Bipolar plate and production

Abstract

The invention relates to a bipolar plate (1) for electrolysis, which has a lower metal sheet (22) and an upper metal sheet (21) that are interlinked, the materials of the metal sheets being distinctly different from each other.

Description

[0001] Description

[0002] Bipolar plate and manufacturing

[0003] The invention relates to a bipolar plate and its production.

[0004] The lifetime of PEM-based water electrolyzers is significantly influenced by the release of multivalent transition metal ions and the associated membrane damage. Particular attention is paid to the corresponding bipolar plate, as it is exposed to both cathodic and anodic potentials and the reactants hydrogen (H2) and oxygen (O2).

[0005] A variety of technical solutions are known from the literature, which are primarily based on PVD-based coatings: TiN, CrN, TiCN or TiC.

[0006] Conductive thin films made of Au, TiN, TiN / C or TaN have been widely used to protect stainless steel from corrosion.

[0007] However, all these coatings fail and do not provide the necessary corrosion protection, especially at high potentials.

[0008] The application of hard coatings, such as TiN, has the disadvantage that they are applied to very thin substrates and are prone to cracking due to mechanical stresses when bent or subjected to mechanical stress. Substrates coated on one side, in particular, are subject to mechanical stress, which promotes detachment of the protective layer. A further disadvantage compared to metallic contact materials is their lower electrical conductivity.

[0009] The technical implementation of PVD coating is usually limited to component dimensions of less than 1.2 m in length, which limits the scalability of the electrolysis cells. Another disadvantage is the increased component costs for coated components. When using single-layer thin sheets (VA steel or Ti) as bipolar plates, corrosion phenomena have been observed:

[0010] Titanium (Ti) tends to form titanium hydride TiH due to the presence of hydrogen and cathodic potential n (n = 0.5-2) , which is subdivided into Ti3C>5 or Ti 3+ can react.

[0011] Stainless steels and nickel-based alloys show corrosion phenomena in the grain boundary area under anodic potential (> 1.5V vs. RHE).

[0012] In the case of chromium-nickel steels, irreversible damage is observed in the area of ​​the chromium oxide passivation layer.

[0013] It is therefore an object of the invention to solve the above-mentioned problem.

[0014] The object is achieved by a bipolar plate according to claim 1 and a method according to claim 12.

[0015] The subclaims list further advantageous measures which can be combined with each other as desired to achieve further advantages.

[0016] It shows

[0017] Figure 1 shows a bipolar plate in plan view,

[0018] Figure 2 shows a cross section through Figure 1,

[0019] Figure 3, 4 Seals in the area of ​​passages,

[0020] Figure 5 shows a clinch connection.

[0021] Specification for bipolar plates for PEM water electrolysis are

[0022] • Corrosion resistance at high potentials (> 1.5V vs. reversible hydrogen electrode; RHE)

[0023] • Temperatures (T) = 60°C - 80°C (333K - 353K)

[0024] • acidic environments (pH = 0 to 6) saturated with O2

[0025] • High electrical conductivity through the plane • Low contact resistance and low frit voltage

[0026] • Cost-effective material and simple and scalable deposition technology

[0027] • Resistance to hydrogen (H 2) -Embrittling (cathode)

[0028] • Resistance to oxygen O2 embrittlement (anode).

[0029] The present invention enables cost-effective and scalable production of large-format bipolar plates.

[0030] Figure 1 shows a plan view of a bipolar plate 1. In particular, four feedthrough areas 4 are present near the four corners of the preferably rectangular design of the bipolar plate 1.

[0031] Electrolyte is added and released at the feedthrough areas 4 .

[0032] Figure 2 shows a cross-section according to Figure 1, in which the two-layer structure of the bipolar plate 1 is shown schematically.

[0033] The bipolar plate 1 has an upper plate 21 and a lower plate 22.

[0034] The thicknesses of the sheets 21, 22 are shown here only schematically, ie the thicknesses of the sheets 21, 22 can be the same thickness or, depending on which material is mechanically more stable for a sheet 21, 22, can be of different thicknesses.

[0035] The sheet thicknesses are in the range of 0.1mm - 5mm, preferably 0.5mm.

[0036] Significantly different materials are used for the sheets, ie the matrix is ​​different, so one sheet is iron-based (steel) or nickel-based and the other sheet is not, in particular 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 proportion of an alloying element differs by at least 10%, in particular by at least 20%.

[0037] The following material combinations for upper sheet 21 and lower sheet 22 are possible:

[0038] For the cathodic side, a

[0039] - Stainless steel, in particular an austenitic stainless steel used :

[0040] - Duplex: Duplex is a steel with a two-tone structure consisting of a ferrite matrix with islands of austenite and containing over 20% chromium (Cr), about 5% nickel (Ni) and 3% molybdenum (Mo),

[0041] - Superduplex: Superduplex has a higher chromium (Cr), nickel (Ni) and molybdenum (Mo) content than Duplex,

[0042] - Hyperduplex: Hyperduplex has slightly increased chromium (Cr), nickel (Ni) or molybdenum (Mo) values ​​compared to Superduplex,

[0043] - Nitronic 50: is a steel with chromium (Cr), nickel (Ni), manganese (Mn), molybdenum (Mo), silicon (Si), niobium (Nb), vanadium (V) and is hardened by nitrogen (N).

[0044] Nickel-based alloys can also be used instead of steel:

[0045] - Alloy C276: is a nickel-chromium-molybdenum alloy with tungsten (W);

[0046] - Incoloy: a nickel-based alloy containing iron (Fe) and chromium (Cr), which may contain additions of aluminum (Al), titanium (Ti), copper (Cu), manganese (Mn), cobalt (Co), silicon (Si), molybdenum (Mo) and / or niobium (Nb);

[0047] - Inconel: a chromium-containing nickel-based alloy with 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);

[0048] - Nickel (Ni);

[0049] - Nilo: Nilo is a steel with nickel (Ni) and small amounts of aluminum (Al), carbon (C), cobalt (Co), manganese (Mn), molybdenum (Mo), silicon (Si);

[0050] - Nimonic: is a nickel-based alloy with proportions of chromium (Cr), cobalt (Co), titanium (Ti) and aluminum (Al);

[0051] - Nitronic: is a chromium-nickel steel with, among other things, manganese (Mn) which is hardened by nitrogen (N);

[0052] - Waspaloy: is a nickel-based alloy based on the hardening of an austenitic, face-centered cubic structure and contains, among other elements, chromium (Cr), molybdenum (Mo), cobalt (Co), aluminum (Al), titanium (Ti), as well as war, carbon (C) and zirconium (Zr) and possibly also iron (Fe), manganese (Mn), silicon (Si), phosphorus (P), sulfur (S) and copper (Cu);

[0053] - Invar: is an iron-nickel alloy with a very low coefficient of expansion;

[0054] - Steel 1.4404: Steel 1.4404 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.

[0055] -Steel 1.4401 is a stainless austenitic chromium-nickel-molybdenum steel. Due to the addition of 2% - 2.5% molybdenum (Mo), it exhibits good corrosion resistance.

[0056] For the anodic side

[0057] - Titanium (Ti) or a titanium alloy,

[0058] - Niobium (Nb) or a niobium alloy,

[0059] - Zirconium (Zr) or a zirconium alloy,

[0060] - Tantalum (Ta) or a tantalum alloy is used.

[0061] For titanium, titanium grade 1, titanium grade 2 is preferably used.

[0062] Titanium Grade 1 and Titanium Grade 2 are unalloyed titanium (Ti) according to ASTM 265B.

[0063] Grade 1 and Grade 2 differ essentially in the permissible impurities of oxygen (O) (Grade 1 max. 0.18 wt.%, Grade 2 max. 0.25 wt.%) and iron (Fe) (Grade 1 max. 0.20 wt.%, Grade 2 max. 0.30 wt.%) and the resulting, quite different mechanical properties.

[0064] Furthermore, titanium (Ti) Grade 1 and titanium Grade 2 can contain impurities of carbon (C) (max. 0.08 wt.%), nitrogen (N) (max. 0.03 wt.%), hydrogen (H) (max. 0.015 wt.%) and other elements (max. 0.1 wt.%).

[0065] A further coating of the media-contacting surfaces of the sheets 21, 22 is possible.

[0066] These are preferably coatings applied by thermal spraying (e.g. atmospheric plasma spraying (APS), vacuum plasma spraying (VPS), flame spraying, high-velocity oxyfuel spraying (HVOF)) or by chemical or physical vapor deposition (CVD and PVD).

[0067] This is done in particular with gold (Au), platinum (Pt) and iridium (Ir) to improve the electrical contact.

[0068] The feedthrough areas 4 of the bipolar plate 1 must be sealed between the two sheets 21, 22.

[0069] Three methods can preferably be used for this purpose:

[0070] The first method is shown in Figure 3.

[0071] There, in the area of ​​the lead-through area 4, a collar pulling 25 and collar flanging 27 takes place, so that, for example, one sheet 21 runs around and through the lead-through area 4 and lies firmly on the surface of the other sheet 22.

[0072] The second method is shown in Figure 4, in which a sealing eyelet 29 with a ring is used, which surrounds the lead-through area 4 and then seals the lead-through area 4 in the area of ​​the upper and lower sheets by means of compression 31.

[0073] The third method is shown by the dashed lines 7, 11 in Figure 1, in which sealant is applied, using in particular well-known sealants such as liquid FKM, liquid PFA or Loctite.

[0074] The two-layer connection of upper and lower sheets 22, 21 is made possible in particular by clinching and the resulting clinch connection 30 (Fig. 5).

[0075] Clinching joints are known from joining technology. This connection enables a separate and media-tight connection between the two sheets 21 and 22.

[0076] The clinch connections can be made at the edge of the bipolar plate.

[0077] In addition, there is also the possibility of a flat and regular arrangement over the entire surface of the bipolar plate.

[0078] Other options for joining two sheets are roll cladding or explosion cladding.

[0079] The present invention enables longer lifetimes for PEM electrolysis and offers a cost-effective alternative to VPS-coated stainless steel / titanium bipolar plates. The method utilizes clinching technology suitable for mass production.

[0080] It exhibits high mechanical robustness with regard to the manufacturing and assembly process as well as fault-tolerant behavior towards surface damage.

[0081] A multilayer concept using clinching as proposed here makes it possible to prevent anodic and cathodic corrosion through a suitable material combination.

Claims

Patent claims 1. Bipolar plate (1) for electrolysis, comprising a lower sheet (22) and an upper sheet (21) connected to each other, wherein the materials of the sheets are distinctly different from each other, where different means in particular: - the matrix is ​​different, in particular one sheet is iron-based (steel) or nickel-based and the other sheet is not, in particular the other sheet 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 degree, or - the proportion of an alloying element differs by at least 10%, in particular by at least 20%.

2. Bipolar plate according to claim 1, wherein a material for a sheet (21) comprises stainless steel, in particular austenite, or a nickel-based alloy.

3. Bipolar plate according to one or both of claims 1, 2, wherein the other material for the other sheet (22) comprises titanium (Ti), in particular grade 1 or grade 2, niobium (Nb), zirconium (Zr) or tantalum (Ta). Bipolar plate according to one or both of claims 1, 2, wherein the other material for the other sheet (22) is a titanium alloy, a tantalum alloy, a zirconium alloy, or a niobium alloy. Bipolar plate according to one or more of the preceding claims 1, 2, 3, or 4, wherein the sheets (21, 22) are of the same thickness. Bipolar plate according to one or more of the preceding claims 1, 2, 3, or 4, wherein the sheets (21, 22) are of different thicknesses and differ by at least 10%, in particular by at least 20%. Bipolar plate according to one or more of the preceding claims 1, 2, 3, 4, 5, or 6, wherein the sheets (21, 22) are 0.1 mm to 5.0 mm thick, preferably 0.8 mm to 2 mm thick, most preferably 0.5 mm thick.A bipolar plate according to one or more of the preceding claims 1, 2, 3, 4, 5, 6 or 7, wherein the sheets (21, 22) have a coating, in particular APS, VPS, HVOF, CVD or PVD coatings, especially with gold (Au), platinum (Pt), iridium (Ir) to improve electrical contact. A bipolar plate according to one or more of the preceding claims 1, 2, 3, 4, 5, 6, 7 or 8, wherein the bipolar plate (1) has feedthrough areas (4) which are sealed, in particular by collar drawing (25) and collar crimping (27). or by a crimped sealing eyelet (29) or by sealant. . Bipolar plate according to one or more of the preceding claims 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the two sheets (21, 22) are connected to each other by a clinch connection. . Bipolar plate according to one or more of the preceding claims 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein a material for one sheet (21) comprises stainless steel, in particular an austenitic stainless steel, duplex, superduplex, hyperduplex, Nitronic 50, Alloy C276, Incoloy, Inconel, nickel, Nilo, Nimonic, Nitronic, Waspaloy, Invar, steel 1.4404 or steel 1.4401. . Method for producing a bipolar plate (1) according to one or more of the preceding claims, wherein the two sheets (21, 22) are firmly joined together, in particular by a clinch connection, by plating or welding.

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