EP4124676A1 - Electrolysis system with a plurality of electrolysis cells - Google Patents

Abstract

The invention relates to an electrolysis system (60) with a plurality of electrolysis cells (12) which are electrically connected in series and which are at least partially arranged one after the other in a stacking direction (14), the series connection being electrically coupled to an electrical energy source (16), and with a cell supply unit (18) for supplying the electrolytic cells (12) with at least one fuel for proper operation, and with supply lines ( 24), wherein at least one of the supply lines (24) has an electrical insulating section (38) with a control electrode (66) protruding at least partially into the interior of the electrical insulating section (38).

Description

The invention relates to an electrolysis system with a plurality of electrolysis cells.

Known electrolysis systems have a large number of electrolysis cells which are used in the conversion of chemical substances into other chemical substances under the action of electricity. As a rule, a chemical reaction, i.e. a material conversion, is brought about with the help of an electric current.

For example, hydrogen is now produced using Proton Exchange Membrane (PEM) electrolysis or alkaline electrolysis. These electrolysis systems then use electrical energy to produce hydrogen and oxygen from the water supplied.

An electrolysis system has a large number of electrolysis cells which are arranged adjacent to one another. By means of water electrolysis, for example, water is broken down into hydrogen and oxygen in the electrolysis cells. In a PEM electrolyser, distilled water is typically fed in as starting material on the anode side and split into hydrogen and oxygen on a proton-permeable membrane (“proton exchange membrane”; PEM). The water is oxidized to oxygen at the anode. The protons pass through the proton-permeable membrane. Hydrogen is produced on the cathode side. In this case, the water is generally conveyed from an underside into the anode compartment and/or cathode compartment.

In water electrolysis, water is broken down into its components, namely hydrogen and oxygen, using electricity. In principle, however, other starting materials can also be subjected to electrolysis as starting materials be, for example carbon dioxide or the like.

These are usually fluid substances that can be fed to the electrolysis cells in an electrolysis system via appropriate supply lines, in which the actual electrolysis is carried out. The electrolysis products are often also in fluid form and are discharged from the electrolysis cells via additional supply lines. The supply lines are usually connected to a cell supply unit, which is used to supply the electrolytic cells with the respective substances or at least one operating substance for normal operation. In this case, supplying means not only supplying the operating material or the substance to be electrolyzed, but also discharging the respective electrolysis product, i.e. it includes the supplying of the educt fluid and the discharging of the product fluid that is obtained from the electrochemical conversion process.

The provision of hydrogen in particular is proving to be particularly interesting on an industrial scale, especially since hydrogen is a versatile energy carrier. Hydrogen can be provided with an electrolysis system, also known as an electrolyser, using regeneratively generated electrical energy. One way of generating hydrogen is to use an electrolysis plant whose electrolysis cells are based on proton exchange membranes (PEM). The principle of a PEM-based electrolysis system or PEM-based electrolysis cell is known in the prior art, which is why further explanations on this are dispensed with. An electrolytic cell for generating hydrogen and oxygen from water is, for example, by the DE 10 2011 007 759 A1 disclosed. But also the DE 10 2019 205 316 A1 describes a corresponding electrolytic cell for energy-efficient hydrogen production. Furthermore, the DE 21 2018 000 414 U1 a hydrogen generation system. Generic electrolysis systems usually have a plurality of electrolysis cells, which are usually electrically connected in series. The series circuit thus formed is electrically coupled to an electrical energy source which provides a suitable electrical voltage, so that the intended process of electrochemical material conversion can be implemented by means of the electrolytic cells.

Furthermore, the electrolytic cells are sequentially arranged in a stacking direction, so that a cell stack is formed. The stacked arrangement makes it possible for the electrolytic cells arranged one after the other to be directly electrically contacted with one another, for example by mechanical pressing, so that separate electrical connections of the electrolytic cells can be largely reduced.

A supply line system (manifold) is also provided within the cell stack, which serves to supply or discharge the at least one fuel to the electrolysis cells. The operating substance can include, for example, the supplied fluid, for example water, and/or the reaction product, for example hydrogen and oxygen. The cell stack is usually operated with a specific electrolysis output in such a way that the electric current is as small as possible, but the electric voltage is as high as possible. This is achieved by suitably stacking the electrolytic cells in the cell stack. As a result, electrical voltages at the respective electrolytic cells in the cell stack can add up to the cell stack voltage, while the electrolytic cells connected in series in this way can be operated with essentially the same current.

The electrolysis power for the operation of the electrolysis system is provided by the energy source that is connected to it Purpose can be connected to respective opposite ends of the cell stack. A large number of electrolytic cells can be arranged in a cell stack, for example more than 100 electrolytic cells, in particular several hundred electrolytic cells, but preferably no more than about 400 electrolytic cells. During the electrolysis of water to form hydrogen and oxygen, the electrical voltage at one of the respective electrolytic cells is around 1.5 V to 2.5 V. This results in the electrical voltage at the cell stack, so that the electrical voltage at the cell stack often exceeds 100 V, can even be several hundred volts.

In addition to the cell stack, the electrolysis system includes other components, such as pumps, heat exchangers, separator tanks, which are required for the intended operation of the electrolysis system or the electrolysis cells. In the present case, these components are combined by the cell supply unit for supplying the electrolytic cells with at least one fuel for the intended operation.

The cell supply unit is connected to the electrolytic cells lined up in a stacking direction via supply lines connected to the opposite ends of the electrolytic cells lined up. The umbilicals are typically formed from a material such as metal or the like.

A correspondingly high electrical voltage occurs between the ends of the cell stack or the electrolytic cells arranged one after the other. It is therefore necessary for the supply lines, which are generally made of a metal, to have respective electrical insulating sections which serve to ensure a good electrical conductive connection between the ends of the electrolytic cells arranged one after the other and thus between the electrical connections of the electrical energy source.

Basically, the application according to the prior art has proven itself, but it has been found that particularly in the area of the supply line adjoining the electrical insulating section, which is subjected to a positive electrical potential of the electrical energy source in normal operation, a corrosion can occur. Oxidative decomposition of the metallic pipe material takes place in this anodic area of the supply line. This is not only harmful to the electrolysis system as such, but can also lead to contamination of the at least one operating material and thus to disruptions in the intended operation of the electrolysis cells.

In order to reduce this problem, it is known in the prior art to keep the specific electrical conductivity of the water as low as possible and to kinetically inhibit corrosion by means of the longest possible insulation section or also a cross-section reduction in the area of the respective insulation section, and thus to increase the effect over time stretch. However, this basically cannot prevent corrosion. In particular, the constant, albeit low, electrical conductivity of water, in particular within the insulating section formed by the insulating section, leads to stray currents in the water, particularly within the insulating section. As a result, the problem of corrosion continues to exist, which is disadvantageous for the service life of an electrolysis system.

The invention is based on the object of specifying an electrolysis system which reduces the aforementioned problem of corrosion.

This object is achieved by an electrolysis system with a plurality of electrolysis cells that electrically connected in series and which are at least partially arranged one after the other in a stacking direction, wherein the series connection can be electrically coupled to an electrical energy source, comprising a cell supply unit for supplying the electrolytic cells with at least one fuel for proper operation, and comprising on the cell supply unit and on opposite Supply lines connected to the ends of the successively arranged electrolytic cells, at least one of the supply lines having an electrical insulating section with a control electrode protruding at least partially into the interior of the insulating section.

Advantageous developments result from features of the dependent claims.

The invention is based on the knowledge that previous operating concepts for electrolysis systems are complex in terms of system technology with regard to avoiding and remedying degradation phenomena, especially with regard to damaging corrosion effects, and have significant economic disadvantages. In particular, effective and sustainable solutions have not yet been proposed in conventional approaches. Rather, the problem of corrosion continued to exist, which is disadvantageous for the service life of an electrolysis system.

Since there are typically several hundred volts across the insulating section resulting from the insulating section during operation of the electrolysis system, there is a significant excess of electrons on one supply line and a corresponding lack of electrons on the other due to the high voltage difference. The voltage here is so great that, from a thermodynamic point of view, electrode reactions take place. By lowering the specific conductivity of the water or by lengthening or narrowing the insulation sections, this reaction can be slowed down, i.e. kinetically inhibited. she lets but never stop it completely, so it's just a workaround. The water within the insulation section always has a low conductivity, so that as a consequence stray currents flow through the operating material, in particular through the water in the case of water electrolysis, in the area of the insulating section of the supply line.

On the cathodic side with excess electrons, water is split, producing hydrogen and hydroxide ions. The hydrogen is in the form of tiny bubbles or dissolved and is transported away with the water. The quantities produced are so small that the hydrogen has no disruptive effects. The hydroxide ions are in dissolved form in the water and, because of their negative charge and the direction of the prevailing electrical field, tend to migrate from the cathodic side of the supply line in the direction of the insulating section and the anodic side of the supply line located behind it and adjoining it.

On the other hand, the metallic pipe material of the supply line is decomposed by oxidation on the anodic side. In the case of a supply line made of stainless steel, for example, metallic iron Fe dissolves as Fe ³⁺ due to anodic corrosion, so that significant amounts of Fe ³⁺ foreign ions are introduced into the water over time. However, other species can also be formed, for example rust, which remains locally on the surface and is recognizable by the characteristic brown color. In addition to iron, other metals present in the steel can also be dissolved and form damaging cations. Because of the positive charge, these metal cations have the tendency to migrate in the opposite direction of the hydroxide, which leads to further adverse consequences through the formation of so-called rouging. Rouging are the finest iron-containing particles that are distributed in the pipes and components of the electrolysis system.

It has also been recognized as a major disadvantage that metal ions can get into the membrane electrode assemblies (MEAs) from the oxygen side and accumulate there. Among other things, this process leads to higher cell voltages. Furthermore, MEA-damaging mechanisms are associated with these metal ions. For example, H ₂ O ₂ formed at the electrodes can be converted into radicals when they come into contact with metal ions, which chemically attack the membrane structure of the MEAs and can thus impair the service life.

This is where the present invention comes in, in that the formation and release of a critical foreign ion concentration of damaging cations in the supply line in the area of the insulation section is avoided as far as possible in an electrolysis system and appropriate precautions are taken. With the control electrode provided for this purpose partially protruding into the interior of the insulating section, a stray current does not flow off via the metallic pipe material of the supply line, particularly on the anodic side of the insulating section, but rather via the control electrode. Corrosion on the anode side is thus suppressed, since no damaging metal cations, such as Fe ³⁺ , can go into solution from the ferrous material of the supply line. The damaging processes, in particular those processes on the anodic side, as explained above, can be very efficiently and, above all, sustainably suppressed and practically completely avoided with the control electrode. The service life of the electrolysis system is advantageously increased. The insulating section has a tubular design and is connected in a flow-tight manner to the supply line, for example as a connecting flange. The operating substance in the supply line having the insulating section can thus be guided in a fluid-tight manner through the insulating section. The insulating section has an axial extent in the axial direction, ie in the direction of flow of the service fluid. The control electrode partially protrudes inside the insulating portion. The control electrode can vary depending on the configuration and achievable control efficiency for corrosion-reducing stray current consumption, between 30% and 70%, preferably about 40% to 60%, protrude in the axial direction into the interior of the insulating section, measured from the anodic side of the insulating section. The control electrode is advantageously in electrical contact with the metallic tube section of the supply line on the anodic side and is set to a corresponding potential, so that the release of metal cations, such as Fe ³⁺ , from the metallic tube material of the connecting line in the anodic section of the supply line is efficiently avoided and corrosion protection is achieved. The control electrode acts electrically and, due to its dimensions and geometry with a correspondingly low flow resistance for a fluid flowing around it, does not impair the delivery of the operating substance in the supply line, or does so only to an insignificant extent.

According to a particularly advantageous development of the electrolysis system, it is proposed that the supply lines be made of metal, with the electrolysis cells being arranged in at least two sub-stacks, with each of the at least two sub-stacks being connected by at least one first to the cell supply unit and to a first end of the respective sub-stack supply line and at least one second supply line connected to the cell supply unit and to a second end of the respective sub-stack opposite the first end in the stacking direction, is connected to the cell supply unit, wherein that first supply line which is connected to the first end of that sub-stack which is connected to a negative electrical Potential of the electrical energy source can be coupled, is electrically conductively connected to the cell supply unit and all other supply lines are electrically connected e have insulating sections, a plurality of the insulating sections having a respective control electrode which projects at least partially into the interior of the insulating section. Advantageously, if necessary, even all insulating sections are equipped with a respective control electrode that protrudes at least partially into the interior of the insulating section.

A particularly comprehensive protection against corrosion is thus achieved in the electrolytic system, since damaging stray currents are discharged in a majority, if necessary, even in each of the electrical insulating sections, insofar as these corrosion effects are to be feared. Thus, the release of metal cations is efficiently and sustainably suppressed even in a complex electrolysis system with several sub-stacks of electrolysis cells. The corrosion protection concept of the invention can therefore also be flexibly applied and adapted to electrolysis systems on an industrial scale with a high electrolysis capacity. The electrical insulating sections of the supply lines that are susceptible to corrosion are specifically equipped with a control electrode that protrudes at least partially into the interior of the insulating section, in particular on the anodically acting side. The control electrode partially protrudes inside the insulating portion. Depending on the design and the control efficiency that can be achieved, the control electrode can protrude in the axial direction into the interior of the insulating section by between 30% and 70%, preferably between 40% and 60%, to reduce corrosion by stray current consumption. This can be designed flexibly depending on the local geometry in the area of the connecting line and insulating section and the requirements for corrosion protection.

A plastic, a ceramic, but also a metal oxide such as, for example, titanium dioxide, aluminum oxide and/or the like can be provided as the material for the electrically insulating section. In addition, a composite material can also be provided, which can be formed from a plastic, for example, which can be fiber-reinforced, for example. Of course, almost any combination of these can also be provided, which preferably are selected in such a way that a chemical reaction with the fuel to be supplied in each case is essentially avoided.

The material of the supply line has at least metal. The metal can, for example, be steel, in particular stainless steel. In addition, another metal, for example titanium or the like, can of course also be used. Appropriate metal alloys can of course also be provided.

The electrical energy source of the electrolysis system can be, for example, any voltage source or current source that is able to provide sufficient power for the electrolysis to be carried out by the electrolysis cells. An electrolysis output can be determined at a specific surface current density as a function of the dimensions of the respective electrolysis cell, in particular of its electrolysis-technically effective areas.

The supply lines have a through-opening with a suitable inside diameter or cross-section in order to be able to lead the respective fuel to the electrolysis cells with as little loss as possible and/or to be able to remove it from the respective electrolysis cells or the sub-stacks with as little loss as possible.

In a further preferred embodiment of the electrolysis system, the control electrode is arranged in such a way that, in normal operation when the fuel is supplied, a stray current in the supply line can be derived via the control electrode due to its anodic effect.

The anode-side electrical connection and effect of the control electrode is particularly efficient and therefore advantageous, since metal cations are released in the area of the anodic side of the supply line adjoining the insulating section is particularly corrosive and therefore damaging due to stray currents.

In a preferred embodiment, the control electrode is wire-shaped, rod-shaped or grid-shaped. In principle, a variety of geometric configurations and material compositions are flexibly available. Designing the control electrode from a metal wire and/or with a rod or lattice geometry is particularly advantageous due to the good local adaptability when installed and the low flow resistance that the control electrode still opposes to the fuel conveyed in the supply line during operation inside the insulating section. It is also possible for the control electrode to be configured from a cylindrical or cup-shaped wire mesh. As a result, a larger effective area of the control electrode is provided over the internal cross section of the supply line in order to practically completely divert or prevent damaging, corrosion-promoting stray currents. At the same time, this geometry ensures that the electrical control electrode has a sufficiently low flow resistance to the conveyance of the fuel inside the supply line.

Furthermore, the control electrode preferably has a carrier metal of high conductivity, in particular titanium, coated with a catalyst material.

For example, the base body of the control electrode can have or be composed of an oxidation-resistant material of high conductivity. Titanium is the preferred option here. For example, a titanium expanded metal can also function as a carrier or base body of the control electrode or, as described, the rod-shaped or wire-shaped configuration. The catalyst material is applied to this base body. The catalyst material of the coating is preferably chosen so that it, for example, the electrochemical Favors decomposition of water into protons and oxygen.

In a preferred embodiment, the catalyst material has a noble metal oxide. More preferably, the coating of the control electrode contains a catalyst material which has a mixed oxide comprising iridium and/or ruthenium.

Thus, for example, a titanium-based control electrode in the form of a titanium mixed-oxide anode can be used, with a titanium carrier that is activated with a mixed-oxide layer. The layers mainly consist of noble metal oxides from the platinum metal group with other dopings, so that so-called metal mixed oxide anodes (MMO) are formed.

Depending on the requirement, an MMO anode, for example, such as is used for an electrophoretic coating process, can also be used as an anodically acting control electrode in the insulating section of the electrolysis system. These are preferably based on an iridium-tantalum activation, 12.5 g iridium per square meter, such as titanium expanded metal type A, for example realized with a fastening element, for example in the form of a welded hook, for fastening and electrical contacting of the control electrode on the anodic side of the supply line .

A plastic, a ceramic, but also a metal oxide such as, for example, titanium dioxide, aluminum oxide and/or the like can be provided as the material for the electrically insulating section. In addition, a composite material can also be provided, which can be formed from a plastic, for example, which can be fiber-reinforced, for example. Of course, almost any combination of these can also be provided, which are preferably selected in such a way that a chemical reaction with the respective fuel to be supplied is essentially avoided.

The material of the supply line has at least metal. The metal can, for example, be steel, in particular stainless steel. In addition, another metal, for example titanium or the like, can also be used. Appropriate metal alloys can of course also be provided.

In a particularly advantageous embodiment of the electrolysis system, the respective ends of the partial stacks facing the respective insulating sections are electrically insulated from the electrolysis cells.

It can thereby be achieved that the corrosion effect is largely avoided in the region between the insulating section and the respective end of the partial stack. The effect of the invention can thereby be further improved.

In a preferred configuration of the electrolysis system, the cell supply unit is at least indirectly electrically grounded. Due to the grounding, the cell supply unit with the supply lines electrically coupled to the cell supply unit can be connected to a predetermined reference potential. As a result, the negative potential of the electrical energy source, which is electrically coupled to the cell supply unit via the supply lines, can also be at least grounded indirectly. In contrast to the prior art, the cell stack formed from the sub-stacks is therefore at a defined electrical potential with respect to ground potential and is therefore no longer subject to floating potential. A defined electrical potential difference or electrical voltage can thus be achieved at the respective electrical insulating sections. This allows the reliability of the function of the invention to be further improved.

Furthermore, in an advantageous embodiment, it is proposed that the grounding be a sacrificial anode and/or a voltage source has, by means of which the cell supply unit can be subjected to an electrical potential which is negative with respect to the ground potential. In this way, "cathodic protection against corrosion" can be achieved. If a voltage source is used, the negative electrical potential of the voltage source can be electrically connected to the cell supply unit and to the supply lines connected to it. The negative electrical potential of the voltage source is preferably grounded accordingly at the same time. For the corrosion protection implemented in this way to function properly, the voltage source can provide an electrical voltage in a range from approximately −2 V to approximately 0 volts in relation to ground potential. It proves to be particularly advantageous if this electrical voltage is selected in a range from approximately -1 V to approximately -0.8 V. With an electrical voltage selected in this range, corrosion of stainless steel, for example, can also be avoided under maritime conditions, especially in off-shore applications. In particular, an external corrosion phenomenon can be reduced or prevented in this way.

In a particularly advantageous embodiment, the partial stacks are connected in parallel to the cell supply unit in terms of supply. In this way, a good supply of the at least one fuel can be achieved for the sub-stacks. The supply can include supplying or also discharging the fuel or substances produced during the electrolysis.

In order to equally reduce or avoid an internal corrosion phenomenon, provision can preferably be made for a further electrode to be arranged in the manner of a counter-electrode for cathodic protection against corrosion in the area of the cell supply unit. The internal corrosion phenomenon refers in particular to corrosion effects within the electrolysis plant, especially within the cell supply unit. For example, it can be This is a titanium electrode or titanium anode, which can be coated with a mixed oxide. Preferably, the anode formed in this way is arranged in a liquid phase of an oxygen separation tank of the cell supply unit.

The partial stacks are particularly advantageously connected in parallel to the cell supply unit in terms of supply. In this way, a good supply of the at least one fuel can be achieved for the sub-stacks. The supply can include supplying or also discharging the fuel or substances produced during the electrolysis.

The features and combinations of features mentioned above in the description and the features and combinations of features mentioned below in the description of the figures and/or shown alone in the figures can be used not only in the combination specified in each case, but also in other combinations without departing from the scope of the invention .

The exemplary embodiments explained below are preferred embodiments of the invention. The features and combinations of features specified above in the description and also the features and combinations of features mentioned in the following description of exemplary embodiments and/or shown alone in the figures can be used not only in the combination specified in each case, but also in other combinations. The invention therefore also includes or is to be regarded as disclosed embodiments which are not explicitly shown and explained in the figures, but which result from the explained embodiments and can be generated by means of separate combinations of features. The features, functions and/or effects illustrated with reference to the exemplary embodiments can in each case be individual features, functions and/or effects that are to be considered independently of one another Represent effects of the invention, which also develop the invention independently of one another. Therefore, the exemplary embodiments are also intended to include combinations other than those in the illustrated embodiments. In addition, the described embodiments can also be supplemented by further features, functions and/or effects of the invention that have already been described.

In the figures, the same reference symbols designate the same features or functions.

FIG 1

in einer schematischen Blockdarstellung eine Elektrolyseanlage zur Elektrolyse von Wasser;

FIG 2

eine schematische Schnittdarstellung einer Versorgungsleitung der Elektrolyseanlage gemäß FIG 1 im Bereich eines Isolierabschnitts;

FIG 3

eine schematische Schnittdarstellung einer Versorgungsleitung der Elektrolyseanlage gemäß FIG 1 im Bereich des Isolierabschnitts mit einer Steuerelektrode;

FIG 4

eine schematische Blockdarstellung einer weiteren Elektrolyseanlage zum Elektrolysieren von Wasser, bei der ein Zellenstapel in vier Teilstapel aufgeteilt ist.

Show it:

FIG 1

in a schematic block diagram, an electrolysis system for the electrolysis of water;

FIG 2

a schematic sectional view of a supply line of the electrolysis system according to FIG FIG 1 in the area of an insulating section;

3

a schematic sectional view of a supply line of the electrolysis system according to FIG FIG 1 in the area of the insulating section with a control electrode;

FIG 4

a schematic block diagram of another electrolysis system for the electrolysis of water, in which a cell stack is divided into four sub-stacks.

FIG 1 shows in a schematic block diagram an electrolysis system 10 which has a cell stack 54 which has a plurality of electrolysis cells 12 which are arranged one after the other in a stacking direction 14 . In the present case, the electrolytic cells 12 are used to electrochemically decompose water into its components, oxygen and hydrogen. The electrolysis system 10 is therefore used in the present case to generate hydrogen and oxygen from water.

In the present case, the electrolysis cells 12 are arranged directly adjacent to one another, so that respective electrodes of the electrolysis cells 12 arranged adjacent can make electrical contact with one another. It is provided that in each case an anode of a first of the electrolytic cells 12 makes electrical contact with a cathode of the second electrolytic cell 12 which is arranged immediately adjacent in each case. As a result, the electrolytic cells 12 are electrically connected in series.

The electrolytic cells 12 are supplied with water to be electrolyzed on the one hand and discharges for the produced substances hydrogen and oxygen are provided on the other hand via an internal supply structure of the cell stack 54 that is not shown in any more detail. This supply can be connected to opposite ends 20, 22 of the cell stack 54 in each case.

An electrical energy source 16 is also connected to the ends 20, 22 via an electrical line 52, which in the present case provides a suitable electrical voltage with a suitable electrical output, so that the electrolytic cells 12 can be supplied with sufficient electrical energy for normal operation.

The electrolysis system 10 also includes a cell supply unit 18, which is used to supply the electrolysis cells 12 or the cell stack 54 with the respective operating materials, which in the present case relate to the supply of water and the removal of hydrogen and oxygen. A discharge line 46 for hydrogen and a further discharge line 48 for the oxygen are provided in the cell supply unit 18 for discharging the products. A corresponding feed 50 for water is connected to the cell supply unit 18 for the supply of water as a reactant of the electrolysis. The cell supply unit 18 also includes a number of components that are required for the intended operation of the electrolysis system 10 are, such as pumps, heat exchangers, separator tanks and/or the like, which, however, are not further illustrated here. The cell supply unit 18 is supply-connected to the cell stack 54 via supply lines 24 which are connected to the cell supply unit 18 and the opposite ends 20, 22 of the cell stack 54. The supply lines 24 thus fluidly couple the supply structure of the cell stack 54. In the present case, the supply lines 24 are formed from a metal such as stainless steel.

In order to avoid a short circuit between the ends 20, 22 of the cell stack 54 caused by the metal supply lines 24, each of the supply lines 24 has an electrically insulating section 38. This ensures that the ends 20, 22 are designed to be electrically insulated from the cell supply unit 18 and thus also electrically insulated from one another. The supply lines 24 are located outside of the cell stack 54.

In the present case, the insulating sections 38 are essentially formed from an electrical insulating material, which can be, for example, a suitable ceramic material or also a suitable plastic or composite material.

FIG 2 FIG. 12 shows a schematic sectional view of one of the supply lines 24. FIG FIG 1 in the area of the insulating section 38. In FIG 2 the supply line 24 is shown with a first region 58 which faces the end 22 of the cell stack 54 , whereas an opposite second region 56 faces the cell supply unit 18 . The areas 56 and 58 are electrically isolated from one another by the insulating section 38 . This arrangement is designed to be fluid-tight overall and has an essentially constant inner diameter 62 through which the corresponding fluid can be guided, which in this case is water.

Corrosion occurs in a region 64 due to the electrical voltage applied to the electrical insulating section 38 . This can be considered to be due to the fact that negative hydroxide ions are formed in the area of a transition from area 56 to the electrical insulation section 38 due to electron absorption from the metal of the wall of the supply line 24 into the water flowing in the inner diameter 62, which is caused by the electric field are conducted to region 58 and there react electrochemically with the metal of the wall of supply line 24, as in FIG FIG 2 shown. As a result, the wall of the supply line 24 corrodes in this area 64. This is undesirable and disadvantageous for the operation of the electrolysis system with regard to the service life.

For this type of corrosion, it must be considered that a DC voltage in the range of several hundred volts can generally be present across the electrical insulating sections 38 during normal operation. This can result in an excess of electrons in the area 56 and in the area 58 an electron deficiency in the area of the electrical insulating section 38 . From a thermodynamic point of view, due to the magnitude of the electrical voltage at the electrical insulating section 38, electrode reactions take place as previously explained. Although the corrosion effect can be extended over time by reducing the electrical voltage, i.e. kinetically inhibited, it cannot be completely prevented. An extension of the insulating distance by means of the electrical insulating section 38 or a reduction in the inner diameter 62 can only inhibit the effect of the corrosion, but cannot prevent it.

In the area 56, the hydrogen formed in this way can be dissolved in the water or it can also be present in the form of very small bubbles and be transported away with the water. The quantities produced are usually so small that the hydrogen itself does not have any disruptive effects.

However, this is not the case with regard to the hydroxide ions, which are present in dissolved form in the water. They tend to migrate from region 56 to region 58 because of their negative charge and the direction of the electric field in the region of the electrically insulating portion 38 . In this area 58, the metallic material of the supply line 24 is then decomposed by oxidation. In FIG 2 this decomposition is shown for the case that the supply line 24 is made of stainless steel. However, this effect is not limited to steel, but can occur with almost any other metallic material.

In addition to the release of iron as the cation Fe ³⁺ , other metals that may be present in the steel can also be dissolved. In this way, further cations can be formed. Because of their positive charge, the metal cations tend to migrate in the opposite direction to the hydroxide ions. This can lead to so-called rouging arising from the metal cations, especially when it comes to iron ions, and the hydroxide ions. Rouging means the finest iron-containing particles that can be distributed in the supply lines 24 and the components of the electrolysis system 10 . They can be observed above all in the supply lines 24, in which hydrogen is also carried. If this rouging gets into the oxygen-carrying part of the electrolysis system 10, the rouging can dissolve again with the formation of ions.

Among other things, cations can then get into the electrolytic cells 12 from the oxygen side and accumulate there. This process can lead to higher cell voltages and thus to reduced efficiency of the electrolysis system 10 . Furthermore, mechanisms damaging to the electrolytic cells 12 can be associated with these cations. For example, hydrogen peroxide formed at the electrodes can be converted into radicals upon contact with metal ions, which can damage a membrane structure of the electrolytic cells 12 attack chemically and so can adversely affect the service life of the electrolytic cells 12.

3 shows a schematic sectional view of a supply line 24, in which the adverse corrosion effect in the area of the insulating section 38, which is based on FIG 2 explained, is avoided very effectively and sustainably. In the 3 Supply line 24 shown is part of an electrolysis system 10, approximately accordingly FIG 1 with an insulating section 38. In 3 the supply line 24 is shown with a first region 58 which faces the end 22 of the cell stack 54 , whereas an opposite second region 56 faces the cell supply unit 18 . The areas 56 and 58 are electrically isolated from one another by the insulating section 38 . This arrangement is designed to be fluid-tight overall and has an essentially constant inner diameter 62 through which the corresponding fluid, the operating substance, can be guided in the axial direction inside the supply line. In this case, the fluid or fuel is water for the water electrolysis.

The supply line 24 has an electrical insulating section 38 with a control electrode 6 which projects at least partially into the interior of the electrical insulating section 38. The control electrode 66 is designed as a wire loop with a base material made of titanium. This results in high electrical conductivity. The control electrode 66 is also coated with a catalyst material 68 which has a mixed oxide comprising iridium and/or ruthenium. The catalyst material 68 is applied to the titanium base body so that a catalytically active layer is formed on the control electrode 66 . Electrical contact is made with the control electrode 66 via the first region 58 of the supply line 24, which forms the anodic side, and is set to a corresponding positive potential, so that stray currents can be derived.

The control electrode 66 is arranged and aligned in such a way that, during normal operation, when the fuel, in this case water, for the water electrolysis is supplied, an undesirable stray current in the supply line 24 is diverted via the control electrode 66 due to its anodic effect. On the anode side, i.e. in area 58, the stray current then no longer flows in a damaging manner via the material of the supply line 24, but instead via the control electrode 66. The catalyst material 68 achieves a catalytic effect on the control electrode 66, which promotes the electrochemical decomposition of the water favored in oxygen and protons. Due to the fact that the control electrode reaches noticeably, in the example between about 50% and 60% of the axial extension of the insulating section 38 , into the interior thereof, the stray current now flows on the anodic side in the area 58 via the control electrode 66 . Furthermore, the catalytic coating with the catalyst material 68 promotes the formation of oxygen at the control electrode 66, since the overvoltage for this electrocatalytically desired reaction is reduced in a targeted manner. Since the stray currents are relatively small, the resulting amounts of oxygen are quite small and do not impair operation, at least as long as these amounts of oxygen cannot accumulate in the insulating section 38 or in the adjacent areas 56, 58 of the supply line 24. However, this is ensured in the present case, since the overvoltage during operation of the electrolysis system 10 causes water to flow through the insulating section 38 on the inside. The accordingly FIG 1 The region 56 of the supply line 24 that is connected to the cell supply unit 18 acts cathodically, which means that no release of metal ions is to be expected there.

The particularly advantageous application of the invention is FIG 4 illustrated in a schematic block diagram of a further electrolysis system 60 for the electrolysis of water. In this complex electrolytic system 60, the aforementioned corrosion effect is in the area of the insulating section 38, based on 3 was explained, avoided sustainably and very effectively. The following explanations are also based on the previous explanations for the FIG 1 and 3 , which is why reference is also made to the relevant statements.

How out FIG 4 As can be seen, the electrolytic cells 12 are arranged in four partial stacks 26, 28, 30, 32. Each of the four sub-stacks 26, 28, 30, 32 is connected to the cell supply unit 18 and at a first end 20 of the respective sub-stack 26, 28, 30, 32 by means of two first supply lines 24 and two to the cell supply unit 18 and at the first end 20 in the stacking direction 14 opposite second end 22 of the respective sub-stack 26, 28, 30, 32 connected second supply lines 24 are connected to the cell supply unit 18. For the cell supply unit 18 essentially apply to the statements FIG 1 and 2 .

The first supply line 24, which is connected to the first end 20 of that partial stack 26 which is coupled to a negative electrical potential 34 of the electrical energy source 60, is electrically conductively connected to the cell supply unit 18. As a result, precisely this first end 20 of the partial stack 26 is electrically connected directly to the cell supply unit 18 . All other supply lines 24 have respective electrical insulating sections 38 .

In the present case, it is provided that the number of the respective electrolytic cells 12 of the sub-stacks 26, 28, 30, 32 is the same for all sub-stacks 26, 28, 30, 32. Depending on requirements, however, this can also be selected differently in other configurations without departing from the spirit of the invention.

The sub-stacks 26, 28, 30, 32 are in turn electrically connected in series, so that—from an electrical point of view—all the electrolytic cells 12 of the sub-stacks are again connected in series 26, 28, 30, 32 - as in the cell stack 54 according to FIG 1 - exists.

This construction of the electrolysis system 60 makes it possible for the cell supply unit 18 to have the lowest electrical potential of the entire electrolysis system 60 when viewed electrically. This electrical potential is also connected to the negative electrical potential 34 of the electrical energy source 16 . In addition, the electrical energy source 16 provides the positive electrical potential 36 . Between the negative and the positive electrical potential 34, 36, the electrical energy source 16 provides the operating voltage for the intended operation of the electrolysis system 60.

In the present embodiment after FIG 4 provision is made for that first supply line 24 which is connected to the first end 20 of that sub-stack 26 which can be coupled to a negative electrical potential 34 of the electrical energy source 16 to be electrically conductively connected to the cell supply unit 18 and all other supply lines 24 to be connected respectively have electrical insulating sections 38 . In this case, all the insulating sections 38 have a respective control electrode 66 which projects at least partially into the interior of the insulating section and which correspondingly 3 arranged and designed. Depending on the corrosion load in the insulating sections 38, however, it is also possible that not all of the insulating sections 38 but a predeterminable majority of the insulating sections 38 have a respective control electrode 66 that protrudes at least partially into the interior of the insulating section 38. If necessary, this can be designed for the respective operating situation of the electrolysis system 60 .

It can also optionally be provided that at the respective ends 20, 22 of the respective partial stacks 26, 28, 30, 32 facing insulating section ends 40 of the respective insulating sections 38 supply line inside an electrical Insulation layer is formed, which is presently formed by a coating of an insulating material. The insulation material is a suitable plastic, for example. Alternatively or additionally, however, a corrosion-resistant metal-containing material can also be provided, for example a metal oxide or the like, in particular a ceramic material, for example.

In addition, it can also be provided that the respective ends 20, 22 of the partial stacks 26, 28, 30, 32, which face the respective insulating sections 38, are designed to be electrically insulated from the electrolysis cells 12. This can further reduce the corrosion effect. It has proven to be particularly advantageous if the cell supply unit 18 is electrically grounded by means of a grounding 42, which can be used as a direct ground fault or--as in FIG 4 shown - can be performed indirectly.

In this advantageous embodiment of the electrolysis system 60, it is provided that the grounding 42 is not connected directly to the cell supply unit 18, but using a voltage source 44, by means of which the cell supply unit 18 can be subjected to an electrical potential that is negative compared to the ground potential. For this purpose, the voltage source 44 provides an electrical voltage of approximately -1 V to approximately -0.8 V. In principle, however, this voltage can also be selected, for example, in a range from approximately −2 V to approximately 0 volts.

With an electrical voltage set in this way, the corrosion effect, for example in the case of stainless steel, can be suppressed even better against corrosion, even under maritime conditions, for example in off-shore applications.

It has proven to be particularly advantageous if the counter-electrode for the cathodic protection against corrosion is also arranged in the area of the cell supply unit 18 . The electrode provided here for grounding 42 is present formed by a titanium anode coated with a mixed oxide. In the present case, the titanium anode with the mixed oxide coating is electrically isolated from the cell supply unit 18 and is arranged in a liquid phase of an oxygen separation container that is not shown in any more detail.

Overall, the exemplary embodiments show that the invention can be used to reduce corrosion by forming a plurality of partial stacks 26, 28, 30, 32 of the electrolysis cells 12, which are all still electrically connected in series, but via their own Supply lines 24 are separately connected to the cell supply unit 18.

The targeted use of the control electrode 66 in the insulating section 38 of the supply line 24 of the electrolysis system 60 can already largely prevent the formation and thus the release of metal ions. The application of this effective corrosion protection concept can be flexibly adapted to different plant configurations of PEM electrolysis plants. Thus, the undesired corrosion can be largely avoided. It has proven to be particularly advantageous that even complex electrolysis systems 60 with a plurality of sub-stacks 26, 28, 30, 32 and respective connections to the supply line 24 for the supply of operating materials can be operated with just one central electrical energy source 16 (DC source) and one central cell supply unit 18 . As described, cathodic protection against corrosion is possible as an additional and advantageous measure.

The invention is by no means restricted to use in the electrolysis of water and can also be used in other electrolyses to be carried out, for example carbon dioxide electrolysis or the like.

The exemplary embodiments serve exclusively to explain the invention and are not intended to limit it.

Claims (11)

Electrolysis plant (60) with - a plurality of electrolytic cells (12) which are electrically connected in series and which are at least partially arranged one after the other in a stacking direction (14), the series connection being able to be electrically coupled to an electrical energy source (16), - A cell supply unit (18) for supplying the electrolytic cells (12) for normal operation with at least one fuel, and - supply lines (24) connected to the cell supply unit (18) and to opposite ends (20, 22) of the successively arranged electrolysis cells (12), wherein at least one of the supply lines (24) has an electrical insulating section (38) with an at least partially Interior of the electrical insulating section (38) protruding control electrode (66). Electrolysis system according to Claim 1, characterized in that a material of the supply lines (24) comprises metal, the electrolysis cells (12) being arranged in at least two partial stacks (26, 28, 30, 32), each of the at least two partial stacks (26, 28, 30, 32) by means of at least one first supply line (24) connected to the cell supply unit (18) and at a first end (20) of the respective partial stack (26, 28, 30, 32) and at least one to the cell supply unit (18) and at a second end (22) of the respective sub-stack (26, 28, 30, 32) opposite the first end (20) in the stacking direction (14), the second supply line (24) is connected to the cell supply unit (18), the first Supply line (24), which is connected to the first end (20) of that partial stack (26) which can be coupled to a negative electrical potential (34) of the electrical energy source (16), electrically l eend is connected to the cell supply unit (18) and all other supply lines (24) respective electrical insulating sections (38), wherein a plurality of the insulating sections (38) has a respective control electrode (66) protruding at least partially into the interior of the insulating section (38). Electrolysis system (60) according to Claim 1 or 2, characterized in that the control electrode (66) is arranged in such a way that, during normal operation when the operating fluid is supplied, a stray current in the supply line (24) via the control electrode (66) due to its anodic effect is derivable. Electrolysis system (60) according to one of the preceding claims, characterized in that the control electrode (60) is designed in the form of a wire, rod or grid. Electrolysis system (60) according to one of the preceding claims, characterized in that the control electrode (66) has a carrier metal of high conductivity, in particular titanium, coated with a catalyst material. Electrolysis system (60) according to Claim 5, characterized in that the catalyst material has a noble metal oxide. Electrolysis plant according to Claim 5 or 6, characterized in that the catalyst material has a mixed oxide comprising iridium and/or ruthenium. Electrolysis system according to one of the preceding claims, characterized in that the respective ends (20, 22) of the partial stacks (26, 28, 30, 32) facing the respective insulating sections (38) are electrically insulated from the electrolysis cells (12). Electrolysis system according to one of the preceding claims, characterized in that the cell supply unit (18) is at least indirectly electrically grounded (42). Electrolysis system according to Claim 9, characterized in that the grounding (42) has a sacrificial anode and/or a voltage source (44) by means of which the cell supply unit (18) can be subjected to an electrical potential which is negative relative to the ground potential (42). Electrolysis system according to one of Claims 2 to 10, characterized in that the partial stacks (26, 28, 30, 32) are connected in parallel to the cell supply unit (18) in terms of supply.

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