Patent ID: 12230851

DESCRIPTION OF EMBODIMENTS

EXAMPLES

Example 1 describes a convenient method of preparing the membrane1by which its specific properties are achieved. The manufacturing method of the membrane1proceeds in the following steps:1. Pure membrane1(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).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.3. By means of a radio frequency power source a plasma is ignited over the surface of CeO2 ceramic target3(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·cm−2. The distance between the target3and the membrane1is in the range from 0.5 to 3 times the radius of the target3. Prior to the actual deposition, the target3is pre-sputtered for couple of minutes (off the membrane1) in order to clean its surface.4. After cleaning of the target3, the deposition system is set into a sputtering configuration with the magnetron perpendicular to the membrane1. Due to the simultaneous plasma etching of the membrane surface1and the CeOx deposition, a fiber-like structure with a large surface area is formed. The membrane1is 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·min−1.5. 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 membrane1is also modified in the same manner as described in step 4.6. Subsequently a thin catalyst layer is deposited onto the membrane1with 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 target3in 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.

Example 2 describes a laboratory-verified method of preparing the double-sided etched catalyst-coated membrane1, type Nafion NE 1035 for use in a water electrolyzer. The manufacturing method of the membrane1proceeds in the following steps:1. From a commercially available membrane1, type Nafion NE 1035, a piece of a size compatible with the respective electrolyzer unit is cut. Membrane1is thoroughly cleaned by blowing with dry nitrogen. It is not recommended to clean it by wet techniques—chemically, since the membrane1should stay dry prior to insertion to the vacuum chamber. The membrane1is 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 membrane1.2. The substrate holder with the membrane1is mounted on a rotary manipulator inside a vacuum deposition chamber, equipped with three magnetrons (targets3in magnetrons: CeO2, Ir, Pt). The oil-free scroll pump and turbomolecular pump evacuate the chamber down to the 5.10-5 Pa.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).4. By means of a radio frequency power source a plasma is ignited over the surface of a four-inch CeO2 ceramic target3(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 target3to membrane1distance is 15 cm. Prior to the actual deposition, the target3is, in order to clean its surface, pre-sputtered for 5 minutes with its shutter still being closed (i.e. no material gets to the membrane1). Next, the shutter is opened and the simultaneous deposition of material and etching of the membrane1begins; the target3is perpendicular to the membrane1. It takes approx. 70 minutes to achieve desired structure, using the above mentioned deposition parameters.5. After 70 minutes, the substrate holder with the membrane1is 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).6. Thin-film catalyst is consequently sputtered onto the modified membrane1with 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.7. By means of a direct current power source a plasma is ignited over the surface of a two-inch metallic Ir target3(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 target3to membrane1distance is 15 cm. Prior to the actual deposition, the target3is, in order to clean its surface, pre sputtered for 5 minutes with its shutter still being closed (i.e. no material gets to the membrane1). Next, the substrate holder is rotated, so the target3is perpendicular to the anode side of membrane1, the shutter is opened and the deposition of material to the membrane1begins. Using the above mentioned deposition parameters, it takes approx. 30 min to deposit 50 nm of Ir.8. By means of a direct current power source a plasma is ignited over the surface of a two-inch metallic Pt target3(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 target3to membrane1distance is 15 cm. Prior to the actual deposition, the target3is, in order to clean its surface, pre sputtered for 5 minutes with its shutter still being closed (i.e. no material gets to the membrane1). Next, the substrate holder is rotated, so the target3is perpendicular to the cathode side of membrane1, the shutter is opened and the deposition of material to the membrane1begins. Using the above mentioned deposition parameters, it takes approx. 35 min to deposit 50 nm of Pt.9. After completion of all four depositions, two for modification of surface of the membrane1and two for catalyst deposition (Ir on the anode side of membrane1, Pt on the cathode side of membrane1), the chamber is vented back to atmospheric pressure and the modified catalyst-coated membrane1is 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

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.