Method for depositing layer of ceramic material onto a metallic support for solid oxide fuel cells

Abstract

A method for depositing a layer of material on a metallic support for fuel cells or electrolysis cells includes the steps of preparing the surface of the metallic support, preparing an apparatus for an electrolytic bath, with the relative actuation means of the apparatus, including an aqueous solution with the cations necessary to obtain at least one material, dipping the metallic support into the electrolytic bath, and commanding the actuation means of the electrolytic bath so as to selectively carry out the electrochemical deposition of at least one layer of material on the metallic support, the layer of material includes an anti-corrosion protective ceramic material and/or a ceramic material with catalytic properties.

Claims

1. A metallic support for solid oxide fuel cells comprising an electrolyte, said metallic support comprising a porous metallic material comprising single sintered grains, at least one additional layer of ceramic material, that constitutes the electrolyte of a fuel cell, coupled to the porous metallic material, and at least one layer of material, arranged on the surface of said porous metallic material, comprising a ceramic material with anti-corrosion properties, wherein said layer of ceramic material is deposited onto the surface of the single grains of the porous metallic material, and wherein said layer of ceramic material with anti-corrosion properties comprises cerium oxide or a mixture of cerium oxide and metallic oxide, which constitutes an effective barrier to the interdiffusion of elements between said porous metallic material and said electrolyte, said metallic support comprising a further layer, made in a mixture of nickel and cerium oxide, which constitutes an anode of the fuel cell, deposited onto said layer of ceramic material with anti-corrosion properties, wherein said anode is deposited following the porosity of said porous metallic material.

2. The metallic support according to claim 1, wherein said layer of ceramic material comprises nickel and/or cerium oxide and/or cobalt and/or manganese.

3. A method for depositing at least one layer of material on a metallic support for solid oxide fuel cells comprising an electrolyte, wherein said metallic support comprises a porous metallic material comprising single sintered grains, comprising the steps of: preparing a surface of the metallic support, said metallic support comprising the porous metallic material comprising the single sintered grains; preparing an apparatus for an electrolytic bath comprising an anode and a cathode, with relative actuation means of the apparatus, containing an aqueous solution with cations necessary to obtain a layer of ceramic material; dipping the metallic support in said electrolytic bath; controlling said actuation means of the electrolytic bath so as to apply a current between the anode and the cathode of said bath, said current causing the deposition, in a selective manner, of the ceramic material on the surface of the metallic support, until said layer of ceramic material is made, wherein said layer of ceramic material comprises a ceramic material with anti-corrosion protection properties, and wherein said layer of ceramic material is deposited onto the surface of the single grains of the metallic support, wherein said layer of ceramic material comprises cerium oxide or a mixture of cerium oxide and metallic oxide, which constitutes an effective barrier to the interdiffusion of elements between said metallic support and said electrolyte; and depositing, by means of the apparatus for electrolytic bath, a further layer, made in a mixture of nickel and cerium oxide, which constitutes an anode of the fuel cell, onto said layer of ceramic material, wherein said anode is deposited following the porosity of said metallic support.

4. The method according to claim 3, comprising a step of washing the metallic support, after the deposition of the layer of material, to eliminate residues of the aqueous solution.

5. The method according to claim 3, comprising a step of carrying out a heat treatment of said metallic support to promote consolidation of the layer of material on said metallic support.

6. The method according to claim 3, wherein said layer of ceramic material comprises nickel and cerium oxide.

7. The method according to claim 3, further comprising a step of periodically modifying the concentration of the cations in said electrolytic bath.

8. The method of claim 7, wherein the step of periodically modifying the concentration of the cations in said electrolytic bath comprises adjusting a restoration cycle of elements that are most rapidly consumed.

9. The method of claim 7, wherein the step of periodically modifying the concentration of the cations in said electrolytic bath enables providing different layers of material of different composition on the metallic support.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The characteristics of the invention shall become clearer to any man skilled in the art from the following description and from the attached tables of drawings, given as a non-limiting example, in which:

(2) FIG. 1 is a schematic cross section of a single repetitive element of a fuel stack of the known type;

(3) FIG. 2 is a schematic section view of a fuel cell supported by metal;

(4) FIG. 3 is a detail of FIG. 2;

(5) FIG. 4 is a schematic representation of single grains of metallic powder sintered to form a porous metallic support of a fuel cell;

(6) FIG. 5 is a schematic representation of the single grains of metallic powder of FIG. 4 on which a layer of anti-corrosion protective material has been deposited, through the method according to the present invention;

(7) FIG. 6 is a schematic section view of a metallic support of a fuel cell, according to the version of FIG. 9;

(8) FIG. 7 is a detail of FIG. 6;

(9) FIG. 8 is a detail of FIG. 6, in which the single grains of the metallic support are coated with a layer of anti-corrosion protective material;

(10) FIG. 9 is a schematic representation of single grains of metallic powder sintered to form a porous metallic support of a fuel cell, according to the version of FIGS. 6, 7 and 8, in which a further layer of material constituting an electrode has been applied onto the layer of anti-corrosion protective material;

(11) FIG. 10 is a microscope photograph of a sintered porous metallic support before and after the deposition of a layer of protective material;

(12) FIG. 11 is a schematic side view of a metallic support of complex geometry consisting of an interconnector of a fuel cell; and

(13) FIG. 12 is a schematic side view of the interconnector of FIG. 11 provided with a layer of anti-corrosion protective material.

DETAILED DESCRIPTION OF THE INVENTION

(14) With reference to the attached FIG. 2, reference numeral 1 wholly indicates a metallic support of a fuel cell.

(15) In particular, the support 1 represented in FIG. 2 is associated with a first layer of ceramic material that constitutes the anode 2 of the fuel cell to be produced, and with a second layer that constitutes the electrolyte 3 of the same cell.

(16) This structure is usually defined as half-cell, because it consists of an electrolyte and just one electrode.

(17) The anode 2 consists, for example, of a mixture of nickel oxide and yttria-stabilized zirconia, or it can be made with another suitable material.

(18) The electrolyte 3 can for example be made from yttria-stabilized zirconia, or from another suitable material.

(19) The layers of ceramic material 2, 3 applied onto the support 1 can in any case be of another type, or having different functions within the fuel cell.

(20) For example, instead of the anode 2, the cathode can be applied on the surface of the metallic support 1.

(21) As schematically illustrated in the detail of FIG. 3, the metallic support 1 is of the porous type, i.e. it is preferably, but not exclusively, made by sintering of raw material in powder form.

(22) For example, the metallic support 1 is made from ferritic steel containing chrome in a certain percentage, for example 22%.

(23) The choice of this material is not however limiting for the purposes of the present invention.

(24) The coupling between the metallic support 1 and the layers of material constituting the anode 2or the cathodeand the electrolyte 3 can be carried out through one of the known technologies suitable for obtaining this result.

(25) Preferably, but not exclusively, the metallic support 1 and the layers of material that constitute the anode and the electrolyte 2, 3 are co-sintered at high temperature in a single production stage.

(26) However, it is possible to use all of the other known technologies described in the preamble of the present description.

(27) In FIG. 4, for the sake of greater clarity, the single sintered grains 4 of the metallic support 1 are represented enlarged.

(28) According to a version of the present invention, the deposition method comprises a step of preparing the surface of the metallic support 1, already joined to the anode 2 and to the electrolyte 3.

(29) In particular, such a preparation step can consist of washing the metallic support 1 with solvents, acids or other products suitable for eliminating all of the impurities from the entire surface of the metallic support 1.

(30) The method also comprises a step of providing an apparatus for an electrolytic bath.

(31) Such a step also foresees the provision of the actuation means of the electrolytic bath itself.

(32) In greater detail, this step foresees the provision, moreover, of a waveform generator suitable for this type of application, of the electrical power supply and of the anode to be inserted in the bath.

(33) Within this step of providing the electrolytic bath, it is foreseen to prepare a suitable aqueous solution containing the cations necessary to obtain at least one ceramic material 5, as better described hereafter.

(34) Then follows a step of dipping the metallic support 1 into the electrolytic bath thus provided.

(35) Following the dipping, it is foreseen for there to be a step of controlling the aforementioned actuation means of the electrolytic bath so as to selectively carry out the electrochemical deposition of at least one layer of material 5 onto the metallic support 1.

(36) In particular, after dipping the metallic support 1 in the electrolytic bath, a current is applied between the anode and the cathode of the bath itself.

(37) In the case in which the material 5 is a ceramic material, such a passing of current causes the deposition, in a selective manner, of the ceramic phase on the surface of the metallic support 1, until the desired layer is made.

(38) During the actuation of the electrolytic bath, in relation to specific requirements, it is possible to carry out an operative step of periodically modifying the concentration of the cations in the electrolytic bath.

(39) In particular, this step can be carried out in the case in which it is necessary to carry out the co-deposition of different elements.

(40) In this case, the mentioned step of providing the electrolytic bath foresees the preparation of a solution containing the various elements that are wished to be deposited.

(41) Some of these elements inserted in the bath, indeed, are characterised by a speed of consumptiongoverned, for example, by Faraday's lawthat is greater than others also present, and therefore they are deposited preferentially.

(42) Thus by varying the concentration of certain cations inside the bath, i.e. by adjusting the restoration cycle of the elements that are consumed most rapidly, it is possible to obtain layers of ceramic material of different composition and/or mixtures of many different ceramic materials.

(43) FIG. 5 schematically illustrates the result that can be obtained with the described method.

(44) Indeed, the method makes it possible to deposit the layer of material 5 onto the surface of the single grains 4 of the metallic support 1, therefore also onto the surfaces of the grains that are enclosed in the pores themselves.

(45) It is important to emphasise that the material is deposited only on the surface of the grains and does not fill the pores.

(46) In this version of the invention, the layer of material 5 consists of an anti-corrosion protective ceramic layer.

(47) For example, said layer of ceramic material 5 can comprise cerium oxide and/or other compounds of similar properties of anti-corrosion, of electrical conductivity and barrier against interdiffusion. There are several technical advantages given by this result.

(48) The protective material phase, as stated, instead of being arranged as a single and homogeneous layer i.e. as a structure of conventional protective materialdevelops at the conductive phasei.e. the metalof which it closely follows the porous structure.

(49) This can clearly be seen in FIG. 10, which illustrates, on the left, a microscope photograph of the metallic support 1 before deposition, and on the right, the same support 1 coated with cerium oxide crystals.

(50) This makes it possible to use small amounts of protective material with respect to other deposition technologies.

(51) Another important advantage consists of the fact that, thanks to this result, it is no longer necessary to apply the layer that acts as a barrier against the interdiffusion of the elements usually present in known cells.

(52) Indeed, the layer of material 5for example in the case of ceramic material, cerium oxide or a mixture of cerium oxide and metallic oxideas well as effectively protecting the metal from corrosion, itself constitutes an effective barrier to the interdiffusion of elements between metal and electrode.

(53) This layer, according to its composition, as well as not hindering the conducting of current, can also perform the function of electrode material.

(54) Cerium oxide can, indeed, replacewith better performancethe yttria-stabilized zirconia normally contained in the anode mixture.

(55) Thanks to this, once the cerium oxide has been deposited, it could be sufficient to deposit just the nickel to complete the composition of the anode.

(56) It should also be noted that in a conventional electrode, only a part of the material actually has a catalytic function, whereas all the rest is only used to transport the current from the interface with the electrolyte up to the current collector.

(57) Therefore, the electrochemical deposition, by applying the phase directly onto the metal, reduces this distance and therefore the need for material to the minimum.

(58) In conventional cells it is important to ensure that the electrode has a suitable porosity, to allow the diffusion of the gases.

(59) A high porosity, however, often leads to poor mechanical properties.

(60) In the application of the method according to the present invention, however, the porosity is dictated by the metallic support 1, and does not substantially change after electrodeposition.

(61) Thanks to the method according to the invention, it is possible to deposit elements that normally are not chemically stable at high temperatures; for example, cerium oxide cannot be co-sintered together with zirconia since at high temperatures they would form a solid solution.

(62) At the end of the electrochemical deposition step of the desired layer of material 5, the method foresees a step of washing the metallic support 1 to eliminate residues of the aqueous solution, and therefore cationic species that are still soluble.

(63) Thereafter, in some embodiments, the method can comprise a step of carrying out a heat treatment of the metallic support 1 to promote the consolidation of the layer of ceramic material 5.

(64) However, it should be emphasised that this step is entirely optional.

(65) At the end of these steps, it is possible to proceed to the completion of the cell by depositing the cathode with one of the known technologies.

(66) In another version of the invention, schematically represented in FIGS. 6, 7, 8 and 9, the metallic support 1 is associated just with a first layer of ceramic material that constitutes the electrolyte 3 of the fuel cell.

(67) Therefore, the ceramic layer that constitutes the anode is not present.

(68) In this version of the invention, a layer of anti-corrosion protective material 5 is deposited on the porous metallic support 1, as described for the previous version of the inventionfor example in the case of ceramic material, cerium oxide or a mixture of cerium oxide and metallic oxide.

(69) This is schematically represented in FIGS. 6, 7 and 8, in a completely analogous way to the previous version of the invention.

(70) Subsequently, again applying the method according to the invention, a further layer, which constitutes an electrode of the cell, preferably the anode 2, is deposited onto the layer of protective ceramic material 5.

(71) Such a further layer can be made, for example, in a mixture of nickel and cerium oxide, and thus possesses catalytic properties.

(72) The result that can be obtained is schematically illustrated in FIG. 9.

(73) The anode 2 deposits following the porosity of the metallic support 1, so as to use a minimum amount of material.

(74) The method according to the present invention thus makes it possible to complete the cell starting from a bilayer semi-worked product comprising the porous metallic support 1 and the electrolyte 3 deposited on it, for example with conventional technologies or with vacuum techniques (e.g. PVD, CVD).

(75) In another version of the invention, schematically illustrated in FIGS. 11 and 12, the method is applied to deposit a protective coating, consisting of a layer of ceramic material 5, onto a dense metallic support 1 having complex geometry. By dense metallic support having complex geometry we mean a support that includes, for example, a pre-perforated surface, or a three-dimensional structure with channels, or similar.

(76) For example, in this case the metallic support 1 can consist of one of the metallic interconnectors that separate the single cells inside a fuel stack. The deposition of a protective coating on metallic supports 1 of this type, especially when their geometry is complex, would be particularly complicated, long and laborious through the common deposition techniques of ceramic films.

(77) In this version of the invention, for example the aforementioned layer of ceramic material 5 comprises cobalt and/or manganese.

(78) It should be specified that another object of the present invention is also a metallic support 1 coated with a layer of material 5 deposited by applying the method according to one of the versions of the invention described earlier.

(79) It has thus been seen how the invention achieves the proposed purposes.

(80) The method according to the invention, thanks to the characteristics of electrodeposition technology, makes it possible to selectively deposit a layer of anti-corrosion protective ceramic material on the metallic support of the fuel cell in an efficient and cost-effective manner even on a support on which one of the electrodes and the electrolyte have already been provided, for example through co-sintering.

(81) As stated, the deposition is selective in the way that it mainly occurs on the surface of the metallic support.

(82) The problems relating to the corrosion of all of the metallic parts support, interconnectors present in a cell or in a stack of cells are thus effectively eliminated, even if they are characterised by complex geometry.

(83) It should be specified that the present invention can be applied both in the field of fuel cells and in that of electrolysis cells: therefore, whenever in the present description reference has been made, as an example, to application to a fuel cell, it should be understood that the same concepts can be applied to electrolysis cells without any limitation.

(84) The present invention has been described according to preferred embodiments, but equivalent variants can be devised without departing from the scope of protection offered by the following claims. In the case in which the technical characteristics mentioned in the claims are followed by reference numerals, such reference numerals are introduced with the sole purpose of increasing the clarity of the claims and consequently the aforementioned reference numerals have no limiting effect on the interpretation of each element identified as an example by such reference numerals.