WO2023128807A1 - Tubular solid oxide fuel cell and method for manufacturing same - Google Patents

Abstract

The invention relates to the field of electrical engineering, and more particularly to elements of electrochemical devices for producing electrical energy, and can be used for creating solid oxide fuel cells (SOFCs). The present method for manufacturing SOFCs consists in applying to a tubular substrate of an anode electrode having a porous gradient structure, said base being formed by phase-inversion extrusion, at least an electrolyte layer and then simultaneously sintering the tubular anode electrode substrate and the applied layer by annealing. After that, at least a cathode electrode layer is applied and sintered. The electrolyte layer is applied to a non-sintered tubular anode electrode substrate, and the electrolyte material is a non-metallic material with a high ionic conductivity. The technical result consists in increasing the efficiency of the SOFC manufacturing process, as well as achieving improved SOFC power characteristics while maintaining a high level of mechanical strength by optimizing the parameters of the manufacturing process, while at the same time reducing the length of the SOFC manufacturing process.

Description

TUBULAR SOLID OXIDE FUEL CELL AND METHOD FOR ITS MANUFACTURE

The invention relates to the field of electrical engineering, namely to the elements of electrochemical devices for generating electricity, and can be used to create solid oxide fuel cells (SOFC).

As a rule, in the manufacture of solid oxide fuel cells, for the formation of functional layers of SOFCs on a carrier base, such deposition methods as magnetron sputtering, electroplasma deposition, screen printing, deposition methods from suspensions (spin-coating, deep-coating) are used. Due to differences in the degree of shrinkage of the deposited layers and their sintering temperatures, each layer, after being applied by the methods described above, is sintered according to a separately specified program.

At present, a method for manufacturing a solid oxide fuel cell is known, including operations for manufacturing and annealing the anode base, followed by deposition and annealing separately of each of the functional layers: electrode and electrolyte layer. This method is currently the standard generally accepted in world practice. The disadvantage of this method is the long duration of the process (from 10 days, taking into account the time for the equipment and samples to reach the necessary annealing modes), since each application of the next layer is accompanied by its sintering according to a separate procedure, in addition, the anode electrode carrier base is subjected to preliminary sintering (only this process usually takes 8 to 40 hours).

An example of a known method for manufacturing a solid oxide fuel cell is the method described in JP 2016071930.

A known method of manufacturing tubular solid oxide SOFC, including operations for the manufacture of a tubular base of the anode electrode, followed by applying layers of electrolyte, cathode layer and current collection, as well as operations for sintering these layers (RU 2342740). The disadvantages of the known method include the following:

The cermet (ceramic-metal composite) anode electrode support is manufactured by traditional extrusion or casting methods, which, even when a blowing agent is added to the cermet, do not provide a sufficiently high porosity of the anode electrode, which is necessary to ensure low diffusion resistance to fuel gases as they move through the thick layer of the supporting anode electrode to the electrochemical reaction zone at the interface of the anode electrode with the electrolyte layer and, as a result, do not provide increased specific power of SOFC from a surface unit. An excessive increase in the content of the blowing agent significantly reduces the strength of the supporting anode electrode even after it has been sintered. In this regard, the techniques for manufacturing the carrier anode electrode indicated in the analogue do not allow achieving high power characteristics simultaneously with maintaining the required strength of the SOFC carrier base.

At the same time, in the specified analogue, it is proposed to achieve increased strength and increased power of SOFC through the use of additives in the form of metal, for example, Ni, introduced into ceramic materials in the composition of all functional layers, in order to better match the thermal expansion coefficients of different layers. A distinctive feature of the authors of the analogue consider the introduction of such additives in the proportion of 0.1-15% vol. and in an ion-conducting electrolyte. However, a metal additive in the electrolyte spoils its ion-conducting properties - during SOFC operation, secondary electronic conductivity of the electrolyte may occur, which lowers the operating electric potential of the SOFC and reduces the reliability of the entire fuel cell, since there is a possibility of the formation of a short circuit of the electrodes (anode and cathode) through the electrolyte from - due to the presence of electronic conductivity of the electrolyte, due to the presence of nickel (or its oxide) in it.

The technical result of the claimed method consists in increasing the efficiency of the process of manufacturing tubular SOFCs, as well as achieving increased power characteristics of SOFCs while maintaining their high mechanical strength, by optimizing the parameters (modes and sequence) of the technological process, while reducing the duration of the technological process of manufacturing SOFCs. The technical result is achieved due to the fact that during the manufacture of a tubular solid oxide fuel cell, at least an electrolyte layer is applied to the tubular base of the anode electrode formed by extrusion with a phase inversion with a porous gradient structure, after which the tubular base of the anode electrode with the applied layer by high temperature annealing, after which at least a cathode electrode layer is deposited and sintered. In this case, the electrolyte layer is applied to the unsintered tubular base of the anode electrode. As the electrolyte material, a non-metallic material with high ionic conductivity is used.

Layers are applied by dipping into a suspension.

On the tubular base of the anode electrode, before applying the electrolyte layer, it is possible to apply an intermediate functional anode layer.

It is possible to apply a buffer layer on the electrolyte layer before applying the cathode electrode layer.

In a preferred embodiment of the method, after applying each layer, it is dried at a temperature of less than 120°C.

The operation of high-temperature sintering is carried out for 2-20 hours, while the first annealing after applying the electrolyte and/or intermediate functional anode layer and/or buffer layer is carried out at a temperature of 1200-1500°C, and the second - after applying the cathode electrode layer, consisting of functional cathode layer and/or cathode current-collecting electrode layer, at a temperature of 800-1300°C.

Ultimately, all of the above leads to an increase in the efficiency of the manufacturing process of tubular SOFCs, an increase in their specific power characteristics, an increase in their mechanical strength, and a decrease in the time spent on their manufacture.

In the manufacture of the carrier base of the anode electrode, the phase inversion method is used, which allows for one technological operation:

- firstly, to obtain an optimally structured macroporous structure in a thick layer of the carrier base of the anode electrode without the need to use additional blowing agents, which ensures low diffusion resistance to the reagent (fuel gas) when it moves to the zone of the electrochemical reaction at the boundary between the anode electrode and the electrolyte;

- secondly, to maintain the optimal strength and microstructure of the surface of the carrier base for the subsequent deposition and retention of SOFC functional layers (electrolyte and cathode layers);

- thirdly, to ensure the high strength of the manufactured SOFCs, which is necessary for the use of SOFCs in power plants for various purposes under conditions of real external influencing factors, in particular, when they are used as mobile (wearable and transport) sources of electricity.

The claimed invention is illustrated graphically:

Fig. 1 - cross section of tubular SOFC;

Fig. 2 - the same, but with additional functional layers (anode and buffer).

In the manufacture of a tubular carrier base 1 by extrusion with phase inversion, without the use of an additional blowing agent, a macroscopic porous structure 2 is formed (emerges) over the thickness of the tube, while a microporous structure 3 is naturally formed on the surface of the tubular base 1, in connection with this, the surface of the carrier base becomes suitable, without additional processing, for further deposition and sintering of SOFC functional layers. In this way, a strong cermet base of the anode electrode with a gradient porous structure is formed, which is clearly visible in Fig. 1. The macroporous structure of the carrier base has a reduced diffusion resistance for the transfer of the reagent (fuel gas) to the zone of the electrochemical reaction at the boundary of the anode electrode and electrolyte 4, which leads to an increase in the specific power characteristics of SOFC (an increase in the generated electric current per unit electrode surface at a given working voltage).

As the electrolyte material, according to the claimed method, it is proposed to use a non-metallic material with high ionic conductivity, which eliminates the possibility of a short circuit of the electrodes (anode and cathode), which can occur in the case of using a material with secondary electronic conductivity as an electrolyte material (as in known methods of SOFC manufacturing).

According to the claimed method, for applying all functional layers of SOFC, the method of dipping into a suspension (or "dip-coating", i.e. the method of applying a layer from a pre-prepared suspension by dipping a sample into it) is used. When describing the essence of the claimed method, functional layers mean, in particular:

- functional anode layer 6 applied to the carrier anode base 1, but not mandatory;

- layer 4 of solid electrolyte;

- layer 5 of the cathode electrode;

- a buffer layer 7 between the electrolyte and the cathode electrode and/or between the anode electrode (supporting anode base with or without a functional anode layer) and the electrolyte;

- cathode current collection layer or current collection bus (optional).

The use of the extrusion method with phase inversion for the manufacture of SOFCs in combination with the subsequent deposition of successively several functional layers on the unsintered (not subjected to high-temperature heat treatment) anode base with their simultaneous sintering (in one cycle of high-temperature annealing) makes it possible to significantly reduce the duration of SOFC manufacture, while ensure its high strength characteristics, as well as the achievement of high power characteristics of SOFC.

The essence of the claimed method is illustrated by an example of its specific implementation.

An example of the implementation of the claimed method

The cermet carrier base 1 of the anode electrode is manufactured by the phase inversion extrusion method: the initial powders of NiO and (¥ ₂ 03)o.08(Zr0 ₂ )o.92(8YSZ) in the ratio of 70/30 wt.%, which has a high solubility in the coagulant [Z. Hanetal. / Journal of Alloysand Compounds 750 (2018) 130-138]. When the resulting paste is extruded from the annular nozzle into the coagulant bath, the solvent in the paste is replaced by the coagulant, as a result, the paste solidifies in the form tubes with the formation of macroporosity, the structure of which depends, in particular, on the thickness of the paste layer in the coagulant, on the temperature and viscosity of the solvent and coagulant. The coagulant used in the example of the claimed method is water. The resulting blanks are cut into segments with a given length, placed in the coagulant for 12 hours (it is possible to place the blanks in the coagulant for 1-20 hours) for the final replacement of the solvent. Further, these bases of the anode electrode are dried in an air atmosphere or in a vacuum at a temperature of 100°C.

A suspension of the anode functional layer from a mixture of NiO and 8YSZ in a ratio of 40/60 wt%, with a solvent, a binder and a dispersant, is applied to the obtained bases of the anode electrode by the "dip-coating" method (by applying coatings to the base by immersing it in a pre-prepared suspension). After applying the anode functional layer, it is dried in a vacuum or in an air atmosphere at a temperature of 100°C.

An electrolyte suspension 4 consisting of 8YSZ powder, a solvent, a binder, a dispersant, and a plasticizer is applied to the dried anode functional layer by the “dip-coating” method. After applying the electrolyte layer, drying is carried out in a vacuum or in an air atmosphere at a temperature of 100°C.

After drying the electrolyte layer, high-temperature annealing is performed with holding at a temperature of 1400°C for 4 hours. A buffer layer suspension consisting of a powder (Сео. gGdo .1) 01.95 (10 GDC), a solvent , binder and dispersant. The resulting layer is dried in a vacuum or in an air atmosphere at a temperature of 100°C, then sintered at a temperature of 1400°C for 4 hours.

A suspension of the cathode functional layer consisting of a mixture of Lao.6SrCo2Fe80a+5 (LSCF-6428) and 10GDC powders in a ratio of 60/40 wt.%, a solvent, a binder, a dispersant, and a plasticizer is applied to the buffer layer by the “dip-coating” method. The resulting layer is dried in a vacuum or in an air atmosphere at a temperature of 100°C, after which a suspension of the cathode current-collecting layer is applied, consisting of LSCF-6428 powder, solvent, binder, dispersant and plasticizer. The applied layer is dried in a vacuum or in an air atmosphere at a temperature of 100°C, then sintered at a temperature of 950°C for 4 hours.

On FIG. 2 shows a cross-section of a tubular SOFC obtained according to the example described above. It should be noted that the stage of applying an anode functional layer and a buffer layer is an optional procedure.

The following are embodiments of high-temperature annealing in the manufacture of SOFC. This list of options is not exhaustive.

1 option:

1 anneal. 1200-1500°С, exposure 2-20 hours. Result: anode carrier base + anode functional layer + electrolyte;

2 annealing. 1200-1500°С, exposure 2-20 hours. Result: deposited buffer layer;

3 annealing. 800-1300°С, exposure 2-20 hours. Result: deposited cathode functional layer;

4 annealing. 8ОО-13ОО°С, exposure 2-20 h. Result: applied cathode current-collecting layer.

Option 2:

1 anneal. 1200-1500°С, holding time 2-20 hours. Result: anode support base + anode functional layer + electrolyte layer;

2 annealing. 1200-1500°С, exposure 2-20 hours. Result: deposited buffer layer;

3 annealing. 800-1300°C, exposure 2-20 hours. Result: applied cathode functional layer + cathode current-collecting layer.

Option 3:

1 anneal. 1200-1500°С, holding time 2-20 hours. Result: anode support base + anode functional layer + electrolyte layer;

2 annealing. 1200-1500°С, exposure 2-20 hours. Result: deposited cathode functional layer;

3 annealing. 8ОО-13ОО°С, exposure 2-20 h. Result: applied cathode current-collecting layer.

4 option: 1 anneal. 1200-1500°C, exposure 2-20 hours. Result: anode support base + anode functional layer + electrolyte + buffer layer;

2 annealing. 800-1300°C, exposure 2-20 hours. Result: applied cathode functional layer + cathode current-collecting layer.

The device manufactured by the claimed method is an electrochemical cell, namely, a tubular SOFC, consisting of functional layers of SOFC, sequentially deposited on the tubular base of the anode electrode having a gradient macroporous structure. Tubular SOFC, manufactured by the claimed method, includes: - a cermet base, consisting of a composition of material(s) with electronic conductivity (for example, but not exclusively, Ni, Cu, Co, W, Ti, Fe) in the oxidized or metallic state and the material(s) ) with ionic conductivity (in particular, YSZ: (Y203)x(2rC>2)(1-x); SSZ: (Sc2O3)x(CeO2) _y (ZrO2)(ixy); GDC: (Ce _x Gd(i _.X ))O(i.5+x/2), etc.) in a weight ratio of 50/50 to 90/10, respectively. The anode material may also contain impurities and additives that improve conductivity, improve sintering, increase catalytic activity, for example, such as: Cu, Co, Al, rare earth metals, their oxides, as well as precious metals Pt, Ro or, but not exclusively , Ag).

- May include an anode functional layer, consisting mostly of materials from which the cermet base is made, but with a changed mass ratio of the components of the material with electronic conductivity and material with ionic conductivity in ratios from 10/90 to 50/50, respectively.

- Electrolyte layer consisting of a material with high ionic conductivity (in particular YSZ: (Y2O3) _x (ZrO2)(ix); SSZ: (Sc2O3) _x (CeO2)y(ZrO2)( ixy); GDC: (Ce _x Gd(i- _X ))O(i 5+x/2) etc.).

- May include a buffer layer consisting of an ionically conductive material that is chemically stable in contact with cathode and electrolyte materials, for example (Ce _x Gd(i -x))O< i .5+x/2).

- Cathode functional layer, consisting of a material with mixed (ionic and electronic) conductivity (in particular, LSCF:La _x Sr(ix)Co _y Fe(i- _Y )Oz + 8, (Lao.758go.25)o.95MnO3 ±b, LSC: LaxSri-xCoO3, as well as their mixtures with buffer layer material or electrolyte material in a ratio of 10-50% wt.).

- Cathode current collection layer consisting of a material with mixed or electronic conductivity (in particular, LSCF:La _x Sr(ix)Co _y Fe(iy)O3 + 5, (LaojsSro 2e) o.95MnOz ± 8; LSC: La.xSri -xCoO3, as well as their mixtures with the material of the buffer layer and electrolyte, as well as with compositions based on precious metals).

A significant advantage of the claimed method for manufacturing tubular SOFCs is that the operation of applying an electrolyte or an anode functional layer and an electrolyte is carried out on a “raw” (non-sintered) supporting tubular anode base (i.e. without its preliminary high-temperature annealing/sintering), and sintering is not each deposited layer sequentially, and at the same time a green carrier base with an electrolyte or a green base with an anode functional layer and an electrolyte (i.e., several layers deposited from suspensions at once). Such one-time sintering in one cycle of high-temperature annealing, in addition to a significant reduction in the time of the SOFC manufacturing process, simultaneously leads to lower ohmic losses between the SOFC layers due to their tighter fit to each other along their interfaces, which ultimately leads to an additional increase in the specific power of the fuel cell. element. In particular, the increase in SOFC specific power reaches 15% and more.

Thus, the claimed set of essential features, expressed in a combination of the technological methods and operations used, with the selection of experimental process parameters, namely the combination of the use of an anode base with a gradient highly porous structure obtained by extrusion with phase inversion without the use of additional pore formers, as well as simultaneous sintering , made it possible to reduce the duration of the solid oxide fuel cell manufacturing process to 35-80 hours (instead of at least 10 days in the known method) with a simultaneous increase in specific power characteristics by 15% or more, as well as an increase in SOFC strength (which increases the reliability of SOFC during operation), made by the claimed method.

Claims

Claim 1. A method for manufacturing a tubular solid oxide fuel cell, which consists in the fact that at least an electrolyte layer is applied to the tubular base of the anode electrode formed by extrusion with a phase inversion with a porous gradient structure, after which the tubular base of the anode electrode with the applied layer by annealing, then at least a layer of the cathode electrode is deposited and sintered, wherein the electrolyte layer is deposited on the unsintered tubular base of the anode electrode, and a non-metallic material with high ionic conductivity is used as the electrolyte material. 2. The method according to p. 1, characterized in that the layers are applied by dipping into a suspension. 3. The method according to claim 1, characterized in that an intermediate functional anode layer is applied to the tubular base of the anode electrode before applying the electrolyte layer. 4. The method according to p. 1, characterized in that a buffer layer is applied to the electrolyte layer before applying the cathode electrode layer. 5. The method according to p. 1, characterized in that after applying each layer, drying is carried out at a temperature of less than 120 ° C. 6. The method according to any one of paragraphs. 1-5, characterized in that the operation of high-temperature sintering is carried out for 2-20 hours, while the first annealing after applying the electrolyte and / or buffer layer is carried out at a temperature of 1200-1500 ° C, and the second - after applying the functional cathode electrode layer and /or cathode current-collecting electrode layer at a temperature of 800-1300°C. 7. Tubular SOFC, including a tubular base of the anode electrode with a porous gradient structure and at least an electrolyte layer and a cathode electrode layer, characterized in that it is manufactured by the method according to any one of paragraphs. 1-6. 8. Tubular SOFC according to claim 7, characterized in that a functional anode layer is located between the base of the anode electrode and the electrolyte. 9. Tubular SOFC according to claim 7, characterized in that a buffer layer is located between the electrolyte and the cathode layer.