METHOD OF MANUFACTURING OF A MEMBRANE WITH SURFACE FIBRE STRUCTURE, MEMBRANE MANUFACTURED BY THIS METHOD AND USE OF SUCH MEMBRANE

Abstract

Method of manufacturing of a membrane with surface fiber structure, in particular for use in an electrolyzer or fuel cell, by inserting the polymer membrane into the vacuum chamber equipped with a magnetron sputtering system with a cerium oxide target in which an atmosphere of O.sub.2 and inert gas is formed and igniting the plasma which leads to simultaneous plasma etching of the membrane surface and deposition of cerium oxide onto the surface of etched membrane resulting in formation of fibers. The membrane is made of polymer and on at least one of its sides features porous surface made of fibers, the cross-sectional dimensions of which are lower than their length and which are integral and inseparable part of membrane body.

Claims

1. A method of manufacturing a membrane with surface fiber structure, the method comprising: inserting the membrane into a vacuum chamber having a magnetron sputtering system with a cerium oxide target, the sputtering system having an atmosphere of inert gas and O.sub.2 as a reactive gas; and igniting plasma as an ionized atmosphere to provide plasma etching of a surface of the membrane and deposition of cerium oxide on the etched surface of the membrane resulting in formation of fibers.

2. The method of claim 1, wherein a cerium oxide film with thickness equal or lower than 10 nm is deposited on the etched surface of the membrane.

3. The method of claim 1, wherein a layer of catalyst includes magnetron sputtered onto the surface of the membrane.

4. The method of claim 3, wherein the layer of catalyst includes a loading lower than 1 mg.Math.cm.sup.−2.

5. The method of claim 3, wherein a single- or multi-elemental noble metal-based catalyst is deposited on the surface of the membrane.

6. The method of claim 1, wherein the membrane is made of polymer and on at least one of its sides features a porous surface made of fibers, the porous surface having cross-sectional dimensions lower than their length and the porous surface being an integral and inseparable part of the membrane.

7. The method of claim 6, wherein the polymer includes an ionomer material.

8. (canceled)

9. (canceled)

10. The method of claim 1, wherein spacing between the fibers is equal or lower than an average length of the fibers.

11. The method of claim 1, wherein the membrane is configured for use in a water electrolyzer.

12. The method of claim 1, wherein the membrane is configured for use in a fuel cell.

13. An apparatus, comprising: a membrane having a surface fiber structure, the membrane formed by: inserting the membrane into a vacuum chamber having a magnetron sputtering system with a cerium oxide target, the sputtering system having an atmosphere of inert gas and O.sub.2 as a reactive gas; and igniting plasma as an ionized atmosphere to provide plasma etching of a surface of the membrane and deposition of cerium oxide on the etched surface of the membrane resulting in formation of fibers.

14. The apparatus of claim 13, wherein the membrane includes a polymer membrane.

15. The apparatus of claim 13, wherein a cerium oxide film with thickness equal or lower than 10 nm is deposited on the etched surface of the membrane.

16. The apparatus of claim 13, wherein a layer of catalyst includes magnetron sputtered onto the surface of the membrane.

17. The apparatus of claim 16, wherein the layer of catalyst includes a loading lower than 1 mg.Math.cm.sup.−2.

18. The apparatus of claim 16, wherein a single- or multi-elemental noble metal-based catalyst is deposited onto the surface of the membrane.

19. The apparatus of claim 14, wherein the polymer membrane includes an ionomer material.

20. The apparatus of claim 13, wherein spacing between the fibers is less than or equal to an average length of the fibers.

21. The apparatus of claim 13, wherein the membrane is configured for use in a water electrolyzer.

22. The apparatus of claim 13, wherein the membrane is configured for use in a fuel cell.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] FIG. 1 depicts a method diagram for the simultaneous plasma etching of a PEM membrane and CeOx deposition by reactive magnetron sputtering from a ceramic CeO2 target in a mixed Ar+O2 working atmosphere and its effect on the membrane.

[0024] FIG. 2 shows a scanning electron microscope image of the modified membrane surface.

[0025] FIG. 3 shows a cross-sectional image of the modified membrane obtained by a scanning electron microscope.

[0026] FIG. 4 exemplifies the modified surface of PEM without the catalyst layer which features the opaque milky colour, contrasting with the glossy transparent surface of the unmodified part of PEM. The modified part of PEM with 50 nm thin film of metal catalyst features the matt black colour, contrasting with the glossy transparent surface of the unmodified part of PEM.

[0027] FIG. 5 depicts the IV curve of a PEM water electrolyser operating at 80° C. using a double-sided modified thin-film catalyst membrane according to Example 2.

DESCRIPTION OF EMBODIMENTS

EXAMPLES

[0028] Example 1 describes a convenient method of preparing the membrane 1 by which its specific properties are achieved. The manufacturing method of the membrane 1 proceeds in the following steps:

[0029] 1. Pure membrane 1 (e.g. Nafion, Aquivion, 3M ionomer) with still a smooth flat surface is attached to a suitable holder and placed in a vacuum chamber equipped with a magnetron deposition system (one magnetron head or multiple magnetron system).

[0030] 2. The chamber is evacuated to the base pressure equal or better than 1.10-4 Pa. A working atmosphere consisting of O2 and Ar in a ratio ranging from 1:400 to 1:40 is mixed using vacuum mass flow controllers and direct vacuum gauges. The resulting pressure of this mixture is kept constant at 0.3-1.0 Pa.

[0031] 3. By means of a radio frequency power source a plasma is ignited over the surface of CeO2 ceramic target 3 (a short-term pressure increase may be required to ignite the discharge). The power density on the magnetron is held constant in range from tenths to units of W.Math.cm−2. The distance between the target 3 and the membrane 1 is in the range from 0.5 to 3 times the radius of the target 3. Prior to the actual deposition, the target 3 is pre-sputtered for couple of minutes (off the membrane 1) in order to clean its surface.

[0032] 4. After cleaning of the target 3, the deposition system is set into a sputtering configuration with the magnetron perpendicular to the membrane 1. Due to the simultaneous plasma etching of the membrane surface 1 and the CeOx deposition, a fiber-like structure with a large surface area is formed. The membrane 1 is etched in places where it is not being protected by sputtered CeOx layer which serves the role of masking element. By this mean a pronounced etched hollows are formed while the parts of the membrane which are being protected by CeOx thin film create the fibres. The deposition rate of CeOx thin film is in range of hundredths to units of nm.Math.min−1.

[0033] 5. If the deposition system is capable of sufficient manipulation with the substrate (i.e. rotating it by 180°) and if desired, the other side of the membrane 1 is also modified in the same manner as described in step 4.

[0034] 6. Subsequently a thin catalyst layer is deposited onto the membrane 1 with modified surface. If the deposition apparatus is equipped with more magnetrons, this step can be carried out immediately; or after venting the chamber, changing the target 3 in the magnetron and re-pumping the vacuum chamber. Base pressure, the composition of the working atmosphere and the deposition parameters in this step must be selected as such that they provably lead to formation of catalytically active thin film.

[0035] Example 2 describes a laboratory-verified method of preparing the double-sided etched catalyst-coated membrane 1, type Nafion NE 1035 for use in a water electrolyzer. The manufacturing method of the membrane 1 proceeds in the following steps:

[0036] 1. From a commercially available membrane 1, type Nafion NE 1035, a piece of a size compatible with the respective electrolyzer unit is cut. Membrane 1 is thoroughly cleaned by blowing with dry nitrogen. It is not recommended to clean it by wet techniques—chemically, since the membrane 1 should stay dry prior to insertion to the vacuum chamber. The membrane 1 is attached to the plate-shaped sample holder with the cut-out in the middle, thereby providing the possibility of deposition on both sides of the membrane 1.

[0037] 2. The substrate holder with the membrane 1 is mounted on a rotary manipulator inside a vacuum deposition chamber, equipped with three magnetrons (targets 3 in magnetrons: CeO2, Ir, Pt). The oil-free scroll pump and turbomolecular pump evacuate the chamber down to the 5.10-5 Pa.

[0038] 3. After reaching the aforementioned value of a base pressure, the vacuum mass flow controllers start to introduce Ar and O2, such that the ratio of flows is O2:Ar 1:65 and the absolute pressure of the mixture is constant at 0.4 Pa (in case of the tested apparatus, this corresponds to the O2 flow of 0.23 sccm, Ar flow of 15 sccm and partially lowered pumping speed of turbomolecular pump; however these values will be different at different setups). It is essential that gases of maximum purity (6.0) are introduced and that all the pipelines and hoses are sufficiently purged (including the vacuum part).

[0039] 4. By means of a radio frequency power source a plasma is ignited over the surface of a four-inch CeO2 ceramic target 3 (a short-term pressure increase may be required to ignite the discharge, in case of tested apparatus to approx. 1 Pa). The power on the magnetron is held constant at 65 W, the target 3 to membrane 1 distance is 15 cm. Prior to the actual deposition, the target 3 is, in order to clean its surface, pre-sputtered for 5 minutes with its shutter still being closed (i.e. no material gets to the membrane 1). Next, the shutter is opened and the simultaneous deposition of material and etching of the membrane 1 begins; the target 3 is perpendicular to the membrane 1. It takes approx. 70 minutes to achieve desired structure, using the above mentioned deposition parameters.

[0040] 5. After 70 minutes, the substrate holder with the membrane 1 is rotated by 180° and the other side of the membrane is treated the same way (provided the rotation of the sample holder is fast enough, there is no need to shut down the magnetron discharge).

[0041] 6. Thin-film catalyst is consequently sputtered onto the modified membrane 1 with large surface. In case of water electrolyzer, Ir on the anode and Pt on the cathode side of PEM. Since both Ir and Pt are being deposited in pure Ar, it is necessary to again evacuate the chamber to 5.10-5 Pa and to create the 0.5 Pa working atmosphere using just Ar mass flow controller. In case of the tested apparatus, this corresponds to the Ar flow of 20 sccm and partially lowered pumping speed of turbomolecular pump.

[0042] 7. By means of a direct current power source a plasma is ignited over the surface of a two-inch metallic Ir target 3 (a short-term pressure increase may be required to ignite the discharge, in case of tested apparatus to approx. 1 Pa). The power on the magnetron is held constant at 30 W, the target 3 to membrane 1 distance is 15 cm. Prior to the actual deposition, the target 3 is, in order to clean its surface, pre sputtered for 5 minutes with its shutter still being closed (i.e. no material gets to the membrane 1). Next, the substrate holder is rotated, so the target 3 is perpendicular to the anode side of membrane 1, the shutter is opened and the deposition of material to the membrane 1 begins. Using the above mentioned deposition parameters, it takes approx. 30 min to deposit 50 nm of Ir.

[0043] 8. By means of a direct current power source a plasma is ignited over the surface of a two-inch metallic Pt target 3 (a short-term pressure increase may be required to ignite the discharge, in case of tested apparatus to approx. 1 Pa). The power on the magnetron is held constant at 20 W, the target 3 to membrane 1 distance is 15 cm. Prior to the actual deposition, the target 3 is, in order to clean its surface, pre sputtered for 5 minutes with its shutter still being closed (i.e. no material gets to the membrane 1). Next, the substrate holder is rotated, so the target 3 is perpendicular to the cathode side of membrane 1, the shutter is opened and the deposition of material to the membrane 1 begins. Using the above mentioned deposition parameters, it takes approx. 35 min to deposit 50 nm of Pt.

[0044] 9. After completion of all four depositions, two for modification of surface of the membrane 1 and two for catalyst deposition (Ir on the anode side of membrane 1, Pt on the cathode side of membrane 1), the chamber is vented back to atmospheric pressure and the modified catalyst-coated membrane 1 is ready for its use in water electrolyzer. It is inserted in between the cathode gas diffusion layer (in this case Sigracet 29BC) and the anode liquid-gas diffusion layer (in this case sintered micro grained Ti plate).

INDUSTRIAL APPLICABILITY

[0045] The membrane produced by a method combining reactive magnetron thin-film sputtering and plasma etching is industrially applicable in particular for use in a proton exchange membrane water electrolyzers. Water electrolyzer is a device that uses electrical current of certain voltage to electrochemically split water into hydrogen and oxygen. As such, it is a key building block of so-called hydrogen economy. Stored hydrogen can be subsequently converted to electricity by means of hydrogen fuel cells. This cycle is relevant with respect to stabilization of modern electrical grids powered by electricity form intermittent renewable sources such as wind and solar. The membrane is also industrially applicable in hydrogen or methanol fuel cells.