RU2634475C1 - Method of producing anode material for fuel component with melted carbonate electrolyte - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes treating the powder of metallic nickel or nickel-containing alloy with an aluminium-containing precursor. As an aluminium-containing precursor, a water-alcohol solution of Al(NO₃)₃⋅9H₂O. The powder is impregnated with a precursor, dried at a temperature of 30-70°C, and then calcined at a temperature of 250-280°C.

EFFECT: invention makes it possible to simplify the producing process and to increase the functional characteristics of the porous gas diffusion anode.

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Description

The invention relates to the field of electrochemical energy, namely to high-temperature fuel cells with molten carbonate electrolyte.

The modern design of a fuel cell with molten carbonate electrolyte (RKTE) involves a planar geometry in which the plates of the porous gas diffusion anode and cathode are separated by a matrix electrolyte plate, which is a porous ceramic matrix impregnated with a liquid electrolyte, which is a metal carbonate melt. Moreover, the pores of the matrix electrolyte should be completely filled with liquid electrolyte, and the pores of the anode and cathode should be filled with liquid electrolyte only partially. For effective and long-term operation of the RHEC, it is important to ensure uniform distribution of the electrolyte between the anode and cathode, as well as long-term stability of the porous structure of the anode, cathode, and matrix electrolyte. The basis of the anode material is metallic nickel, the electrolyte wettability of which is much lower than the wettability of the cathode material, which leads to unequal distribution of the electrolyte between the anode and cathode. To increase the wettability and stabilization of the porous structure of the anode, nickel alloys with aluminum or chromium are used. The cost of preparing fine powders from such alloys is much higher compared to the traditional carbonyl technology for the preparation of powders from pure nickel. In addition, in the case of nickel-aluminum alloys, the region where the alloy exists is limited to 5 mol% of aluminum, which may not be enough to ensure good wettability by the electrolyte and stabilization of the porous structure. To overcome these drawbacks, technical solutions have been proposed in which ceramic additives, such as Al ₂ O ₃ , LiAlO ₂ , CeO _2, and several others, are introduced into the anode material to increase the wettability and stability of the anode porous structure.

In general, the process for preparing a porous gas diffusion anode involves the following steps: (1) preparing a nickel precursor; (2) preparing a slip; (3) production of a crude anode plate by slip casting; (4) burning the ex situ ligament and optionally further treating the annealed plate. The last stage is not always necessary, since the burning of the bundle can be carried out directly in the fuel cell during the technological start-up. Technological solutions are known involving the introduction of a stabilizing ceramic additive at any one of these stages.

A known method of manufacturing an anode of RKTE [patent US 6585931 B1, IPC H01M8 / 14, publ. 07/01/2003], in which a mixture of metallic nickel powder with aluminum oxide powder is used as the initial nickel-containing material, on the surface of which nickel is deposited by solution deposition. This method allows to increase the stability of the anode with respect to plastic deformation.

However, this method does not provide the necessary increase in wettability of the surface of the anode by electrolyte. Another disadvantage of this method is the need for two high-temperature anneals at 400 ° C and 800 ° C in a reducing atmosphere, which complicates the method of manufacturing the anode and increases its cost.

A known method of manufacturing an anode of RKTE [patent US 6824913 B2, IPC H01M8 / 14, publ. November 30, 2004], in which metallic nickel or metallic nickel-containing alloys and mixtures are used as the anode starting material, and the ceramic additive is introduced not by processing the initial metal powder, but by treating the already formed porous plate of the anode. The plate is impregnated with a sol containing a ceramic additive, and then dried in air at 100 ° C. The impregnation and drying procedure is repeated several times until the required density of the ceramic coating is obtained. This method improves both the stability of the anode with respect to plastic deformation and the wettability of the electrolyte.

The disadvantage of this method is the need for additional manipulations with the formed anode plate, which increase the risk of damage to the plate and increase the complexity of the method. This method also includes annealing at high temperature in a reducing atmosphere, which complicates the procedure for manufacturing the anode and increases its cost.

A known method of manufacturing an anode of RKTE [patent US 8163437 B2, IPC H01M8 / 14, publ. 04.24.2012], in which powders of a nickel alloy and a ceramic additive are mixed during the preparation of a slip. After slip casting and drying, the resulting anode plate is laminated to a nickel mesh. This method improves both the stability of the anode with respect to plastic deformation and the wettability of the electrolyte and does not require prior high-temperature annealing of the anode plate.

The specified method involves the ceramic content in the anode plate from 5 to 50 vol.%. Such a high content of ceramic additives significantly reduces the area of the active surface of the electrode and increases ohmic losses in it, which leads to a decrease in the efficiency of the fuel cell as a whole.

Closest to the claimed invention is a technical solution [Lee H., Lee I., Lee D., Lim H. Novel application of aluminum salt for cost-effective fabrication of a highly creep-resistant nickel-aluminum anode for a molten carbonate fuel cell // J. Power Sources. 2006. V. 162. No. 2. P. 1088.], which is selected for the prototype. In this method, carbonyl nickel powder is used as the starting anode material, and Al ₂ O ₃ oxide is used as a ceramic additive, which is introduced in the form of a powder of an aluminum-containing precursor Al (OH) (CH ₃ COO) ₂ at the stage of preparing the slip. This method allows to increase the stability of the anode with respect to plastic deformation and to increase the wettability of the electrolyte.

The disadvantage of this method is the need for high-temperature annealing of 1000–1100 ° C of the formed anode plate in a reducing atmosphere, which complicates the technology and increases its cost.

The claimed invention solves the problem of simplifying the technology and improves the functional characteristics of the manufactured anode due to the technical result, which consists in a more uniform distribution of the ceramic additive and the formation of an additional ultrafine fraction of nickel. The crude anode plate formed by slip casting does not require high temperature ex situ annealing in a reducing atmosphere.

The technical result is achieved by the fact that for the processing of the initial nickel powder as an aluminum-containing precursor, a water-alcohol solution of Al (NO ₃ ) ₃ ⋅ 9H ₂ O is used. In the known technical solutions, the ceramic precursor has the form of a suspension rather than a solution, which requires additional measures for uniform distribution of the precursor over the anode material, whereas in the proposed technical solution, to ensure uniform distribution of the ceramic additive, it is sufficient to impregnate the original nickel-containing powder creates a precursor of the desired concentration. In contrast to the known technical solutions, the proposed form of the dissolved precursor is not chemically inert with respect to nickel, and the ongoing chemical interaction gives two additional technical results. First, the formation of nuclei of crystals of the ceramic phase Al ₂ O ₃ occurs on the surface of nickel, which provides better adhesion in comparison with mechanical mixing of solid phases; secondly, partial oxidation of metallic nickel to NiO occurs, which upon subsequent reduction during the technological start-up of the fuel element forms an additional finely divided fraction of metallic nickel, which gives an additional increase in the wettability and electrochemical activity of the anode.

The flowing chemical interaction has a complex nature. At the same time, hydrolysis of aluminum nitrate proceeds, nucleation and growth of the Al ₂ O ₃ phase, reduction of the nitrate ion, oxidation of ethyl alcohol, partial oxidation of nickel. The total process is exothermic, so it is important to choose the ratio of water, ethyl alcohol and Al (NO ₃ ) ₃ ⋅ 9H ₂ O in such a way that, on the one hand, the process proceeds at a practically sufficient speed, on the other hand, so that spontaneous overheating of the reaction does not occur mixtures.

After treating the nickel powder with a water – alcohol solution of Al (NO ₃ ) ₃ ⋅ 9H ₂ O, the resulting composite powder is dried at a temperature of 30–70 ° С, then calcined at a temperature of 250–280 ° С to remove nitrate residues. The resulting nickel-containing composite powder can be used to prepare a slip and to manufacture a crude anode plate using slip casting or calendering technology.

The following examples confirm, but do not exhaust, the invention.

Example 1

According to the claimed technical solution for the manufacture of anode material, carbonyl nickel powder is pre-treated with an aluminum-containing precursor. For this, a water-alcohol mixture is prepared - 50 ml of ethyl alcohol is added to 60 ml of water and mixed. 4.18 g of Al (NO ₃ ) ₃ ⋅ 9H ₂ O is added to the resulting mixture and mixed until completely dissolved. Carbonyl nickel powder with an average particle size of 2.5 μm is sieved through a sieve with a mesh size of 20 μm to separate possible impurities of agglomerated particles. A sample of sifted powder of 99 g is taken, placed in a cuvette and poured with a prepared aqueous-alcohol solution of Al (NO ₃ ) ₃ ⋅ 9H ₂ O. The mixture is aged for one hour until the completion of the reaction, then it is dried at 40 ° C for 4 hours, then calcined in an atmosphere of air at 260 ° C for 8 hours. After cooling, the calcined mixture is dispersed and sieved through a sieve with a mesh size of 20 μm. The anode material thus prepared is then used for the manufacture of a porous gas diffusion anode using the known slip casting technology. In figures 1 and 2 presents micrographs of the source and treated carbonyl nickel, respectively. Figure 2 shows that the initial Nickel powder is coated with the reaction products evenly. The content of Al ₂ O ₃ additive in the treated powder is 0.57 wt.%.

To prepare the slip, 100 g of the prepared anode material are mixed with an organic composition containing 14 ml of cyclohexanone, 17 ml of isobutanol, 10 g of polyvinyl butyral, 6 ml of dibutyl phthalate and 1.5 ml of DISPERBYK-104S dispersant. The resulting slip mixture is homogenized in a planetary mill for 40 hours, after which it is used to make a crude anode plate using slip casting.

The crude anode plate obtained at the previous stage according to the claimed technology does not require additional ex situ processing and can be used to assemble a stack of a fuel cell with burning an organic binder directly during a technological start-up. The figure 3 presents the test results of a laboratory model of a carbonate fuel cell with anodes made from untreated carbonyl nickel powder and a powder containing 0.57 wt.% Al ₂ O ₃ . It is shown that the introduction of a ceramic additive leads, first, to an increase in the maximum current density from 198 to 305 mA / cm ² at a voltage of 0.7 V per unit cell; secondly, the available region of optimal degrees of electrolyte filling expands and, thirdly, the optimal region shifts toward higher degrees of electrolyte filling. All three results are beneficial for efficient and long-term operation of the fuel cell.

Example 2

Preparing 110 ml of a water-alcohol mixture with a concentration of ethyl alcohol of 40 vol.%. 2.0 g of Al (NO ₃ ) ₃ ⋅ 9H ₂ O is added to the resulting mixture and mixed until completely dissolved. X20H80 nickel-chrome alloy powder is sieved through a sieve with a mesh size of 20 μm. A sample of 99.5 g sifted powder is taken, placed in a cuvette and poured with a prepared aqueous-alcohol solution of Al (NO ₃ ) ₃ ⋅ 9H ₂ O. The mixture is aged for one hour until the completion of the reaction, then dried at 70 ° C for 4 hours, then calcined in an atmosphere of air at 250 ° C for 8 hours. After cooling, the calcined mixture is dispersed and sieved through a sieve with a mesh size of 20 μm. The content of Al ₂ O ₃ additive in the treated powder is 0.27 wt.%. The anode material thus prepared is then used for the manufacture of a porous gas diffusion anode using the slip casting technology described in Example 1. The introduction of a ceramic additive leads, first, to an increase in the maximum current density from 198 to 265 mA / cm ² at a unit voltage of 0.7 AT; secondly, the available region of optimal degrees of filling with electrolyte expands and, thirdly, the optimal region shifts toward higher degrees of filling with electrolyte (Fig. 3).

Example 3

Preparing 110 ml of a water-alcohol mixture with a concentration of ethyl alcohol of 50 vol.%. To the resulting mixture, 12.5 g of Al (NO ₃ ) ₃ ⋅ 9H ₂ O is added and mixed until completely dissolved. PNK-1 carbonyl nickel powder is sieved through a sieve with a mesh size of 20 μm. A sample of the sifted powder is taken 97 g, placed in a cuvette and poured with a prepared aqueous-alcohol solution of Al (NO ₃ ) ₃ ⋅ 9H ₂ O. The mixture is aged for one hour until the completion of the reaction, then it is dried at 30 ° C for 8 hours, then calcined in air at 280 ° C for 8 hours. After cooling, the calcined mixture is dispersed and sieved through a sieve with a mesh size of 20 μm. The content of Al ₂ O ₃ additive in the treated powder is 1.73 wt.%. The anode material thus prepared is then used for the manufacture of a porous gas diffusion anode using the slip casting technology described in Example 1. The introduction of a ceramic additive leads, first, to an increase in the maximum current density from 198 to 282 mA / cm ² at a unit voltage of 0.7 AT; secondly, the available region of optimal degrees of filling with electrolyte expands and, thirdly, the optimal region shifts toward higher degrees of filling with electrolyte (Fig. 3).

Claims (1)

A method of manufacturing an anode material for a fuel cell with a molten carbonate electrolyte, comprising treating a powder of metallic nickel or a nickel-containing alloy with an aluminum-containing precursor, characterized in that the powder of metallic nickel or a nickel-containing alloy is treated with a water-alcohol solution of aluminum nitrate with an ethyl alcohol concentration of 40-50 vol.% and the powder obtained after treatment with a precursor is dried at a temperature of 30–70 ° C, and then calcined in an atmosphere of air at a temperature of 2 50–280 ° C.

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