Bipolar plate and production thereof

Abstract

The invention relates to a bipolar plate (1) for electrolysis, comprising a lower sheet metal part (22) and an upper sheet metal part (21) which are connected to one another, the materials of the sheet metal parts being significantly different from one another.

Description

Technical Field

[0001] The present invention relates to bipolar plates and their manufacture. Background Art

[0002] The service life of a PEM-based water electrolysis device is greatly affected by the release of multivalent transition metal ions and the associated occurrence of membrane damage. Particular attention is required for the corresponding bipolar plate, since it is exposed to both cathode and anode potentials, or to the reactants hydrogen (H2) and oxygen (O2).

[0003] A large number of technical solutions are known from the literature, which are mainly based on PVD-based coatings: TiN, CrN, TiCN or TiC.

[0004] Conductive films made of Au, TiN, TiN / C or TaN have been widely used to protect stainless steel from corrosion.

[0005] However, all of these coatings fail and, especially at high potentials, do not provide the necessary corrosion protection.

[0006] The use of hard layers (e.g. TiN) has the disadvantage that these are applied to very thin substrates and are susceptible to cracking due to mechanical stresses when bending or under mechanical load. In particular, substrates coated on one side are subject to mechanical stresses, which can promote the detachment of the protective layer. Another disadvantage compared to metallic contact materials is the lower electrical conductivity.

[0007] The technical realization of PVD coating is usually limited to component sizes less than 1.2 meters in length, which limits the scalability of electrolytic cells. Another disadvantage is the high component cost of the coated components.

[0008] When using single-layer thin sheet materials (VA steel or Ti) as bipolar plates, signs of corrosion are found:

[0009] Due to the presence of hydrogen and the cathode potential, titanium (Ti) tends to form titanium hydride TiH n (n = 0.5-2), which can react to form Ti3O5 or Ti 3+ .

[0010] Stainless steels and nickel-based alloys show signs of corrosion within the grain boundary regions at anodic potentials (>1.5 V vs. RHE).

[0011] In the case of chrome-nickel steels, irreversible damage is found in the area of ​​the chromium oxide passive layer. Summary of the invention

[0012] Therefore, an object of the present invention is to solve the above-mentioned problems.

[0013] This object is achieved by a bipolar plate according to claim 1 and a method according to claim 12 .

[0014] Further advantageous measures are listed in the dependent claims, which can be combined with one another as desired to achieve further advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a top view of the bipolar plate;

[0016] Figure 2 yes Figure 1 The cross section of

[0017] Figure 3 , 4 The seal in the through-hole region is shown;

[0018] Figure 5 A punch riveted connection is shown. DETAILED DESCRIPTION

[0019] The specifications of bipolar plates for PEM water electrolysis are:

[0020] Corrosion resistance at high potentials (>1.5 V vs. reversible hydrogen electrode; RHE);

[0021] Temperature (T) = 60°C-80°C (333K-353K);

[0022] O2-saturated acidic environment (pH = 0 to 6);

[0023] High conductivity of the plane;

[0024] Low contact resistance and low welding voltage;

[0025] The materials are cheap and the deposition technique is simple and scalable;

[0026] Resistant to hydrogen (H2) embrittlement (cathode);

[0027] ·Resistant to oxygen (O2) embrittlement (anode).

[0028] The present invention enables the manufacture of large bipolar plates in a cost-effective and scalable manner.

[0029] Figure 1 The bipolar plate 1 is shown in a top view. In particular, in the vicinity of the four corners of the preferably rectangular design of the bipolar plate 1 there are in particular four through-going regions 4 in each case.

[0030] The electrolyte is introduced and discharged at the through-pass region 4 .

[0031] Figure 2 is based on Figure 1, in which the double-layer structure of the bipolar plate 1 is schematically shown.

[0032] The bipolar plate 1 has an upper plate member 21 and a lower plate member 22 .

[0033] The thickness of the sheet metal parts (metal plates) 21 , 22 is shown here only schematically, ie the sheet metal parts 21 , 22 may be of equal thickness or may be designed to have different thicknesses depending on which material of the sheet metal parts 21 , 22 is more mechanically stable.

[0034] The thickness of the sheet material is in the range of 0.1 mm to 5 mm, preferably 0.5 mm.

[0035] For the sheet metal parts, completely different materials are used, i.e. the matrix is ​​different, that is, one sheet metal part is based on iron (steel) or on nickel and the other sheet metal part is not, in particular it is based on titanium (Ti), niobium (Nb), tantalum (Ta) or zirconium (Zr), or at least one alloying element is present to a greater or lesser extent, or the proportions of the alloying elements differ by at least 10%, in particular by at least 20%.

[0036] The following material combinations can be used for the upper plate member 21 and the lower plate member 22:

[0037] For the cathode side, use

[0038] - Stainless steel, especially austenitic stainless steel:

[0039] - Duplex steel: Duplex steel is a steel with a two-color structure, which consists of a ferrite matrix with austenite islands and has more than 20% chromium (Cr), about 5% nickel (Ni) and 3% molybdenum (Mo);

[0040] -Super Duplex Steel: Super Duplex Steel has higher chromium (Cr), nickel (Ni) and molybdenum (Mo) content than Duplex Steel;

[0041] -Ultra-super duplex steel: Compared with super duplex steel, the content of chromium (Cr), nickel (Ni) or molybdenum (Mo) in ultra-super duplex steel is again slightly higher;

[0042] -Nitronic 50: A steel with chromium (Cr), nickel (Ni), manganese (Mn), molybdenum (Mo), silicon (Si), niobium (Nb), vanadium (V), and hardened by nitrogen (N).

[0043] Likewise, nickel-based alloys can be used instead of steel:

[0044] -C276 alloy: a nickel-chromium-molybdenum alloy with tungsten (W);

[0045] - Incoloy: a nickel-based alloy containing iron (Fe), chromium (Cr), which may have additions of aluminum (Al), titanium (Ti), copper (Cu), manganese (Mn), cobalt (Co), silicon (Si), molybdenum (Mo) and / or niobium (Nb);

[0046] - Inconel: A nickel-based alloy containing chromium, iron (Fe), molybdenum (Mo), niobium (Nb), cobalt (Co), manganese (Mn), copper (Cu), aluminum (Al), titanium (Ti), silicon (Si), sulfur (S), phosphorus (P) and boron (B);

[0047] -Nickel (Ni);

[0048] -Nilo: Nilo is a steel with nickel (Ni) and small amounts of aluminum (Al), carbon (C), cobalt (Co), manganese (Mn), molybdenum (Mo), and silicon (Si);

[0049] - Nimonic: is a nickel-based alloy with shares of chromium (Cr), cobalt (Co), titanium (Ti) and aluminum (Al);

[0050] Nitronic: A chromium-nickel steel which contains, inter alia, a proportion of manganese (Mn) and is hardened by nitrogen (N);

[0051] Waspaloy: a nickel-based alloy based on austenite, hardened face-centered cubic structure and containing, inter alia, chromium (Cr), molybdenum (Mo), cobalt (Co), aluminum (Al), titanium (Ti) and carbon (C) and zirconium (Zr), and optionally iron (Fe), manganese (Mn), silicon (Si), phosphorus (P), sulfur (S) and copper (Cu);

[0052] -Invar alloy: an iron-nickel alloy with a very low coefficient of expansion;

[0053] -1.4404 steel: 1.4404 steel is a stainless austenitic chromium-nickel-molybdenum steel with a low carbon (C) content. Due to the addition of 2%-2.5% molybdenum (Mo), it has high corrosion resistance;

[0054] -1.4401 steel, is a stainless austenitic chromium-nickel-molybdenum steel. It has good corrosion resistance due to the addition of 2%-2.5% molybdenum (Mo).

[0055] For the anode side, use

[0056] - Titanium (Ti) or titanium alloys;

[0057] - Niobium (Nb) or niobium alloys;

[0058] - Zirconium (Zr) or a zirconium alloy;

[0059] -Tantalum (Ta) or tantalum alloy.

[0060] As for titanium, grade 1 titanium or grade 2 titanium is preferably used.

[0061] Titanium Grade 1 and Titanium Grade 2 are unalloyed titanium (Ti) according to ASTM 265B.

[0062] The main difference between Grade 1 and Grade 2 is the permitted oxygen (O) impurities (Grade 1 up to 0.18 wt. %, Grade 2 up to 0.25 wt. %) and iron (Fe) impurities (Grade 1 up to 0.20 wt. %, Grade 2 up to 0.30 wt. %) and the resulting completely different mechanical properties.

[0063] In addition, titanium (Ti) grade 1 and titanium (Ti) grade 2 may contain carbon (C) impurities (up to 0.08 wt%), nitrogen (N) impurities (up to 0.03 wt%), hydrogen (H) impurities (up to 0.015 wt%), and other elements (up to 0.1 wt%).

[0064] The surfaces of the sheet metal parts 21 , 22 which come into contact with the medium can be further coated.

[0065] These coatings are preferably coatings applied by thermal spraying, such as atmospheric plasma spraying (APS), vacuum plasma spraying (VPS), flame spraying, high velocity flame spraying (HVOF) or by chemical or physical vapor deposition (CVD and PVD).

[0066] This is done, in particular, with gold (Au), platinum (Pt), iridium (Ir) in order to improve the electrical contact.

[0067] The through-region 4 of the bipolar plate 1 must be sealed between the two sheet metal parts 21, 22. Three methods are preferably used for this purpose:

[0068] The first method is Figure 3 shown.

[0069] In this method, edge stretching 25 and edge curling 27 are performed in the region of the through-pass region 4 so that, for example, a sheet metal part 21 extends around and through the through-pass region 4 and lies firmly against the surface of another sheet metal part 22 .

[0070] The second method is Figure 4 As shown, a sealing collar 29 with a ring is used, which surrounds the passage region 4 and then seals the passage region 4 in the region of the upper and lower sheet-metal part by means of a clamping 31 .

[0071] The third method is Figure 1As indicated by the dashed lines 7 and 11 in FIG. 1 , in this method a sealing material is applied, wherein known sealing materials such as liquid FKM, liquid PFA or Loctite are used as the sealing material.

[0072] The double-layer connection of the upper and lower sheet metal parts 22, 21 is realized in particular by clinching (also known as punch riveting) and the punch riveted connection 30 produced in this case ( Figure 5 ).

[0073] Punch riveting connections are known in joining technology and allow two sheet metal parts 21 , 22 to be connected individually and in a media-tight manner.

[0074] Punch riveting connections can be performed at the edges of the bipolar plates.

[0075] Furthermore, a planar and regular arrangement over the entire surface of the bipolar plate is also possible.

[0076] Other methods used to join two sheet materials are roll cladding and explosion cladding.

[0077] The present invention allows for longer service life of PEM electrolysis and enables a cheap alternative to VPS coated stainless steel / titanium bipolar plates. The method utilizes punch riveting technology suitable for large scale manufacturing.

[0078] It has high mechanical robustness in terms of manufacturing and assembly processes and is tolerant of surface damage.

[0079] The multi-layer concept proposed here with the aid of punch-riveted connections makes it possible to prevent anodic and cathodic corrosion by means of a suitable material combination.

Claims

1. A bipolar plate (1) for electrolysis, the bipolar plate comprising a lower plate member (22) and an upper plate member (21), the lower plate member and the upper plate member being connected to each other, wherein: The materials of the sheet metal parts are clearly different from one another, wherein “different” means in particular: - the matrices are different, in particular one sheet metal part is based on iron (steel) or on nickel and the other sheet metal part is not, in particular the other sheet metal part is based on titanium (Ti), niobium (Nb), tantalum (Ta) or zirconium (Zr); or, - the presence of at least one alloying element to a greater or lesser extent; or, The proportions of the alloying elements differ by at least 10%, in particular by at least 20%.

2. The bipolar plate according to claim 1, wherein: The material of a sheet metal part (21) comprises stainless steel, in particular austenite, or comprises a nickel-based alloy.

3. The bipolar plate according to any one or both of claims 1 and 2, wherein: The other material of the other sheet metal part (22) comprises titanium (Ti), in particular grade 1 or 2 titanium (Ti); niobium (Nb); zirconium (Zr) or tantalum (Ta).

4. The bipolar plate according to any one or both of claims 1 and 2, wherein: A titanium alloy, a tantalum alloy, a zirconium alloy or a niobium alloy is used as another material of the other sheet metal part (22).

5. The bipolar plate according to one or more of the preceding claims 1, 2, 3 or 4, wherein: The plate members (21, 22) have equal thickness.

6. The bipolar plate according to one or more of the preceding claims 1, 2, 3 or 4, wherein: The sheet metal parts (21, 22) have different thicknesses and differ by at least 10%, in particular at least 20%.

7. A bipolar plate as claimed in one or more of the preceding claims 1, 2, 3, 4, 5 or 6, wherein: The thickness of the sheet metal parts (21, 22) is 0.1 mm-5.0 mm, preferably 0.8 mm to 2 mm, and most preferably 0.5 mm.

8. The bipolar plate according to one or more of the preceding claims 1, 2, 3, 4, 5, 6 or 7, wherein: The sheet metal parts (21, 22) have a coating, in particular an APS, VPS, HVOF, CVD or PVD coating, in particular with gold (Au), platinum (Pt), iridium (Ir), for improving the electrical contact.

9. The bipolar plate of one or more of the preceding claims 1, 2, 3, 4, 5, 6, 7 or 8, wherein: The bipolar plate (1) has a through-region (4) which is sealed, in particular by edge drawing (25) and edge curling (27) or by a pressed sealing collar (29) or by a sealing compound.

10. The bipolar plate of one or more of the preceding claims 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein: The two sheet metal parts (21, 22) are connected to each other by punch riveting.

11. A bipolar plate as claimed in one or more of the preceding claims 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein: The material of a sheet metal part (21) includes stainless steel, in particular austenitic stainless steel, duplex steel, super duplex steel, ultra super duplex steel, Nitronic50, C276 alloy, Incoloy, Inconel, Nickel, Nilo, Nimonic, Nitronic, Waspaloy, Invar, 1.4404 steel or 1.4401 steel.

12. A method for producing a bipolar plate (1) according to one or more of the preceding claims, wherein: The two sheet metal parts (21, 22) are firmly connected to one another, in particular by riveting, by cladding or welding.

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