CERAMIC ION-SELECTIVE MEMBRANE ASSEMBLY

Abstract

A self-healing ceramic ion-selective membrane assembly including a ceramic ion-selective membrane, and at least one additive layer. The at least one additive layer includes an ionic ceramic material which is porous or ion-selective. The at least one additive layer having a metal cation diffusivity higher than the metal cation diffusivity of the ceramic ion-selective membrane. When a defect occurs through the ceramic ion-selective membrane, metal cation transport will be enhanced by orders of magnitude towards and into the defect, driven by the chemical or electrical potential difference between the two sides of the membrane.

Claims

1. A self-healing ceramic ion-selective membrane assembly, comprising: a ceramic ion-selective membrane, and at least one additive layer, wherein said at least one additive layer comprises an ionic ceramic material which is porous or ion-selective, wherein said at least one additive layer has a metal cation diffusivity higher than the metal cation diffusivity of the ceramic ion-selective membrane.

2. The self-healing ceramic ion-selective membrane assembly of claim 1, wherein the metal cation diffusivity of the at least one additive layer is at least 6 orders of magnitude higher than the metal cation diffusivity of the ceramic ion-selective membrane.

3. The self-healing ceramic ion-selective membrane assembly of claim 1, wherein the ceramic ion-selective membrane comprises a first oxide material and the at least one additive layer comprises a second oxide material.

4. The self-healing ceramic ion-selective membrane assembly of claim 3, wherein the first oxide material has a fluorite-related structure or a perovskite-related structure.

5. The self-healing ceramic ion-selective membrane assembly of claim 1, wherein during operation of the membrane assembly, a chemical and/or electrical gradient across the membrane causes the metal cations of the at least one additive layer to diffuse towards and into any occurring defect(s) through the membrane and form a plug.

6. The self-healing ceramic ion-selective membrane assembly of claim 1, wherein the ceramic ion-selective membrane comprises La6-xWO12-y, and the at least one additive layer comprises La2NiO4.

7. The self-healing ceramic ion-selective membrane assembly of claim 1, wherein during operation of the membrane assembly, a chemical and/or electrical gradient across the membrane causes metal cations of the at least one additive layer to react with the ceramic ion-selective membrane in the presence of the atmosphere on an opposite side and a third material is formed in the defect of the ceramic ion-selective membrane.

8. The self-healing ceramic ion-selective membrane assembly of claim 7, wherein the ceramic ion-selective membrane comprises La2NiO4 and the at least one additive layer comprises CoO.

9. The self-healing ceramic ion-selective membrane assembly of claim 1, further comprising two additive layers made of different oxide materials, the two additive layers are arranged on opposite sides of the ceramic ion-selective membrane.

10. The self-healing ceramic ion-selective membrane assembly of claim 9, wherein during operation, when a defect through the ceramic ion-selective membrane occurs, a gradient in chemical potential will be established between the two oxide materials, and the two oxide materials react and form a third oxide material in the defect.

11. The self-healing ceramic ion-selective membrane assembly of claim 9, wherein the oxide material of one of the two additive layers is selected from the group of La6-xWO12-y, Nb-doped TiO2, and TiNb2O7 and the oxide material of the other additive layer is selected from the group of NiO and Ca- or Sr-doped LaMnO3.

12. The self-healing ceramic ion-selective membrane assembly of claim 1, comprising two additive layers made of different oxide materials, wherein the ceramic ion-selective membrane is formed by a reaction between the two additive layers when the two additive layers are in contact with each other.

13. The self-healing ceramic ion-selective membrane assembly of claim 12, wherein one of the two additive layers comprises an oxide material selected from the group of La6-xWO12-y and Nb-doped TiO2, TiNb2O7, and the other additive layer comprises an oxide material selected from the group of NiO and Ca- or Sr-doped LaMnO3.

14. A method of forming a self-generating and self-healing ceramic ion-selective membrane assembly, comprising the steps of: providing a first layer made of an oxide material, contacting the first layer with a second layer made of an oxide material different than the first layer, reacting the first and second layers during heating to an operating temperature of the membrane assembly to form an ion-selective membrane having a metal cation diffusivity lower than the metal cation diffusivities of the first and second layer.

15. The method of claim 14, wherein the membrane assembly is heated above the operating temperature to accelerate the formation of the ion selective membrane.

16. A method of using the self-healing ceramic ion-selective membrane assembly of claim 1, in high-temperature electrochemical devices which have ceramic electrolyte membranes, selected from solid oxide fuel cells (SOFC), solid oxide electrolyser cells (SOEC), proton ceramic fuel cells (PCFC) and proton ceramic electrolyser cells (PCEC).

17. A method of using the self-healing ceramic ion-selective membrane assembly of claim 1, in applications which use mixed ionic-electronic conduction to achieve selective gas permeation, selected from oxygen transport membranes (OTM) or hydrogen transport membranes (HTM) for gas separation processes.

18. A method of using the self-healing ceramic ion-selective membrane assembly of claim 1, comprising initiating catalytic reactions in catalytic membrane reactors.

Description

FIGURES

[0048] FIGS. 1 a-d show the chemical creep repair of a self-healing ion-selective membrane assembly.

[0049] FIGS. 2 a-d show the reactive creep repair of a self-healing ion-selective membrane assembly.

[0050] FIGS. 3 a-e show the reaction growth repair of a self-healing ion-selective membrane assembly.

[0051] FIGS. 4 a and b show the self-generating and self-healing ion-selective membrane assembly.

[0052] An example on how a self-healing ceramic ion-selective membrane according to the present invention will repair itself (self-heal) when a defect occurs during use is schematically shown in FIGS. 1a to 1d. FIG. 1a shows the intact membrane assembly, i.e. without any defects. The membrane assembly consists of a dense functional ion-selective layer 1 and a porous or ion-permeable additive layer 2. The dense functional ion-selective layer 1 is gastight (when there are no defects) and only permits transport of certain ions through the gastight layer.

[0053] In FIG. 1a, on the additive layer side 3, the anion component activity is lower than the anion component activity on the ion-selective layer side 4. For example in an operating fuel cell, there will be a chemical gradient across the membrane assembly such as a lower oxygen partial pressure on the additive layer side 3 compared with the higher oxygen partial pressure on the ion-selective layer side 4. FIG. 1b shows the situation where a defect has resulted in an opening 5 through the membrane assembly. Because of the difference of the anion component activity on both sides of the membrane assembly, the metal ions of the additive layer will immediately start to diffuse toward and into the opening and thereby begin repairing the defect; see FIG. 1c. The additive layer compound creeps towards the high anion component activity side. FIG. 1d shows the completely repaired membrane assembly, where the opening is plugged with the same material as of the additive layer 2.

[0054] FIGS. 2a-2d schematically show another self-healing process of a self-healing ceramic ion-selective membrane according to the present invention. FIG. 2a shows the intact membrane assembly consisting of a dense functional ion-selective layer 1 and a porous or ion-permeable additive layer 2. FIG. 2b shows the situation where a defect has resulted in an opening 5 through the membrane assembly. FIG. 2c shows the beginning of the repair of the opening 5. In this case, the additive layer compound diffuses towards the high anion component activity side and in the presence of this higher anion component activity reacts with the functional material of the ion selective layer and starts forming a third material 6. The materials of the dense functional ion-selective layer 1 and the porous or ion-permeable additive layer 2 are selected so that they will chemically react when a defect resulting in an opening through the membrane occurs. FIG. 2d shows the completely repaired membrane assembly, having a plug 7 closing the opening with the newly formed third material.

[0055] FIG. 3 schematically shows the self-healing process of another embodiment of the self-healing ceramic membrane assembly of the present invention. FIG. 3a shows an intact membrane assembly consisting of a dense functional ion-selective layer 1 and two porous or ion-permeable additive layers, 2 and 2, arranged on each side of the dense functional ion-selective layer 1. Depending on the materials selected for the two additive layers, two routes are possible; 3b-3c or 3d-3e. FIGS. 3b and 3d show the situation where a defect has resulted in an opening through the membrane assembly and the self-healing has started. Depending on the materials selected for the two porous or ion-permeable additive layers 2 and 2, either a non-functional product phase or a functional ion-selective product phase is formed. FIGS. 3c and 3e show completely repaired membrane assemblies, wherein the defect in FIG. 3c is plugged by a non-functional product phase and in FIG. 3e, the defect is plugged by a functional ion-selective product phase.

[0056] As a first example of formation of a functional product phase, the additive layers 2 and 2 may be made of TiNb.sub.2O.sub.7 and Ca-doped or Sr-doped LaMnO.sub.3. Ions from these materials can react to form the proton conducting electrolyte Ca-doped LaNbO.sub.4, which seals the defects (Route 3d-3e) As another example, the additive layers 2 and 2 may be made of NiO and La.sub.6-xWO.sub.12-y, where x and y are deviations smaller than 1.0 from the integer stoichiometric coefficients, which react to form a gas separation membrane material of LaNiO.sub.3 or La.sub.2NiO.sub.4 (Route 3d-3e).

[0057] FIG. 4 schematically shows the process of preparing a self-generating ceramic membrane assembly according to the invention. FIG. 4a shows the start where two porous or ion-permeable additive layers, 2 and 2, are contacting each other. The materials of the two additive layers 2 and 2 are selected so that they may react and form a dense functional ceramic ion-selective membrane during heating to an operating temperature of the membrane assembly to form an ion-selective membrane. FIG. 4b shows the completed membrane assembly having a dense functional ion-selective layer 1 between the two porous or ion-permeable additive layers 2 and 2. This membrane assembly will also be self-healing, because when a defect occurs through the dense functional membrane the two porous or ion-permeable additive layers 2 and 2 will react and the defect will be repaired.