JPS6035471A - Electrode for fuel cell - Google Patents

Abstract

PURPOSE:To reduce the amount of metal used for an electrode and stabilize cell performance by applying electroless deposition of active metal layer to the surface of a ceramic porous body which is chemically stable to molten carbonate electrolyte. CONSTITUTION:At least one of ceramics powder and fiber such as lithium aluminate which is chemically stable to molten carbonate electrolyte at operating temperature of a fuel cell is sintered. Electrochemically active metal layer such as nickel is formed on the surface of the ceramic porous body formed by sintering by applying electroless deposition. By this process, an electrode for unit cell of a fuel cell is obtained. The amount of nickel metal used for electrode is reduced and cost of electrode is also decreased. Shape and diameter of pores in the electrode are uniform and operation of the fuel cell is steady over a long period of time.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an electrode that is incorporated into a unit cell of a fuel cell using molten carbonate as an electrolyte, and particularly relates to an electrode that is incorporated in a unit cell of a fuel cell using molten carbonate as an electrolyte, and in particular, an electrode that is designed to be low in price and have a long life. Regarding electrodes.・ [Technical issues and problems with the invention] Conventionally, a gas that easily oxidizes, such as hydrogen, and a gas that has oxidizing power, such as oxygen, were reacted through an electrochemical reaction process. Fuel cells that obtain direct current power are widely known.

Fuel cells are broadly classified into phosphoric acid type, molten carbonate type, solid electrolyte type, etc. depending on the electrolyte used.

By the way, among the above-mentioned fuel cells, bath-molten carbonate fuel cells are designed to operate at temperatures around 650°C, and their main components are usually carbonaceous materials such as lithium carbonate and potassium carbonate. A unit battery is constructed by applying nickel alloy gas diffusion electrodes to both sides of an electrolyte layer made by integrating a salt electrolyte and a ceramic holding material such as tium aluminate into a flat plate. It is constructed as a laminate in which the individual electrodes are laminated with bipolar separators interposed between them.

However, the molten carbonate fuel cell configured as described above has the following problems. That is,
Although a porous nickel sintered plate is used as an electrode incorporated in a unit battery, this sintered plate is expensive, so there is a problem in that the entire battery becomes expensive. In addition, the porous nickel sintered plate has the problem that sintering progresses among the nickel particles during long-term battery operation, resulting in changes in the pore size and shape of the electrode, resulting in a short lifespan. In general, the characteristics of batteries are electrolyte,
It greatly depends on the amount of electrochemically active sites at the three-phase interface consisting of the electrode and the reactant gas. Therefore, even if the electrode has an optimal structure at the initial stage of operation, if the pore shape and diameter change during battery operation, the battery characteristics will deteriorate.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to reduce the amount of expensive nickel used in electrodes incorporated in unit cells of molten carbonate lunar batteries. An object of the present invention is to provide an electrode for a fuel cell, which can maintain cell characteristics stably without significant changes in pore shape and pore diameter even during long-term cell operation.

[Summary of the invention]

The electrode according to the present invention has a porosity of 50 to 90 and is formed by sintering at least one of ceramic particles or fibers that are chemically stable against molten carbonate at the operating temperature of the battery.
%, and a metal layer that is electrochemically active for battery reactions and formed on the surface of the ceramic of this porous body by electroless plating.

More specifically, the ceramic constituting the porous body is selected from lithium aluminate, strontium titanate, lithium titanate, lithium zirconate, zirconium oxide, boron nitride, silicon nitride, and mixtures thereof. and the metal layer is
It is made of one metal selected from nickel, nickel-chromium alloy, nickel-cobalt alloy, and nickel-aluminum alloy.

〔Effect of the invention〕

According to the present invention, it is possible to obtain an electrode that uses a small amount of nickel-based metal, which can contribute to lowering the price of the entire battery. In addition, compared to those formed from porous nickel-based retention plates, there are fewer changes in pore shape and pore diameter, and therefore the fuel cell can operate stably over a long period of time.

[Embodiments of the invention]

The present invention will be explained in detail below.

Example 1 γ-type lithium aluminate with a diameter of 1μ and an average length of 5μ
Using ceramic particles of γ-LiAtO2), a methanol solution of 1 weight it % polyvinyl butyral binder was mixed and stirred under cooling, and then dried. The dry powder was cold pressed at 9/an2 to 200 and 1/2 in air.
After heating at 000° C. for 1 hour, the mixture was cooled to room temperature in the furnace.

A plate-shaped porous body (porosity 65
%) was sensitized for electroless nickel plating.

The sensitizing solution was 1oi7t S HCl2 and 4tt% H
The porous body was immersed in an aqueous solution consisting of Cl at room temperature for 2 minutes while stirring with ultrasonic waves. Next, after washing the sensitizing solution with water and drying the porous body, the porous body was
of PdCl2, 10 cc of HCl, and 4.5 t of water at 40° C. for about 2 minutes while stirring. Next, the activation liquid was washed with water, and the porous body was dried. The activated porous body is sealed in this way.
5 times solution of Mar 8680 (manufactured by Nippon Kanigen Co., Ltd.) with water.
It was immersed in a diluted nickel electroless plating solution. The plating solution temperature was 50° C. and the immersion time was 5 minutes. After plating was completed, it was washed with distilled water and dried to obtain a plate-shaped electrode.

The electrode made of the nickel-coated lithium aluminate porous material thus obtained has an average pore diameter of 3 to 4 μm1 about 6
It had a porosity of 2.

Example 2 Using the ceramic particles in Example 1 as strontium titanate, an electrode was created using the same procedure as in Example 1, consisting of a nickel-covered titanium strontium porous body with an average pore diameter of 1 to 3 μm and a porosity of about 60 parts. did.

Example 3 The ceramic particles in Example 1 were used as lithium titanate fibers, and the average pore size was adjusted to 2 to 3 μm using the same procedure as in Example 1.
An electrode made of a porous material with a porosity of 63% was prepared.

Example 4 An electrode made of a porous body was prepared in the same manner as in Example 1 except that cerium oxide was used as the ceramic particles in Example 1.

Example 5 As the electroless plating solution in Example 1, a nickel-cobalt alloy plating solution was used. The porous plate was sensitized and activated in the same manner as in Example 1, and the electroless plating solution was 301//l of cobalt chloride, 30fi/l of nickel chloride, 2001//l of rosocel salt, and 501//l of nickel chloride. A mixed solution of 1/l of ammonium chloride and 2011/l of sodium hypophosphite adjusted to -19/l with aqueous ammonia was used. Plating was performed by dipping at 90°C for 2 minutes. After plating, the porous plate was washed with distilled water and dried. The thus obtained electrode consisting of a porous plate of lithium aluminate had an average pore diameter of 3 to 4 μm, approximately 61
% porosity.

Example 6 Surface layer made of β-L1At02, diameter 3μ, inverseness 300
Alumina fibers of μ~1.5 mm are mixed with a 3% by weight butanol solution of polymethyl methacrylate, made into a slurry, and poured onto a tape cast 7A) r: Yoshi polyester film at room temperature of 90°C. Dry, thickness 0-
8 Tan's flexible sheet was tormented. Similarly, the average particle size is 0.
A slurry of 1 μm fine particles of β-N+hto2 was mixed with a getanol solution containing 3 parts by weight of polymethyl methacrylate, and the slurry was poured and dried to obtain a flexible sheet with a thickness of 6 parts. These two sheets were passed between rollers whose surfaces were coated with alumina to form a flexible dry sheet with a thickness of 1.3, and then placed between porous alumina plates and subjected to a pressure of approximately 20117σ2. Alumina with different average pore diameters in the thickness direction - γ-L +
An Ato 2 porous body was obtained. The average pore diameter on the alumina fiber side is 5 μ, and the β-Li 1102 side (after firing is γ-LIA
It is tO2. ) had an average pore diameter of 0.7μ.

In order to perform the sensitization and activation treatment only on the larger pore side of this double-pore porous sintered body, first impregnate only the smaller pore side with a brazing material with a melting temperature of 80°C to apply water repellent treatment. did. This was subjected to sensitization and activation treatment in the same manner as in Example 1.

Next, after removing the brazing material used as a water repellent in warm acetone, the electrode was decorated with electroless plating of nickel in the same manner as in Example 1. The nickel-coated side of this electrode has an average pore diameter of 4.58 m1 and a porosity of 65
%, the average pore diameter on the side not coated with nickel was 7 μm, and the porosity was 60%.

The electrodes made of the metal-coated ceramic porous bodies of Examples 1 to 5 were used as anodes, and the electrodes were heated to 40"10.
ノLI AZO2, 32w10ノ 2COλ1. , vertical 28" 10 Li2CO3 mixed powder was pressurized and heated to form a unit cell, and the battery was heated to 650°C.
The current-voltage characteristics of each were measured. As a result, 5
The characteristics after 00 hours were as shown in the figure. In the figure, I indicates the electrode of Example 1, ■ indicates the electrode of Example 2, and ■, ■
1 shows the characteristics using the electrode of Example 3.4, and 2 shows the characteristics using the electrode of Example 5, respectively.

As a comparative example, Ni-
Current after 500 hours for a unit battery with the same configuration except that a porous sintered body of 10% Cr alloy powder was used as an anode,
When the voltage characteristics were measured, the results indicated by X in the figure were obtained. As can be seen from this figure, it has been confirmed that the electrode of the present invention can provide almost the same performance as that using the conventional anode. In addition, the anode was taken out from each unit battery that had been operated for 500 hours, and charcoal was added with acetic anhydride. The salt was washed away and the pore size distribution was measured using a mercury intrusion string. the result,
In the anodes of Examples 1 to 5 of the present invention, the degree of increase in average pore diameter was within 5% of that before the start of the operational test. On the other hand, in the case of the conventional anode, it was about 15%, and it became clear that the degree of sintering progressed in the electrode of the present invention was small.

Example 60 Hydrogen gas, carbon dioxide gas,
Li2CO3/
was impregnated with carbonate with a molar ratio of 2CO3 to 62738.

This carbonate-impregnated body is used as an integral component of an anode and an electrolyte layer, and a unit cell is constructed using a nickel powder porous sintered body with an average pore diameter of 911fn and a porosity of 70cm as a cathode,
A power generation test was conducted at 650°C. The voltage of this unit battery at 150 mA/crn2 after 500 hours is 0.75
A value 50 mV higher than that of the comparative example described above was obtained. −
In addition, the AC resistance of the power supply battery measured at a current of 1 kHz was lower by 0.1Ω・sub2 than that of the comparison series, and such -(
4. It was confirmed that the forming element structure reduces the resistance caused by the gigang between the electrode and the electrolyte.

Note that the present invention is not limited to the embodiments described above.

For example, as a material for forming porous ceramic bodies,
Lithium zirconate, zirconium oxide, boron nitride,
Silicon nitride etc. can also be used.

Furthermore, nickel-chromium, nickel-aluminum, etc. can also be used as the metal for electroless plating on the ceramic porous body. Further, the electrode according to the present invention is
Of course, it can also be used as a cathode. Furthermore, Examples 1-
For the electrolyte layer of the battery combined with electrode 5, in addition to pressure-molding mixed powder of lithium aluminate and alkali metal carbonate electrolyte, fibers or powder of lithium aluminate, strontium titanate, or lithium zirconate may be used. It is also possible to use a porous body obtained by sintering a single substance or a mixture thereof, or a layer formed by depositing it on the electrode surface of Examples 1 to 5 by electrophoresis and impregnating it with an alkali metal carbonate electrolyte. be.

[Brief explanation of the drawing]

The figure is a diagram showing a comparison between the characteristics of a unit battery incorporating an electrode according to the present invention and the characteristics of a unit battery incorporating a conventional electrode.

Claims (6)

[Claims] (1) An electrode to be incorporated into a unit cell of a fuel cell using molten carbonate as an electrolyte, in which at least one of ceramic particles or fibers that are chemically stable to molten carbonate at the operating temperature of the cell is sintered. A porous body with a porosity of 50 to 90 is formed, and the ceramic of this porous body is electrochemically active against the cell reaction formed by electroless plating on the surface of the ceramic. 1. An electrode for a fuel cell, comprising a metal layer. (2) The porous body 'f6: The constituting ceramic is selected from lithium aluminate, strontium titanium, lithium titanate, lithium zirconate, zirconium oxide, cerium oxide, boron nitride, silicon nitride, and mixtures thereof. The electrode for a fuel cell according to claim 1, wherein the electrode is an electrode for a fuel cell according to claim 1. (3) The metal layer is formed of one kind of metal selected from nickel, nickel-chromium alloy, nickel-cobalt alloy, nickel-aluminum alloy. The fuel cell electrode described above. (4) The fuel mold hole electrode according to claim 1, wherein the metal layer is formed only on one side of the porous body divided into two in the thickness direction. (5) The side of the porous body on which the metal layer is not formed is
5. The electrode for a fuel cell according to claim 4, wherein the electrode is formed as a porous layer having a smaller average pore diameter from the side where the metal layer is formed. (6) The electrode for a fuel cell according to claim 5, wherein the porous layer having a small average pore diameter also serves as an electrolyte layer holding molten carbonate.