Material layers for fuel cells

Abstract

The present invention relates to a composite material layer for a fuel cell, a single layer solid oxide fuel cell, and a method for manufacturing the same. According to the present invention, a material layer for a single layer solid oxide fuel cell includes fused nanoparticles selected to provide reaction sites for hydrogen oxidation and oxygen reduction and to provide ion transport within the layer. The surface of at least one side of the layer is engraved (preferably both sides are engraved) to increase the surface area of ​​the fuel cell layer.

Description

[Technical Field]

[0001] The present invention relates to a uniquely designed material layer for a single layer solid oxide fuel cell and a method for fabricating the same. [Background technology]

[0002] The present invention relates to fuel cells, and specifically to monolayer fuel cells. In such cells, a single layer of material performs all of the functions of a more conventional trilayer fuel cell. Thus, monolayer fuel cells perform the primary fuel cell functions: hydrogen oxidation reaction, oxygen reduction reaction, and ion transport with minimal electron leakage.

[0003] A conventional tri-layer fuel cell consists of an anode layer, an electrolyte layer, and a cathode layer. The electrodes (anode and cathode) are porous and made of materials with mixed ionic and electronic conductivity for efficient electrode reactions, i.e., the hydrogen oxidation reaction (HOR) at the anode and the oxygen reduction reaction (ORR) on the cathode side of the cell. The electrolyte layer, sandwiched between the anode and cathode, is dense and only allows ionic transport through it (i.e., blocks electrical current).

[0004] In contrast, single layer ceramic fuel cells are constructed with one homogeneous functional layer formed by mixing semiconductors (usually both n-type and p-type) with ionic conductors.

[0005] Due to the presence of different bandgap materials in a monolayer fuel cell, a bulk junction exists within the fuel cell, where the anodic reaction occurs on the p-type material (e.g., NiO) and the cathodic reaction occurs on the n-type material (e.g., ZnO). As a result, the cell reaction: H → 2H on the fuel side + +2e - , O+2e on the air side - →O 2-According to the formula, hydrogen ions and oxygen ions are generated at the fuel-side and air-side surfaces, respectively. To balance the charge neutrality, electrons are activated and accumulated on the air side. Short circuits can be prevented due to the depletion of charge carriers at the heterojunction formed by the semiconducting oxide component in the mixture, which forces the electrons to travel through an external circuit.

[0006] A heterojunction refers to the interaction region formed by the contact of two dissimilar semiconductors with different dominant charge carriers. In the case of a bulk pn heterojunction, each spatial pn heterojunction undergoes the following processes (at the micro- and grain scale):

[0007] When p and n semiconductors come into contact, the concentration difference causes electrons to diffuse from the n-type to the p-type conduction band and vacancies to diffuse from the p-type to the n-type valence band. These processes continue until the Fermi levels of the n-type and p-type semiconductors are aligned. This results in p-to-n energy band bending, forming a built-in electric field barrier (BIEF) that prevents further electron movement from the n-type to the p-type layer and vacancies from the p-type to the n-type layer. The formed interaction region is defined as a space charge region that supports interfacial superionic transport while blocking internal electron transport and thus mitigating the threat of potential electronic shorting. Subsequently, fuel cell performance is enhanced.

[0008] 1000mWcm at 550℃ -2 Achieving such high performance values ​​raises fundamental questions about the mechanisms within the cell with respect to the composition of the semiconducting ionic materials. The current position of understanding is that protection against short circuits is due to pn, Schottky, or bulk heterojunctions created by oxides in the material mixture. The issue of porosity, i.e., the surface area of ​​the catalytic material, which is critical for efficient reaction kinetics within the cell, has not yet been addressed in the monolayer fuel cell literature.

[0009] With regard to the mixed ionic and electronic conduction capabilities, a triple-phase boundary (TPB) is necessary to facilitate the cell reaction. The TPB is the contact area between the three phases required for the electrochemical reaction at the electrode: the anion-conducting phase, the electron-conducting phase, and the gas phase. On the one hand, monolayer ceramic fuel cells should be porous so that the number of reaction sites, as determined by the triple-phase boundary (TPB), is large to support high current generation. On the other hand, monolayer cells need to be dense to prevent gas from crossing through the cell and ensure that ion transport occurs without much resistance. As a result, the performance of monolayer fuel cells is generally limited by the low concentration of reagents due to the low amount of TPB. Therefore, there is a need to find an improved method for fabricating monolayer fuel cells that would provide a solution to this problem. Summary of the Invention [Problem to be solved by the invention]

[0010] Object of the invention The objective of the present invention is to develop a composite layer for a novel monolayer fuel cell and a method for fabricating such a fuel cell. According to the present invention, an increase in the cell's three-phase interfacial area is achieved, resulting in improved fuel cell output power density. A reverse mode of operation is also envisioned, in which steam and voltage applied to the cell will result in hydrogen production. [Means for solving the problem]

[0011] The objects of the invention are achieved by what is specified in the appended claims. [Brief explanation of the drawings]

[0012] Various embodiments of the invention are described in more detail below by reference to the accompanying drawings. [Figure 1] 1 shows a schematic structure of a monolayer fuel cell that can support at least some embodiments of the present invention. [Figure 2A]1 illustrates an embodiment of a material layer for a solid oxide fuel cell according to the present invention. [Figure 2B] 1 illustrates an embodiment of a material layer for a solid oxide fuel cell according to the present invention. [Figure 2C] 1 illustrates an embodiment of a material layer for a solid oxide fuel cell according to the present invention. [Figure 2D] 1 illustrates an embodiment of a material layer for a solid oxide fuel cell according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Reference is now made to Figure 1, which shows a partial cross section of a monolayer fuel cell 10 in the form of a disk. The material layer 11 is made up of various nanoparticles and molecules according to the following legend: [Table 1]

[0014] The fuel cell further comprises current collectors 12 on both sides of the disk. The current collectors 12 can be gold mesh in the form of a porous, non-catalytic layer of Au particles. The current collectors are applied to the material layer in any suitable manner (mesh, deposition, etc.) and can be of any suitable material, as discussed below. The current collectors should be porous or have gaps that allow gas to contact the material layer 11. In this example, the particle size of the Au particles was 100-300 nm, and the layer thickness was 5-10 μm.

[0015] In the fuel cell operating mode, hydrogen H gas and oxygen O gas are supplied to opposite sides of the fuel cell. The oxidation of hydrogen gas to hydrogen ions (HOR) occurs on one side, and the reduction of oxygen gas to oxide ions (ORR) occurs on the other side, thereby reducing the amount of multi-ion O within the cell. 2- , H + conduction, and thus the current e across the current collector 12 - results.

[0016] Conversely, when steam is supplied on one side of the cell and a voltage (e.g., 1.2 V) is applied across the single-layer ceramic fuel cell, resulting in current flow through the fuel cell, the cell operates in reverse mode and produces hydrogen.

[0017] It has been shown that the operating principle of single-component nanocomposite fuel cells can be explained by the electron blockade of the resistivity and catalytic activity of wide-bandgap oxides. The resistance to transport of charge carriers and leakage currents will be the dominant performance-limiting factor of a monolayer fuel cell. Furthermore, H + governs ion transport within the cell, while O 2- The contribution from ions was found to be small.

[0018] [1](B.Zhu,R.Raza,G.Abbas,M.Singh,An electrolyte-free fuel cell constructed from one homogenous layer with mixed conductivity,Adv.Funct.Mater.21(2011)2465-2469).

[0019] According to at least some embodiments of the present invention, a monolayer fuel cell layer of the present invention can be fabricated from wide-bandgap lithium-nickel-zinc oxide (LNZ) and gadolinium-doped cerium oxide (GDC) nanoparticles (40-70 nm) using an Au current collector. The LNZ compound functions as the electrode material, and the GDC particles function as the ionic conductor. Fuel cell material fabricated from a homogeneous mixture of LNZ-GDC and a non-catalytic Au current collector exhibited an energy density of 357 mW / cm. 2 A power density of 1000 W was achieved. Au was used to ensure a truly single-layer fuel cell configuration.

[0020] It was found that in monolayer fuel cells, efficient catalysis would require a large specific surface area [1].

[0021] The band gap is the distance that exists between the valence band and the conduction band of electrons. Essentially, the band gap represents the minimum energy required to excite an electron to a state in the conduction band that can participate in conduction. The band gap energy of a semiconductor tends to decrease with increasing temperature. The relationship between band gap energy E and temperature T is given by Varshni's empirical formula, Eg(T) = Eg(0) - αT 2 / (T+β), where α and β represent material constants.

[0022] The band gaps of Li2O, NiO, and ZnO are 16.7 eV, 3.6-4 eV, and 3.3 eV, respectively. The band gap of LNZ nanopowder material (grain size 20-70 nm) was optically determined by reflectance measurements to be 3.6 eV. These oxides are wide-bandgap materials with very low electronic conductivity at room temperature. Operating at higher temperatures reduces the band gap, according to the Varshni equation, which will slightly improve electronic conduction. Electronic conduction depends on both the electron mobility and the charge carrier concentration. Generally, above 200 K, the electron mobility (μ) is limited by lattice scattering and decreases as a function of temperature (T):

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[0023] The fluorite structure of Gd-doped CeO2 primarily supports oxygen ion conduction through oxygen vacancies created by substituting trivalent Gd atoms for tetravalent Ce atoms. Here, 20% Gd-doped CeO2 is used, and the fluorite crystal structure remains stable and efficiently supports oxygen ion conduction through the vacancies. Oxygen ions primarily migrate through vacancies within the oxide phase, while hydrogen ions conduct through a hopping mechanism on the protonated oxide within the cell.

[0024] To more specifically describe the material composition, the ionic conductor particles of FIG. 1, according to some embodiments of the present invention, may be composed of 70-100 wt. % gadolinium-doped ceria (GDC) and 30-0 wt. % of the following: -sodium carbonate, lithium carbonate, and potassium carbonate; - binary carbonates, i.e., sodium carbonate and lithium carbonate; -lithium carbonate and potassium carbonate; or - a ceramic nanoparticle material comprising a material selected from at least one of: sodium carbonate and potassium carbonate.

[0025] The electrode material (LiNiZnO) of FIG. 1, according to some embodiments of the present invention, can include Li2CO3, NiCO3·2Ni(OH)2·xH2O, and Zn(NO3)2·6H2O, which are mixed, ground, and sintered in an oven, for example, at 800°C for 3 hours.

[0026] The molar composition of the metal elements can be Li:Ni:Zn=3:9:8. This electrode material composition was chosen because a single-component fuel cell can achieve 600 mW / cm at 550 °C. 2 This is because it has been reported to generate [1].

[0027] To fabricate material layer 11, GDC and LNZ powders were mixed in a ball milling machine in a ratio of 60:40 wt.% respectively. After mixing, the powders were sintered at 700°C for 4 hours and then ground in a mortar for 20 minutes. The nanoparticle material was mixed together with a solvent (e.g., terpineol) and other additives (binder, dispersant) to form a paste with suitable rheological properties.

[0028] The resulting nanocomposite powders can be fused into layers, for example, by direct writing, extrusion-based 3D printing, pressing in a die (e.g., isostatic or coaxial pressing) at pressures of 100-300 MPa for 1-10 minutes, or by sintering at 700°C for 1 hour. The nanocomposite powders can be adapted to be fabricated into monolayer fuel cells by the following methods: -For fabrication by extrusion-based 3D printing, the inventors have developed a unique paste of nanocomposite with suitable rheological properties and suitable printing parameters; -Regarding sintering, we have developed a specific thermal profile for sintering the printed cells; High pressure processing can be performed directly on the nanocomposite material.

[0029] Gold (Au) paste or gold mesh can be applied to both sides of the layer. Alternatively, silver (Ag) or NCAL (Ni 0.8 Co 0.15 Al 0.05 LiO2) coated Ni foam can be used for current collection. However, Ni / NCAL current collectors exhibit catalytic effects, and such cells may not correspond to the original 1-layer device and would more closely resemble conventional 3-layer fuel cells.

[0030] Obviously, various embodiments of the present invention can be envisaged in which the shape and size of the material layer, and therefore the fuel call, can vary from the examples presented herein, i.e., the layer can have the shape of a disk or any other conceivable shape.

[0031] Referring now to FIG. 2A, a monolayer fuel cell disk 20 prepared in accordance with at least some embodiments of the present invention is shown. Disk 20 has an outer diameter D, which may be, for example, 13 mm. Disk 20 has an outer edge 22 having a height b, which may be 1-2 mm. Inside edge 22, the surface of disk 20 is engraved with a comb-like structure having parallel grooves, for example, with a width w of 100 μm and a depth d of 200 μm. In FIG. 2C, the engraved portion of disk 20 is shown in perspective. Disk 20 may have a thickness t, for example, of 0.5-2 mm.

[0032] In Figure 2B, another embodiment of a single layer fuel cell disk 23 of the present invention is shown having an edge 25 and spiral engraving 24. The dimensions may otherwise be the same as in Figures 2A and 2C.

[0033] It is clear that a sculptured surface provides a much larger contact surface with the environment than a flat one. As shown in FIG. 2D and for the dimensions discussed above in connection with FIG. 2C, a symmetrically sculptured groove cross-section consisting of the top surface s of the ridge (100 μm), the groove sidewall d (2 × 200 μm), and the bottom w (100 μm) provides a total surface distance of 600 μm. For any given cross-sectional length of the surface, there is a calculated difference of three times the corresponding surface distance of a flat surface, which is 200 μm. Obviously, again, various embodiments of the present invention can be envisioned in which the shape and size of the grooves can vary from the examples presented herein, thus providing even greater or lesser differences in the surface contact area of ​​the fuel cell. The grooves can have rounded corners, as shown in FIG. 2D. Also, as shown in FIG. 2B, the grooves can also have alternative shapes to the comb-like structure of FIG. 2A.

[0034] Engraving of the unique pattern can be performed with a high-energy laser with appropriate scanning speed (50%), laser intensity (15% of 23 watts), and frequency (500 Hz). The pattern was engraved to maximize the surface area of ​​the disk without adversely affecting the mechanical stability of the engraved structure. Typical depths and widths of the engraved sections were 200 micrometers and 100 micrometers. After engraving, the monolayer ceramic fuel cell material is ready for use in a fuel cell.

[0035] The engraving pattern can be freely defined according to design choice. Here, a comb-like structure is used simply to describe a pattern with many parallel grooves, but other patterns, such as those shown in FIG. 2B, are possible as well. Groove is used in this context as a more general term to describe the result of engraving any pattern. The engraved grooves can be rectangular in cross section, rounded, or the like.

[0036] In fact, we found that the three-phase interfacial area (TPB) of the cell increased by 45% on both sides, and we found that the output power density of the fuel cell improved by 30% at low temperature operation (550°C) when fuel and air were supplied to each side of the cell.

[0037] The electrochemical performance of the monolayer cells of the present invention was measured at 550°C. The cells operate in a stable manner based solely on the fuel cell reaction. Because the open circuit voltage (OCV) of these fuel cells does not exceed 1.2 V, power density and performance were measured within conventional voltage limits (0 to OCV). Cells with different thicknesses (1, 2, and 3 mm) were used to analyze the pattern of increase in cell resistance with increasing cell thickness.

[0038] It is clear to a person skilled in the art that the various embodiments of the invention are not limited to the examples given above, but may vary within the scope of the appended claims.

Claims

1. A material layer for a solid oxide fuel cell, the layer comprising fused nanoparticles selected to provide reaction sites for hydrogen oxidation and oxygen reduction and to provide ion transport within the layer, and a surface on at least one side of the layer is sculpted to increase the surface area of ​​the fuel cell layer.

2. The layer of material of claim 1 , wherein both surfaces of the layer are engraved.

3. % of the material, wherein the material comprises 70-100 wt. % gadolinium-doped ceria and 30-0 wt. % of the following: - sodium carbonate, lithium carbonate, and potassium carbonate; binary carbonates, i.e. sodium carbonate and lithium carbonate; lithium carbonate and potassium carbonate; or - a material selected from at least one of sodium carbonate and potassium carbonate.

4. 2. The material layer of claim 1, wherein the material comprises a ceramic nanoparticle material comprising 70-100% by weight of BaZr0.4Ce0.4Y0.1Yb0.1O3-d and / or BaZr0.35Ce0.5Y0.15O3 as proton conductors.

5. The material comprises: ｣uFe ２ . ４ 4 -La0.6Sr0.4Co0.8Fe0.2O3-d; -La0.6Sr0.4CoO3-d; NiCoAlLi oxide; or The material layer according to any one of claims 1 to 4, comprising nanoparticles of at least one electrode material of the following group: LiNiZn oxide. -Ba0.5Sr0.5Co0.8Fe0.2O3-d -BaCo0.4Fe0.4Zr0.1Y0.1O3-d

6. 6. The material layer of any one of claims 1 to 5, wherein the layer is made of a nanoparticle material that is mixed together with a solvent and other additives to form a paste with suitable rheological properties that is fused into a layer for a fuel cell by direct-write or extrusion-based 3D printing.

7. 5. The material layer of any one of claims 1 to 4, wherein the layer is made of nanoparticle materials mixed by pressing at a pressure of 100 to 300 MPa or by sintering to form a fused mixture in a layer for a fuel cell.

8. 6. A layer of material according to any one of claims 1 to 5, wherein the at least one engraved surface of the layer is engraved to have a grooved structure with engraved recesses having a maximum dimension of 200 μm deep and 100 μm wide.

9. 1. A solid oxide fuel cell comprising a fused material layer of a ceramic nanoparticle material selected to provide reaction sites for hydrogen oxidation and oxygen reduction and to provide ion transport within said layer, wherein the surface of at least one side of said layer is sculpted to increase the surface area of ​​said fuel cell layer, and a layer of current collector material is deposited on at least said sculpted surface.

10. The ceramic material comprises 70 to 100 wt. % gadolinium-doped ceria as an ionic conductor and 30 to 0 wt. % of one of the following: - sodium carbonate, lithium carbonate, and potassium carbonate; binary carbonates, i.e. sodium carbonate and lithium carbonate; lithium carbonate and potassium carbonate; or - a material selected from at least one of sodium carbonate and potassium carbonate.

11. 8. The solid oxide fuel cell of claim 7, wherein the ceramic material comprises a nanoparticle material comprising 70-100 wt. % BaZr0.4Ce0.4Y0.1Yb0.1O3-d and / or BaZr0.35Ce0.5Y0.15O3 as proton conductors.

12. 10. The solid oxide fuel cell of any one of claims 7 to 9, wherein the layers are comprised of nanocomposites mixed to form a paste fused into layers for the fuel cell by direct-write or extrusion-based 3D printing.

13. 10. A solid oxide fuel cell according to any one of claims 7 to 9, wherein the layers are made of nanocomposite materials mixed to form a mixture and fused into a layer for the fuel cell by pressing at a pressure of 100 to 300 MPa or by sintering.

14. 11. A solid oxide fuel cell as claimed in any one of claims 7 to 10, wherein the at least one engraved surface of the layer is engraved to have a grooved structure with engraved recesses having a maximum dimension of 200 μm deep and 100 μm wide.

15. 10. A method for manufacturing a layer of material for a solid oxide fuel cell, comprising the ceramic nanoparticle material of any one of claims 1 to 7, said method comprising the steps of: - providing a mixture of said nanocomposites; - By the following method: Direct writing; Extrusion-based 3D printing; - pressing at a pressure of 100-300 MPa; - engraving a structure into the surface area of ​​said cell on at least one side.

16. 16. A method for manufacturing a material layer as recited in claim 15, including the step of sintering said cells to remove any organic impurities and achieve a suitable density for said monolayer.

17. 13. The method for manufacturing a material layer according to claim 12, wherein said engraving is carried out using a laser having a laser head scanning speed=50%, an intensity of 3-5 watts, and a frequency of 500 Hz.

18. 14. A method for manufacturing a material layer according to claim 12 or 13, wherein the engraving is carried out to create a grooved structure having grooves with a depth of 200 μm and a width of 100 μm.

19. A method for manufacturing a material layer according to any one of claims 12 to 14, wherein said engraved structure is provided with a current collector material, such as gold, deposited on said engraved surface.

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