RU2280926C2 - High-temperature solid-electrolyte fuel cell - Google Patents

Abstract

FIELD: electrical engineering; high-temperature solid-electrolyte fuel cells.

SUBSTANCE: proposed high-temperature solid-electrolyte fuel cell has effectively functioning part-to-part metal interconnections made of iron and chromium alloy with cobalt and nickel newly introduced therein, proportion of ingredients being as follows, mass percent: chromium, 5 - 15; nickel, 30 - 45; cobalt, 20 - 35; iron, the rest; nickel and cobalt to chromium content ratio ranges between 4 and 13. Alloy may incorporate associated impurities, such as carbon, nitrogen, silicon, sulfur, phosphor, and copper whose total content is not over 1% which does not impair alloy quality.

EFFECT: enhanced service life and operating reliability of fuel cell.

2 cl, 1 tbl, 4 ex

Description

The invention relates to the field of electrical engineering, to devices for the direct conversion of chemical energy into electrical energy, in particular to high-temperature fuel cells with a solid electrolyte, including zirconia ceramics.

The relevance of the problem being solved lies in the fact that the efficiency of the operation of devices of this type, in addition to other significant factors, is also influenced by the materials from which individual elements of components and parts are made, such as for example down conductors, interconnectors, bipolar boards (plates), separator boards and others.

Among the requirements for materials for the above metal interelement compounds, the most important are the following:

1. Low thermal coefficient of linear expansion (TEC) close to that of zirconium ceramics (for example, ZrO ₂ + (8 ÷ 12)% Y ₂ О ₃ ) in the temperature range 20 ÷ 1000 ° С, which is in the range (7 ÷ 12, 5) × 10 ^-6 K ^-1 . The consistency between the thermal expansion coefficient of these two materials is especially important in the region of low (below 500 ° С) temperatures, at which relaxation processes are hindered.

2. The stability of the properties during thermal cycling in a wide temperature range of 20 ÷ 1000 ° C.

3. Heat resistance up to 1000 ° C.

Known electrochemical battery, the collector of which is made of powder (fibers) of carbon or graphite [US Patent No. 4960655, NKI 429-192, publ. 10/02/1990]. Such a collector can be used for both the negative and the positive electrode. However, a battery with a graphite or carbon down conductor is not designed to operate at elevated temperatures (up to 1000 ° C), since such a down conductor burns above 750 ° C. In addition, the thermal expansion of such a carbon collector (TECL = (3 ÷ 5) × 10 ^-6 K ^-1 ) is much less than the TECL of a solid electrolyte. This can lead to large internal stresses and structural failure during thermal cycling (20 ÷ 1000 ° C).

High temperature solid electrolyte fuel cells are known in which metallic inter-element compounds are made of heat-resistant alloys based on Ni-Cr and Co-Ni-Cr. In particular:

- Co (50-55%) - Ni (9-10%) - Cr (20%) - W (14-15%) coated with La ₂ O ₃ / SrCO ₃ [US patent 4950562, NCI 429/32, publ. . 08/21/1990];

- Inconel 600 (Ni-Cr (15.5%) - Fe (8%) or Ni-Cr (23%) coated with lanthanum-manganese oxide or lanthanum-manganese oxide with the addition of strontium oxide [US patents 5049458, NKI 429 / 32, published on September 17, 1991];

- Ni (80%) - Cr (14%) - Fe (6%) with La-Mn perovskite coating on the oxygen side [US patent 5034288, NCI 429/32, publ. 07/23/1991];

- A composite material consisting of a metal alloy Ni (50-80%) - Cr (50-20%) - Fe (0-15%) and 50-85% oxide (SiO ₂ or Al ₂ O ₃ or a mixture of SiO ₂ - Al ₂ About ₃ ) [US patent 5279906, NKI 429/30, publ. 01/18/1994];

- Ni-Cr (15%) - Ti (2.5%) - Al (0.7%) - Fe (7%) - Nb (1%) - Si (0.4%) - Mn (0.5 %) - C (0.04%) [US patent 4997727, NKI 429/33, publ. 03/05/1991];

The above alloys have a fairly good heat resistance in oxygen-containing environments, but they have very high (≈ (16 ÷ 20) × 10 ^-6 K ^-1 ) values of thermal expansion coefficient, significantly higher than the thermal expansion coefficient of zirconium ceramic (≈ (7 ÷ 12.5) × 10 ^{- 6} K ^-1 ). Such large differences in the thermal expansion of alloys and ceramics can lead to high internal stresses during heating of ceramic-metal compounds and their destruction.

Known high-temperature solid electrolyte fuel cells in which metallic inter-element compounds are made of chromium-based alloys with various additives:

- Cr + 5% Fe + Y ₂ O ₃ [EP 578855, IPC H 01 M 8/02, publ. 01/19/1994];

- Cr + (5-15)% Ni [DE 4009138, IPC H 01 M 8/12, publ. 09/26/1991];

- Cr + (3-10) at.% Fe and / or (0.5-5) at.% Of rare earth elements or their oxides [US patent 5407758, NCI 429/33, publ. 04/18/1995].

Chromium-based alloys have fairly good heat resistance, but have serious drawbacks.

- The technology of smelting and metallurgical redistribution is very complex and expensive. In particular, special and expensive smelting methods are required, including electron-beam and vacuum-arc remelting. Deformation-heat treatment at elevated temperatures should be carried out in high vacuum.

- Low ductility, which greatly complicates the machining processes in the manufacture of final products.

- Thermal expansion differs significantly from the thermal expansion coefficient of zirconium ceramic, which can lead to high internal stresses in metal-ceramic compounds during the operation of fuel cells.

These disadvantages significantly limit the use of chromium-based materials for the manufacture of conductive structures of fuel cells.

Fuel cells are known in which current collectors and bipolar boards are made of iron-based alloys containing the following components, wt.%:

Chromium 8.25 ÷ 46.5 Molybdenum 1.25 ÷ 14.0 Nickel 2.25 ÷ 40.5 Nitrogen 0,02 ÷ 1 Iron Rest

The alloy may additionally contain the following components, wt.%:

Carbon 0 ÷ 0.03 Silicon 0 ÷ 1.0 Copper 0 ÷ 2.0 Manganese 0 ÷ 6.5 Niobium 0 ÷ 0.25 Phosphorus 0 ÷ 0,045 Sulfur 0 ÷ 0.03

[US patent 6300001, NKI 429/44, publ. 10/09/2001].

This material is mainly used in membrane type fuel cells. Its chemical composition does not allow one to obtain LTEC close to the thermal expansion of zirconium ceramics.

The closest analogue to the claimed invention in terms of its technical nature and technical result is a high-temperature solid electrolyte fuel cell, in which the collector is made of a metal oxide-resistant alloy containing, wt.%:

Chromium 25.0-30.0 Rare earth metals 0.1-2.0 Rhenium or one of the other elements of the platinum group 2.0-4.0 Iron Rest

[RF patent No. 2068603, IPC N 01 M 8/10, publ. BI No. 30 dated 10.27.1996].

Depending on the composition, these alloys in the temperature range of 20 ÷ 1000 ° C have a thermal expansion coefficient from 9.5 × 10 ^-6 to 11 × 10 ^-6 K ^-1 , which is quite close to the thermal expansion coefficient of zirconium ceramics containing 8% Y ₂ O ₃ . The disadvantages of these alloys include the following:

- Inconsistency according to the thermal expansion coefficient with zirconium ceramic containing 10 and 12% Y ₂ O ₃ .

- The danger of possible embrittlement in the range of 450-600 ° C as a result of separation of the solid solution ("brittleness 475"), which can lead to the destruction of products from these alloys during thermal cycling in the range of 20 ÷ 1000 ° C.

- Low strength and reduced ductility, which significantly impairs the performance of metal / ceramic compounds.

The problem to which the invention is directed, is to develop a high-temperature fuel cell with an extended service life, increase the reliability of the fuel cell through the use of metal, efficient interconnects: down conductors, interconnectors, bipolar boards (plates), separator boards and others, made of heat-resistant alloy with thermal expansion coefficient close to that of zirconium ceramic.

A new technical result of the invention is to increase the efficiency of the fuel cell due to the use of a heat-resistant material, stable during thermal cycling, with low thermal expansion coefficient in the temperature range 20 ÷ 1000 ° C, and also with thermal expansion coefficient similar to thermal expansion of zirconium ceramic containing 8-12 % Y ₂ O ₃ , especially in the range 20 ÷ 600 ° C, in which relaxation processes in metal-ceramic compounds are difficult.

An additional technical result is to maintain the stability of the properties of the alloy.

The indicated technical results are achieved by the fact that in the known high-temperature solid electrolyte fuel cell, metal intercell elements are made of an alloy containing iron and chromium, to which, according to the invention, cobalt and nickel are additionally introduced at the following content of components, wt.%: Chromium - 5 ÷ 15 , nickel - 30 ÷ 45, cobalt - 20 ÷ 35, iron - the rest, while the ratio of the total content of Nickel and cobalt to the chromium content is in the range 4 ÷ 13.

In addition, the alloy may further contain concomitant impurities, such as carbon and / or nitrogen, and / or silicon, and / or sulfur, and / or phosphorus, and / or manganese, and / or copper, and / or oxygen, which with their total content not exceeding 1%, the properties of the alloy are not impaired.

The introduction of nickel and cobalt is necessary for the formation of local atomic and magnetic configurations in the alloy in which the iron atoms in the immediate environment have from 3 to 6 nickel and / or cobalt atoms.

The maximum nickel content, which provides the required set of local configurations, is 45%. When the nickel content is less than 30%, the solid solution becomes unstable and at temperatures below 200 ° C the γ⇒α transformation occurs with the formation of a body-centered cubic (BCC) phase, the TEC of which substantially exceeds 12 × 10 ^-6 K ^-1 . In addition, the formation of the bcc phase affects the mechanical properties, as well as heat resistance and corrosion resistance.

Cobalt also provides an increase in the Curie temperature and, as a result, an increase and expansion of the temperature range in which the required TEC values are realized. With a cobalt content of more than 35% and less than 20% in the alloys, it is not possible to realize the required set of local atomic configurations (3–6 Co and / or Ni atoms near the iron atoms).

Chromium in a concentration of 5-15% is introduced to give the alloys of the Fe-Ni-Co system an increased level of heat resistance. The minimum chromium content, which is necessary to increase the heat resistance, is 5%. At lower chromium concentrations, the alloys are not heat resistant. If the chromium content exceeds 15%, then the technological properties are deteriorated, in particular, ductility decreases significantly, and the thermal expansion coefficient significantly increases.

Impurities in these concentrations do not significantly affect the properties of the proposed alloys.

The proposed alloy composition provides high stability properties during thermal cycling 20-1000 ° C. This is achieved due to the formation of a face-centered (fcc) structure in the proposed alloys, which provides higher phase stability compared to Fe-Cr-based ferritic alloys. In Fe – Ni – Co – Cr alloys with fcc crystal lattice, no delamination processes occur.

The ratio of the total nickel and cobalt content to the chromium concentration in the range 4–13 provides, on the one hand, the necessary level of heat resistance, and on the other hand, the required values of thermal expansion coefficient and stability of the fcc structure.

Thus, the use of the proposed fuel cell provides a heat-resistant, stable during thermal cycling material with low thermal expansion coefficient in the temperature range 20 ÷ 1000 ° C, as well as with thermal expansion coefficient close to thermal expansion of zirconium ceramics containing 8-12% Y ₂ O ₃ , features in the range of 20 ÷ 600 ° C, in which relaxation processes in metal / ceramic compounds are difficult.

The proposed heat-resistant Invar alloy can be used for the manufacture of down conductors and metal interelement compounds of high-temperature solid fuel cells with solid electrolyte. The conductive components made of the claimed alloy provide a low level of internal stresses in the metal / ceramic compounds, especially in the temperature range 100 ÷ 500 ° C, in which the relaxation processes in the metal are inhibited and, as a result, the long-term, stable operation of fuel cells with solid electrolyte.

The proposed heat-resistant invar alloy can also be used for the manufacture of heat-resistant structures, which must be coordinated by thermal expansion coefficient with ceramics or other materials characterized by thermal expansion coefficient in the range of ≈ (5 ÷ 11) × 10 ^-6 K ^-1 at temperatures from 20 to 1000 ° C.

The possibility of industrial application can be confirmed by the following examples of specific performance.

Example 1

Alloys of various compositions were smelted for the manufacture of metal inter-element compounds of high-temperature fuel cells with a solid (oxide) electrolyte. Smelting was carried out in a high-frequency open or vacuum induction furnace with a capacity of 1 ÷ 50 kg. Ingots were forged at 1000 ÷ 1150 ° С. LTEC measurements were carried out in the range 25–900 ° С using the dilatometric method using a Linseis type dilatometer.

The chemical compositions and the results of measuring the properties of the studied alloys are given in table 1. The data on thermal expansion presented in table 1 refer to three temperature ranges: 20–100 ° С, 20–500 ° С, and 20–800 ° С.

From table 1 it can be seen that, compared with the prototype, the thermal expansion of the proposed alloys is closer to the thermal expansion coefficient of ZrO ₂ (10-12)% Y ₂ O ₃ ceramics, especially in the range of 100 ÷ 500 ° C, in which relaxation processes in the metal are difficult. This leads to lower stresses in the metal / ceramic compounds during thermal cycling. In addition, the proposed alloy has a higher level of strength properties and high stability of properties during thermal cycling while maintaining the thermal expansion coefficient close to zirconia ceramics.

Chemical composition, wt.%

TECL × 10 ^-6 K ^-1 in the temperature range (° C) Ni With Cr Fe FROM N Mn Si Cu S R one hundred 500 800 34 thirty fourteen 22 4.6 10.0 13.0 14.6 thirty thirty 10 thirty 6.0 10.0 12,2 13.5 34 thirty 6 thirty 10.7 10.3 11.3 13.6 32 twenty 6 42 8.7 8.1 9.6 12.8 34.1 29.8 6.2 29.28 0.1 0.01 0.25 0.16 0.05 0.02 0,03 10.3 10,2 11,4 13.8 29.8 30.1 9.9 29.51 0.1 0.34 0.02 0.02 6.1 10,2 12.3 13,4 Prototype 0.4% Y, 2.0% Ru 29th 68.6 0 10-11

Claims (2)

1. High temperature solid electrolyte fuel cell, in which the metal intercell elements are made of an alloy containing iron and chromium, characterized in that the alloy further comprises cobalt and nickel in the following ratio of components, wt.%: Chromium 5 ÷ 15 Nickel 30 ÷ 45 Cobalt 20 ÷ 35 Iron Rest the ratio of the total content of Nickel and cobalt to the chromium content is in the range of 4 ÷ 13. 2. The high temperature solid electrolyte fuel cell according to claim 1, characterized in that the alloy contains related impurities such as carbon, nitrogen, silicon, sulfur, phosphorus, manganese and copper, while their total content does not exceed 1%.