

<B> A </ B> the outcome of this process, a complete electrode assembly <B> - </ B> membrane <B> - </ B> # electrode is obtained. It is worth noting that this method also makes it possible to improve the gas impermeability of the proton exchange membrane.

Advantageously, according to the invention, it is possible to produce assemblies in which the membrane is reinforced by a reinforcement, in particular to improve the mechanical properties thereof.

In the coating process, it is thus possible to apply, spread, the thermostable polymer solution on a substrate or support, as described above, a reinforcement having been previously disposed on said support.

Such reinforcement may consist of a fabric, for example glass, PEEK, PTFE, a mat, for example glass, a porous material, for example PEEK, PTFE.

The preparation of the solution and all other process steps and the conditions thereof are similar to those described above for the coating process, the only difference being that the reinforcement previously <B> to </ B> step a) on the substrate or support.

In other words, the polymer, for example the sulfonated polyimide employed, is in solution in a solvent which may be of a variable nature, such as phenol, chlorophenol, cresol, NMP, DMF, DMAc, etc. The concentration, the viscosity and the temperature of the solution are adjusted to allow the production of a homogeneous film by a coating system such as a <B> </ B> Hand-Coater <B>. </ B>

The polymer solution, for example of sulfonated polyimide is then spread on a flexible or rigid substrate, for example glass, perfectly clean on which is placed the reinforcement. The thickness of the wet film is calibrated <B> to </ B> a thickness of <B> 500 to <B> 5000 </ B> pm, for example in the vicinity of <B> 3000 < / B> pm. The temperature of the substrate is maintained, for example, in the vicinity of <B> 120 ° C, </ B> to cause rapid evaporation of the solvent. After a few minutes <B> (60 to </ B> 120), the viscosity of the wet film reached a level sufficiently high to support the electrode. The active face of the electrode containing, for example, the platinum carbon is then gently disposed on the surface of the wet film. This slowly permeates the active layer, for example, platinum carbon <B> at the surface of the electrode. Drying of the membrane electrode assembly is continued for several minutes to remove all of the residual solvent.

The reinforced membrane electrode assembly is then peeled off from the initial substrate and then, in turn, used as a substrate to perform a second step.

A new wet film is poured onto the membrane of the previous assembly. During the drying of this wet film, a second electrode is carefully deposited according to <B> at <B> already </ B> given above.

At the end of these two steps, a complete electrode <B> - </ B> reinforced membrane <B> - </ B> electrode assembly is obtained. Or, in the coating process and in the same optics to reinforce the membrane, the reinforcement may be disposed within the wet film of polymer solution prepared by casting during step a) <B>. </ B > Such a reinforcement is analogous to the one already described above.

The <SEP> preparation <SEP> of <SEP> the <SEP> solution <SEP> and <SEP> all <SEP> the
<tb> other <SEP><SEP> steps of the <SEP> process, <SEP> and <SEP> than <SEP><SEP><SEP> conditions of
<tb> these <SEP> are <SEP> analogs <SEP><B><SEP> those <SEP> described <SEP> above
<tb> for <SEP> the <SEP> process <SEP> by <SEP> coating, <SEP> the <SEP> only <SEP> difference
<tb> being <SEP> that <SEP> one <SEP> has <SEP> the <SEP> reinforcement <SEP> on <SEP> within <SEP> same <SEP> of the <SEP> movie
<tb> wet, <SEP><B> to </ B><SEP> smooth <SEP> of <SEP> step <SEP> a). <SEP> In <SEP> other <SEP> terms <SEP><B>:</B>
<tb> the <SEP> polymer, <SEP> by <SEP> example <SEP> polyimide <SEP> sulfonate <SEP> employee <SEP> is
<tb> in <SEP> solution <SEP> in <SEP> a <SEP> solvent <SEP> which <SEP> can <SEP> be <SEP> of <SEP> nature
<tb> variable, <SEP> such <SEP> as <SEP> phenol, <SEP> chlorophenol, <SEP> cresol, <SEP><B> NMP, </ B>
<tb> DMF, <SEP> DMAc, <SEP> etc. <SEP> The <SEP> concentration, <SEP><SEP> viscosity <SEP> and <SEP> the
<tb> temperature <SEP> of <SEP> the <SEP> solution <SEP> are <SEP> adjusted <SEP> so <SEP> of
<tb> allow <SEP> the <SEP> realization <SEP> of a <SEP> film <SEP> seamless <SEP> by <SEP> a
<tb><SEP> system of <SEP> coating, <SEP> such <SEP> as <SEP><B><SE> Hand-Coater <SEP><B>.</B>
<tb> The <SEP> solution <SEP> of <SEP> polymer, <SEP> by <SEP> example <SEP> of
<tb> sulfonated polyimide <SEP>, <SEP> is <SEP> then <SEP> widespread <SEP> on <SEP> a <SEP> substrate,
<tb> by <SEP> example <SEP> in <SEP> glass, <SEP> perfectly <SEP> clean. <SEP> The thickness
<tb> of the <SEP> film <SEP> wet <SEP> is <SEP> calibrated <SEP><B> to </ B><SEP> a <SEP> thickness <SEP> of <SEP><B> 500 <SEP> to </ B>
<tb><B> 5 <SEP> 000 </ B><SEP> pm, <SEP> by <SEP> example <SEP> at <SEP> neighborhood <SEP> from <SEP><B> 3 <SEP> 000 <p> pm.
<tb> The <SEP> reinforcement <SEP> is <SEP> so <SEP> arranged <SEP> by <SEP> any
<tb> technique <SEP> appropriate, <SEP> by <SEP> example <SEP> by <SEP> rolling <SEP> at <SEP> within
<tb> of <SEP> film <SEP> wet, <SEP> on <SEP> the <SEP> substrate. <SEP> The <SEP> temperature <SEP> of
<tb> substrate <SEP> is <SEP> maintained, <SEP> by <SEP> example <SEP> at <SEP> neighborhood <SEP> of
<tb><B>120'C,<SEP> so <SEP> to drive <SEP> fast <SEP> evaporation <SEP> from
<tb> solvent. <SEP> After <SEP> few <SEP> minutes, <SEP> the <SEP> viscosity <SEP> of <SEP> film
<tb> wet <SEP> a <SEP> reaches <SEP> a <SEP> level <SEP> sufficiently <SEP> high <SEP> to support the electrode. The active face of the electrode containing, for example, the platinum carbon is then gently disposed on the surface of the wet film. This perfectly impregnates the active layer, for example carbon platinum <B> to </ B> the surface of the electrode. Drying of the membrane electrode assembly is continued for several minutes to remove all of the residual solvent.

The electrode assembly <B> - </ B> membrane is then detached from the substrate and used to make a reinforced electrode <B> - </ B> electrode assembly <B> - </ B> </ B> what has <B> already </ B> been described above.

The method according to the invention, for preparing a complete electrode <B> - </ B> membrane <B> - </ B> reinforced electrode assembly, may alternatively be carried out by <B> </ B> impregnation <B>. </ B>

A polymer solution is prepared in the same manner as above, the polymers and solvents employed for the preparation of this solution are the same as those already mentioned for the coating process. The concentration, the viscosity, and the temperature of the polymer solution are adjusted in this case, in order to allow the impregnation of a reinforcement, this reinforcement being of the type <B> already </ B> described above, <B > to </ B> know, for example, fabric, mat or porous material, for example glass, PEEK or PTFE. As a result, these concentrations, viscosities and temperatures may differ from those indicated in the case of the coating process.

<SEP> concentration, <SEP><SEP> viscosity <SEP> and <SEP>
<tb> temperature <SEP> of <SEP> the <SEP> solution <SEP> of <SEP> polymer <SEP> serving <SEP><B> to </ B>
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<tb> possibly <SEP> of <SEP> that <SEP> of <SEP> reinforcement, <SEP> but <SEP> of <SEP> ranges
<tb> adequate <SEP> will be, <SEP> by <SEP> example <SEP> from <SEP><B> 80 <SEP> to </ B><SEP> 120 <SEP><B> g / l, </ B><SEP> for <SEP> the
<tb> concentration, <SEP> of <SEP><B> 5 <SEP> to <SEP> 15 </ B><SEP> Pa.s, <SEP> for <SEP><SEP> viscosity <SEP> and <SEP> of
<tb><B> 70 <SEP> to <SEP>120'C<SEP> for <SEP> the <SEP> temperature <SEP> of <SEP> the <SEP> solution
<tb> impregnating <SEP> the <SEP> reinforcement <SEP> (in <SEP> the <SEP> case <SEP> of a <SEP> polymer <SEP> of
<tb> type <SEP> sulfonated polyimide <SEP>.
<tb> Impregnation <SEP> and <SEP> usually <SEP> performed <SEP> in
<tb> diving <SEP> simply <SEP> the <SEP> reinforcement <SEP> in <SEP> the <SEP> solution <SEP> of
<tb> polymer.
<tb> On <SEP> gets <SEP><B> at </ B><SEP> the result <SEP> of <SEP> this <SEP> impregnation
<tb> a <SEP> film <SEP> of <SEP> solution <SEP> of <SEP> reinforced polymer <SEP> thermostable <SEP>
<tb> and <SEP> autosupported, <SEP> this <SEP> movie <SEP> is <SEP> a <SEP> film <SEP><B></B><SEP> wet <SEP><B>,</B>
<tb> that is <SEP> rich <SEP> in <SEP> solvent <SEP> and <SEP> comprising
<tb> noticeably <SEP> the <SEP> integer of <SEP> solvent <SEP> present <SEP> in <SEP> la
<tb> solution <SEP> used <SEP> for <SEP><SEP> impregnation of <SEP> reinforcement.
<tb> Thickness <SEP> of the <SEP> film <SEP> wet <SEP> of <SEP> solution <SEP> of <SEP> polymer <SEP> is
<tb> variable, <SEP> it <SEP> is <SEP> typically <SEP> calibrated <SEP><B> to </ B><SEP> a
<tb> thickness <SEP> of <SEP><B> 1 <SEP> 000 <SEP> to </ B><SEP> 2 <SEP><B> 000 </ B><SEP> pm, <SEP> by <SEP> example <SEP> of <SEP><B> 1 <SEP> 500 </ B><SEP> pm.
<tb> On <SEP> proceeds <SEP> then <SEP> to the <SEP><SEP> partial <SEP> drying of
<tb> film <SEP> of <SEP> solution <SEP> of <SEP> polymer <SEP> reinforced <SEP> and <SEP> self-supported,
<tb> by <SEP> evaporation <SEP> of <SEP> solvent <SEP> from <SEP> said <SEP> solution.
<tb> In <SEP> this <SEP> purpose, <SEP> the <SEP> film <SEP> wet <SEP> enhanced <SEP> and
<tb> self-supported <SEP> is <SEP> maintained <SEP> usually <SEP><B> to </ B><SEP> a
<tb> temperature <SEP> of <SEP><B> 70 <SEP> to <SEP> 1500C, <SEP> by <SEP> example <SEP> of <SEP><B>120'C,</B><SEP> so
<tb> to cause <SEP> a <SEP> rapid <SEP> evaporation <SEP> of the <SEP> solvent. <SEP> One
<tb> such <SEP> temperature <SEP> can <SEP> be <SEP> obtained <SEP> by <SEP> setting <SEP> the <SEP> movie
<tb> wet <SEP> reinforced <SEP> self-supporting <SEP> of <SEP> solution <SEP> of <SEP> polymer
<tb> in <SEP> a <SEP> oven. The drying is a partial drying, i.e. the self-supported reinforced polymer solution film still contains solvent, generally the solvent fraction still present is <B> 5 to 15% </ B> of the amount of solvent initially present. In other words, the drying is stopped after a variable period, generally from <B> 60 to </ B> 120 minutes, when the viscosity of the self-supported reinforced polymer film has reached a high enough level to withstand the electrodes on both sides. This viscosity, which may be different from that in the similar step of the coating process, may be readily determined by those skilled in the art, but is generally from <B> 15 to <20> Pa.s.

The electrodes are thus deposited on each of the surfaces of said reinforced wet film, which is self-supported with thermostable polymer solution being dried, before it is completely dry, the active face of each of the electrodes containing, for example platinum carbon, forming face <B> to </ B> each of said surfaces.

This operation is performed by a device called <B> </ B> <B>. </ B>

The electrodes are conventional electrodes of the type commonly used in fuel cells and have already been described above. These electrodes generally comprise a so-called active face containing the catalyst, for example platinum carbon, it is the active surface of each of the electrodes which is deposited gently on each of the surfaces of the self-supported reinforced wet film of thermostable polymer solution.

It slowly permeates each of the active layers, for example platinum carbon layers <B> to </ B> the surface of the electrodes and thus directly forms a complete electrode assembly <B> - </ B> membrane (still wet) <B> - </ B> electrode.

In the next step, the drying of the membrane electrode assembly obtained is continued for a variable duration of <B> 30 to 60 </ B> minutes <B> to </ B>. temperature of <B> 70 to 150 ° C, for example 1200 ° C., in order to eliminate all residual solvent still present and form the complete final EME assembly. In fact, it is during this stage that is actually formed the <B> </ B> membrane <B>. </ B>

This process allows in just two simple steps to obtain a complete assembly.

The EME assemblies, prepared according to the invention, can be used, in particular, in a fuel cell that can operate, for example, with the following systems: <B> <B> </ B> <B> - hydrogen, alcohols, such as methanol, <B> to </ B> the anode <B>; </ B> <B> - </ B> oxygen, air, <B> to </ B> the cathode.

The present invention also relates to a fuel cell device comprising at least one EME assembly prepared by the method according to the invention.

Such a cell <B> / </ B> has <B>. </ B> all the properties related to the thermostable membranes for example because of the excellent mechanical properties ,, the membrane can undergo without damage the stresses (clamping, etc.). The properties of thermostable membranes of the sulfonated polyimide type are, for example, described in document FR-A-2 <B> 748 </ B> 485, <B> already </ B> cited .

For example, the <B> to </ B> fuel stack may correspond to the <B> already </ B> scheme given in figure <B> 1. </ B>

Such a fuel cell, in which the EME assembly (s) are prepared by the process according to the invention has, as a result, all the advantages due to these assemblies and <B> to </ B> the excellent quality of their interface <B>: </ B> in particular, excellent joint strength, reliability, excellent mechanical and electrochemical properties (voltage evolution as a function of current density at least similar to <B> </ B> all NAFION® (<B>), gas impermeability, etc., all of these properties being perfectly reproducible and not degrading over time.

These properties are significantly greater than those of batteries comprising prior art assemblies, for example: the battery temperature is generally maintained between <50> </ sup>. B> and 800C and, under these conditions, it produces for example a current density of <B> 0.5 </ B> A / cm 2 with a voltage of <B> 0.6 </ B> V and this over a very long period of up to 3,000 hours, which demonstrates the excellent properties theymic and mechanical stability and other assemblies and its excellent electrical properties. The invention will now be described with reference to the following examples, given <B> to </ B> illustrative and non-limiting title.

les valeurs de x sont généralement de<B>0<U> < </U></B> x,<B>y<U> < </U></B> 20 et par exemple dans le cas présent x<B≥ 8</B> et<B>y = 10.</B> <U> Examples </ U><U> Example <B> 1 </ U></U><U> Making an elementary assembly </ U><U> electrode <B> - </ B> membrane by the method according to the invention </ U> This is the realization of a membrane electrode assembly <B> - </ B> membrane in a sulfonated polyimide whose molecular structure is described below.

the values of x are generally <B> 0 <U><</U></B> x, <B> y <U></U></B> 20 and for example in this case x <B≥ 8 </ B> and <B> y = 10. </ B>

The sulfonated polyimide employed is in solution in metacresol. The concentration, the viscosity and the temperature of the solution are adjusted to allow the production of a homogeneous film by a system of <B> <B> </ B> Hand-Coater <B> </ B> and are as follows <B >: </ B> <B> - </ B> concentration <B>: 70 </ B> g / l <B> - </ B> viscosity <B>: </ B> 4 Pa.s <B > <B> - <B> temperature <B>: 120'C. </ B>

The solution of the sulfonated polyimide is then spread on a glass substrate of rectangular shape <B> 3 </ B> mm thick and perfectly clean. The thickness of the wet film is calibrated in the vicinity of <B> 3000 </ b> pm. The temperature of the substrate is maintained in the vicinity of <B> 120 ° C </ B> to cause rapid evaporation of the solvent.

After a few minutes, the viscosity of the wet film has reached a level sufficiently high to support the electrode. This electrode is an electrode provided by SORAPEC The face of the electrode containing the platinum carbon is then delicately disposed on the surface of the wet film, which slowly permeates the platinum carbon layer <B> at </ B > the surface of the electrode The drying of the electrode assembly <B> - </ B> membrane is continued for a further <B> ... </ B> minutes in order to eliminate all the residual solvent.

The electrode assembly <B> - </ B> membrane is then detached from the substrate. <U> Example 2 </ U> <U> Realization of a complete assembly </ U> electrode <B> - </ B> membrane <B> - </ B> electrode by coating This is the real / lisation of an electrode assembly <B> - </ B> membrane <B> - </ B> sulfonated polyimide electrode in two distinct stages <B>: </ B> Step <B> <U> 1 </ U> </ B> <U> <B> <B> </ B> realization of an elementary assembly </ U> <U> electrode <B> - </ B> membrane </ U> A first electrode assembly <B> - </ B> membrane is made according to <B> to </ B> the description of example <B> 1. </ B> The electrode assembly <B> - </ B> membrane thus obtained is used as substrate to perform the second step.

 Step <U> 2 </ U> <U> Realization </ U> of a <U> -second assembly </ U> <U> elementary electrode <B> - </ B> membrane </ U> A new wet film is poured on the membrane of the previous assembly. During drying of this wet film, a second electrode is carefully deposited, in accordance with the description of Example <B> 1. </ B>

At the end of these two steps, a complete electrode <B> - </ B> membrane <B> - </ B> electrode assembly is obtained. This methodology also improves the gas impermeability of the proton exchange membrane. <U> Example <B> 3 </ U> </ U> <U> Making a complete assembly </ U> <U> electrode </ U> <B> - </ B> <U> reinforced membrane <B> - </ B> </ U> <U> <U> Coating </ U> The sulfonated polyimide employed is the same as above. The concentration, the viscosity and the temperature of the solution are adjusted to allow the realization of a homogeneous film by a system of <B> <B> </ B> Hand-Coater <B> </ B> and are the same as in Example <B> 1. </ B> The solution of sulfonated polyimide is then spread on a perfectly clean glass substrate on which is placed a reinforcement, which is a PEEK fabric from the company SEFAR The thickness of the film wet is calibrated in the vicinity of <B> 3,000 </ b> pm. The temperature of the substrate is maintained in the vicinity of <B> 120 ° C </ B> to cause rapid evaporation of the solvent. After a few minutes, the viscosity of the wet film has reached a level sufficiently high to support the electrode, <B> to </ B> know <B> 15 </ B> Pa.s. The face of the electrode containing the platinum carbon is then delicately disposed on the surface of the wet film. It slowly permeates the platinum carbon layer <B> at </ B> the surface of the electrode. The drying of the membrane electrode assembly is continued <B> 60 </ B> minutes in order to remove all of the residual solvent.

The reinforced membrane electrode assembly is then detached from the substrate and used as a substrate to perform a second step. A new wet film is cast on the membrane of the previous assembly. During drying of this wet film, a second electrode is carefully deposited, in accordance with the description of Example <B> 1. </ B>

At the end of these two steps, a complete electrode <B> - </ B> reinforced membrane <B> - </ B> electrode assembly is obtained.

<U> Example 4 </ U> <U> Realization of a complete assembly </ U> <U> electrode <B> - </ B> reinforced membrane <B> - </ B> electrode by </ U> <U> Coating </ U> This is the realization of an assembly electrode <B> - </ B> membrane <B> - </ B> electrode reinforced with PEEK fabric from the company SEFAR Polyimide The sulfonate employed is the same as above and is in solution in a solvent which is metacresol.

The concentration, the viscosity and the temperature of the solution are adjusted in order to allow the realization of a homogeneous film by a system of <B> </ B> Hand-Coater <B>, </ B> they are identical <B <B> 1. </ B> The solution of sulfonated polyimide is then spread on a perfectly clean glass substrate. The thickness of the wet film is calibrated in the vicinity of <B> 3000 </ B> / lim.

The reinforcement is then deposited within the wet film on the substrate. Under the action of its own weight, the reinforcement penetrates into the thickness of the wet film until it comes into contact with the substrate. The temperature of the substrate is maintained at around 1200C in order to cause rapid evaporation of the solvent. After a few minutes, the viscosity of the wet film has reached a level sufficiently high to support the electrode. The face of the electrode containing the platinum carbon is then delicately disposed on the surface of the wet film. This perfectly impregnates the platinum carbon layer <B> at </ B> the surface of the electrode. Drying of the membrane electrode assembly is continued for a further 60 minutes to remove all of the residual solvent.

The electrode assembly <B> - </ B> membrane is then detached from the substrate and used to make a reinforced electrode <B> - </ B> electrode assembly <B> - </ B> </ B> the description of example 2. <U> Example <B> 5 </ U> </ U> <U> Making a complete assembly </ U> <U> electrode <B> - < / B> membrane <B> - </ B> electrode reinforced by </ U> <U> impregnation </ U> This is the realization of an assembly electrode <B> - </ B> membrane <B > - </ B> reinforced electrode. The sulfonated polyimide employed is in solution in a solvent which is metacresol. The concentration, the viscosity and the temperature of the solution are adjusted to allow the impregnation of the reinforcement and are as follows: <B>: </ B> <B> - </ B> concentration <B>: 80 </ B > g / l <B> - </ B> viscosity <B>: </ B> 2 Pa.s <B>; </ B> <B> - </ B> temperature <B>: </ B> 1200C.

The thickness of the self-supported reinforced wet film is calibrated in the vicinity of <B> 3,000 </ b> pm.

The temperature of the self-supported reinforced wet film is maintained at around 1200 ° C, in order to cause the rapid evaporation of the solvent. After a few minutes, the viscosity of the self-supported reinforced wet film has reached a sufficiently high level, <B> to </ B> <B> 15 </ B> Pa.s, to support the electrodes on both sides. The face of the electrodes containing the platinum carbon is then delicately disposed on the surface of the self-supported reinforced wet film. This perfectly impregnates the platinum carbon layer <B> at the </ B> surface of the electrodes. Drying of the electrode <B> - </ B> electrode <B> - </ B> assembly is continued for several minutes to remove all of the residual solvent. The assemblies obtained in Example <B> 1, </ B> with the sulfonated polyimide membrane whose structure is described in Example <B> 1, </ B> are characterized by the fact that the electrode interface <B> - </ B> membrane is of very good quality as shown in Figure 2. Indeed, in this photograph, obtained by electron microscopy <B> to </ B> sweep, the electrode interface <B > - </ B> membrane is perfectly regular and flawless and no homogeneity is visible.

While going through the photograph from bottom to top, we distinguish several levels which correspond respectively to the heart of the electrode (Teflon felt charged with carbon black, part <B> 1), to </ B> the platinum carbon layer (light gloss level, part 2) with a thickness of 20 μm and finally <B> at </ B> the proton exchange membrane (part <B> 3) </ B> with a thickness of <B > 15 </ B> pm. The cohesion between the electrode and the membrane is such that it is no longer possible to separate them unlike assemblies made by existing methods. This type of electron microscopy <B> to </ B> scanning aimed to <B> to </ B> characterize the membrane interface <B> - </ B> electrode makes it possible to distinguish the assemblies obtained by the method of the invention, assemblies obtained by any other method based on the pressing of a formed membrane and an electrode.

Indeed, any other process based on the pressing of a <B> (<B>) </ B> membrane and an electrode results in the formation of <B> defects at </ B> the membrane interface <B> - </ B> electrode, as shown in Figure <B> 3 </ B> in which the reference numbers have the same meaning as in Figure 2.

In this figure <B> 3, </ B> which represents the membrane interface <B> - </ B> electrode of an assembly obtained by pressing, according to the prior art, there are clearly distinct vacuoles and defects. These defects are <B> to </ B> the origin of the poor electrochemical performance of these assemblies.

In fact, in addition to adhesion problems, various heterogeneities, such as air vacuoles, folding zones, etc., are visible <B> at </ B> the electrode interface <B> - </ B> membrane assemblies obtained by conventional methods.

 In addition, a mapping of the sulfur element was carried out using a castaing probe on an assembly obtained by the method of the invention according to the description of the example <B>. > 1. </ B> In this cartography, the sulfur element makes it possible to identify the presence of the proton conductor. <B> It is clear that the process of the invention makes it possible to drive a fraction of the proton conductor into the area rich in platinum.

Claims (1)

<U> CLAIMS </ U> <B> 1. </ B> A process for preparing an assembly comprising at least one electrode having an active face, and a membrane made of a heat-stable polymer, in which the following steps are carried out < B>: </ B> a) a solution of a heat-stable polymer is cast on a support so as to obtain a thermostable polymer solution film <B>; </ B> then <B b) partially drying said thermostable polymer solution film by evaporation of the solvent from said solution; b) depositing an electrode on the surface of said thermostable polymer solution film, drying course, before it is completely dry, the active face of the electrode facing <B> to </ B> said surface, so as <B> to </ B> obtain an assembly comprising a membrane in thermostable polymer and said electrode <B>, </ B> <B> d) </ B> the said assembly obtained in step c) <B> is completely dried, then e) we take off the assembly comprising said membrane and said electrode of the substrate. 2. The method of claim 1, wherein, prior to step a), a reinforcement is disposed on said support. <B> 3. </ B> Preparation process according to claim 1, wherein, at the end of step a), a reinforcement is provided. within <B> / </ B> of the thermostable polymer solution film. The method of claim 3, wherein said reinforcement is laminated within the thermostable polymer solution film. <B> 5. </ B> Process according to any one of claims <B> 1 to </ B> 4, for preparing an electrode assembly <B> - </ B> membrane <B> - </ B> electrode (EME) consisting of a thermostable polymer membrane and two electrodes further comprising, <B> to </ B> the outcome of step e), the following steps <B>: </ B> <B> f) </ B> is poured on the face of the assembly, by the membrane, a solution of a thermostable polymer, so <B> to </ B> get a film of polymer solution thermostable <B>; </ B> then <B> g) </ B> the heat-stable polymer solution film is partially dried by evaporation of the solvent from said solution <B>; h) a second electrode on the surface of said thermostable polymer solution film, being dried, before it is completely dry, the active face of the second electrode facing <B> to </ B> the surface of said film, so <B> to </ b> get an electrode assembly <B> - </ B> ther polymer membrane most <B> - </ B> electrode <B>; </ B> then i) completely dry said electrode assembly <B> - </ B> membrane <B> - </ B> electrode obtained during the step h). <B> 6. </ B> Process for preparing an electrode <B> - </ B> membrane <B> - </ B> electrode (EME) <B>, </ B> assembly in which the following steps a) a reinforcement is impregnated with a solution of a heat-stable polymer, so as to obtain a film of thermostable polymer solution which is reinforced and self-supporting, then <B> b) partially drying said film of thermostable reinforced and self-supporting polymer solution by evaporation of the solvent from said solution; b) depositing an electrode on each of the faces of said solution film of thermostable polymer, in the event of drying, before it is completely dry, the active face of each of the electrodes facing <B> to </ B> each of the surfaces of said film <B>; </ B> <B d), the assembly obtained in step c) is completely dried. <B> 7. </ B> A process according to any one of claims 1 to 6 </ B> carried out continuously. <B> 8. A process according to any one of claims 1 to 7, wherein said thermostable polymer is an ion exchange polymer, such as a proton conductive polymer. <B> 9. </ B> The process according to claim 8, wherein said polymer is selected from sulfonated polyimides, sulfonated polyethersulfones, sulfonated polystyrenes and their sulfonated derivatives, sulfonated polyetheretherketones and the like. sulphonated derivatives, sulphonated polybenzoxazoles, sulphonated polybenzimidazoles, sulphonated polyparaphenylenes and their sulphonated derivatives. <B> 10. </ B> An assembly comprising at least one electrode and a membrane obtainable by the method according to any of claims <B> 1 </ B> <B> to </ B> 4 and <B> 7-9. </ B> <B> il. </ B> Assembly electrode <B> - </ B> membrane <B> - </ B> <B> electrode susceptible </ B> > be obtained by the process according to any one of claims <B> 5 to 9. </ B> 12. Battery <B> to </ B> fuel comprising at least one electrode assembly <B> - </ B> membrane <B> - </ B> electrode according to claim <B> 11. </ B>