Electrodes and methods for manufacturing them

Abstract

To provide an electrode for an electrochemical reaction bath, and to provide a method for producing the same.SOLUTION: An electrode includes a substrate, an active side adapted to come into contact with a reaction bath, and a passive side adapted to come into contact with at least one conductor. The passive side includes a doped carbon coating.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrode for an electrochemical reaction bath, comprising a substrate, an active side configured to contact the reaction bath, and a passive side configured to contact at least one conductor. The present invention also relates to a method for manufacturing such an electrode. [Background technology]

[0002] Such electrodes may have an active side with a doped diamond coating. They are called diamond electrodes and have been known for some time. However, the present invention is not limited to them, although diamond electrodes are advantageous for many applications. Electrodes, in particular diamond electrodes, are typically coated only on the active side that is in contact with the reaction bath. The passive side, which is located opposite the active side in particular, is left uncoated. The electrode is placed in the reaction bath such that only the coated active side is in contact with the reaction bath. On the passive side, the electrode is electrically contacted, i.e., made to contact, by at least one conductor. A common method for sealing the reaction bath from the atmosphere or preventing leakage of the reaction bath is to place a corresponding seal on the active side of the electrode. This has the advantage, among other things, that the entire surface of the passive side can be used for electrical contact. However, it is not necessary to place a seal on the active side of the electrode. In addition to this, or instead, it is also possible to use a seal on the passive side of the electrode.

[0003] A range of different forms of electrical contacts are known. Typically, these have multiple individual contact points through which only a small portion of the current is transmitted from the power source to the electrodes. The individual contacts are formed, particularly as pins, and especially preferably with a spring load in the direction of the electrodes, and are advantageously made of a material that conducts electricity well, particularly metals, such as copper. Alternatively, or in addition to these, the contacts can also be formed as full-surface or partial-surface contact plates, particularly with a nonwoven fabric layer between the contact plate and the electrode substrate. This forms multiple individual contacts that transport the current.

[0004] During the operation of such electrodes, the size, or dimensions, of the electrodes may change in at least one spatial direction, but generally in several spatial directions, based on temperature changes. Therefore, it is advantageous when individual electrical contacts are not fixedly and inseparably connected to the electrodes. This applies to contacts formed as individual elements, such as pins, as well as to contacts in the form of nonwoven fabric, or contacts that do not use nonwoven fabric. This allows for relative motion between the contact, i.e., the conductor, and the electrode.

[0005] Leakage in the seals that keep the reaction bath closed to the atmosphere can introduce aggressive and corrosive gases outside the original reaction bath. These are detrimental, particularly in the passive region, as corrosion, oxidation, or other changes in the substrate and / or conductive materials can degrade or completely block electrical contact at at least some of the contacts. In this case, the current transmitted to the electrodes through the contacts must flow through fewer contacts. The current density at the remaining contacts, and therefore the thermal load, also increases, leading to further failure. This also applies to electrodes with substrates made from silicon. In addition, localized temperature increases at the remaining contacts can lead to localized temperature increases at the electrode substrate, potentially damaging the substrate.

[0006] Silicon is used particularly for resistivity below 20 mOhm*cm. For this reason, it may need to be doped in some cases.

[0007] It is known from the prior art that metal layers with high electrical conductivity, such as copper, silver, or gold, are used for electrical contact. For example, a silver-based contact material is described in European Patent No. 2826576. European Patent No. 1433867 describes another type of contact material based on silver or tin. These can be bonded to the passive side by appropriate adhesion promoters and surface preparation of a silicon substrate. However, in many electrode applications, such as semiconductor technology, the use of metals is impossible to avoid metal contamination. In addition, metal coatings often form an oxide layer, resulting in associated drawbacks. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] European Patent No. 2826576 [Patent Document 2] European Patent No. 1433867 [Overview of the project]

[0009] This invention is based on the objective of avoiding, or at least reducing, the drawbacks of the prior art.

[0010] The present invention solves the set problem with the electrode described in the premise of paragraph 1, characterized in that the passive side has a doped carbon compound. The specific resistivity of the carbon layer is about three orders of magnitude greater than that of one of the above metals, but the doped carbon coating provides a layer on the passive side of the electrode substrate that provides sufficiently good electrical contact on the one hand, and good protection against aggressive and / or corrosive gas phases on the other hand. This also applies in the case of leakage resulting in liquid contact between the electrolyte and the passive side of the electrode. [Modes for carrying out the invention]

[0011] The present invention is based on the recognition that when a carbon coating is formed particularly as a doped diamond coating, it significantly reduces wear and corrosion on the passive side of the electrode while still maintaining sufficient conductivity. In addition, the rough surface of the carbon coating, especially the diamond coating, may have an activating effect on the individual elements or pins used to transmit current, as oxide layers formed on the individual elements or pins are mechanically removed by the relative motion between the electrode and the individual elements or pins.

[0012] In particular, doped carbon coatings are doped diamond coatings. For example, doping with boron increases the electrical conductivity of the diamond coating to a degree that allows it to transmit the current necessary for the operation of the electrodes.

[0013] In particular, the substrate is made from silicon. Alternatively, or in addition to this, the doped carbon coating is doped with boron. The silicon is specifically designed for high conductivity.

[0014] In one preferred embodiment, the electrode has a doped diamond coating on the active side, which is particularly doped with boron.

[0015] In addition, the present invention relates to a method for manufacturing electrodes of the type described herein, a) A step of coating the active side of the substrate with a doped diamond coating, b) A process of cleaning the passive side, c) A step of covering the passive side with a doped carbon coating, The problem is solved by a method that encompasses all aspects.

[0016] In step a), a doped diamond coating is first applied to the active side of the substrate. This is done by vapor deposition, which is particularly known from the prior art as the CVD (chemical vapor deposition) method. In this case, it is advantageous if this coating is applied only to the active side of the substrate. However, since this is difficult to achieve with vapor deposition, after step a) is performed, the passive side of the substrate, located opposite the active side, also has a small amount of coating. By appropriately selecting the distance between substrates that are coated simultaneously in one step, the coating on each passive side of the substrate can be reduced.

[0017] Therefore, in step b), the passive side of the substrate is cleaned. In this case, the deposits and precipitates that were present on the passive side of the substrate in step a) are removed. Then, the cleaned passive side is coated with a doped carbon coating. This is also carried out, in particular, by the CVD method.

[0018] In that case, the doped carbon coating is only necessary in the area of ​​the passive side used for electrical contact. In the case of full-surface contact, a flat contact element, such as a plate, is placed on the passive side and pressed against it in particular. In this case, the entire passive side needs to be doped with a carbon coating. Similarly, if at least one flat contact element is used, but only partial surface contact is used where its surface is smaller than the passive side of the electrode, then the doped carbon coating only needs to be applied to the area of ​​the passive side that will be in contact with at least one contact element. It may be advantageous to use multiple, for example, two, three, or four flat contact elements. Even in the case of partial surface contact, it may be advantageous to apply a carbon coating to the entire passive side of the electrode.

[0019] Similarly, when contacting by a pin or a similar element, a carbon coating doped only in the area on the passive side that will contact the contacting element may be provided. It is advantageous to cover a larger area, particularly the entire passive side.

[0020] When at least one flat contact element is used, it is advantageous to polish the passive side and, optionally, etch it before coating it with the doped carbon coating. Thereby, even without a flat contact element, the passive side can be processed.

[0021] Particularly, before coating the passive side, the passive side is polished, and particularly preferably, the material of the substrate is removed. Coating the active side of the substrate causes slight bending and deformation of the substrate, thereby also deforming the passive side of the substrate. In particular, this affects the flatness of the passive side of the substrate. Therefore, in step b), not only is the passive side cleaned, but it is also polished flat. Particularly in the case of contact on the entire surface or a partial surface where a current distribution as uniform as possible should be achieved for various individual contacts, the bending of the passive side makes it difficult to achieve uniform electrical contact on the passive side. Furthermore, when polishing the passive side, residues that may have been formed on the passive side during CVD coating are removed. It is particularly preferable that a natural silicon surface becomes available after cleaning the passive side. Polishing the passive side is particularly advantageous when contact is to be made on a large surface of the passive side, particularly the entire surface. When only individual elements or pins are used, the effect of polishing is small but still advantageous.

[0022] In a preferred embodiment, a substrate to be polished, which already has a diamond coating doped on its active side, is placed on a support that specifically protects the coated active side for polishing. For this purpose, a foil assembly is used, for example, to compensate for slight irregularities on the coated active side and at the same time prevent mechanical shock and damage. In particular, a two-part polishing process is used. In the first polishing step, the diamond-coated area on the passive side is removed. Other incidentally deposited carbon layers, such as graphite or amorphous carbon, are also removed in this step. In this case, feeding to the silicon surface is kept to a minimum. Once the carbon layer has been removed from the passive side, the substrate material, particularly silicon, is removed in the second polishing step. Each polishing step is performed with a feed rate of, for example, 10 μm. Multiple such polishing steps can be performed sequentially, in which case it has been found advantageous that up to five such feed rates are used, thereby removing up to 50 μm of substrate material.

[0023] In particular, after polishing, the passive side is potassium hydroxide (KOH) aq ) or hydrofluoric acid (HF aq The passive side is etched with hydrogen or sulfuric acid (H2SO4) to remove carbon, especially graphite. In this case, the sulfuric acid treatment is quite rough. If the passive side is polished, there is usually no longer any carbon or graphite present on the passive side. In this case, the passive side can be etched with potassium hydroxide, for example, to remove wear damage from the surface.

[0024] In one preferred embodiment, when cleaning the passive side, the passive side is cleaned in at least one vapor-phase etching step, particularly using hydrogen (H2) gas. Vapor-phase etching further cleans the surface of the passive side of the substrate. By fitting the diamond nucleus, it is possible to achieve as few defects as possible in the layer when the passive side is subsequently coated with a doped carbon coating.

[0025] In particular, the doped carbon coating has a thickness of less than 5 μm, preferably less than 2 μm. It is preferable that it has a thickness of at least 1 μm. For a closed, but not necessarily defect-free, coating, the thinnest possible layer thickness is aimed for. The thinner the carbon coating, the less influence the coating has on the substrate. By making the coating as thin as possible, new bending and mechanical stress on the substrate are reduced. In addition, costs are reduced. The carbon coating is particularly a diamond coating. However, it can also be formed as a graphite layer, or a combination of a graphite layer and a diamond layer. While it is advantageous for the carbon layer to be completely defect-free, it is not necessary. The applied carbon coating is loaded only at points at individual electrical contacts.

[0026] In particular, the passive side had a surface roughness of 0.2 μm before being coated with a doped carbon coating. <R a <0.6, and / or after coating, R z <10 μm and / or R a It is <1 μm.

[0027] In one preferred embodiment, the doped carbon coating is sp 3 The composition is a doped polycrystalline diamond coating. Similarly possible sp 2 The doped carbon coating of the structure has lower chemical corrosion resistance and inferior mechanical properties. In its neutral ground state, a carbon atom has four electrons in its outermost shell, two of which are in the so-called "s" orbitals and two in the so-called "p" orbitals. These four orbitals are hybridized in the diamond structure, forming what is called "sp" orbitals. 3 "Forms an orbit." The following is a direct reproduction of the claims as originally filed. [1] An electrode for an electrochemical reaction bath, a. Substrate and, b. The active side is set to be in contact with the reaction bath, c. An electrode having a passive side configured to contact at least one conductor, wherein the passive side is characterized by having a doped carbon coating. electrode. [2] The electrode according to [1], characterized in that the doped carbon coating is a doped diamond coating. [3] The electrode according to [1] or [2], characterized in that the substrate is made of silicon and / or the doped carbon coating is doped with boron. [4] The electrode according to any one of [1] to [3], characterized in that the active side has a doped diamond coating, wherein the diamond coating is doped in particular with boron. A method for manufacturing an electrode as described in any one of the items [5] [1] to [4], a. A step of coating the active side of the substrate with a doped diamond coating, b. The process of cleaning the passive side, c. A step of covering the passive side with the doped carbon coating, A method of including. [6] The method according to [5], characterized in that, before coating the passive side, the passive side is polished, in particular the material of the substrate is removed. [7] The method according to [6], characterized in that, after polishing, the passive side is etched with potassium hydroxide (KOH) or hydrofluoric acid (HF). [8] In order to clean the passive side, the passive side is subjected to at least one gas-phase etching step, particularly hydrogen (H 2 The method according to [5], [6], or [7], characterized by being washed in a gas. [9] The method according to any one of [5] to [8], characterized in that the doped carbon coating has a thickness of less than 5 μm, preferably less than 2 μm, and particularly at least 1 μm.

[10] The passive side had a surface roughness of 0.2 μm before being coated with the doped carbon coating. <R a <0.6 μm, and / or after the coating, R z <10 μm and / or R a The method according to any one of [5] to [9], characterized in that the size is <1.0 μm.

[11] The doped carbon coating is sp 3 The method according to any one of [5] to

[10] , characterized in that the composition is a doped polycrystalline diamond coating.

Claims

1. An electrode for an electrochemical reaction bath, a. Substrate and, b. An active side set to be in contact with the electrolyte in the electrochemical reaction bath, c. An electrode having a passive side set to be in contact with at least one conductor outside the electrochemical reaction bath, wherein the passive side has a doped carbon coating, The doped carbon coating is a doped diamond coating, The aforementioned doped carbon coating is doped with boron, An electrode characterized in that the active side has a doped diamond coating, and the doped diamond coating on the active side is doped with boron.

2. The electrode according to claim 1, characterized in that the substrate is made of silicon.

3. A method for manufacturing the electrode described in claim 1, a. A step of coating the active side of the substrate with a doped diamond coating, b. A process of cleaning the passive side, c. A step of covering the passive side with the doped carbon coating, A method of including.

4. The method according to claim 3, characterized in that, before coating the passive side, the passive side is polished and the substrate material is removed.

5. The method according to claim 4, characterized in that, after polishing, the passive side is etched with potassium hydroxide (KOH) or hydrofluoric acid (HF).

6. To clean the passive side, the passive side is subjected to at least one gas-phase etching step, which involves hydrogen (H ２ The method according to claim 3 or 4, characterized in that it is washed in a gas.

7. The method according to claim 3 or 4, characterized in that the doped carbon coating has a thickness of less than 5 μm.

8. The passive side, before being coated with the doped carbon coating, has a surface roughness of 0.2 μm < R ａ <0.6 μm, and / or after coating, R ｚ <10 μm and / or R ａ The method according to claim 3 or 4, characterized in that it is <1.0 μm.

9. The doped carbon coating, sp ３ The method according to claim 3 or 4, characterized in that the composition is a doped polycrystalline diamond coating.