JPH031453A - Solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To obtain steady, excellent cell operation characteristics without use of expensive platinum by using nickel in a fuel electrode and LaMnO3 doped with barium in an oxidizing agent electrode in a fuel cell using a BaCeO3 family solid electrolyte. CONSTITUTION:A BaCeO3 family ceramic used as a solid electrolyte has a composition of BaCe1-xMxO3-alpha (wherein M is Nd, La, or Y, 0<=x<=0.15, alpha is 0-0.075) which contains 5-15% Nd, La, or Y in BaCeO3. BaCe0.9 Nd0.1O3-alpha and BaCe0.9Y3-alpha are preferable and the latter is a high temperature type proton conductive oxide and shows the highest conductivity. By using nickel as a fuel electrode, voltage and current density show linear relation and a fuel cell shows steady operation characteristics. The reason why LaMnO3 doped with barium is used as an oxidizing agent electrode is that it has an affinity to the BaCeO3 family solid electrolyte having perovskite crystal structure, and the electrode resistance and polarization resistance are lowered. Its composition is represented by La1-xBaxMnO3-alpha (x<0.15, preferably 0.05<x<0.10, and 0.025<alpha<0.05).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high-temperature fuel cell using a BaCe0a system as a solid electrolyte, and particularly to a BaCe0. The present invention relates to solid oxide fuel cells.

[Conventional technology]

High-temperature solid electrolyte fuel cells have almost no activation polarization, have high output voltage, high output current density, and high energy conversion efficiency. Furthermore, they can be operated with low-purity and inexpensive fuel gas, and exhaust gas It has the advantage of being able to be used for the next stage of power generation because of its high temperature, and is currently being developed as a third-generation fuel cell. Among these, high-temperature solid electrolyte fuel cells that use zirconia stabilized with calcia, ittria, etc. as a solid electrolyte (oxygen ion conductor) are the most actively researched and developed.

The present inventors have been conducting research on high-temperature fuel cells using perovskite oxides as solid electrolytes, and
Results have already been announced regarding various fuel cells using aCeO3-based and CaT+[]3-based sintered bodies as solid electrolytes. Among them, BaCeO3-based ceramics exhibit relatively high proton-oxide ion mixed conductivity at high temperatures;
Since it functions stably, it is promising as a solid electrolyte for fuel cells.

[Problem to be solved by the invention]

As mentioned above, BaCeO3-based ceramics are excellent as solid electrolyte materials for high-temperature fuel cells, but platinum, which has been used as an electrode material so far, is expensive, so we have developed an inexpensive and high-performance electrode to replace it. material is desired.

Therefore, an object of the present invention is to provide an inexpensive, high-performance, and stable electrode material to replace platinum in BaCeO3 solid electrolyte fuel cells.

[Means to solve the problem]

In order to achieve the above object, the present invention is characterized in that a Raced 3 solid electrolyte overall electrolyte temperature solid electrolyte fuel cell uses LaMnO3 doped with nickel for the fuel electrode and Ba for the oxidizer electrode. Provides high temperature fuel cells.

In order to eliminate the use of platinum as an electrode material, L was doped with nickel in the fuel electrode and 8a in the oxidizer electrode.
It is preferable to use aMnO3, but if nickel is used for the fuel electrode and platinum is used for the oxidizer electrode, or conversely, Ba-doped LaMnO3 is used for the oxidizer electrode and platinum is used for the fuel electrode. This also has the effect of halving the amount of platinum used as an electrode material, and these cases are also within the scope of the present invention.

BaCe0. used as a solid electrolyte in the present invention. , based ceramics are based on BaCeO3 and Nd
, composition aCe+ containing about 5 to 15% La or Y
-JxO3-& (where M is Nd, La or Y, 0≦x0.15, and α is 0 to 0.075). As such, aCeO, based ceramics have higher proton conductivity than known 5rCe03 based high temperature proton conductive ceramics, and
At high temperatures above ℃, it exhibits oxide ion mixed conductivity, so
Excellent as a solid electrolyte for fuel cells. Preferred are BaCeo, 9NdO,+03-” and BaCe
o-sYo, +03-tx, especially the latter at 1000℃
It exhibits the highest conductivity of the existing high-temperature proton conductive oxides at 7 XIO''Scm-'.

When nickel is used as the fuel electrode in the present invention, the voltage and output current density show a linear relationship, and the operating characteristics are stable.

Although the output current that can be extracted is lower than that of a battery using a platinum fuel electrode, it has been found that the operating characteristics are stable, and that the output current can be improved by creating a microstructure that facilitates fuel gas diffusion. It is an excellent material as an alternative to platinum because it is a low-cost material.

LaMnO3 doped with Ba as an oxidant electrode in the present invention
is used for B, which has a perovskite crystal structure.
aCe0. It has good compatibility with solid electrolytes, has low electrode material resistance and low polarization resistance, and exhibits good performance.

The composition of LaMn[l, doped with Ba is La, xB
aJn03m (o<x<0.15, preferably 0.05
< x < 0.10.0.025 < a < 0
．． 05), Lao-5Bao, JnO3-
& is particularly preferable in terms of performance.

The structure of the high-temperature solid electrolyte fuel cell of the present invention is not particularly limited, except that a specific material is used as the electrode material, and conventional methods can be followed (eg, Japanese Patent Application No. 1983-96757). Also, common fuels (hydrogen, carbon oxide, hydrocarbons, etc.) and oxidizers (pure oxygen, air) are used.

[For production]

Ni is BaCe0. A catalytic effect can be expected if methane or the like is used as a fuel without causing a solid-state reaction with the system electrolyte. Ba-doped AlnQ3 is a perovskite-type oxide similar to the electrolyte BaCeO3, and both contain Ba, so it is compatible and has high electronic conductivity. Therefore, these are 13a
Excellent as an electrode material for CE03 electrolyte fuel cells.

〔Example〕

Example 1 CeO2, Ban, Nd2O3 powder at 15.3
:15.5 :3.36 ratio (weight ratio), calcined in air at 1300℃ for 10 hours, and then finely ground to produce 2 tons.
/cn hydrostatic pressure, then molded in air at 1500℃ for 10
A dense sintered body was obtained by firing for several hours. This is 12mm in diameter
It was cut out into a disk shape with a thickness of approximately 0.5 m, and the surface was thoroughly polished to obtain an electrolyte disk. One side of this disk was coated with platinum paste, and the other side was coated with nickel paste, and baked to form an air electrode and a fuel electrode, respectively. The thickness of each electrode material is 50I! It was ra. This was sandwiched between alumina porcelain tubes via a glass gasket to separate the two polar chambers. When heated, the glass gasket becomes semi-molten, preventing fuel and air from leaking to the outside.

When hydrogen as a fuel and air as an oxidizer were introduced into each electrode chamber, a stable voltage of about 0.95V was generated, and a steady current could be obtained by connecting the load.

Figure 1 shows the performance of this fuel cell. From FIG. 1, it is recognized that in this fuel cell, there is a linear relationship between the terminal voltage and the output current density at 800 to 1000°C. Although the output current that can be extracted from this battery was lower than that of a battery using a platinum fuel electrode (dashed line in FIG. 1), the decrease was slight and the operating characteristics were stable. The electrolyte thickness of this battery is approximately 500J! Ia and its maximum output is about 0
．． 11W/Cn, but if this thickness is made 50 to 100 Ja, which is comparable to the zirconia batteries currently being developed, the maximum output will be 0.3 to 0.7 even considering polarization at the electrodes.
W/c++f can be expected.

Next, methane was introduced into the same cell as a fuel gas together with water vapor (concentration 13-30%). When the exhaust gas on the fuel electrode side of this cell was analyzed by gas chromatography, it was found that the temperature was 1000℃.
In this case, H2 is about 33%, CD is about 10%, and there is also a trace amount of C2H due to the coupling reaction of several percent of CO2 and methane.
,,C2116 was included. This composition was almost the same as that of the platinum anode.

In other words, in this test cell, regardless of the type of fuel electrode material,
Since the ratio of H2 and CD was approximately 3, it was thought that the main reaction was the steam reforming reaction of methane CH4+H20→3H2+CO of the following formula.

Figure 2 shows the operating characteristics of this battery. With this battery,
Although the short-circuit current was lower than that of batteries using hydrogen as fuel,
The operating characteristics were stable.

Next, in order to evaluate the performance of this type of fuel cell, we calculated the electrode reaction resistance and electrode material resistance (contact resistance with electrolyte) of the nickel electrode material, and found that they were each 0.23.
~0.37ΩcrA and 0.11~0.21ΩC[+! This value was sufficient for practical use.

SE of the nickel fuel electrode and platinum fuel electrode used in the above experiment
When the M photo was taken, it was found that the platinum electrode had many pores with a size of several microns uniformly distributed, but the nickel particles were relatively large and distributed in the form of islands, and the effective reaction area was currently quite small. That seems to be the case. Therefore, if electrodes are attached with such microstructure in mind, it is thought that the performance of batteries using nickel can be further improved.

Example 2 BaCeo, 5oNdo, +o in the same manner as Example 1
An Os-* solid electrolyte fuel cell was fabricated. However, platinum was used for the fuel electrode, and various conductive oxides were used for the air electrode. Specifically, Sr-doped LaMn was used as the air electrode.
AlJn doped with O3, LaCoTo, and Ba
03 and LaCoO3, and convert them into BaCeo, 5
oNdo, 1003-& A fuel cell was formed with the air electrode side of the solid electrolyte disk.

Next, an operation test of the cell was conducted under the same conditions as in Example 1, using hydrogen as the fuel and air as the oxidizing agent.

Then, in the same manner as in Example 1, the electrode material resistance and polarization resistance were determined. The results are shown in the table below.

Resistance (air electrode side) operating temperature in hydrogen-air fuel cell: 1000°C As shown in the table, Sr-doped system (LaMnO
, and 1aco03 series), both the electrode material resistance and polarization resistance are high, and the compatibility with the electrolyte is poor. however,
LaMnOs doped with Ba, which is a component of the electrolyte
In the case of using B, the compatibility with the electrolyte was improved, and in particular, the one doped with 40% Ba showed good performance in both electrode material resistance and polarization resistance.

FIG. 3 shows the operating characteristics of a fuel cell using LaMnO3 doped with 40% Ba as the air electrode material.

As described above, when Ba-doped LaMnO3 is used as the fuel electrode and the N11 oxidizer electrode in a BaCeO3-based solid electrolyte fuel cell, a stable fuel cell with excellent operating characteristics can be obtained. Both properties are somewhat inferior to those of platinum, but the nickel electrode has a fine structure that facilitates fuel gas diffusion, and Ba-doped LaMn0. By making the electrode have a structure with a high effective reaction area that is compatible with the electrolyte, the properties will be further improved, and its value as an alternative material to expensive platinum will be further improved.

〔Effect of the invention〕

According to the present invention, a BaCe 0° solid electrolyte fuel cell is provided that uses an electrode material having stable and excellent cell operating characteristics in place of platinum.

[Brief explanation of drawings]

1 to 3 are graphs showing the operating characteristics of various solid oxide fuel cells according to the present invention. Current density [mA 7cm2] Current density [mA/cm21 2nd

Claims (1)

[Claims] 1. A solid electrolyte fuel cell characterized in that a BaCeO_3-based electrolyte is used as a solid electrolyte and nickel is used for the fuel electrode. 2. A solid electrolyte fuel cell characterized in that a BaCeO_3-based electrolyte is used as a solid electrolyte and Ba-doped LaMnO_3 is used as an oxidizer electrode.