JP4931423B2 - Heat-resistant conductive member, alloy member for fuel cell, current collecting member for fuel cell, cell stack, fuel cell - Google Patents

Description

  The present invention relates to a heat-resistant conductive member obtained by coating the surface of an alloy containing Cr with a surface layer, an alloy member for a fuel cell, a current collector for a fuel cell, a cell stack, and a fuel cell.

  In recent years, for example, various fuel cells in which a stack of fuel cells is accommodated in a storage container have been proposed as next-generation energy.

  A solid oxide fuel cell is configured by storing a cell stack in which a plurality of fuel cells are electrically connected in a storage container, and flowing a fuel gas (hydrogen) to the fuel electrode side of the fuel cell, and the air electrode side Power is generated at a high temperature of 600 to 900 ° C. by flowing air (oxygen) through the tube. In order to electrically connect the fuel cells, a felt-shaped or plate-shaped current collecting member has been conventionally used.

  As such a current collecting member, an alloy having a high electrical conductivity is employed, and since it is used at a high temperature, a heat resistant alloy is desirably employed. As such a heat resistant alloy having a high electrical conductivity, Cr is 10 to 10. An alloy containing 30% by mass is generally used.

  However, when a current collecting member made of an alloy containing Cr is interposed between the fuel cells and a plurality of fuel cells are electrically connected, if the fuel cell generates power for a long time, Cr in the current collecting member Diffuses to the outside of the current collector, and the diffused Cr reaches the interface between the air electrode and the solid electrolyte and degrades the activity. This phenomenon is referred to as so-called Cr poisoning, and leads to a result that lowers the power generation capacity of the fuel cell.

In order to prevent such Cr poisoning, conventionally, the surface of an alloy containing Cr is coated with Mn, Fe, Co, and Ni (see Patent Document 1).
Japanese National Patent Publication No. 11-501764

  However, as described in Patent Document 1, when the surface of the Cr-containing alloy is coated with Mn, Fe, Co, Ni, this surface layer can suppress the diffusion of Cr from the Cr-containing alloy to some extent. Although it was possible, there was still a problem that the amount of Cr diffusion was still large.

  An object of the present invention is to provide a heat-resistant conductive member, an alloy member for a fuel cell, a current collecting member for a fuel cell, a cell stack, and a fuel cell with little Cr diffusion.

The heat-resistant conductive member of the present invention is characterized in that the surface of a heat-resistant alloy containing 10 to 30% by mass of Cr is covered with a surface layer made of an oxide containing Zn and Mn.

  In the heat-resistant conductive member of the present invention, the diffusion of Cr from the alloy to the surface layer is suppressed by the presence of the surface layer made of an oxide containing Zn and Mn, and so-called Cr poisoning can be suppressed. The reason is not clear, but it is considered that Cr is difficult to dissolve in the surface layer due to thermodynamic stability.

In the heat-resistant conductive member of the present invention, the oxide is composed of at least one of a spinel structure, a corundum structure, a wurtzite structure, and a rock salt structure, or a structure similar to these because of thermodynamic stability. Is good. For example, the composition formula is represented by (Zn, Mn) Mn ₂ O ₄ or the like for a spinel structure, (Zn, Mn) ₂ O ₃ for a corundum structure, or ZnO for a wurtzite structure or a rock salt structure. -MnO solid solution. In addition, these oxides may contain metals such as Fe, Ni, Co, and Cu within a range in which Cr diffusion can be suppressed. In such a heat-resistant conductive member of the present invention, particularly excellent Cr diffusion prevention An effect can be obtained.

The surface layer is made of (Zn, Mn) Mn ₂ O ₄ , but is mainly made of (Zn, Mn) Mn ₂ O ₄ and may contain a ZnO—MnO solid solution.

  The fuel cell alloy member of the present invention is characterized in that the heat-resistant conductive member is used for a fuel cell. Such an alloy member for a fuel cell has conductivity as an alloy, and suppresses Cr diffusion by the surface layer, thereby suppressing so-called Cr poisoning.

  Moreover, the current collecting member for a fuel cell according to the present invention is characterized in that the current collecting member for collecting current from the fuel cell comprises the above-mentioned alloy member for fuel cell. In such a current collector for a fuel cell, as described above, it has good conductivity as an alloy, and the diffusion of Cr from the current collector made of an alloy containing Cr is suppressed, so that Cr is a fuel cell. It is possible to prevent the activity from deteriorating by reaching the interface between the air electrode of the cell and the solid electrolyte.

  Furthermore, the cell stack of the present invention is characterized in that the fuel cell current collector is interposed between a plurality of fuel battery cells and electrically connected. The fuel cell and the fuel cell current collecting member are joined and electrically connected by a conductive ceramic material. Such a cell stack is stored in a storage container to constitute a fuel cell.

  According to the cell stack and the fuel cell of the present invention, a fuel cell with a low voltage drop and excellent long-term reliability can be obtained.

According to the present invention, the oxide layer containing Zn and Mn can significantly suppress the diffusion of Cr from the heat-resistant alloy containing 10 to 30% by mass of Cr, and reaches the interface between the air electrode and the solid electrolyte. So-called Cr poisoning can be prevented, and a decrease in power generation capacity over time of the fuel cell can be suppressed.

  FIG. 1 is a perspective view showing a current collecting member 20 for a fuel cell according to the present invention, and FIGS. 2 and 3 are explanatory views showing a covering state of a surface layer of the current collecting member 20 shown in FIG. Is a cross-sectional view taken along line AA shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB shown in FIG.

As shown in FIG. 1, the current collecting member 20 for a fuel cell according to the present invention is configured, for example, by processing a heat-resistant alloy plate into a comb blade shape and alternately bending adjacent blades to the opposite side. The current collecting member 20 is configured such that a surface layer 202 made of a material containing Zn and Mn is provided on the surface of a current collecting body 201 made of an alloy containing Cr, and the surface layer 202 is exposed to the outside. And is the outermost layer of the current collecting member 20. The entire surface of the current collector body 201 is covered with a surface layer 202 made of an oxide containing Zn and Mn. The current collecting member for a fuel cell of the present invention is not limited to the shape shown in FIG. 1, and may be, for example, a cylindrical shape or a mesh shape.

As the current collector body 201, an alloy containing 10 to 30% by mass of Cr having high conductivity and heat resistance, such as an Fe—Cr alloy, a Ni—Cr alloy, or the like is employed. The surface layer 202 is a metal oxide containing Zn and Mn, for example, (Zn, Mn) Mn ₂ O ₄ , but the metal oxide containing Zn and Mn hardly dissolves Cr. Has the effect of suppressing the diffusion of.

  Since Cr in the current collector body 201 is gasified and diffuses from the gap, the surface layer 202 needs to be densely provided so as to cover at least the entire surface of the current collector body 201. At this time, the surface layer 202 is coated by dipping (a dip coating method in which the current collector body 201 is immersed in the surface layer paste) or plating or vapor deposition, but dipping is desirable in terms of cost.

  The thickness of the surface layer 202 depends on the lifetime of the current collector body, but in the case of dipping, it is preferably 5 to 100 μm, more preferably 10 to 50 μm. By setting the thickness to 5 μm or more, generation of voids due to air entrainment can be prevented, and by setting the thickness to 50 μm or less, internal stress due to a difference in thermal expansion from the current collector body 201 can be suppressed to the minimum. The formation of the layer 202 can be facilitated, and the decrease in conductivity can be suppressed.

  2 and 3, the surface of the current collector body 201 containing Cr is covered with a surface layer 202 made of an oxide containing Zn and Mn, and the surface layer 202 is exposed. A layer made of an oxide can be formed on a part of the surface layer 202 from the viewpoints of handling, protection, and the like.

A powder containing mainly (Zn, Mn) Mn ₂ O ₄ is prepared in advance using ZnO and MnO powder, and this powder can be used as a surface layer paste for dipping. Further, ZnO and MnO powder mixed in a predetermined ratio so as to form a powder mainly composed of (Zn, Mn) Mn ₂ O ₄ can be used as a surface layer paste for dipping.

  The fuel cell current collector configured as described above can exhibit the following effects. That is, in order to generate electric power in the solid oxide fuel cell, it is necessary to set the temperature to about 600 to 1000 ° C., and the current collecting member 20 is also used at a high temperature of 600 to 1000 ° C. From the main body 201, Cr is going to diffuse as Cr gas. However, in the case of the present invention in which the surface layer 202 made of a material containing Zn and Mn is provided on the surface of the current collector body 201, the diffusion of Cr to the outside can be suppressed by the surface layer 202. Thereby, the so-called Cr poisoning in which the Cr gas reaches the interface between the air electrode and the solid electrolyte can be prevented.

  In the above embodiment, the comb-shaped current collecting member 20 has been described. However, in the present invention, the shape of the current collecting member is not limited, and various shapes can be adopted.

(Cell stack, fuel cell)
A cell stack and a fuel cell produced using the current collecting member 20 of the present invention will be described. FIG. 4 shows a fuel cell, and FIG. 5 shows a cell stack in which the fuel cell is electrically connected by a current collecting member.

  As shown in FIG. 5, the current collecting member 20 for a fuel cell of the present invention is disposed between the fuel cells of FIG. 4, and a plurality of fuel cells are electrically connected to form a cell stack of the present invention. ing. First, the fuel cell will be described.

  As shown in FIG. 4, the fuel battery cell 1 includes a flat plate-like support substrate 10 provided therein at appropriate intervals in the width direction and having a plurality of fuel gas passages 16 extending in the axial direction. It has a structure in which various members are provided on the support substrate 10.

  The support substrate 10 is porous and conductive, and the cross section is composed of a flat portion and arc-shaped portions at both ends of the flat portion. A porous fuel electrode layer 2 is provided so as to cover one of a pair of opposed surfaces of the flat portion and arc-shaped portions on both sides thereof, and further, a dense solid electrolyte so as to cover the fuel electrode layer 2 A layer 3 is laminated, and an air electrode layer 4 made of a porous conductive ceramic is laminated on the solid electrolyte layer 3 so as to correspond to the fuel electrode layer 2. A dense interconnector 5 is formed on the other surface of the flat portion where the fuel electrode layer 2 and the solid electrolyte layer 3 are not laminated. An air electrode material layer 14 made of an air electrode material is formed on the surface of the interconnector 5. The air electrode material layer 14 is not necessarily formed. As is clear from FIG. 4, the fuel electrode layer 2 and the solid electrolyte layer 3 extend to both sides of the interconnector 5 and are configured so that the surface of the support substrate 10 is not exposed to the outside.

  In the fuel cell 1 having such a structure, the portion of the fuel electrode layer 2 facing the air electrode layer 4 operates as a fuel electrode to generate electric power. That is, an oxygen-containing gas such as air is allowed to flow outside the air electrode layer 4, and a fuel gas (hydrogen) is allowed to flow through the gas passage 16 in the support substrate 10, and is heated to a predetermined operating temperature. Then, an electrode reaction of the following formula (1) is generated, and power is generated by generating an electrode reaction of the following formula (2), for example, in the portion that becomes the fuel electrode of the fuel electrode layer 2.

Air electrode: 1 / 2O ₂ + 2e ⁻ → O ²⁻ (solid electrolyte) (1)
Fuel electrode: O ²⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻ (2)
The current generated by the power generation is collected through the interconnector 5 attached to the support substrate 10.

  As shown in FIG. 5, the current collecting member 20 of the present invention is interposed between the plurality of fuel cells as described above, and is electrically connected to form a cell stack. That is, the current collecting member 20 is joined to the air electrode layer 4 of one fuel cell 1 by the conductive joining material 25 made of porous conductive ceramic, and the current collecting member 20 is connected to the other fuel cell adjacent thereto. It joins to the air electrode material layer 14 of the cell 1 with the electroconductive joining material 25, Thereby, the some fuel cell 1 is electrically connected in series, and the cell stack is comprised. As the conductive bonding material 25, an air electrode material is usually used, and for example, La-Co-based conductive perovskite complex oxide, Ag, Ag-Pd, or the like is used.

  Although not shown, such a cell stack is arranged in a manifold to which fuel gas is supplied, and the fuel gas supplied into the manifold passes through the gas passage 16 of the fuel cell 1 upward.

  In the fuel cell, the cell stack described above is accommodated in a storage container, and a fuel gas introduction pipe for supplying fuel gas such as city gas and an air introduction pipe for supplying air are disposed in the storage container. Composed.

  In the above embodiment, the case where the fuel cell alloy member of the present invention is used as the current collecting member 20 has been described. However, a component made of another heat-resistant alloy housed in the housing container, for example, for the above-described manifold And can be used for a reformer.

  Moreover, although the case where the heat-resistant conductive member of the present invention is used for a fuel cell has been described, for example, those having conductivity in a high temperature atmosphere such as a lead portion of an oxygen sensor, specifically, conductive in a conventional high temperature atmosphere. It can be used as a substitute for Pt, which has been used to show sex. By the way, lead parts such as oxygen sensors use precious metals such as Pt in order to ensure conductivity at high temperatures, and are expensive. However, by using the heat-resistant conductive member of the present invention, the lead parts should be made inexpensive. Can do.

First, ZnMn ₂ O ₄ powder with an average particle size of 0.6 μm, Fe ₂ O ₃ powder with an average particle size of 0.4 μm, Co ₃ O ₄ powder with an average particle size of 0.5 μm, NiO powder with an average particle size of 0.5 μm Then, an acrylic binder and a mineral spirit as a diluent were blended in a weight ratio of 100: 5: 72 to prepare a surface layer dipping solution.

  Thereafter, a current collector body made of a Fe—Cr heat-resistant alloy plate (containing 75% by mass of Fe, containing the remaining Cr, Mn, and Ni) having a thickness of 0.4 mm, a width of 20 mm, and a length of 120 mm is wetted with the dipping solution. In order to improve the properties, the film was heat-treated at 1050 ° C. in the atmosphere, then immersed in a dipping solution, applied to the entire surface of the current collector body, and dried. Thereafter, the binder was removed at 130 ° C. for 1 hour and at 500 ° C. for 2 hours, and then baked at 1050 ° C. for 2 hours to form a surface layer having a thickness of 15 μm.

In a slurry obtained by adding La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ (LSCF) powder having an average particle size of 0.5 μm, an acrylic binder, and a glycol solvent. Then, the current collecting member on which the surface layer was formed was dipped, and a LSCF film having a thickness of 15 μm was formed on the surface layer surface to prepare a test piece (sample).

This test piece was manufactured and exposed to an air atmosphere containing 20% water vapor at 850 ° C. for 100 hours, and then the cross section of the LSCF film was confirmed by EPMA (wavelength dispersive X-ray microanalyzer). EPMA analysis using JXA-8100 manufactured by JEOL, as the measurement condition, accelerating voltage 15kV, probe current 2.0 × ^{10 -7} A, was analyzed area 50 [mu] m × 50 [mu] m. The spectroscopic crystal was LiF. A count proportional to the Cr content was measured at 10 μm from the interface between the surface layer and the LSCF layer toward the LSCF layer, and the results are shown in Table 1. Further, based on the count of Cr in the surface layer made of Fe ₂ O ₃ , the ratio was set to 1.0, and the ratio with the count of Cr in each surface layer was determined and described in parentheses in Table 1.

  The LSCF film easily reacts with Cr to form a reaction product. Therefore, when Cr diffuses from the surface layer to the outside, the LSCF film always forms a reaction product of Cr. Therefore, the smaller the Cr count in the cross section of the LSCF film, the smaller the amount of Cr diffusion from the surface layer to the outside.

In addition, by analyzing the formed surface layer with a TEM (transmission electron microscope), the ZnMn ₂ O ₄ powder, Fe ₂ O ₃ powder, Co ₃ O ₄ powder, and NiO powder used respectively existed as crystals. Confirmed that. Moreover, when the surface layer cut out using FIB (focused ion beam processing apparatus) was expanded 30,000 times with TEM (transmission electron microscope), it was confirmed that the surface layer had no voids and was dense. For the analysis of TEM, JEM2010F manufactured by JEOL Ltd. was used and observed at an acceleration voltage of 200 kV.

As can be seen from Table 1, the sample using ZnMn ₂ O ₄ powder (sample No. 2) was 100 hours after production (after exposure to 850 ° C. in an atmosphere containing 20% water vapor for 100 hours) The count ratio is as small as 0.05, and it can be seen that Cr diffusion is very small in the fuel cell alloy member of the present invention.

It is a perspective view which shows an example of the current collection member coat | covered with the surface layer of this invention. It is sectional drawing along the AA line shown in FIG. It is sectional drawing along the BB line shown in FIG. It is a cross-sectional perspective view of a fuel battery cell. It is explanatory drawing of the fuel cell stack of this invention.

Explanation of symbols

20 ... Current collecting member 201 ... Current collecting body 202 ... Surface layer

Claims (7)

A heat-resistant conductive member obtained by coating the surface of a heat-resistant alloy containing 10 to 30% by mass of Cr with a surface layer made of an oxide containing Zn and Mn. The heat-resistant conductive member according to claim 1, wherein the surface layer is made of (Zn, Mn) Mn ₂ O ₄ .   An alloy member for a fuel cell, wherein the heat-resistant conductive member according to claim 1 or 2 is used for a fuel cell.   A current collecting member for a fuel cell, wherein the current collecting member for collecting current from the fuel cell comprises the alloy member for a fuel cell according to claim 3.   A cell stack, wherein the fuel cell current collector is interposed between a plurality of fuel cells and electrically connected.   6. The cell stack according to claim 5, wherein the fuel cell and the current collecting member for the fuel cell are joined and electrically connected by a conductive ceramic material.   7. A fuel cell comprising the cell stack according to claim 5 or 6 in a storage container.

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