RU2332754C1 - Tubular solid-oxide fuel element with metallic support, its tubular metallic porous basic layer and methods of their production - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: invention proposes a tubular solid-oxide fuel element with a metallic support containing a tubular metallic basic layer, a tubular pack of functional layers in concentric interface contact with the basic layer, the metallic porous basic layer being made from metal or metal alloy powders. The said basic layer is made up of, at least, two layers and the said powders possessing anti-oxidation properties at 700°C to 900°C. The tubular functional layers pack incorporates additionally a protective layer with functional layers being arranged in the following sequence, i.e. an anode layer, a solid-gas electrolyte layer, a protective layer and a cathode layer. The method of producing the aforesaid element comprises the following jobs, i.e. (a) production of, at least, two-layer metallic porous basic layer from metal or metal alloys, (b) application of anode layer on the basic layer, the anode layer being composed of the nickel-zirconium dioxide cermet stabilised by yttrium oxide, (c) application of the zirconium dioxide solid-gas electrolyte stabilised by yttrium oxide in the metal-organic complex thermolysis process on the anode layer, (d) application of the GDC () protective layer on the electrolyte, (e) application of the cathode layer composed of LSM (solid solutions of the La_0.8Si_0.2MnO₃ composition) on the GDC protective layer.

EFFECT: high-temperature fuel elements sustain heat treatment without shrinkage and reduction in porosity.

30 cl, 4 dwg

Description

This group of inventions relates to the field of direct direct conversion of chemical energy of fuel into electrical energy, and in particular, to high-temperature electrochemical devices with solid oxide electrolyte (TOE), and can be used for the manufacture of high-temperature fuel cells (VTTE), namely tubular solid oxide fuel cells with metal support.

The most important feature of VTE is the direct conversion of the chemical energy of certain types of fuel into electrical energy, due to which such energy conversion does not fall under the limitations of the Carnot cycle and it is possible to achieve an efficiency of 80%. In addition, compared with traditional methods of generating electricity, fuel cells have several other advantages: modular design; high efficiency at partial electric load; the possibility of joint generation of electric and thermal energy; significantly lower yield of polluting products compared to other methods of generating electrical energy; lack of moving parts and assemblies.

A solid oxide fuel cell (SOFC) includes two electrodes (anode and cathode) separated by a ceramic electrolyte. To ensure adequate ionic conductivity in such a ceramic electrolyte, SOFC operates at elevated temperatures, usually between 750 and 1000 ° C. In typical SOFCs, the electrolyte material is dense, gas-tight zirconia stabilized with yttrium oxide (YSZ). It is a good conductor for negatively charged oxygen ions at high temperatures. Typical SOFC anodes are made of porous nickel / zirconia cermet stabilized with yttrium (Ni-YSZ). The cathodes are made from magnesium doped lanthanum manganate (LaMnO ₃ ) or strontium doped lanthanum manganate (LSM). When a fuel cell operates, hydrogen or carbon monoxide (carbon monoxide, CO) in the fuel stream above the anode reacts with oxide ions passing through the electrolyte, resulting in water and / or CO ₂ and electrons. Electrons pass from the anode to the outside of the fuel cell, then through the external circuit and through the load and return back to the cathode, where oxygen from the air stream receives electrons and is converted into oxide ions, which are injected into the electrolyte.

The fuel cell includes the following concentric tubular layers: an inner electrode layer, a middle electrolyte layer and an outer electrode layer. The internal and external electrodes can be respectively the anode and cathode, and in this case, fuel can be supplied to the anode by passing through the tube, and air can be supplied to the cathode by passing over the outer surface of the tube.

As mentioned above, SOFCs operate at high temperatures. It is known that reducing the wall thickness or increasing the conductivity of the electrolyte allows the fuel cell to operate at lower temperatures. Reducing the entire wall thickness of the fuel cell provides additional benefits, such as a reduction in thermal mass and an increase in heat resistance of the fuel cell, which contributes to a reduction in the startup and shutdown times of the fuel cell. Moreover, a decrease in wall thickness in combination with a decrease in the diameter of the fuel cell leads to a decrease in the size of the fuel cell and allows it to work in low power applications: in travel computers, cell phones and other portable electronic devices. Small fuel cell systems, commonly known as the "fuel cell systems" currently under development, typically use direct methanol fuel cell (DMFC) or polymer electrolytic membrane (PEM) technology. Solid oxide fuel cells have one of the highest energy conversion efficiencies for any fuel cell technology, typically of the order of 35-60%. However, a decrease in the SOFC wall thickness decreases its mechanical strength. Relatively large fuel cells with diameters in excess of 5 mm are used in all known designs of tubular SOFC batteries. They have at least one relatively thick layer. For example, in a “supporting anode” fuel cell, this is the anode layer, which is a mechanical support and ensures the structural integrity of the fuel cell. Such thick-walled tubular SOFCs having a large diameter are not suitable for low power applications. For this, it is desirable to create a thin-walled fuel cell of small diameter.

A known method of manufacturing SOFCs in the form of a tube (or tubes with a large ratio of length to diameter), according to which the synthesis of an electrolyte on a cathode made in the form of a tube of doped lanthanum manganite, is carried out by plasma spraying of yttrium stabilized zirconium, and then CVD process in the atmosphere of gaseous zirconium and yttrium halides. In accordance with this method, the gas density of an electrolyte layer sprayed by a plasma method is solved [US Patent 5085742, IPC H01M 6/00, publ. 1992].

This method, although it allows you to solve the problem of the gas density of the electrolyte layer, is unsafe, since work is carried out with aggressive gaseous halides.

A known method and device for the manufacture of high-temperature SOFC within the framework of a single technological process by pyrolysis of organometallic complexes (IOC) formed on the basis of 2-ethylhexanoic acid. The functional layers of the fuel cell are applied by rolling the MOC precursors of each of the layers onto the VTTE billet, which is heated to the pyrolysis temperature of the corresponding precursor. Due to the heating of the surface of the workpiece upon contact of the liquid precursor with the workpiece, the organic component of the precursor evaporates, accompanied by the formation of an oxide film of the corresponding functional layer. The temperature of the surface of the workpiece during the formation of the layers is changed in the range from 240 to 600 ° C, depending on the formed layer. To implement the method, a device is used that has a device for rotating a billet-cathode made of strontium lanthanum manganite and a device for applying precursors to the cathode. The layers are applied using a roller, which is in direct contact with the VTTE blank. It is possible to apply layers to the surface of the VTTE billet both along the generatrix of the cathode and along a spiral line. All functional layers of VTTE are deposited on the specified installation, and the proposed method and device are also applicable for the application of functional layers when the VTTE anode is used as a preform (RF Patent No. 2224337, publ. 02.20.2004). The technical result of this invention is to provide a safe and cheap method of manufacturing a fuel cell in a simple and reliable installation.

Closest to the proposed invention is, adopted as a prototype, a group of inventions (WO / 2004/012287, publ. 05.02.2004), in which a tubular solid oxide fuel cell with a metal support contains:

- a tubular metallic porous support layer having a mechanical strength sufficient to support a stack of functional layers and a porosity sufficient to allow a reagent stream to flow through it;

- a tubular bag of functional layers in concentric boundary contact with the support layer, having a wall thickness less than or equal to 80 μm and which contains in a concentric arrangement a ceramic or cermet layer of the inner electrode, a ceramic middle layer of electrolyte and a ceramic or cermet layer of the outer electrode. In this case, the electrolyte contains a material selected from the group consisting of zirconia stabilized with yttrium oxide and CeO ₂ doped with Gd ₂ O ₃ and has a thickness less than or equal to 5 μm.

The supporting layer has a thickness of 20 to 500 μm and can be made of metals and alloys selected from the group consisting of stainless steel and ferritic steel. Its porosity varies from 20 to 75 vol.%. If necessary, it may contain ceramic material in an amount of from 0 vol.% To the limit of leakage of ceramics.

A method of manufacturing a tubular solid oxide fuel cell assembly according to the prototype method includes the following operations:

(a) coating the tubular mainly metal support layer with a ceramic or cermet layer of the inner electrode using technology selected from the group consisting of electrophoretic deposition, dip coating and spraying;

(b) coating the inner electrode layer with a ceramic electrolyte layer using a technology selected from the group consisting of electrophoretic deposition, dip coating, sol-gel coating and spraying;

(c) coating the electrolyte layer with a ceramic or cermet layer of the outer electrode,

and then

(d) sintering the layers to obtain a hollow tubular fuel cell with a metal support.

A metal support layer is obtained by adding additives to the initial metal powder that burn out during sintering of the layers, resulting in a porous metal support layer.

For the manufacture of tubular SOFC of small diameter, a wooden rod was used as a stencil for assembling the fuel cell, the shape and size of which corresponded to the required shape and size of the fuel cell.

The described method has a significant drawback consisting in the presence of a filler (additive) during the formation of a porous support layer, which burns out during sintering and pores are formed in its place. The difficulty is that removing all the filler is usually not possible. Fillers are chemicals that, even in small amounts, can adversely affect the mechanical properties of the remaining metal core. Usually they embrittle metals and alloys.

When the filler is burned out, pores of the order of several microns are obtained (namely, with such a size, pores are typically formed when fillers are used). Despite their large volume content, during subsequent heat treatments that will be required to sinter the functional layers deposited on the metal support layer, the porosity of the support layer will decrease, as a result of which it will undergo significant shrinkage.

The use of a protective GDC sublayer with an LSM cathode, in comparison with a SOFC without a sublayer and an LSCF cathode, gives an increase in the peak power removed from SOFC by more than 5 times.

The proposed group of inventions solves the problem of creating a SOFC with an electrical power of more than 0.25 Bamm / cm ² at operating temperatures of 650-800 ° C, the tubular metal porous support layer of which has increased mechanical strength and reduced electrical resistance while maintaining high porosity.

The technical result of the invention is to obtain SOFC with a support layer capable of withstanding subsequent heat treatments without shrinkage and porosity reduction, obtained without additives requiring burning, and lower gas resistance due to the high porosity of the inner part of the metal tubes. In addition, the obtained SOFC contains a packet of functional layers in which the cathode reacts with an electrolyte.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a tubular solid oxide fuel cell with a metal support, comprising

a tubular metallic porous support layer having a mechanical strength sufficient to support a stack of functional layers and a porosity sufficient to allow a reagent flow to flow through it,

- a tubular bag of functional layers in concentric boundary contact with the support layer, which contains in a concentric arrangement a cermet layer of the inner electrode, a ceramic middle layer of electrolyte and a ceramic layer of the outer electrode,

the novelty of which is that the porous metal support layer is made of at least two layers of metal powders or their alloys that are resistant to oxidation at a temperature of 700-900 ° C, and the inner layer of the support layer has minimal shrinkage during annealing at temperatures of 1200 -1400 ° С, the top layer of the support layer provides quick and high-quality deposition of functional layers, the tubular bag of functional layers additionally contains a protective layer, and the functional layers are located in the next sequence: an anode layer, a layer of gas-tight electrolyte, the protective layer and the cathode layer.

In particular, the inner diameter of the porous metal support layer may be 8-12 mm, and the thickness 1-2 mm.

The total thickness of the functional layer assembly may be less than or equal to 52 microns.

It is preferable to perform an anode layer of cermet nickel-zirconia stabilized with yttrium oxide with a thickness of 20 μm.

The gas-tight electrolyte layer is preferably made of zirconia stabilized with yttrium oxide with a thickness of 10 μm

The protective layer is preferably made of GDC (Ce _0.8 Gd _0.2 O) with a thickness of 2 μm.

The cathode layer is preferably made of LSM lanthanum manganate (solid solutions of the composition La _0.8 Sr _0.2 MnO ₃ ) with a thickness of 20 μm.

In accordance with another aspect of the present invention, there is provided a tubular metal porous support layer of a fuel cell having mechanical strength sufficient to support a stack of functional layers and porosity sufficient to allow reagent flow to flow through it, the novelty of which is the fact that it is made of at least two layers of metal powders or their alloys that are resistant to oxidation at a temperature of 700-900 ° C, and the inner layer of the support layer has with minimal shrinkage during annealing at temperatures of 1200-1400 ° C, the top layer of the support layer provides fast and high-quality deposition of functional layers.

In particular, the pore sizes of its inner layer exceed 100 microns and the bulk porosity is 40-60%, while the pore sizes of the outer layer do not exceed 50 microns and the bulk porosity is 30-50%.

More specifically, the inner layer of the metal porous support layer can be made of ferritic stainless steel powder and have pore sizes of 100-160 μm.

In particular, the inner layer can be made of stainless steel grade 14X17H2.

The outer layer of the porous metal support layer can be made of ferrite stainless steel powder ПХ17Н2 and have pore sizes less than 50 microns.

In accordance with another aspect of the present invention, a method for manufacturing a tubular solid oxide fuel cell with a metal support, which includes the following operations:

(a) the manufacture of at least a two-layer metal porous support layer of metal powders or their alloys, resistant to oxidation at a temperature of 700-900 ° C, having a mechanical strength sufficient to support a package of functional layers, and porosity, sufficient to allow the reagent flow to flow through it, with the inner layer of the support layer having minimal shrinkage during annealing at temperatures of 1200-1400 ° C, the upper layer of the support layer provides fast and high-quality bearing functional layers;

(b) coating the support layer by dyeing or dipping with an anode layer of nickel-zirconia cermet stabilized with yttrium oxide;

(c) coating the anode layer with a layer of a gas-tight electrolyte zirconia stabilized with yttrium oxide by the method of thermolysis of organometallic complexes;

(d) coating the electrolyte layer with a protective layer of GDC (Ce _0.8 Gd _0.2 O);

(e) coating the protective layer of GDC with the cathode layer of LSM lanthanum manganate (solid solutions of La _0.8 Sr _0.2 MnO ₃ composition) by staining.

In particular, the anode layer can be applied to the support layer as a coating using a paste prepared on the basis of polyethylene glycol and a powder mixture of 60 vol.% NiO and 40 vol.% Zirconia stabilized with yttrium oxide (YSZ), followed by drying of the applied layer at a temperature of 140-155 ° C for 10-15 hours, then the resulting preform is annealed in vacuum according to the mode: heating to 1100 ° C for 3.5 hours and holding at this temperature for 2 hours

The electrolyte layer can be deposited on the anode layer by layer-by-layer deposition of a colloidal suspension of YSZ (ZrO ₂ - 8 mol% Y ₂ O ₃ ), followed by annealing of each layer in vacuum at 1150-1200 ° С for 2.5 hours.

The protective layer can be applied to the electrolyte layer in the form of a coating of organometallic complexes of Gd and Ce carboxylic acid (2-ethylhexanoic acid (2-EHC) (99%), C ₈ H ₁₆ O ₂ , CH ₃ (CH ₂ ) ₃ CH ( C ₂ H ₅ ) COOH) with their subsequent decomposition by thermolysis or by immersion in a suspension of GDC powder (Ce _0.8 Gd _0.2 O) in polyethylene glycol, followed by drying in air at 140-155 ° С for 10-15 h and sintering in vacuum at 1150-1200 ° C for 2.5 hours

The cathode layer can be applied to the protective layer by immersion in a suspension of LSM powder (La _0.8 Si _0.2 MnO ₃ ).

In accordance with another aspect of the present invention, there is provided a method for producing a tubular metal porous support layer of a fuel cell having mechanical strength sufficient to support a stack of functional layers and porosity sufficient to allow reagent flow to flow through it, novelty which consists in the fact that it is made of at least two-layer of metal powders or their alloys, resistant to oxidation at a temperature of 700-900 ° C, by performing following operations:

- the formation of the inner supporting layer by filling the powder from at least one metal or its alloy, with a particle size exceeding 100 microns, into the annular space formed by coaxially arranged pipes, the inner of which is made of quartz or stainless steel, and the outer of quartz ;

- preliminary sintering of the obtained powder billets of the inner support layer in a hydrogen atmosphere;

- removing the sintered billet of the inner support layer from the tool;

- the final sintering of the blanks of the inner support layer in an atmosphere of hydrogen, inert gas or vacuum at a temperature of 1200-1400 ° C;

- the formation on the surface of the sintered blanks of the inner support layer of the outer layer of powder, similar to the powder of the inner support layer, but with a particle size <50 μm.

In particular, the formation of the inner support layer is carried out from ferritic stainless steel, for example, grade 14X17H2.

The preform formation of the inner support layer is preferably carried out by compaction after filling by vibration.

Additionally, coarse-grained alumina powder can be poured into the inner tube, after which the inner tube is removed before sintering.

Preliminary sintering of the powder blanks of the inner support layer is preferably carried out at a temperature of 1050-1100 ° C for 1-5 hours

When conducting preliminary sintering of the inner support layer, it is desirable to hold at 350-400 ° C until gas evolution ceases.

The final sintering of the blanks of the inner support layer is carried out with a gradual increase in temperature.

The formation of the outer support layer is preferably carried out from a powder of ferritic stainless steel grade ПХ17Н2 with a particle size of less than 50 microns.

The formation of the inner support layer of the outer layer on the surface of the powder billets is carried out by applying a layer of a suspension of stainless steel powder in polyethylene glycol, after which the resulting product is dried and then annealed in vacuum.

Drying is preferably carried out at a temperature of 140-155 ° C for 10-15 hours in air.

Annealing in vacuum is preferably carried out according to the regime: heating to 950 ° C for 2 hours, then heating to 1150-1250 ° C for 1-2 hours and holding for 2-5 hours.

Alternatively, the formation of the outer layer on the surface of the powder billets can be accomplished by filling the powder into the annulus formed by coaxially arranged additional outer quartz tube and the billet of the inner support layer, followed by sintering of the entire billet in a hydrogen atmosphere.

The sintering of a bilayer support blank is preferably carried out in two stages: first, at a temperature of 1050-1100 ° C for 1-5 hours, then the workpiece is removed from the tooling and sintering is carried out at a temperature of 1200-1400 ° C for 1-3 hours hydrogen atmosphere, inert gas or vacuum.

A brief description of the drawings.

Figure 1 schematically shows a side section of the inventive fuel cell with a two-layer tubular metal porous support layer.

Figure 2 schematically shows a side section of a two-layer tubular metal porous support layer of the fuel cell.

Figure 3 shows the sequence diagram of operations in the manufacture of tubular SOFC with a two-layer tubular metal porous support layer.

Figure 4 shows the sequence diagram of operations in the manufacture of a two-layer tubular metal porous support layer of the fuel cell, which provides for the formation of the outer layer from a suspension of metal powder in polyethylene glycol.

DETAILED DESCRIPTION OF THE INVENTION

In the description of the present invention, the terms used have the following meanings, unless expressly indicated otherwise. All other terms have the usual meanings recognized by experts.

The term "ceramic material" refers to an inorganic non-metallic solid material with a predominant covalent or ionic bond, including (but not limited to) metal oxides and ceramic solid ionic conductors (such as yttrium-stabilized zirconia, beta-alumina, and cerate) .

The term “cermet” refers to a composite material that includes ceramics in combination with a metal, usually (but not necessarily) sintered metal, the cermet having high heat resistance, corrosion resistance and wear resistance.

The term "porous" in the context of hollow ceramic, metal and cermet membranes and matrices means that the material contains pores (voids). Therefore, the density of the material of the porous membrane will be lower than the theoretical density of the material. The voids in the porous membranes and matrices can be connected (channel-type voids) or disconnected (i.e. isolated). In a porous hollow membrane or matrix, most pores are connected. In order to be considered a porous membrane in accordance with the definition adopted here for membranes, the membrane must have a density that is at most approximately 95% of the theoretical density of the material. The value of porosity can be determined by measuring the bulk density of the porous body, using the theoretical density of the materials of the porous body. Pore size and their distribution in a porous body can be measured using mercury or non-mercury porosimeters, BET analysis, or microstructure image analysis, which is well known per se.

According to a first aspect of the present invention, there is provided an assembly of a tubular solid oxide fuel cell with a metal support. The fuel cell assembly (FIG. 1) has a two-layer tubular metal porous support layer of the fuel cell 1 having mechanical strength sufficient to support the stack of functional layers and porosity sufficient to allow the reagent flow to flow through it, made at least from powders of metals or their alloys, resistant to oxidation at a temperature of 700-900 ° C. The inner layer 1a of the support layer 1 (Fig. 2) practically does not shrink and does not reduce porosity during annealing at temperatures of 1200-1400 ° C, and the upper layer 1b of the support layer 1 provides fast and high-quality application of the functional layers. The implementation of the support layer in the proposed way allows you to create a support layer, which has increased mechanical strength and relatively low electrical resistance while maintaining high porosity.

Preferably, the diameter of the backing layer 1 is 8-12 mm and the thickness is 1-2 mm. However, these sizes can be increased or decreased depending on the desired size of the fuel cell.

Four functional layers (Fig. 1) with a total thickness of 52 μm are sequentially deposited on the support layer 1, namely: a layer of a porous anode 2 of nickel and zirconia stabilized with yttrium oxide (Ni-YSZ), 20 μm thick; a gas-tight layer of electrolyte 3 of zirconia stabilized with yttrium oxide (YSZ), a thickness of 10 μm; a protective sublayer 4 of GDC with a thickness of 2 μm and a porous layer of the cathode 5 of LSM with a thickness of 20 μm. The indicated thicknesses are optimal, but not necessary for the operation of the entire SOFC. The electrodes serve as current collectors (current collectors) and accelerate the electrochemical reaction. The electrolyte allows oxygen ions to pass from one electrode (cathode) to another electrode (anode), and it is impermeable to nitrogen in the air, while the fuel gas flows from both sides of the electrolyte layer. Functional layers are mechanically supported by a tubular metal backing layer. The use of a protective sublayer led to a significant improvement in the transport characteristics of the model SOFC, which is apparently due to the absence of reactions that cause the formation of a non-conducting SrZrO ₃ phase at the YSZ-LSM interface. In order to improve the quality of Ni-YSZ composite ceramic anodes, we have improved the technology and improved the surface structure of porous ferritic stainless steel support tubes.

For the purposes of this invention, we have developed (FIG. 2) a tubular metallic porous support layer of a fuel cell 1 having a mechanical strength sufficient to support a stack of functional layers and a porosity sufficient to allow a reagent flow to flow through it made at least two-layer of metal powders or their alloys resistant to oxidation at a temperature of 700-900 ° C, the inner layer 1a of which has minimal shrinkage during annealing at temperatures of 1200-1 400 ° C, and the upper layer of the support layer 1b provides fast and high-quality application of functional layers.

Such a support layer is an independent technical solution and can be used in other SOFC designs.

Alloys of iron with chromium and nickel, compatible in terms of thermal expansion coefficients (KTP) with the anionic conductor YSZ, were proposed as a material for obtaining a two-layer metal porous support layer. To increase the mechanical strength of the support layer, a tube wall thickness of 1 to 2 mm was chosen. In this case, the inner layer with a thickness was formed from a powder larger than 100 μm and had a bulk porosity of 40-60%. This layer provided heat resistance and had minimal shrinkage during annealing at temperatures of 1200-1400 ° C. The upper layer with a thickness of up to 20-50 microns was formed from a powder with a grain size of less than 50 microns and had a bulk porosity of 30-50%. This layer provided quick and high-quality application of functional layers. This primarily relates to the porous anode layer and the gas-tight electrolyte layer. It should be noted that two-layer tubes, in addition to heat resistance and almost complete absence of shrinkage, are also characterized by lower gas resistance due to the high porosity of the inner part of the metal tubes. Such tubes were obtained from ferritic stainless steel grade 14X17H2 with a grain size of 100-160 microns, on which an outer layer was applied based on powders of ferritic stainless steel grade PH17H2 with a grain size of ≤50 microns.

To obtain a tubular metal porous support layer of a fuel cell, a simple and efficient “quartz tube” method has been developed and repeatedly tested (Fig. 4), which is a special modification of the classical method of powder metallurgy, attractive in that it uses powder without any fillers. This is one of its main advantages over all known molding methods. The addition of certain additives to the powder, for example, to improve its compactness in the next stages of the technology would necessarily set the task of their removal. Often the removal of impurities is incomplete, and this almost always leads to a deterioration in the functional properties of the powder material. Typically, the remaining impurities embrittle the product material. In addition, the implementation of our proposed method requires a minimum set of devices. All of them are easy to manufacture and all but one item can be used many times.

When assembling the structure forming the powder billet, two coaxially located quartz tubes, the inner of which is made of quartz or stainless steel, and the outer of quartz, formed an annulus, into which stainless steel powder was poured with the funnel of the original design, after which preliminary sintering was carried out the obtained powder billet inner support layer.

The compaction of the powdered powder was carried out on a special vibrating stand.

To maintain a given shape of the inner surface of the inner support layer, the inner quartz or metal tube was filled with coarse-grained aluminum oxide powder. After that, the inner tube was removed.

The use of a quartz tube did not allow the sintering temperature to rise above 1100 ° C, since at higher temperatures quartz began to interact with stainless steel powder.

In order to increase the strength characteristics and minimize shrinkage during annealing, which are subsequently necessary for sintering the functional layers deposited on the support layer, sintering of the powder billet must be carried out in two stages: preliminary sintering of the powder billet, which occurred in a quartz tube in a hydrogen stream at 1050 1100 ° C, and the final sintering, which was carried out after removing the preform from the quartz tube, in vacuum at temperatures of 1200-1400 ° C. For the inner supporting layer of 14X17H2 ferritic stainless steel powder with a grain size of 100-160 μm, the optimal pre-sintering mode is to conduct the process at a temperature of 1050-1100 ° C for 1-5 hours in a stream of hydrogen.

It was very useful in the process of preliminary sintering of the inner support layer, even before the sintering temperature was reached directly, to hold at 350-400 ° C until gas evolution ceased.

The final sintering of the blanks of the inner support layer, which is carried out after removing the sintered blank from the tool, at a temperature of 1200-1400 ° C in an atmosphere of hydrogen, inert gas or vacuum, it is desirable to carry out with a gradual increase in temperature.

The final sintering of the inner support layer at a temperature of 1400 ° C made it possible to increase its strength characteristics and make it practically non-shrinking during subsequent annealing. At the same time, high-temperature sintering of the resulting porous tubes increased their mechanical strength by 12–15 times, and increased their conductivity by more than 2 times while maintaining open porosity of more than 50%.

The upper layer of the tubular metal porous support layer of the fuel cell, providing the surface quality necessary for applying the porous composite anode and gas-tight electrolyte, was formed from a powder similar to the powder of the inner support layer, but with a particle size of ≤50 μm, while the pore size of the formed outer layer did not exceed 50 μm and bulk porosity was 30-50%.

Currently, we have developed a simple and productive method of applying a suspension of fine powder of a fine fraction of stainless ferritic steel based on polyethylene glycol, based on immersion of a tube made of steel 14X17H2 with a grain size of 100-160 μm in a vessel with this suspension, previously intensively mixed.

The formation of the outer support layer was carried out from a powder of ferritic stainless steel grade ПХ17Н2 with particle sizes less than 5 μm.

A powder of a fraction of ≤50 μm was obtained in advance by sifting a powder of stainless steel grade ПХ17Н2, having a bulk of particles with a size of ≤60 μm, and, according to specifications, 100 or less microns, through a sieve with a cell lumen of 50 μm.

After applying the suspension, the tubes were dried in an oven at a temperature of 140-160 ° C for 10-12 hours in air. After drying, the tubes were vacuum annealed according to the regime: heating to 950 ° C in 2 hours, then heating to 1150 ° C in 1.5 hours and holding for 2 hours.

Alternatively, the formation of the inner support layer of the outer layer on the surface of the blanks can be accomplished by filling the powder into the annulus formed by coaxially arranged additional outer quartz tube and the blank of the inner support layer, followed by sintering of the entire blank in a hydrogen atmosphere.

When using ferrite stainless steel powder ПХ17Н2, the sintering of the bilayer support was carried out in two stages: at a temperature of 1050-1100 ° С for 1-5 hours, then the workpiece was removed from the equipment and sintering was performed at a temperature of 1200-1400 ° С, in for 1-3 hours in an atmosphere of hydrogen, inert gas or vacuum.

After the initial sintering of the tubular metal porous support layer at T = 1400 ° C, the density of the tubes increased to 3.4-4.0 g / cm ³ and the porous layer obtained from a powder with a particle size of 100-160 μm had an apparent density equal to ~ 2.9 g / cm ³ and an open porosity of 60%. After high-temperature final sintering of the billets in vacuum at 1200 ° С - it decreased to 48-55%.

The strength of such a tubular metallic porous support layer was determined from testing samples for 3-point bending. Samples 3-4 mm wide and 40 mm long were cut from the walls of the tubes on a machine for spark cutting of metals. The tests were carried out at room temperature and 500 ° C. The bending strength after sintering at 1200 ° C, regardless of the test temperature, was not higher than 5-10 MPa. After sintering at 1400 ° C, the strength increased to 30-40 and 55-65 MPa, respectively, for testing at 500 ° C and room temperature.

The electric resistance of the tubes was measured by a four-contact method when passing through the current ends of 3 A. The measurements were carried out at room temperature on a device manufactured at the Institute of Physics and Technology of the Russian Academy of Sciences. With increasing sintering temperature, the electrical resistance monotonically decreased from 4 mOhm / cm at 1200 ° C to 1.2-2.2 mOhm / cm at 1400 ° C.

The manufacture of tubular SOFC with a metal support was carried out according to the scheme indicated in figure 3.

The first functional layer to be applied to the support layer is an anode layer made of Ni-YSZ cermet.

We have optimized the composition of the powders used to obtain Ni-YSZ cermet.

Getting connection YSZ

1. Extraction of zirconium.

13.2 g of zirconium nitrate are dissolved in 50 ml of water.

An aqueous solution of nitrate is mixed with 50 ml of 2-EHC.

Extraction is carried out by adding ammonia water to pH 5 and stirring with a mechanical stirrer. The extraction time is 0.5 hours

Separation of phases in a separatory funnel with sedimentation during the day.

Dehydration of the organic phase in vacuo at 105 ° C.

2. Extraction of yttrium.

124 g of yttrium nitrate are dissolved in water to a solution volume of 180 ml.

An aqueous solution of nitrate is mixed with 360 ml of 2-EHC.

Extraction is carried out by adding 57 ml of ammonia water to pH 5 and stirring with a mechanical stirrer. The extraction time is 2 hours.

Phase separation in a separatory funnel with settling for 12 hours

3. Nickel extraction.

20 g of nickel nitrate are dissolved in water to a solution volume of 420 ml.

An aqueous solution of nitrate is mixed with 280 ml of 2-EHC.

Extraction is carried out by adding ammonia water to a pH of 4.44 and stirring with a mechanical stirrer. The extraction time is 1 hour.

Phase separation in a separatory funnel with settling for 12 hours

Dehydration of the organic phase in vacuum at 105-108 ° C.

Preparation of organometallic complexes

The synthesis of organometallic complexes was carried out by the extraction method in a two-phase system of an aqueous solution of a metal nitrate - an organic acid. The reaction proceeds according to the exchange mechanism:

(Mn ⁺ ) _aq. + CH ₃ (CH ₂ ) ₃ CH (C ₂ H ₅ ) COOH → M [CH ₃ (CH ₂ ) ₃ CH (C ₂ H ₅ ) COO] _n + nH ⁺ ,

where Mn ⁴ is the n-valent metal cation, n = 2, 3. Extraction was carried out from acidic and slightly acidic solutions. An aqueous solution of NH ₄ OH was used to maintain the pH of the medium. The extraction time is 30-60 minutes. The separation of the aqueous and organic phases was carried out in a thermostatically controlled separatory funnel when heated to a certain temperature in order to more effectively separate the phases. In some cases, the extract was further centrifuged to remove the residual aqueous phase. The concentration of the obtained product was determined by the gravimetric method after calcining a specific sample of the extract. Using the methods of differential thermal analysis (DTA) and thermograviometric analysis (TGA), we studied the main thermal transformations of the obtained complexes in the temperature range of 20-530 ° C. The onset of decomposition was accompanied by a small heat release, probably due to proceeding hydrolysis. Further decomposition proceeded with absorption of heat. On thermograms, these processes corresponded to exothermic and endothermic peaks and weight loss at temperatures of 90-510 ° C. Based on the concentrations of Zr and Y solutions in the extracts (ZrO ₂ - 100 g / kg and Y ₂ O ₃ - 84.6 g / kg), they were mixed in the calculated proportions and heated for 1 h at 105-108 ° С. Visually, no changes were observed, additional drying was not carried out.

The following are specific examples of the preparation of organometallic complexes by the above method.

1. A mixture of Zr (IV) and Y (II) -organic extracts.

Composition 19YSZ (81 wt.% ZrO ₂ +19 wt.% Y ₂ About ₃ ).

81 g of a Zr (IV) extract with a ZrO ₂ content of 11% by weight are placed in the flask.

29.3 g of Y (III) extract are added with a Y ₂ O ₃ content of 7.14 wt.%.

Stirring with heating at 105 ° C for 5 minutes

2. A mixture of Ni (II), Zr (IV) and Y (III) -organic extracts.

Composition NiO (50 wt.%) + 19YSZ (50 wt.%).

73.6 g of a Zr (IV) extract with a ZrO ₂ content of 11% by weight are placed in the flask.

26.6 g of Y (III) extract was added with a Y ₂ O ₃ content of 7.14 wt.%.

89.2 g of Ni (II) extract was added with a NiO content of 11.2 wt.%.

Stirring with heating at 105 ° C for 5 minutes

A suitable method for coating the support layer with the anode layer is by immersion coating, in which the support layer is immersed in a vessel containing a suspension of a powder mixture of NiO-YSZ based on polyethylene glycol, which is known per se. Alternatively, the first layer of the composite anode was applied by the staining method, which is known per se using a paste prepared on the basis of polyethylene glycol and powders NiO (60 vol.%) And YSZ (40 vol.%).

After applying the paste, the tubes were dried in an oven at a temperature of 150-170 ° C for 10 hours. After drying, a coating was formed on the surface of the porous tubes, filling the pores of the upper layer of a two-layer metal tube. The resulting coating had sufficient mechanical strength, allowing polishing of the surface layer of the coating in order to smooth out irregularities and roughnesses. After the polishing operation, the ceramic anode was annealed in vacuum according to the regime: heating to 1160 ° С for 3 h and holding for 2.5 h at this temperature

The temperature and composition of the annealing atmosphere are limited by the need to prevent oxidation of the surface of ferritic stainless steel.

The developed method allowed to obtain smooth ceramic layers of Ni-YSZ. The resulting layers are characterized by the absence of cracks and uniform pore distribution with a characteristic size of about 1-3 microns.

To obtain gas-tight layers of the YSZ anion conductor, we used a technology based on the thermolysis of organometallic complexes. Organometallic complexes were deposited onto porous ferritic tubes using an apparatus for applying liquid organometallic compounds to cylindrical surfaces of UFTS-3 using a solution of organometallic complexes Zr and Y (19 wt.% Y). X-ray diffraction and electron microscopy studies showed that the obtained films of the YSZ anion conductor had an amorphous or nanocrystalline structure. To obtain gas-tight ceramic films, the YSZ film obtained by the thermolysis of organometallic complexes was annealed. The presence of a supporting ferrite tube dictates the need to change the traditional methods of sintering in an air atmosphere and switch to ceramic sintering in vacuum.

Sintering of ceramic layers was carried out in a horizontal resistance-to-heat resistance furnace with tungsten heaters. The furnace was adapted both to work in vacuum (10 ^-5 mm Hg) and in a stream of argon and / or hydrogen. Our studies showed that the layers obtained by thermolysis with a thickness of more than 0.2 μm during synthesis in vacuum are covered by large cracks and were not suitable for further use. At the same time, a decrease in the thickness of films obtained by thermolysis to 0.15 μm or less led to the “forced shrinkage” mode during sintering, which is accompanied by shrinkage of the ceramics across the film and the absence of shrinkage in the film plane. To obtain gas-tight YSZ ceramic films, we optimized the temperature conditions of sintering of thin YSZ films obtained by thermolysis of organometallic complexes. The studies showed that with a thickness of the films obtained by thermolysis of the order of 0.15 μm and their annealing at a temperature of 1150-1200 ° C for 2.5 hours, dense ceramic layers without microcracks were obtained. Under the indicated sintering regime, the grain size in each subsequent layer increased, reaching 2–3 μm in the film plane. The required electrolyte thicknesses of ~ 20 μm could be obtained as a result of 10-15 cycles of deposition of electrolyte layers, followed by vacuum annealing after each deposition of an electrolyte layer.

From literature data it is known that the cathode materials of the La-Sr-Mn-O family when sintering an electrode with a YSZ substrate can form poorly conducting phases: SrZr-O ₃ and La ₂ Zr ₂ O ₇ . Therefore, to prevent the cathode from reacting with YSZ, these layers were separated by a protective layer of Ce _0.8 Gd _0.2 O ₃ (GDC). This material has high ionic conductivity, which is close to the other elements by a coefficient of linear thermal expansion (12.1 × 10 ^-6 K ^-1 ) and does not react with either the cathode material or the YSZ substrate. But in a reducing atmosphere, the GDC loses oxygen. This process is accompanied by an increase in the electron current and embrittlement of the material, which does not allow its use for the manufacture of gas-tight SOFC membranes. The rather large porosity of the GDC layer is associated with the difficulty of sintering this material. But for the protective sublayer, this is not so critical.

Our studies showed that the use of a protective GDC sublayer with an LSM cathode, in comparison with a SOFC without a sublayer, gives an increase in the peak power removed from SOFC by more than 5 times. The protective layer can be applied to the electrolyte layer by thermolysis of the corresponding organometallic complexes with their subsequent decomposition or by immersion in a suspension of GDC powder (Ce _0.8 Gd _0.2 O) in polyethylene glycol.

Currently, complex oxides of the La-Sr-Mn-O family are widely used as cathode materials for SOFC, the most applicable of which is La _0.8 Sr _0.2 MnO ₃ (LSM). It has a close value of the coefficient of linear thermal expansion (CTE) equal to 12.3 × 10 ^-6 K ^-1 , with a CTE for the anionic conductor YSZ equal to 10.8 × 10 ^-6 K ^-1 used as a membrane, a good electron conductivity (~ 200 S · st ^-1 at 900 ° C) and high activity to dissociation of gaseous oxygen. At the same time, the anionic conductivity of LSM is low (10 ^-7 S · st ^-1 at 900 ° C), which limits the applicability of this material, especially for SOFCs operating in the medium temperature range (500-700 ° C). The compounds were synthesized by the Sol gel method, which is known per se.

For the synthesis of solid solutions of La _0.8 Sr _0.2 MnO ₃ (LSM) composition, the corresponding nitrates were used as starting materials, the mixture of which was dissolved in citric acid, adding another 5% solution of polyvinyl alcohol. The resulting solution was evaporated with vigorous stirring at a temperature of 300 ° C. In this case, partial decomposition of salts occurred with the formation of the corresponding oxides. The final decomposition was carried out at 700 ° C for 5 h in air until the residual organic matter was completely burned. Next, the obtained powder in ethanol was milled using a planetary mill, dried and annealed.

Although a preferred embodiment of the invention has been described, it is clear that those skilled in the art may make changes and additions that do not, however, fall outside the scope of the claims.

To test the SOFC of planar and tubular geometry at the Institute of Physics and Technology of the Russian Academy of Sciences, two gas test benches were designed and manufactured. These installations made it possible to change the compositions and velocities of gas flows in the cathode and anode chambers.

To measure the current-voltage characteristics, the four-contact method was used. A device was assembled at the Institute of Theoretical Physics and Technology, which makes it possible to maintain a constant current and, therefore, measure current-voltage characteristics with an accuracy of hundreds of nanovolts. GSPF-052 (DAC) is used to set the current to the UST, and LA-1.5RSI (ADC) to take the potential values.

The above tests confirmed the creation of a SOFC of a tubular structure with an electric power of more than 0.25 watts / cm ² at operating temperatures of 700-800 ° C, in which the tubular metal porous support layer has increased mechanical strength and reduced electrical resistance while maintaining high porosity.

Claims (30)

1. Tubular solid oxide fuel cell element with a metal support, comprising a tubular metal porous support layer having a mechanical strength sufficient to support a stack of functional layers, and a porosity sufficient to allow a reagent flow to flow through it, a tubular pack of functional layers in concentric boundary contact with the support layer, which contains in a concentric arrangement the cermet layer of the inner electrode, the ceramic middle layer of electrolyte This and the ceramic layer of the outer electrode, characterized in that the porous metal support layer is made of at least two layers of metal powders that are resistant to oxidation at a temperature of 700-900 ° C, or their alloys, and the inner layer of the support layer has minimal shrinkage in the annealing process at temperatures of 1200-1400 ° C, and the upper layer of the support layer contributes to the rapid and high-quality deposition of functional layers, and the tubular package of functional layers additionally contains a protective layer, and in the functional nye layers arranged in the following sequence: an anode layer, an electrolyte gas-tight, protective layer and the cathode layer. 2. The fuel cell according to claim 1, characterized in that the inner diameter of the metal porous support layer is 8-12 mm, and the thickness is 1-2 mm. 3. The fuel cell according to claim 1, characterized in that the total thickness of the package of functional layers is less than or equal to 52 microns. 4. The fuel cell according to claim 1, characterized in that the anode layer is made of porous nickel-zirconia cermet stabilized with yttrium dioxide and has a thickness of 20 μm. 5. The fuel cell according to claim 1, characterized in that the gas-tight electrolyte layer is made of yttrium stabilized zirconia and has a thickness of 10 μm. 6. The fuel cell according to claim 1, characterized in that the protective layer is made of GDC (Ce _0.8 Cd _0.2 O) and has a thickness of 2 μm. 7. The fuel cell according to claim 1, characterized in that the cathode layer is made of lanthanum manganate doped with strontium and has a thickness of 20 μm. 8. A tubular metal porous support layer of a fuel cell having mechanical strength sufficient to support a stack of functional layers and porosity sufficient to allow the flow of reagent to flow through it, characterized in that it is made at least , two-layer, from metal powders resistant to oxidation at a temperature of 700-900 ° C, or their alloys, the inner layer of the support layer having minimal shrinkage during annealing at temperatures of 1200-1400 ° C, and the upper layer of supports th layer facilitates rapid application quality and functional layers. 9. The tubular metal porous support layer of the fuel cell according to claim 8, characterized in that the pore sizes of the inner layer exceed 100 microns and the bulk porosity is 40-60%, while the pore sizes of the outer layer do not exceed 50 microns and the bulk porosity 30-50%. 10. The tubular metal porous support layer of the fuel cell according to claim 8, characterized in that the inner layer of the metal porous support layer is made of ferritic stainless steel powder and has pore sizes of 100-160 μm. 11. The tubular metal porous support layer of the fuel cell according to claim 10, characterized in that the inner layer is made of stainless steel grade 14X17H2. 12. The tubular metal porous support layer of the fuel cell according to claim 8, characterized in that the outer layer of the metal porous support layer is made of ferrite stainless steel powder ПХ17Н2. 13. A method of manufacturing a tubular solid oxide fuel cell with a metal support, which includes the following operations: (a) the manufacture of at least a two-layer metal porous support layer of metal powders resistant to oxidation at a temperature of 700-900 ° C, or alloys having a mechanical strength sufficient to support a stack of functional layers, and a porosity sufficient to allow a reagent stream to flow through it, the inner layer of which has by shrinkage during annealing at temperatures of 1200-1400 ° C, and the upper layer of the support layer provides fast and high-quality deposition of functional layers, (b) coating the support layer by dyeing or immersion with an anode layer of porous nickel-zirconia cermet stabilized with yttrium oxide ; (c) coating the anode layer with a layer of a gas-tight electrolyte from zirconia stabilized with yttrium oxide by the method of thermolysis of organometallic complexes; (d) coating the electrolyte layer with a protective layer of Ce _0.8 Gd _0.2 O; (e) coating the protective layer with a cathode layer of lanthanum manganate doped with strontium by the staining method. 14. The method according to item 13, wherein the anode layer is applied to the support layer in the form of a coating using a paste or suspension prepared on the basis of polyethylene glycol and a powder mixture of 60 vol.% NiO and 40 vol.% Zirconia stabilized with oxide yttrium, followed by drying of the applied layer at a temperature of 145-155 ° C for 10-15 hours, then the resulting preform is annealed in vacuum according to the regime: heating to 1100 ° C for 3.5-4 hours and holding at this temperature for 2 h 15. The method according to item 13, wherein the electrolyte layer is obtained by layer-by-layer deposition of colloidal zirconia stabilized with yttrium oxide, ZrO ₂ composition - 8 mol.% Y ₂ O ₃ on the anode layer, followed by annealing of each layer in vacuum at 1150- 1200 ° C for 2.5 hours 16. The method according to p. 13, characterized in that the protective layer is applied to the electrolyte layer in the form of a coating of organometallic complexes of Gd and Ce carboxylic acid (2-ethylhexanoic acid (2-EHC) (99%), C ₈ H ₁₆ O ₂ , CH ₃ (CH ₂ ) ₃ CH (C ₂ H ₅ ) COOH) followed by thermolysis or by immersion in a suspension of powder (Ce _0.8 Gd _0.2 O) in polyethylene glycol, followed by annealing of the layer in vacuo at 1150- 1200 ° C for 2.5 hours 17. The method according to p. 13, characterized in that the cathode layer is obtained by immersion in a suspension of powder from solid solutions of lanthanum manganate doped with strontium composition La _0.8 Si _0.2 MnO ₃ . 18. A method of obtaining a tubular metal porous support layer of a fuel cell, comprising the following operations: forming an internal support layer by filling powder of at least one metal or its alloy, with a particle size exceeding 100 microns, into the annular space formed by coaxially arranged pipes, the inner of which is made of quartz or stainless steel, and the outer of quartz; preliminary sintering of the obtained powder billets in a hydrogen atmosphere; removing the sintered billet from the tooling; final sintering of the blanks of the inner support layer in an atmosphere of hydrogen, inert gas or vacuum at a temperature of 1200-1400 ° C; the formation on the surface of the workpieces of the inner support layer of the outer layer of powder, similar to the powder of the inner support layer, but with a particle size of ≤50 μm. 19. The method according to p. 18, characterized in that the formation of the workpiece of the inner support layer is carried out by its compaction after filling with vibration. 20. The method according to p. 18, characterized in that the coarse-grained alumina powder is additionally poured into the inner tube, after which the inner tube is removed before sintering. 21. The method according to p. 18, characterized in that the formation of the inner support layer is carried out from ferritic stainless steel, for example, grade 14X17H2. 22. The method according to item 21, wherein the preliminary sintering of the powder blanks of the inner support layer is carried out at a temperature of 1050-1100 ° C for 1-5 hours 23. The method according to item 21, characterized in that when conducting preliminary sintering of the inner support layer, exposure is carried out at 350-400 ° C until gas evolution ceases. 24. The method according to item 21, wherein the final sintering of the blanks of the inner support layer is carried out with a gradual increase in temperature. 25. The method according to p. 18, characterized in that the formation on the surface of the workpieces of the inner support layer of the outer layer is produced by applying a suspension of powder in polyethylene glycol, after which the resulting product is dried and then annealed in vacuum. 26. The method according A.25, characterized in that the formation of the outer support layer is carried out from a powder of ferritic stainless steel grade ПХ17Н2 with particle sizes ≤60 μm. 27. The method according to p. 26, characterized in that the drying is carried out at a temperature of 140-160 ° C for 10-12 hours in air. 28. The method according to p. 26, characterized in that the annealing in vacuum is carried out according to the mode: heating to 950 ° C for 2 hours, then heating to 1150-1250 ° C for 1-2 hours and holding for 2-5 hours. 29. The method according to p. 18, characterized in that the formation on the surface of the workpieces of the inner support layer of the outer layer is carried out by filling the powder into the annulus formed by coaxially arranged additional outer quartz tube and the workpiece of the inner support layer, followed by sintering of the entire workpiece in a hydrogen atmosphere. 30. The method according to clause 29, characterized in that when using a powder of ferritic stainless steel grade ПХ17Н2, sintering of a bilayer of a two-layer support is carried out in two stages: first, at a temperature of 1050-1100 ° C for 1-5 hours, then the billet is removed from the tool and sintering is carried out at a temperature of 1200-1400 ° C for 1-3 hours in an atmosphere of hydrogen, inert gas or vacuum.

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