WO2010037670A1

WO2010037670A1 - Tubular high-temperature fuel cell, method for the manufacture thereof and fuel cell system comprising the same

Info

Publication number: WO2010037670A1
Application number: PCT/EP2009/062275
Authority: WO
Inventors: Alessandro Zampieri; Robert Fleck; Horst Greiner
Original assignee: Siemens Aktiengesellschaft
Priority date: 2008-09-30
Filing date: 2009-09-22
Publication date: 2010-04-08
Also published as: EP2342777A1; DE102008049694A1

Abstract

Fuel cells known from the prior art include full-ceramic high-temperature fuel cells in particular, wherein a cathode-side ceramic substrate is the support for the solid electrolytes and the electrodes. According to the invention, a metal substrate (10, 20, 40, 50) is provided as a support for the functional layers, wherein the metal substrate is porous for allowing reactants and reaction products to flow therethrough. A fuel cell system constructed of said fuel cells is suitable for operation at lower operating temperatures, in particular at temperatures of between 500 and 700°C. The novel fuel cells can be manufactured using comparatively simple powder-metallurgical methods.

Description

description

TUBULAR HIGH TEMPERATURE FUEL CELL, METHOD FOR THE PRODUCTION THEREOF, AND A FUEL CELL PLANT CONTAINING SUCH A METHOD

The invention relates to a tubular high-temperature fuel cell according to the preamble of claim 1. In addition, the invention relates to the thus constructed fuel cell system and to a method for their production.

Solid electrolyte high-temperature fuel cells are essentially characterized by a ceramic solid electrolyte, which is generally formed as an oxide ceramic layer between two see electrodes. Such a fuel cell (SOFC = S_olid Oxide Fuel Cell) generally has an operating temperature between 600 ⁰ C and 1000 ⁰ C. At this temperature, the electrochemical conversion is optimized. Low operating temperatures tend to lower the costs of a fuel cell system.

In the power range> 100 kW, only high-temperature fuel cell systems (SOFC) with a tubular design have so far been operated worldwide. The associated cells are all-ceramic, with the various functional layers are applied to a ceramic carrier. The carrier is located on the air side of a cell and consists of Kathodenmateπal. This design has significant advantages over the planar fuel cell. The potential of such fuel cells is different

Jobs have been presented to the public, eg. For example, with the publication "Fuel Cells Systems: Towards Commerz- alition" in Power Journal 2001, pp. 10-13 (publisher: Siemens AG).

In the latter fuel cell systems, the high operating temperatures, which are necessary for a full ceramic cell, although deliberately accepted, as on the other Extremely low degradation values can be achieved in these systems, which are in the range below 0.1% in the relevant for the assessment of fuel cells "1000 hours operation".

With all-ceramic tubular fuel cells Proble ^¬ me may occur in the production of Kathodentragers. Inhomogeneities in the pipe increase the probability of breakage of the carrier and thus influence the production output. Furthermore arise in all-ceramic cells because of

Variety of manufacturing steps increased manufacturing tolerances, which may also limit the usability.

It has already been discussed in the literature that fuel cells operating at low or medium temperatures contain a number of new possibilities. This applies in particular to the choice of materials in the cells and the associated peripherals. Low working temperatures of about 600 ^° C. allow the use of high-alloyed stainless steels and / or other metal alloys in the individual fuel cell module and in the associated periphery.

On this basis, it is an object of the invention to propose a new tubu ^¬ lar fuel cell with ceramic electrolyte, which in particular gives the possibility of a reduced operating temperature in order to build a fuel cell system, and to specify suitable manufacturing method.

The object is solved erfmdungsgemaß by a fuel cell according to claim 1. The use of a series connection of such fuel cells for constructing a corresponding fuel cell system is the subject matter of patent claim 15 and a method for producing such a fuel cell or fuel cell system constructed therewith. Further developments of the fuel cell or fuel cell system and of the associated production method are disclosed in US Pat given the dependent claims. An essential object of the new hard ceramic fuel cell ^¬ that on the cathode side, a porous metallic exchangers for the functional layers (cathode, electrolyte, anode) is present. With such metallic carriers such fuel cells can be operated in the range of 400 ° C to 800 ° C (optimally at 600 ⁰ C). At such temperatures, considerably less demands are placed on the structure of the periphery, but also on the structure of the fuel cell itself. Due to the reduction of the temperature, the production costs can be reduced. Likewise, at lower temperatures, better mechanical properties of the cells can be achieved and there is the potential for better process control. This applies in particular also to the production of the electrodes and / or of the electrolyte as functional layers on the metallic support.

The life of such a fuel cell is hardly affected by the use of a metallic carrier. The wall thickness of the metallic Tragers can be significantly reduced compared to the ceramic execution. As a result, the polarization resistances influencing the oxygen diffusion also become smaller on the cathode side. Furthermore, high-alloyed stainless steel powders are significantly less expensive than ceramic cathode powders such as the well-known LSM or LCM.

Overall, the invention resulted in significant cost savings with at least equivalent electrochemical performance of the entire cell.

The new porous metallic carrier for the functional layers can be produced by conventional powder metallurgical processes. These are rather cheaper compared to ceramic manufacturing processes. From the prior art, in particular the publication NP Branden et al. Although the construction of a fuel cell with a metallic carrier on the anode side is known in particular in "Journal of Materials Engineering and Performance" 13 (2004), pages 253 to 256. However, the use of a metal substrate on the cathode side becomes first-time with the invention presented as technically feasible for a functioning fuel cell system.

A further significant advantage of the present invention with the metal substrate on the cathode side is that the sheet resistance on the cathode side can thereby be kept negligible. This is one of the weak points in all SOFCs with anodal side truncated tubular cell design. There, the electrons z. B. be distributed with silver wire on the cathode.

When using porous metal structures on the cathode side, it must be taken into account that the chromium oxide cover layers which form on the surface of the chromium-containing metal structures are relatively poorly conductive and the chromium compounds which escape from these surfaces evaporate the electrochemical properties of the cathode can affect negatively. These properties are taken into account in the invention in that special alloys are selected which show a particularly slow growth of the chromium oxide topcoat (eg Plansee Werk ^¬ ITIl fabric). Since the ohmic resistance is dependent on the layer thickness, a very small voltage drop across the oxide layer can be expected here. As a thermally activated process, the chromium evaporation is also highly temperature-dependent and is therefore significantly reduced when the operating temperature is lowered. In the event that the evaporation rates have to be lowered even further, the carrier can be provided with corresponding barrier layers.

As suitable materials for use as a porous carrier substrate for the cathode, electrolyte and anode in the According to the invention SOFC are known from the prior art Sin ^¬ termetalle, for example, provided on the basis of high-alloy, ferritic stainless steels with high chromium contents. In particular, types of materials known in the art as CROFER22APU (Thyssen Krupp) or IT11-IT14-ITM26 (Plansee) or ZMG32 (Hitachi) appear suitable.

Further details and advantages of the invention will become apparent from the following description of exemplary embodiments play with reference to the drawing in conjunction with the claims.

It show in a rough schematic representation

1 shows the longitudinal section through a tubular fuel cell, FIG. 2 shows the cross section through a tubular fuel cell according to FIG. 1,

FIG. 3 shows the cross-section through an arrangement with several adjacent triangular air ducts (Δ design),

FIG. 4 shows the structure of the metallic carrier in a fuel cell according to the HPD principle,

5 shows the layer sequence of the functional layers on a ^¬ me-metallic substrate and Figure 6 is a metallographic micrograph of a porous metal structure for use as a substrate in FIG. 5

Identical parts are provided in the figures with corresponding reference numerals. The figures are partly described together.

FIG. 1 shows the section through a tubular fuel cell 1 with a closed end. Here, 10 represents the metallic carriers of a sintered material having a specified ^differently bene porosity, wherein the functional layers are applied to the outer side of such tubular assembly. The functional layers consist in detail of the cathode K, the electrolyte E and the anode A. In each case intermediate layers may be present.

From the sectional view of Figure 2 results in same shall, where is here essential that for contacting a plurality of fuel cells 1 on the periphery of Brennstoffzel ^¬ le in the axial direction, a narrow strip 5 of non-porous material, that is present from solid, well leitfahigem metal is. This strip 5 is referred to in practice as the inner connector 5. About the interconnectors 5 individual tubular fuel cells can be contacted, in particular electrically connected in series. It is essential that, in deviation from the prior art, the sleeve 10 is made of porous metallic material. For this purpose, a sintered stainless steel alloy with comparatively high chromium content may be considered

As an alternative, such a structure 2 is ^illustrated in FIG. 3, in which a metal substrate is folded in such a way that triangular structures with individual air channels 35 are formed. The individual air ducts 35 have an approximately Δ-shaped form. On the metallic support structure 20, the functional layers are again applied with cathode, electrolyte and anode. The base surface of the metallic carrier is formed by a metallically dense plate 25 of conductive material, whereby an interconnector is realized. Via the interconnector 25 individual Gebil ^¬ de 2, 2 ',., Each of which realize a so-called Δ-cell, stacked. This produces fuel cell bundles with fuel cells 2, 2 'connected electrically in series,

To illustrate an HPD cell, reference is made to FIG. 4 in addition to FIG. Here, a metallic porous carrier part 40 is present, which has a plurality of rectangular air channels 45 and on one side the functional layers with cathode K, electrolyte E and anode A and on the other side again with a metallically dense layer 25 ', which forms the interconnector , is completed. 5 shows a specific sequence of layers of function is ^¬ layers with layer structure 100 shows. Substantially, in turn, the porous metallic structure 50 as a carrier of the functional layers. A section of such a structure is shown in FIG. 6, which alternately shows metallic particles 51 and pores 52. The magnification is visible here from the dimension. The cut is pitted so that the particles 51 result in bright areas. Clearly visible so the open porosity of sintered metallic material, the egg ^¬ NEN sufficient passage for the reactants or reaction products is ensured. The porosity is> 5%, for example about 10%.

All described with reference to Figures 1 to 4 fuel cell geometries with porous metallic structures as a support for the cathode can with a "closed-end" design, for example, when using so-called. "Air Feed Tubes" or with an "open-end" design getting produced.

The structures described above have considerable advantages over the all-ceramic structures. It is essential that the metallic substrates allow lower operating temperatures than the ceramic fuel cells. This is also associated with lower temperatures in the units of the fuel cell periphery. Although these properties are known in principle. However, not be ^¬ denied the use of a porous metallic Tragers for the functional layers on the air side. If appropriate, the metallic carrier can also be coated with further layers in order to hinder the penetration of Cr into the cathode. In particular, a diffusion barrier layer can be applied between the substrate and the cathode. The diffusion barrier layer may be:

(A) A thin and dense film on the inner and outer surfaces of the metal substrate. Possible manufacturers The proceedings for this are, for. As CVD, dip-coating or galvanic treatment,

(B) See porous mesh (eg LaCrO ₃ ) on the outer surface of the metal substrate. Possible manufacturing processes are z. Plasma spraying, LPPS, APS or wet

Powder Spraying with subsequent thermal treatment.

Alternative (A) inhibits Cr evaporation and Cr solid-state diffusion, thereby reducing unwanted degradation of the cathode. In alternative (B) above all the solid diffusion of Cr is hindered.

The production of a metallic cathode-substrate cell can, for. B. be done as follows. - Preparation of a tubular metallic cathode substrate carrier z. B. by extrusion or so-called.

Casting.

- If necessary, a coating of the carrier with a Cr diffusion barrier layer z. B. by CVD. If the support material contains aluminum, an AL ₂ O ₃ diffusion protection layer is formed during the sintering process "in situ".

- As cathode materials in a known manner z. For example, LSF, LSCF, LSC, nickel latex or mixed oxides (LSM / YSZ, ScSZ, GCO) can be applied by PVD or plasma spraying. Reference is made to the relevant literature. In the present case Warme- to be finishing about 800 ⁰ C avoided.

The electrolyte is applied in a process which yields directly dense layers. Here come APS,

LPPS and PVD techniques are considered. The electrolyte can be made from the following materials: YSZ, ScSZ, GDC, SDC. The electrolyte may also consist of several of these materials to z. B. to prevent interfacial reactions with the cathode and anode.

Ni and / or Cu-based cermets which are applied by the abovementioned processes are suitable as the anode. - The interconnector can be applied either as a ceramic layer on the metal substrate, wherein the above-mentioned methods can be used. Alternatively, the relevant surface areas of the substrate are sealed with a metal solder.

In all cases, this results in practical solid electrolyte fuel cells with tubular design, namely cylindrical, in HPD or Delta execution, as described in detail with reference to Figures 1/2, 3 and 4.

To construct the functional layers, reference is again made below to FIG. 5. The stack of functional layers in this case consists of a diffusion barrier layer 101 ', the cathode 101, the electrolyte layer 102 and the anode 103, which are applied to the metallic support 50 as a porous structure.

The porous metal layer 50 consists of sintered metal particles, as already described above with reference to FIG. In particular, there are stainless steels in question. Since stainless steels have proven with comparatively high chromium content than ge ^¬ suitable for the support layer, however, care must be taken that little chrome material cell when operating the fuel evaporates even at the low operating temperature.

Possibilities for minimizing the chromium evaporation are described in detail in a parallel patent application of the applicant with the same application specification and the description "Method for protecting a chromium-containing, sintered metal substrate for use in a high-temperature fuel cell and associated high-temperature fuel cell or fuel cell system".

In the tubular high-temperature fuel cell (SOFC) described above, it is essential that the support for the functional layers has a porous metal structure on the air side (cathode side) of the fuel cell. For sintered metals based on stainless steel in question. The functional layers can be applied thereon, for example by means of PVD methods, if necessary magnetron sputtering.

Claims

claims

1. tubular high-temperature fuel cell with ceramic solid electrolyte, which consists of cathode and anode as electrodes with intermediate solid electrolyte layer, said cathode, anode and solid electrolyte layer form functional layers on a support, characterized in that the support for the functional layers (A, E, K ) is a porous metal structure (10, 20, 40, 50) on the air side (cathode side).

2. Fuel cell according to claim 1, characterized by a triangular or quadrangular shape of the air ducts (35, 45) whose edges are rounded.

3. Fuel cell according to claim 2, characterized in that a group of fuel cells with triangular air ducts forms a common structure.

4. Fuel cell according to claim 1, characterized in that the porous structure of the metallic support is permeable to the diffusion of the reactants or reaction products.

5. Fuel cell according to claim 4, characterized in that the porosity of the sintered metal is large 5%.

6. Fuel cell according to claim 4, characterized in that the metallic carrier (10, 20, 40, 50) is a sintered stainless steel.

7. Fuel cell according to claim 4, characterized in that a FeCrR alloy is used, wherein R stands for further metallic components.

8. Fuel cell according to claim 4, characterized in that FeCrTiNb alloys are used.

9. Fuel cell according to one of claims 1 to 8, characterized in that the working temperature of the Brennstoffzel ^¬ le is between 400 and 800 ° C, preferably between 500 and 700 ° C, to lower the kinetics of the oxidation of the metal substrate as much as possible ,

10. Fuel cell according to claim 9, characterized in that the tubular and / or Δ-shaped structure of the individual fuel cells to a seal-free composite of the fuel cell bundle has.

11. Fuel cell according to claim 9, characterized in that an interconnector for the electrical connection of individual fuel cells is present.

12. Fuel cell according to claim 1, characterized in that the electrolyte consists of several partial layers.

13. Fuel cell according to claim 1, characterized in that the cathode consists of partial layers.

14. Fuel cell according to one of the preceding claims, characterized for stationary or mobile applications

15. Use of a series connection of fuel cells according to one of the preceding claims, in particular according to claim 10, in a fuel cell system

16. A method for producing a fuel cell and for building a fuel cell system in which individual tubular or HPD fuel cells are combined into a bundle and electrically connected in series or in groups, characterized by sintered metallurgical process for the construction of the porous metallic support structure.

17. The method according to claim 16, characterized in that functional layers are applied to the porous metallic carrier structure.

18. The method according to claim 17, characterized in that the functional layers are applied to the porous metallic support structure by PVD method.

19. The method according to claim 18, characterized in that the functional layers are applied to the porous metallic support structure by magnetron sputtering.