Process for producing a solid oxide fuel cell by depositing an electrically conductive and gas permeable layer on a porous support substrate

Abstract

A process for depositing an electrically conductive, preferably perovskitic layer uses a pulsed sputtering process. The layer has a low diffusivity for the elements in the iron group and is especially suitable for use in solid oxide fuel cells (SOFC). An assembly of the electrically conductive ceramic layer on a porous support substrate is also provided.

Claims

1. A process for producing a metal-supported solid oxide fuel cell, the process comprising the following steps: providing a porous metallic support substrate formed of sintered grains of a Fe-based alloy, the support substrate having an open-pore structure, being gas permeable and having a density of 40% to 70% of a theoretical density; depositing an electrically conductive ceramic diffusion barrier layer directly on the metallic porous support substrate by a pulsed sputtering process retaining the open-pore structure of the substrate and a gas permeability thereof, forming a coated porous metallic support substrate that is gas permeable; and applying an anode in direct material contact with the coated porous support substrate to produce a support structure with an anode of the metal-supported solid oxide fuel cell.

2. The process according to claim 1, wherein the ceramic layer has a perovskitic structure.

3. The process according to claim 1, which further comprises using an oxide-ceramic sputtering target in the pulsed sputtering process.

4. The process according to claim 1, which further comprises using a sputtering target in the pulsed sputtering process, wherein a concentration of elements in the sputtering target differs at most by 5% from a concentration of respective elements in the layer.

5. The process according to claim 1, which further comprises depositing the layer at a frequency of a pulsed voltage of 1 to 1000 kHz.

6. The process according to claim 5, which further comprises depositing the layer at a frequency of the pulsed voltage of 100 to 350 kHz.

7. The process according to claim 1, which further comprises depositing the layer with a voltage root-mean-square value of +100 to 1000 V.

8. The process according to claim 7, which further comprises depositing the layer with a voltage root-mean-square value of +100 to 500 V.

9. The process according to claim 1, which further comprises depositing the layer with a mean power density of 1 to 30 W/cm.sup.2.

10. The process according to claim 1, which further comprises using an inert gas as a process gas with a pressure of 110.sup.4 to 910.sup.2 mbar.

11. The process according to claim 10, which further comprises using argon as the process gas.

12. The process according to claim 1, wherein the layer has a structural formula ABO.sub.3, where A includes one or more elements selected from the group consisting of La, Ba, Sr and Ca; and B includes one or more elements selected from the group consisting of Cr, Mg, Al, Mn, Fe, Co, Ni, Cu and Zn.

13. The process according to claim 1, which further comprises depositing the layer with a thickness of 0.1 to 5 m.

14. The process according to claim 1, which further comprises depositing the layer with a density>99% of a theoretical density.

15. The process according to claim 1, which further comprises depositing the layer with an impurity content<0.5% by weight.

16. The process according to claim 15, wherein the impurity content is <0.1% by weight.

17. The process according to claim 1, wherein the porous substrate is gas permeable and the porous substrate with the conductive ceramic layer is gas permeable.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is an illustration diagrammatically showing a configuration of a perovskitic layer on a porous substrate; and

(2) FIG. 2 is a group of photographs showing EPMA measurements of a porous substrate with an LSC layer and an Ni layer deposited thereon, after ageing for 1000 h at 850 C.

DETAILED DESCRIPTION OF THE INVENTION

(3) Reference will now be made in detail to the figures of the drawings, with which examples are described.

Example 1

(4) A porous support substrate having a composition of 26% by weight Cr, 0.5% by weight Y.sub.2O.sub.3, 2% by weight Mo, 0.3% by weight Ti and 0.03% by weight Al and a remainder of Fe was coated through the use of a pulsed, non-reactive DC process. This was done using an Edwards sputter coater fitted with an LSM target (La.sub.0.8Sr.sub.0.2Mn oxide) with a diameter of 72 mm. A sputtering power of 400 W, a voltage of 149 V, a current of 2.01 A, a frequency of 350 kHz (with a pulse duration of 1.1 s) and a process pressure of 5*10.sup.3 mbar were also set. This produced LSM layers being 3 m thick and having the composition La.sub.0.8Sr.sub.0.2Mn oxide (LSM).

(5) FIG. 1 diagrammatically shows the configuration of the deposited layers on the porous support substrate.

Example 2

(6) Porous and dense support substrates having a composition of 26% by weight Cr, 0.5% by weight Y.sub.2O.sub.3, 2% by weight Mo, 0.3% by weight Ti and 0.03% by weight Al and a remainder of Fe were coated through the use of a pulsed, non-reactive DC process. This was done using an Edwards sputter coater fitted with an LSC target (La.sub.0.8Sr.sub.0.2Cr oxide) with a diameter of 72 mm. A sputtering power of 400 W, a voltage of 149 V, a current of 2.01 A, a frequency of 350 kHz (with a pulse duration of 1.1 s) and a process pressure of 5*10.sup.3 mbar were also set. This produced LSC layers being 3 m thick and having the composition La.sub.0.8Sr.sub.0.2CrO.sub.3.

(7) The LSC layers were then coated with an APS nickel layer being 50 m thick. This structure of an iron/chromium alloy (porous and non-porous)LSC layer (3 m)APS nickel layer (50 m) was used to investigate the diffusion barrier effect of the thin LSC layer with respect to nickel into iron or iron into nickel. In this case, the structure was aged in air for 100 h at 850 C. to 1000 C. The diffusion properties were documented using EPMA measurements, as seen in FIG. 2. The LSC layer prevents diffusion of nickel into iron or iron into nickel under the stated test conditions. The LSC layers deposited have a high electrical conductivity (corresponding to the target used), a high density>99.9%, a homogeneous layer structure and a smooth surface with a mean roughness value which is the same as the mean roughness value of the substrate. As a result of the process, no foreign atom inclusions can be measured through the use of EPMA and EDX.