KR20200092977A - A positive electrode plate for assembling elements of a fuel cell unit and a method for manufacturing the positive electrode plate, a fuel cell unit including the positive electrode plate, and a fuel cell comprising the unit - Google Patents

Abstract

The present invention is a bipolar plate for assembly of elements of a fuel cell unit, consisting of a stainless steel substrate coated on at least one of two sides by a layer of electrically conductive material, the material being bivalent Or a trivalent Ti compound or a mixture of such compounds, wherein the layer contains oxygen, but at% oxygen measured by X-ray photoelectron spectroscopy (XPS) on the top 10 nm of the layer The amount of is related to the positive electrode plate, characterized in that, according to the measured at% content of Ti, the content does not exceed 1.5 times the at% content of oxygen corresponding to a coating composed entirely of TiO. The invention also relates to a method of manufacturing such a plate, a fuel cell unit comprising at least one such plate, and a fuel cell comprising at least one such unit.

Description

A positive electrode plate for assembling elements of a fuel cell unit and a method for manufacturing the positive electrode plate, a fuel cell unit including the positive electrode plate, and a fuel cell comprising the unit

The present invention relates to a method for manufacturing a metal strip or sheet and a strip or sheet produced accordingly.

PEMFC type fuel cells, ie fuel cells with proton exchange membranes, are anode/electrolyte/cathode assemblies, each called a membrane electrode assembly (MEA), and a gas diffusion layer (GDL) extending on both sides of the MEA assembly It includes a gas diffusion layer and a battery unit consisting of bipolar plates (bipolar plates). The positive electrode plate ensures the assembly of the elements of the battery unit. The positive electrode plate also limits the range of the fluid circulation channel and ensures the distribution of gas, refrigerant and discharge of water generated in the cell, which can control the humidity of the proton exchange membrane. In addition, the positive electrode plate has a function of collecting current generated at the electrode.

As the essential role played by the positive electrode plate in a fuel cell and the importance of such a battery in many fields are increasing, it is desired to develop a compact positive electrode plate having a low manufacturing cost and a long life of the fuel cell. Their contact resistance (“Interfacial Contact Resistance” or ICR) should be as low as possible. An ICR of 10 mΩ.cm ² under a contact pressure of 100 N.cm ⁻² will be the maximum value, which should be optimal and should not be exceeded.

The documents WO-A-2016/151356 and WO-A-2016/151358 have proposed a method for producing a metal strip or sheet, particularly suitable for the manufacture of a positive electrode plate, the method comprising the provision of a substrate made of stainless steel; And a chromium nitride-based layer onto the substrate by physical vapor deposition (PVD) in a deposition facility comprising a deposition chamber that can be evacuated and also supplied with a mixture of inert gases such as argon and nitrogen. It includes the deposition of. The chamber also includes a chromium target disposed on the top surface (eg) of the substrate, the substrate passing through the deposition chamber in the longitudinal direction. An appropriate potential difference is applied between the target and the substrate. The deposition chamber comprises a deposition zone of a length that is strictly shorter than the length of the deposition chamber taken in the longitudinal direction and at least a first “prohibited zone” adjacent the longitudinal deposition zone, and during deposition , Chromium nitride is deposited on the substrate only in the deposition region. In the first "forbidden zone" there is no deposit of chromium nitride on the substrate.

The first "prohibited zone" can be located downstream of the target on the path of the substrate.

The rate of chromium deposition on the substrate can be above a predetermined threshold in the deposition zone downstream of the target.

Typically, the deposition chamber includes a downstream cover impermeable to chromium atoms that prevents the injection of chromium nitride from the first “forbidden zone” onto the substrate and allows the injection of chromium nitride from the deposition zone onto the substrate. . To this end, the downstream cover is typically interposed on the trajectory of the chromium atoms injected towards the first zone, to prevent deposition of chromium atoms on the substrate originating from a target whose deposition rate is strictly lower than a predetermined threshold. It is arranged in the deposition chamber.

The deposition chamber may further include a second “forbidden zone” without deposition of chromium nitride on the substrate during the deposition step, and the second “forbidden zone” may include a first “forbidden zone” (downstream zone) and a second “ A "prohibited zone" (upstream zone) is present adjacent the deposition zone to surround the deposition zone in the longitudinal direction of movement of the strip or sheet. Typically, the chamber then further comprises an upstream cover impermeable to the chromium atom, the upstream cover being placed in the chamber and interposed in the trajectory of the chromium atom injected from the target towards the second "forbidden zone", The injection of chromium nitride into the substrate in the deposition zone is allowed and the injection of chromium nitride into the substrate in the second "forbidden zone" is prevented.

Throughout the deposition zone, the rate of deposition of chromium atoms on the substrate during deposition is preferably above a predetermined threshold.

The method includes determining a predetermined threshold for a given deposition facility by calibration prior to the deposition step, the predetermined threshold corresponding to the minimum deposition rate at which a coating layer having a desired contact resistance is obtained.

The metal strip or sheet is made of stainless steel, whose thickness is typically on the order of 0.1 mm, but can be much less, which initially includes a passive layer of oxidation on its surface, and the passive oxide layer as a coating layer. It is completely removed in small portions in the area intended to be coated, so that in these areas, no residue of the passive layer remains at the start of the deposition step.

Deposition on both sides of the strip or sheet is possible if the chamber has two chrome targets placed on both sides of the strip or sheet and is spaced apart from each other on the path of the strip or sheet and the cache(s) associated with each target. Do.

Accordingly, the metal strip or sheet comprises a coating layer on at least one side thereof based on a stainless steel substrate and chromium nitride, the coating layer optionally comprising oxygen, the coating layer being physical vapor deposition (PVD) Is obtained by It will be noted that the oxygen that may be present in the coating layer is due to inevitable sealing defects in the chamber and desorption from the walls or even substrate of the chamber. It is not derived from spontaneous addition of oxygen to the processing atmosphere, which aims to obtain a layer comprising a proportion of metal oxides.

The coating layer comprises on its surface a surface region having an atomic oxygen content that is strictly lower than its atomic nitrogen content. Typically, the surface area has a height of 15% or less of the total thickness of the coating layer.

The coating layer includes an interface region at the interface with the substrate that contains an atomic oxygen content that is strictly lower than its atomic nitrogen content. Typically, the interfacial zone has a height of 15% or less of the total thickness of the coating layer.

The coating layer can thus have a contact resistance (ICR) of 10 mΩ.cm ² to less than 100 N.cm ⁻² .

The coating layer is formed directly on the stainless steel substrate without the intervening of a passive layer between the coating layer and the stainless steel of the substrate. The coating layer is textured and in particular has an epitaxial relationship with the stainless steel of the substrate. This epitaxy must continue to exist even after plate formation. The difference in mechanical properties between the substrate and the coating means that these conditions are maintained at the expense of local rupture of the CrN layer, and this difference is not really a problem. When the substrate is exposed, the passivation layer is reconstituted and prevents severe corrosion of the plate, especially since the surrounding medium is relatively weakly acidic (pH 4 to 5).

Thus, it is possible to obtain a positive electrode plate for a fuel cell comprising at least one plate obtained by deformation of a blank or sheet cut from a strip as described above.

In the example described herein, the plate is prepared and coated with a CrN based coating layer on only one of its sides. To this end, there is only one PVD target in the chamber, which overhangs the continuous path of the strip or sheet over the side to be coated. However, in practice there is always a small CrN deposited on the opposite side of the strip or sheet when moving within the processing chamber, which is not a problem in itself.

However, fuel cell manufacturers hope to have a more efficient plate than just described. On the one hand, CrN is not the best performing material for constructing a textured coating layer, and it is possible to obtain reliable contact resistance at all points of the plate at a prescribed threshold value of 10 mΩ.cm ² to 100 N.cm ^-2 . There is only a small margin that can be.

On the other hand, when the plates are deformed to perform assembly of the positive electrode plate and then welded to each other and welding is performed on the uncoated side, a single-sided coating of the plate is suitable because the material solder contributes to the electrical conductivity of the assembly. . However, when the assembly is performed by other means, the contact resistance deteriorates in the area where the metal is exposed during the forming of the plate by causing reconstitution of the passivation layer. Therefore, the performance of the assembly is deteriorated in terms of electrical conductivity.

Finally, more incidentally, if the strip or sheet has two faces whose coatings are different, or if one of them has no coating and is not visually identifiable, the cause of possible errors when assembling the positive electrode plate It becomes.

It is an object of the present invention to propose a metal strip or sheet for the construction of a positive electrode plate of a fuel cell element that best solves the above-mentioned problems.

To this end, the subject of the invention relates to a positive electrode plate for the assembly of elements of a fuel cell unit, which consists of a stainless steel substrate coated on at least one of two sides with a layer of electrically conductive material, The material is a divalent or trivalent Ti compound or a mixture of such compounds, the layer containing oxygen, but measured by X-ray photoelectron spectroscopy (XPS) on the top 10 nm of the layer The amount of oxygen in at% is less than or equal to 1.5 times the at% oxygen content corresponding to the coating composed entirely of TiO, according to the measured at% Ti content.

The Ti compound may be a divalent Ti compound selected from TiN, TiO, and mixtures thereof.

Each of the two sides of the plate can be coated with a layer of at least one divalent or trivalent Ti compound, each layer containing oxygen, but X-ray photoelectron spectroscopy on the top 10 nm of the layer (X The amount of at% oxygen measured by -ray photoelectron spectroscopy (XPS) is less than or equal to 1.5 times the at% oxygen content corresponding to a coating composed entirely of TiO, according to the measured at% Ti content .

One side of the plate may be coated with a divalent or trivalent Ti compound or a mixture of these compounds, and the other side may be coated with CrN.

The present invention also relates to a method of manufacturing a positive electrode plate for assembly of an element of a fuel cell unit consisting of a stainless steel substrate coated on at least one of two sides by an electrically conductive material, said material being bivalent Or a trivalent Ti compound or a mixture of such compounds, wherein the layer contains oxygen, but at% oxygen measured by X-ray photoelectron spectroscopy (XPS) on the top 10 nm of the layer The amount of is not more than 1.5 times the at% oxygen content corresponding to the coating composed entirely of TiO, according to the measured at% Ti content;

-Stainless steel substrates are provided in strip or sheet form;

-A layer of a divalent or trivalent Ti compound or a mixture of Ti compounds, comprising: at least one deposition chamber; Means for passing the substrate inside the chamber in the longitudinal direction; Means for limiting or controlling the amount of air and oxygen entering the chamber; And at least one side of the plate by physical vapor deposition (PVD) in a deposition facility comprising at least one Ti target;

Then, the substrate coated with a divalent or trivalent Ti compound is cut and molded to provide a desired shape and dimension and obtain a positive electrode plate for a fuel cell.

The Ti compound may be a divalent Ti compound selected from TiN, TiO, and mixtures thereof.

The chamber may also include at least one forbidden zone on at least one side of the substrate, wherein deposition of a divalent or trivalent Ti compound is not performed on the substrate.

The at least one forbidden zone can be obtained by interposing at least one impermeable cover to a Ti atom disposed on the path of the Ti atom between the target and the substrate.

A divalent or trivalent Ti compound or a mixture of these compounds can be coated on one side of the substrate, and the other side can be coated with CrN deposited by PVD from a Cr target.

The invention also relates to a PEMFC type fuel cell unit composed of an anode/electrolyte/cathode assembly, wherein the anode and cathode consist of a positive electrode plate comprising a stainless steel substrate coated on one or more of its sides by an electrically conductive material, At least one of the anode and the cathode consists of a positive electrode plate of this type.

The invention also relates to a fuel cell comprising a unit of a positive electrode plate for assembling elements of the unit, at least one of which is a unit of the type mentioned above.

As will be understood, the present invention is primarily directed to the selection of TiN as well as TiO as a coating material for divalent or trivalent titanium compounds, especially for strips or sheets, and by PVD on one or both sides of the strip or sheet. It is based on the deposition.

TiN will actually be a more suitable material than CrN because it can achieve an ICR of less than 5 mΩ.cm ² to 100 N.cm ⁻² .

In general, according to the invention, the strip or sheet is coated essentially with a material based on divalent or trivalent Ti, for example, in particular TiN, TiO or a mixture of these two Ti compounds divalent. In fact, considering the experiments carried out by the inventors, it is the divalent or trivalent properties of the Ti compound deposited on the strip or sheet that is based on the performance of the positive electrode plate; And TiN, TiO, and mixtures thereof is also low contact resistance, typically less than 5 mΩ.cm ² to 100 N.cm ^- that are found to be quite adequate to provide a significant ^2. Conductive compounds of trivalent Ti such as Ti ₂ O ₃ are also suitable.

In contrast, tetravalent titanium compounds such as TiO ₂ are avoided in this coating, at least above the first 10 nm of the top layer, which is most important to ensure suitable contact resistance for the strip or sheet.

In general, according to the present invention, a coating based on a divalent or trivalent Ti should not exceed more than half of the oxygen content measured at% (i.e., 1.5 times or less) at this surface thickness of 10 nm at % Should have the total content of oxygen% (ie expressed in atomic percentages), based on the analysis of the coating carried out by the so-called “XPS” process of X-ray photoelectron spectroscopy, the measured Ti content (also at% Considering) corresponds to a coating formed entirely of TiO.

Indeed, it is sufficient to perform this analysis on the top 10 nm of the coating layer, since the O content of the coating and the tetravalent Ti formation that can be generated therefrom is highest at its end surface, this zone is the Ti during the deposition operation. Because it was the most distant area from the target. This thickness of 10 nm also corresponds to the existing resolution of the XPS method.

Of course, ideally, it would be desirable to be able to differentiate between a divalent or trivalent Ti compound (required) and a tetravalent (unwanted) compound during deposition analysis. However, various conventional analytical methods make it possible or not exactly sufficient to make this distinction, which makes it possible, for example, to settle an acceptable content of TiO _{2 in} the coating so that the contact resistance is sufficiently low. Thus, we understand this content of tetravalent Ti compounds, which is indirectly allowed by the measurements and calculations cited based on the atomic percentages of Ti and O.

The literature “Thin layer of titanate nitride: reactivity as an original means of physicochemical properties” (J. Guillot's 2002 paper by the University of Burgundy) describes a method for analyzing this type of deposit. Provide information. The present invention will be better understood from the following description.

TiN is a high performance material in terms of contact resistance. A method of depositing CrN by PVD performed under conditions comparable to those presented in the literature of the prior art cited in the introduction proved to be suitable for TiN deposition. However, the surface of the metal support needs to be cleaned very well before the deposition of TiN, and it is desirable to clean it by a conventional chemical pickling process suitable for the material used. In the case of stainless steel, preferably, argon plasma pickling will be used.

Another difficulty faced by those skilled in the art is that when the nitride deposition by PVD is performed only on one side of a strip or sheet moved by a prior art method, the other side, especially its edge, also has a fatal effect on the operation, and of the nitride It is that the deposits also occur in a minimal but completely non-negligible way, and cannot be controlled under conditions that make the composition of the deposits precise, especially for the main deposit in the presence of an oxygenated phase.

This phenomenon is not very troublesome when trying to obtain a single-sided deposit. On the other hand, deposit the Cr or Ti target on both sides of the strip or sheet, for example by placing it on either side of the strip or sheet (one placed in the upstream part of the chamber and the other in the downstream part of the chamber). If it is desired to obtain, the coating deposit in the downstream portion can be accompanied by a parasitic coating deposit on the surface which is already coated on the upstream portion of the chamber and can degrade its properties. This is particularly the case when the atmosphere of the chamber is not as poor as the optimum oxygen to form only TiN due to leakage at the level, especially at the entry and exit of the strip or sheet, or oxygen or water on the walls of the chamber. This is especially true if the oxygen or water supplied by the strip or sheet has not been sufficiently emptied prior to the adsorption and implementation of the coating. As can be seen, if the formation of TiO can be accepted even if desired, this training should be well mastered to avoid obtaining too much Ti0 ₂ . In any case, the presence of oxygen or water vapor in the chamber should be well controlled and parasitic air or water vapor should be avoided.

However, in the case of two-layer deposition of TiN according to the present invention, the problem of parasitic deposition on the other side of the strip or sheet other than that associated by one of the two Ti targets does not occur, or only one target It occurs much less than the cross-section deposition used.

Indeed, the fact that the two sides of the strip or sheet have the same coating is essentially the same as the material that can be deposited in an uncontrolled manner in a way other than what a given target has to deal with. It has the result of property. Thus, the properties of the surface of the layer deposited on the first side of the strip or sheet are preferentially not altered by parasitic deposition due to the deposition of the same layer normally deposited on the second side of the strip or sheet.

In addition, having two sides coated with the same material provides reversibility to the strip or sheet. Thus, it is not necessary for the operator or device for manufacturing the fuel cell unit to visually or differently distinguish between the two sides of the strip or sheet which should be directed towards the electrolyte after assembly of the relevant MEA.

Optimally, when the strip or sheet is coated on its two sides, it is preferable to place two Ti targets on either side of the strip or sheet, and to face each other at substantially the same distance from the strip or sheet. , Is not required. The covers defining the forbidden zones and the zones approved for the deposition of layers on each side are also arranged symmetrically with respect to the strip or sheet. In this way, the two sides are coated substantially simultaneously and with the same parameters. When parasitic deposits occur, they occur in a very similar way on both sides, which minimizes their effect on the final properties of the coated material, so that both sides are coated in substantially the same way.

In the case of TiN, the reaction of oxygen and Ti present in the chamber results in the formation of Ti oxides of various valences, namely TiO and/or Ti ₂ O ₃ and/or TiO ₂ . The formation of pure TiO ₂ should be avoided because it is an insulating phase. On the other hand, TiO is a conductive phase in the same way as TiN, and its presence in the TiN layer, or at its surface or substrate/TiN interface, does not result in deterioration of the contact resistance. TiO can even be an exclusive or semi-exclusive component in the conductive phase, the main component of which consists of a divalent conductive Ti compound (TiN, TiO) ₂ , which should be avoided. Trivalent Ti compounds such as Ti ₂ O ₃ are also suitable. Cr oxides which are easy to form are not conductive, and in any case, it is not desirable to deposit CrN, because it is detrimental to the conductivity of the deposit, and therefore to the contact resistance.

Another advantage of double-sided deposition (whether the two layers are the same or not) is that the manufacturer of the fuel cell unit can minimize or eliminate the step of welding the micro-channels together. This also increases the number of depot cells and increases the installation capacity of the manufacturing tool. Thus, manufacturing costs for a given number of units are reduced. In addition, when working with several continuous cells, each of the continuous cells comes after the previous cell without the sheet to be coated exposed to the external atmosphere between each cell, which is the air intake parasite in the coating system, thus oxygen content and deposits It is possible to better control the degree of oxidation.

Therefore, precautions are taken to prevent the formation of too much pure TiO ₂ .

To this end, if most of the TiN formation is required, it is desirable to take the same precautions as in the deposition method described above, preferably to limit as much of the air intake parasites as possible. The thermodynamics and kinetics of Ti oxide formation mean that TiO is formed in a privileged manner, and pure TiO ₂ is formed remarkably only when the amount of available oxygen is sufficient for this purpose with respect to the temperature at which deposition occurs.

Analysis of the deposit can be performed by any suitable method that provides a direct or indirect indication of the chemical nature of the deposit and the excessive presence of tetravalent Ti in the form of pure TiO ₂ . As mentioned earlier, X-ray photoelectron spectroscopy (XPS) is a particularly suitable method, because it clearly clarifies the quantitative presence of different possible phases (TiN, TiO, Ti(NO), Ti ₂ O ₃ , Ti0 ₂ ...). Although not denotable, nevertheless, if the probability of excessive presence of tetravalent Ti in the entire coating is too high to be considered to be able to constitute the positive electrode plate according to the present invention, at a depth of approximately 10 nm. This is because it can be deduced by comparing the respective atomic contents of Ti and O measured across the surface of the coating. From this point of view, as mentioned earlier, analysis of the first 10 nm of the outer surface of the layer is sufficient to determine whether the coating has the required quality, because on the one hand they are the most important for obtaining good contact resistance, and others On the one hand, this is because oxygen contamination caused by excessive oxygenation of Ti is maximized.

In routine experiments, the operator can easily determine whether the setting of his batch facility allows for a suitable composition of a TiN or TiO layer or a mixture of these two compounds. (Or, in general, divalent or trivalent Ti conductive compounds), and TiO ₂ (or other tetravalent and non-bivalent or trivalent Ti compounds) are prevented from being present in excessive amounts. In order to obtain a sufficiently small amount of TiO ₂ in the coating, it is necessary that the chamber or deposition is performed under reduced pressure for a sufficient time to remove a sufficient amount of air and water vapor originally present. Also, while maintaining the strip or sheet in this chamber, air intake needs to be minimized so that the deposition atmosphere is well controlled. In practice, neutral gas and / or 10 when nitrogen is not added ^- pressure below ⁴ mbar is a signal that the atmosphere will not be sufficiently oxidized to an excessive formation of the TiO _2. The tests conducted at the disposal facility at disposal allow the skilled person to achieve the objectives by accurately determining which precautions are needed, particularly with regard to sealing the chamber at the parasitic air inlet. As mentioned earlier, oxygen and water entering the chamber by the product itself to be coated must be calculated, as it is sometimes adsorbed on the surface. In this regard, the Ti target(s) is not positioned too close to the inlet of the strip leading from the chamber, so that the adsorbed oxygen and water possibly also contains a TiN/TiO coating containing a trivalent Ti compound such as Ti ₂ O ₃ It may be desirable to have time to be evacuated by the pumping facility prior to the portion of the strip that is introduced into the region in the form of.

If the formation of TiO instead of TiN as a divalent Ti compound is accepted or pursued as possible as possible, the reactive gas may be a nitrogen/oxygen mixture, the composition and flow rate of which are by those skilled in the art for sputtering power and the geometry of the installation. Adjusted so that tetravalent titanium is not observed on the surface of the deposit as described above.

In addition to the elements mentioned, the installation moves the chamber with a controlled atmosphere, such as means for moving the substrate longitudinally within the chamber when the substrate is a moving strip, means for imposing an appropriate potential difference between the target and the substrate. It goes without saying that it includes everything that is necessary and customary to produce a coating of PVD coating on a substrate.

The mechanical properties of TiN and TiO are not fundamentally different from the mechanical properties of CrN, so they do not react more preferably than CrN to the cutting and shaping of strips or sheets for the manufacture of plates. They also occur with significant epitaxy on the surface of the substrate, forming columns that match the particles of the substrate. This epitaxy can be seen by an X-ray diffraction test by a transmission electron microscope: the correspondence between the diffraction spots due to TiN and TiO and the diffraction spots due to particles on the substrate is very good.

Stainless steel substrates typically do not exceed 50 μm, and are preferably polycrystalline with particles having a size of 10 to 30 μm.

Deposition of TiN, TiO, mixtures thereof, or any other divalent or trivalent conductive Ti compound to be formed by optimizing the atmosphere and processing pressure as known to those skilled in the art can be achieved by placing the Ti target on either side of the substrate. When facing each other in the chamber, it can be performed simultaneously on both sides of the substrate. When the substrate is a moving strip, if the two targets are offset from each other, deposition can also be performed sequentially on the two sides of the strip. However, facing the two targets of Ti from either side of the strip in front has the advantage that the deposition facility can be made more compact than if the target were moved. In addition, as described above, this makes it possible to reduce the drawbacks caused by parasitic deposition of TiN or TiO and other compounds other than those specifically targeted by a given target.

Regarding the deposition of CrN described in the prior art described above, a cache defining the range of the deposition zone and the "forbidden zone" of the Ti compound is used to suppress the introduction of oxygen of the Ti compound layer according to the present invention as much as possible. Can. However, one of the advantages of using Ti instead of Cr is that the presence of oxygen in the TiO type deposits is not actually detrimental to the contact resistance of the deposits. Under these conditions, it may not be very necessary to actively limit the presence of this oxygen other than by the usual sealing of the inlet and outlet of the chamber, and the CrN deposit whose O content is carefully controlled for Cr and N content In the case of one of the targets useful for limiting the scope of the forbidden zone, the use of an impermeable cover for the atom can be omitted.

If it turns out to be advantageous even within certain limits of TiO and/or Ti ₂ O _{3 in the} deposit (but not TiO ₂ ), control of this presence may be considered by measuring and controlling the amount of oxygen present in the chamber. . This control can be performed with respect to the external environment, in particular by changing the hermeticity of the chamber at the level of the inlet and outlet of the substrate and/or by introducing a controlled amount of oxygen into the blown nitrogen into the chamber.

Through a simple experiment, those skilled in the art can use the cache to define the "prohibited zone" under a given operating condition to obtain sufficient properties for the deposition of Ti compounds, and the speed at which one of the factors depends on the relationship of Ti, N and O inside the coating. You can decide whether it is actually useful for controlling

If under consideration, both sides of the sheet or strip can be coated with two different materials based on divalent Ti, which can all comply with the requirements of the present invention (e.g., one side consists essentially of a coating consisting of TiN. The other side has a coating consisting essentially of TiO, but the two sides are coated with a TiN-TiO mixture, but each side is coated in different proportions). To do this, you can do the following:

-Turn over the substrate and modify the installation settings (e.g., composition of the processing atmosphere), then use a coating facility that processes only one side of the substrate at a time and performs two successive passes of the substrate in the installation, Thus, for example, the coating on one side is essentially TiN and the coating on the other side is essentially TiO;

Or by adjusting the operating parameters of the two zones in different ways to obtain each desired composition on each side of the substrate, using equipment consisting of two very different coating zones; One processes the first side of the substrate, and the other processes the second side of the substrate.

Other variations coat one side of the substrate with a divalent Ti compound (typically TiN, TiO or mixtures thereof) or a trivalent based coating, and for example WO-A-2016/151356 and WO-A -2016/151358 consists of coating the other side with CrN, as is known from the method described in 2016/151358. To do this, you can do the following:

-Make two deposits in the same chamber and in the same atmosphere and at the same pressure, using a Ti target and a Cr target, which are arranged offset on the sides of the substrate, or on the opposite side or in the path of the substrate if they are connected; A set of covers can be used to limit the risk of parasitic deposits of one of the two coatings on the side of the unintended substrate;

If, in two different chambers, the atmosphere and/or deposition pressure of the two layers proved to be unsuitable to reach the desired coating quality, apparently, in this case, two speakers (there is enough between them) There is a seal so that their atmosphere is connected to each other), and the substrate is not exposed to air during transport (whether in motion or not), leading to contamination of the surface. Which may interfere with deposits in the second chamber; Here again, it is preferred that the cache can be used in each chamber to limit the risk of parasitic deposits on the side of the substrate that should not be considered.

Of course, in this case, if the difference in the composition of the coating on each side is not caused by a clear visual aspect, it is possible for the two sides to be identified in one way or another by the operator for the correct assembly of the fuel cell membrane. Very desirable.

The use of TiN, TiO, Ti ₂ O ₃ or mixtures thereof is, in fact, not much more expensive than CrN for the production of positive electrode plates. An alternative solution would be the realization by PVD of gold deposits, which will have good contact resistance and will allow particularly significant epitaxy while the deposits grow on the substrate. However, industrially, this solution has the problem of cost that is too dependent on fluctuations in gold prices, and will obviously require special monitoring in the transportation and storage of raw materials, which can be difficult to use on an industrial scale.

After double-sided deposition of TiN, TiO or any divalent or trivalent Ti conductive compound, the strip or sheet is suitable for the application to be used, by cutting and shaping using conventional methods for this purpose, in particular cold deformation by stamping. It is typically conditioned to obtain a positive electrode plate of shape and dimension.

The present invention can be applied to coatings of any stainless steel known to be suitable for use as a substrate for a positive electrode plate, especially because of the mechanical properties that control its proper forming ability. Stainless steel 1.4404 (AISI 316L), 1.4306 (AISI 304L), 1.44510 (AISI 409) or 1.4509 (AISI 441), and thus both ferritic stainless steel and austenitic stainless steel can be mentioned without limitation.

The present invention also relates to a PEMFC type fuel cell, which typically comprises a cell unit, at least one of the plates, and preferably both of the plates and a positive electrode plate to ensure their assembly, and the present invention It is formed accordingly.

Claims (11)

A bipolar plate for assembly of elements of a fuel cell unit, consisting of a stainless steel substrate coated on at least one of two sides by a layer of electrically conductive material, the material being bivalent or trivalent Ti compound or a mixture of such compounds, wherein the layer contains oxygen, but the amount of oxygen in at% as determined by X-ray photoelectron spectroscopy (XPS) on the top 10 nm of the layer, According to the measured at% Ti content, the positive electrode plate characterized in that the content is not more than 1.5 times the at% oxygen content corresponding to a coating composed entirely of TiO. According to claim 1,
The divalent Ti compound is a positive electrode plate, characterized in that selected from TiN, TiO and mixtures thereof. The method of claim 1 or 2,
Each of the two sides of the plate is coated with a layer of at least one divalent or trivalent Ti compound, the layer containing oxygen, but measured by X-ray photoelectron spectroscopy (XPS) at 10 nm above the layer. The amount of oxygen, according to the measured at% Ti content, is a positive electrode plate characterized in that the content does not exceed 1.5 times the at% oxygen content corresponding to a coating composed entirely of TiO. The method of claim 1 or 2,
A positive electrode plate for assembly of elements of a fuel cell unit, wherein one of the faces of the plate is coated with a divalent or trivalent Ti compound or a mixture of these compounds, and the other side is coated with CrN. A method of manufacturing a positive electrode plate for assembly of elements of a fuel cell unit, comprising a stainless steel substrate coated on at least one of two sides having an electrically conductive material,
The material is a divalent or trivalent Ti compound or a mixture of such compounds, the layer contains oxygen, and the amount of oxygen measured by X-ray photoelectron spectroscopy (XPS) at the top 10 nm of the layer is measured. According to the at% Ti content, the content is not more than 1.5 times the at% oxygen content corresponding to a coating composed entirely of TiO, and
-Stainless steel substrates are provided in strip or sheet form;
-The compound layer or a mixture of divalent or trivalent Ti compounds comprises at least one deposition chamber; Means for extending the substrate inside the chamber in the longitudinal direction; Deposited on at least one side of the plate by physical vapor deposition (PVD) in a deposition facility comprising at least one Ti target and means for limiting or controlling the amount of air and oxygen entering the chamber;
And cutting and molding the substrate coated with a bivalent or trivalent Ti compound to provide a desired shape and dimension and obtain a positive electrode plate for a fuel cell. The method of claim 5,
The divalent compound is TiN, TiO and a method for producing a positive electrode plate, characterized in that selected from mixtures thereof. The method according to claim 5 or 6,
The chamber also includes at least one forbidden zone on at least one side of the substrate, wherein the deposition of a divalent Ti compound is not performed on the substrate. The method of claim 7,
Wherein the at least one forbidden zone is obtained by interposing at least one mask impermeable to Ti atoms disposed on a path of Ti atoms between the target and the substrate. The method according to any one of claims 5 to 8,
A method of manufacturing a positive electrode plate, characterized in that one side of the substrate is coated with a divalent or trivalent Ti compound or a mixture of these compounds, and the other side is taken as CrN deposited by PVD from a Cr target. A PEMFC type fuel cell unit consisting of an anode/electrolyte/cathode assembly,
The anode and the cathode consist of a positive electrode plate comprising a stainless steel substrate coated on at least one of its sides by an electrically conductive material, wherein at least one of the anode and the cathode is any one of claims 1 to 4 Fuel cell unit, characterized in that it comprises a positive electrode plate according to. A fuel cell comprising a positive electrode plate unit for assembling elements of a unit, wherein at least one of the units is a unit according to claim 10.