Solid-state compressor and method for providing back pressure on a stack of solid-state compressor cells

Abstract

The invention relates to a solid-state compressor for electrochemically compressing a fluid, comprising: a stack of compressor cells, including at least one compressor cell having a membrane-electrode assembly sandwiched between two cell plates; a housing, securing the stack of compressor cells on its opposite sides; and at least one contact body, interposed between the stack of compressor cells and the housing and in contact with an external surface of the stack of compressor cells, in which a space is contained between the housing and the contact body, which space is configured to contain a pressurized hydraulic fluid. The invention further relates to a method of operating such a solid-state compressor.

Description

Title of the invention: Solid state compressor and method for providing back pressure on a stack of solid state compressor cells

[0001] The present invention relates to a solid-state compressor for electrochemical compression of a fluid. The invention further relates to an enclosure for a solid-state compressor and a pressure adjustment mechanism for use in a solid-state compressor. The invention further relates to a method of operating a solid-state compressor according to the invention.

[0002] While conventional mechanical compressors use mechanical means such as pistons or rotors for the compression of a fluid, solid-state compressors rely on the electrochemical transport of said fluid across a membrane using an ionic transport mechanism. In order to compress the working fluid in an electrochemical manner, a solid-state compressor typically comprises a compressor cell that is made up of one or more stacked membrane electrode assemblies (also known as MEAs). The electrodes of the MEA are connected to a power supply to maintain an electrical potential difference between the electrodes.This potential difference is necessary to electrochemically move the ionized working fluid across the proton exchange membrane (commonly referred to as the PEM) against the pressure gradient that exists across the membrane. The direction of the electric current thus determines the direction of ion transport, in which the low-pressure working fluid is ionized at the positively charged anode and is recombined with the separated electrons on the high-pressure cathode side of the MEA.

[0003] The electrochemical hydrogen compressor is a commonly known solid-state compressor, in which hydrogen is supplied to the compressor cell and oxidized into protons and electrons. The protons are then driven through the membrane and the electrons are transferred by an external circuit, after which the protons and electrons are reduced to molecular hydrogen. In this process, the hydrogen moves against a pressure gradient from a low-pressure area to a high-pressure area, resulting in an increase in pressure across the membrane. Compression of other working fluids, such as water or ammonia, is also possible.

[0004] Solid-state compressors have a number of significant advantages over mechanical compressors. Indeed, solid-state compressors do not have no moving parts and are generally compact in design. In addition, solid-state compressors can compress fluids to very high pressures, up to 1000 bar and more, with higher operating efficiencies than mechanical compressors. Electrochemical compression has another advantage: it allows for the purification of the working fluid, as the membrane only allows the transport of ionized working fluid.

[0005] During the process of compressing the working fluid, there are very high pressure differences on different sides of the compressor cell. To maintain these pressure differences and achieve sufficient sealing of the compressor cell, a sufficiently high back pressure must be exerted on the compressor cell. To achieve this, the compressor cell is generally fixed between two flanges held together by a series of bolts that engage the flanges near their peripheral edges.

[0006] A disadvantage of this fastening structure is that due to the high pressures in the compressor cell, the compressor cell exerts a uniformly distributed gas pressure force on the flanges. As a result, the flanges will tend to bend in their center, away from the point of engagement of the set of bolts that hold the flanges together. This results in poor electrical contact in the central portion of the compressor cell or even rupture of the cell internals.

[0007] Another problem with the fastening structure described above is caused by contraction and expansion of the compressor cell due to thermal and pressure effects occurring during electrochemical compression of the working fluid, which causes the sealing and contact pressure between the compressor cell and the respective flanges to vary. Due to this pressure variation and the continuous movement of the compressor cell during expansion and contraction, the bolted assemblies gradually loosen over time. This causes leaks and requires regular inspection and re-tightening of the bolted assemblies.

[0008] The object of the present invention is to provide a solution for at least one of the drawbacks mentioned above.

[0009] The present invention provides a solid-state compressor for electrochemically compressing a fluid, comprising: a compressor cell stack, comprising at least one compressor cell having a membrane-electrode assembly sandwiched between two cell plates, an enclosure, securing the compressor cell stack on its opposite sides, and at least one contact body, interposed between the compressor cell stack and the enclosure and in contact with an outer surface of the compressor cell stack, in wherein a space is contained between the enclosure and the contact body, which space is configured to contain a pressurized hydraulic fluid.

[0010] The solid-state compressor may be an electrochemical hydrogen compressor, but may also be configured to compress other working fluids such as water or ammonia. The operating principle of these solid-state compressors is the same, i.e., they compress the working fluid by passing the working fluid through a membrane-electrode assembly that is part of a compressor cell. The compressor cell may thus be part of a compressor cell stack comprising several compressor cells. Each of the compressor cells therefore comprises a membrane-electrode assembly that is fixed between two cell plates, wherein the cell plates serve to separate and support the different membrane-electrode assemblies as well as to supply the working fluid to the membrane-electrode assembly and to guide the working fluid away from it.

[0011] However, the invention does not explicitly relate to an electrolyzer or any other similar apparatus for changing H2O into H2 and O. The apparatus according to the invention is an apparatus for receiving H2 with a low pressure and for delivering H2 with a high pressure. The compressor cell stack comprises an outer surface which is oriented away from the at least one membrane-electrode assembly contained therein. In order to compensate for internal pressures in the compressor cell stack during operation of the solid-state compressor, the enclosure which secures the cell stack is configured to exert a back pressure on the cell stack at least equal to and generally greater than this internal pressure in the compressor cell stack.Said counter pressure is thus exerted on the outer surface of the compressor cell stack via an interface entity in the form of a contact body. The contact body is in contact, and in particular in full contact, with the outer surface of the compressor cell stack, which outer surface is in a common case formed by an outermost cell plate of the cell stack. This enables the contact body to efficiently transmit the forces exerted by the compressor cell stack onto the enclosure and vice versa.

[0012] Since a space is contained between the enclosure and the contact body, the counter pressure provided by the enclosure is however not exerted directly on the contact body. Instead, a pressurized hydraulic fluid is contained in the aforementioned space and is thus interposed between the enclosure and the contact body. The forces exerted by the enclosure on the compressor cell stack are thus transmitted both by the contact body and by the hydraulic fluid.

[0013] A major advantage of this construction is that contact and distribution of uniform pressure on the contact body and consequently on (the outer surface of) the compressor cell stack is achieved at all times. Even though the enclosure itself may bend or deform under the high pressures prevailing in the compressor cell stack, the compressor, according to the present invention, is able, thanks to the space containing the pressurized hydraulic fluid, to maintain a uniformly distributed / distributed back pressure on the contact body and the compressor cell stack. This thus solves the problem of poor electrical contact in the central part of the compressor cell stack and possible rupture of the cell internals.

[0014] An additional advantage of allowing the enclosure to exert the necessary back pressure on the compressor cell stack via the contact body and the pressurized hydraulic fluid is that, in the event that the back pressure on the cell stack exceeds the internal pressure of the compressor cell stack, the gradual loosening of the connections between the various parts of the enclosure that push the enclosure together, allowing the enclosure to compress the cell stack, has no immediate effect on the integrity of the cell stack. In the case of a direct connection between the cell stack and the enclosure, the loosening of the connections and subsequent relative movement of the various parts of the enclosure will result in a loss of contact between the enclosure and the compressor cell stack, thereby causing the cell stack to leak.The pressurized hydraulic fluid will, however, maintain uniform contact with the contact body at the cost of only a slight decrease in hydraulic pressure in the event that the connections between the various parts of the enclosure become so loose as to cause some displacement of the parts of the enclosure, thus increasing the volume of the space to a small extent.

[0015] In an advantageous embodiment of the solid-state compressor according to the present invention, the solid-state compressor comprises a pressure adjustment mechanism configured to adjust or regulate the pressure of the hydraulic fluid contained in the space. It is, however, also possible that the space between the enclosure and the contact body is fixed in volume and that a fixed quantity of pressurized hydraulic fluid is contained in said space. In this case, the hydraulic fluid is pressurized to a fixed pressure. This pressure must, however, aim to compensate for the highest possible internal pressure of the stack of compressor cells. The compressor, including the stack of cells and the enclosure, must therefore constantly withstand pressures equal to or greater than the highest possible internal pressure for which the stack of compressor cells is designed.

[0016] The possibility of adjusting the pressure of the hydraulic fluid contained in the space between the enclosure and the contact body makes it possible to choose counter-pressures greater than the current operating pressure inside the cell block and thus ensure the necessary sealing. However, these back pressures can now be chosen lower than the highest possible internal pressure of the compressor cell stack because the hydraulic fluid pressure and therefore the back pressure can be increased with increasing cell stack operating pressures.

[0017] The pressure adjustment mechanism may be configured to adjust the pressure of the hydraulic fluid based on the pressure on a cathode side of at least one membrane electrode assembly. The cathode side of the membrane electrode assembly is the side where the working fluid is compressed. An increase in the internal pressure of the cell stack such as that on the cathode side will in most cases require a higher hydraulic fluid pressure to provide the necessary back pressure and thus ensure proper sealing of the cell stack of the compressor. In the case where the pressure of the hydraulic fluid is controlled based on a pressure on the cathode side of at least one membrane electrode assembly, it can be ensured that the back pressure provided by the pressurized hydraulic fluid is automatically equal to or greater than the internal pressure of the cell stack.

[0018] To further ensure the sealing and integrity of the compressor cell stack, the pressure adjustment mechanism may be configured to maintain a fixed ratio between the pressure prevailing on the cathode side of the at least one membrane-electrode assembly and the pressure of the hydraulic fluid. It is therefore preferable for the pressure of the hydraulic fluid to be higher, preferably between 1.5 times and 2.5 times higher, and more preferably 2 times higher than the pressure prevailing on the cathode side of the at least one membrane-electrode assembly. This provides dynamic control of the hydrostatic pressure within the space contained between the enclosure and the contact body.

[0019] In another embodiment of the solid state compressor according to the invention, the space contained between the enclosure and the contact body is hydraulically connected to a hydraulic fluid reservoir. The reservoir effectively increases the total volume of hydraulic fluid which acts to provide the back pressure exerted on the contact body and simultaneously on the outer surface of the compressor cell stack. In the event of a hydraulic fluid leak where some of the hydraulic fluid escapes, the increased volume of hydraulic fluid will ensure a decrease in the pressure drop. It is therefore less likely that a hydraulic fluid leak will immediately cause a pressure drop to a level below that of the internal pressure of the cell stack. In addition, the presence of a hydraulic fluid reservoir allows access to the hydraulic fluid contained in the reservoir and to the space contained between the enclosure and the contact body, away from the compressor cell stack itself.

[0020] As a possible means of adjusting the hydraulic fluid pressure in the space, the combination of the contact body and the compressor cell stack may be movably connected to the enclosure so that it is movable relative to the enclosure. In this way, the space contained between the enclosure and the contact body may be changed in volume, thereby adjusting the pressure prevailing in the hydraulic fluid. In the case where the space is hydraulically connected to a hydraulic fluid reservoir, the hydraulic fluid reservoir may alternatively or additionally have a variable volume in order to change the total volume of the closed system comprising the hydraulically connected space and the hydraulic fluid reservoir, thereby adjusting the degree of compression of the hydraulic fluid and consequently the amount of back pressure exerted on the compressor cell stack.The pressure adjustment mechanism can thus be configured to adjust the volume of the aforementioned hydraulic fluid reservoir.

[0021] To adjust the volume of the hydraulic fluid reservoir, the pressure adjustment mechanism may include a displacement piston, including a first piston head surface in contact with the hydraulic fluid reservoir, for changing the volume of the hydraulic fluid reservoir upon displacement of the piston head. The displacement piston is typically contained within a housing, the housing encircling the piston head in a fluid-tight manner. The housing connects to or merges with a wall of the hydraulic fluid reservoir, such that the first piston head interfaces with the hydraulic fluid. When the displacement piston is moved inwardly toward the hydraulic fluid reservoir, the volume of the hydraulic fluid reservoir is effectively reduced, with the hydraulic fluid contained therein being further compressed.When the displacement piston is moved outward from the hydraulic fluid reservoir, the volume of the hydraulic fluid reservoir is effectively increased, causing the hydraulic fluid within it to be less compressed.

[0022] The displacement piston may also include a second piston head surface opposite the first piston head surface, which second piston head surface is in contact with a pressurized fluid reservoir to change the volume of the pressurized fluid reservoir upon displacement of the piston head. Like the first piston head, the second piston head may be contained within a housing, the housing encircling the piston head in a fluid-tight manner and connecting to or merging into a wall, in this case of the pressurized fluid reservoir. When the displacement piston is moved inwardly toward the pressurized fluid reservoir, the volume of the pressurized fluid reservoir is effectively reduced, the pressure fluid contained therein being more compressed. When the displacement piston is moved outward from the pressure fluid reservoir, the volume of the pressure fluid reservoir is increased, the pressure fluid contained therein being compressed to a lesser extent. Since the first and second piston heads are part of the same piston, an inward movement of the first piston head will cause an outward movement of the second piston head and vice versa. With this simultaneous movement of the piston heads, the volumes of the reservoirs are adjusted in dependence on each other, thus balancing the pressures prevailing in the hydraulic fluid reservoir and in the pressure fluid reservoir.

[0023] It is particularly advantageous if the cathode side of at least one membrane electrode assembly is connected to the pressure fluid reservoir, whereby the fluid in the pressure fluid reservoir is under the same pressure as the working fluid compressed on the cathode side of the membrane electrode assembly. In one possible embodiment, the connection between the cathode side of the membrane electrode assembly and the pressure fluid reservoir is a fluid connection, in which the fluid contained in the pressure fluid reservoir is in fact the same as the working fluid pressurized by the solid-state compressor.The advantage of such a fluid connection between the cathode side of the membrane-electrode assembly and the pressure fluid reservoir is that the hydraulic fluid pressure and thus the back pressure on the compressor cell stack is automatically adjusted according to the internal pressure of the cell stack.

[0024] With the fluid connection, a pressure change on the cathode side of the membrane-electrode assembly causes a similar change in the fluid pressure in the pressure fluid reservoir. Since the two opposing but dependently displaceable piston heads of the displacement piston are in contact with the hydraulic fluid reservoir and the pressure fluid reservoir respectively, the pressure change in the pressure fluid reservoir will cause the displacement piston to move, thereby changing the pressure in the hydraulic fluid reservoir simultaneously. Since the space contained between the enclosure and the contact body is hydraulically connected to a hydraulic fluid reservoir, the hydraulic fluid pressure contained in the space will also change, which will influence the amount of back pressure exerted on the compressor cell stack via the contact body.

[0025] In order to obtain a fixed pressure ratio between the pressures prevailing in the hydraulic fluid reservoir and the pressure fluid reservoir, the surface areas of the first piston head surface and the second piston head surface may differ from each other. In particular, the ratio between the surface areas of the first piston head surface and the second piston head surface that are in contact with the hydraulic fluid and the pressurized fluid determines the ratio of the pressures prevailing in the hydraulic fluid reservoir and the pressurized fluid reservoir. In other words, the forces applied to the piston heads perpendicular to their surfaces interfacing with the pressurized fluids are equal to the pressure multiplied by their surface areas. By choosing the surface areas of the first piston head surface and the second piston head surface according to the desired pressure difference between the hydraulic fluid reservoir and the pressurized fluid reservoir, the relative back pressure exerted on the stack of compression cells can thus be automatically and dynamically controlled.

[0026] In yet another embodiment of the solid state compressor according to the invention, the solid state compressor comprises two contact bodies, each interposed between the enclosure and a different side of two opposite sides of the stack of compressor cells, wherein a space is contained between the enclosure and the respective contact bodies, which spaces are configured to contain a pressurized hydraulic fluid. An advantage of this embodiment is that the hydraulic fluid contained in the two spaces allows for uniform contact and pressure distribution across the contact bodies. The pressure of the hydraulic fluid contained in either of these spaces may be adjusted by a pressure adjustment mechanism according to one of the previously described embodiments.

[0027] In order to create a self-balancing system, the contact bodies may be movably embedded in the enclosure such that the volume of the spaces between the enclosure and the respective contact bodies changes upon movement of the contact bodies relative to the enclosure. Since the contact bodies are in contact with opposite sides of the compressor cell stack, the cell stack will move along with the contact bodies. This movement of the combination of contact bodies and cell stack within the enclosure allows the pressures of the hydraulic fluid respectively contained in each of the spaces to be balanced.In the event that the pressure of the hydraulic fluid in one of the spaces is changed, for example by means of a pressure adjustment mechanism as described in one of the previously discussed embodiments, the contact bodies and the cell stack move within the enclosure, thereby changing the volume of the spaces and equalizing the pressures prevailing in each of the spaces.

[0028] As another means of creating a self-balancing system, the spaces between the enclosure and the contact bodies can be hydraulically connected to each other. In this way, the pressure in each of the spaces will also be kept equal.

[0029] In a particular embodiment, the enclosure may comprise two flanges opposed and interconnected which respectively grip around each of the contacting bodies, thereby completely encircling a surface of said contacting bodies opposite the surface in contact with an outer surface of the compressor cell stack. An advantage of completely encircling this surface of the contacting bodies is that no direct contact is made between the enclosure (the flanges) and the surfaces of the contacting bodies on which the compressive forces are exerted. Instead, the surfaces are fully in contact with the hydraulic fluid, which ensures a uniform distribution or distribution of the pressure thereon. In a common case, the flanges grip around each of the contacting bodies far enough to allow the contacting bodies to move relative to the flanges while maintaining a fluid seal between the flanges and the contacting bodies.

[0030] It is possible for the opposing flanges to be connected together by a tensionally pre-stressed connection, which pushes the opposing flanges towards each other so that the hydraulic fluid contained in the spaces is compressed. By compressing the hydraulic fluid, the connection simultaneously introduces a compressive pre-stress into the stack of fixed compressor cells. The pre-stress is generally chosen to be equal to or greater than the highest possible pressure under which the stack of compressor cells is designed to operate.

[0031] The opposing flanges may be connected together by one or more bolted joints. In order to counteract the effects of tightening and loosening of the bolted assemblies, which results in a loss of the initial preload of the bolted assemblies, one or more Belleville washers may be placed between at least one of the flanges and a bolt head or nut of the bolted assembly.

[0032] The invention also relates to an assembly of an enclosure and at least one contact body for a solid-state compressor according to the invention. The invention further relates to a pressure adjustment mechanism for adjusting the pressure in a hydraulic fluid contained in a space contained between an enclosure and a contact body of a solid-state compressor according to the invention. The specific features as well as the advantages of the assembly and the pressure adjustment mechanism are already described in detail in relation to the various possible embodiments of the solid-state compressor according to the invention.

[0033] Finally, the invention relates to a method for operating a solid-state compressor according to the invention, comprising introducing a pressurized hydraulic fluid into the space between the enclosure and the contact body. The method may further comprise adjusting the pressure in the hydraulic fluid. The pressure in the hydraulic fluid may thus be adjusted as a function of the pressure prevailing on a cathode side of the at least one membrane-electrode assembly. It is possible to maintain a fixed ratio between the pressure prevailing on the cathode side of the membrane-electrode assembly and the pressure of the hydraulic fluid. The pressure in the hydraulic fluid can in this case be kept higher, preferably between 1.1 times and 2.5 times higher, and more preferably 2 times higher than the pressure prevailing on the cathode side of the at least one membrane-electrode assembly. The specific features as well as the advantages of one or other of these methods for the operation of a solid-state compressor are already described in detail with regard to the various possible embodiments of the solid-state compressor according to the invention.

[0034] In order to further elucidate the invention, embodiments will be described by way of non-limiting examples with reference to the figures, among which:

[0035] [Fig-1] [Fig.l] shows a perspective view of a solid state compressor according to the invention,

[0036] [Fig.2] [Fig.2] shows an exploded view of the solid state compressor of [Fig.l] , And

[0037] [Fig.3] [Fig.3] shows a schematic sectional view of a state compressor solid according to the invention.

[0038] The figures represent specific exemplary embodiments of the invention and should not be construed as limiting the invention in any way or form. Throughout the description and figures, corresponding reference numerals are used for corresponding elements.

[0039] Figures 1 and 2 show respectively a perspective view and an exploded view of a solid state compressor 1 according to the invention. The solid state compressor 1 comprises a stack of compressor cells 2 comprising multiple membrane-electrode assemblies 3 sandwiched between cell plates 4. The outermost plates 5 of each stack of cells 2 are generally formed by current collector plates to serve as a passage for electrically connecting the electrodes to a power source. The stack of compressor cells 2 is, on opposite sides, fixed between an enclosure 6 which maintains pressure on the stack of cells 2. The illustrated housing 6 comprises two flanges 7 which are interconnected near their peripheral edges by a set of bolted joints formed by bolts 8 and nuts 9.Between the opposite outer surfaces 10 of the cell stack 2 and the enclosure 6 are interposed two contact bodies 11 which are in contact with said outer surfaces 10. As can be seen in [Fig.3] explained below, a space is contained between each of the flanges 7 and the contact bodies 11, which space contains a pressurized hydraulic fluid. In order to supply hydraulic fluid or to retract the hydraulic fluid from this space, the contact bodies 11 are provided on their sides with hydraulic fluid supply openings 12.

[0040] [Fig. 3] shows a schematic sectional view of a solid state compressor 20 according to the invention. Here too, a stack of compressor cells 21 is illustrated, two opposing outer surfaces 22 of which are secured between two contact bodies 23. The combination of the cell stack 21 and the contact bodies 23 is contained in an enclosure 24, comprising two opposing flanges 25 connected together by means of bolted joints 26. The flanges 25 thus surround each of the contact bodies 23, completely encircling the surfaces of the contact bodies opposite the surfaces in contact with the outer surfaces 22 of the cell stack 21. Between the flanges 25 and the contact bodies 23, spaces 27 are contained, which contain a pressurized hydraulic fluid 28. Seals 29 are provided between the sides of the flanges 25 and the contact bodies 23 in order to obtain a closed volume capable of containing the pressurized hydraulic fluid 28.The upper space of the spaces 27 is hydraulically connected to a hydraulic fluid reservoir 30 by means of a hydraulic fluid line 31. The lower space of the spaces 27 is in this shown embodiment of the solid-state compressor which is neither hydraulically connected to a hydraulic fluid reservoir nor hydraulically connected to the upper space. Thus, a passive pressure compensation system is obtained on the lower side of the solid-state compressor 20. The last mentioned variations are however within the scope of the invention.

[0041] The volume of the hydraulic fluid reservoir 30 is variable by means of a pressure adjustment mechanism 32 comprising a displacement piston 33. The displacement piston 33 is movable within the piston housing 34 and comprises a first piston head surface 35 which is in direct contact with the hydraulic fluid 28 contained in the hydraulic fluid reservoir 30. The displacement piston further comprises a second piston head surface 36 opposite the first piston head surface 35, which second piston head surface 36 is in direct contact with a pressurized fluid 37 contained in a pressurized fluid reservoir 38. Since the first and second piston head surfaces 35, 36 are part of the same piston, they perform a simultaneous movement, thus balancing the pressures in the pressurized fluid reservoir and in the hydraulic fluid reservoir 30, 38.The ratio between the pressures in the two reservoirs therefore depends on the surface areas of the piston head surfaces 35, 36. The pressure fluid reservoir 38 is connected to the cathode side of the membrane-electrode assemblies contained in the cell stack 21 by a pressure fluid line 39. The pressure fluid 37 contained in the pressure fluid reservoir 38 is therefore the same as the working fluid of the compressor 20.

Claims

Claims

1. A solid-state compressor for electrochemically compressing a fluid, comprising: a compressor cell stack, comprising at least one compressor cell having a membrane-electrode assembly sandwiched between two cell plates, an enclosure, securing the compressor cell stack on opposite sides thereof, and at least one contact body, interposed between the compressor cell stack and the enclosure and in contact with an outer surface of the compressor cell stack, wherein a space is contained between the enclosure and the contact body, which space is configured to contain a pressurized hydraulic fluid, wherein the enclosure comprises two opposing and interconnected flanges which respectively grip around each of the contact bodies,thereby entirely encircling a surface of said contacting bodies opposite the surface in contact with an outer surface of the stack of compressor cells, and wherein the opposing flanges are mutually connected via a pre-stressed connection in tension, which pre-stress pushes the opposing flanges towards each other so that the hydraulic fluid contained in the spaces is compressed.,

2. The solid-state compressor of claim 1, wherein the solid-state compressor comprises a pressure adjustment mechanism configured to adjust the pressure of the hydraulic fluid contained in the space, and wherein the pressure adjustment mechanism is configured to adjust the hydraulic fluid pressure based on a pressure on a cathode side of the at least one membrane-electrode assembly, and wherein the pressure adjustment mechanism is configured to maintain a fixed ratio between the pressure on the cathode side of the at least one membrane-electrode assembly and the pressure of the hydraulic fluid, and wherein the hydraulic fluid pressure is greater, preferably between 1.1 times and 2.5 times greater, and more preferably 2 times greater than the pressure on the cathode side of the at least one membrane-electrode assembly, and wherein the space is hydraulically connected. to a hydraulic fluid reservoir, and wherein the reservoir has a variable volume, wherein the pressure adjustment mechanism is configured to adjust the volume of the hydraulic fluid reservoir, and wherein the pressure adjustment mechanism comprises a displacement piston, comprising a first piston head surface in contact with the hydraulic fluid reservoir, for changing the volume of the hydraulic fluid reservoir upon displacement of the piston head, and wherein the displacement piston comprises a second piston head surface opposite the first piston head surface, which second piston head surface is in contact with a pressurized fluid reservoir to change the volume of the pressurized fluid reservoir upon displacement of the piston head, and wherein the cathode side of the at least one membrane-electrode assembly is connected to the pressurized fluid reservoir.

3. The solid-state compressor of claim 2, wherein the surface areas of the first piston head surfaces and the second piston head surfaces are different from each other, and wherein the solid-state compressor comprises two contact bodies, each interposed between the enclosure and a different one of two opposite sides of the compressor cell stack, wherein a space is contained between the enclosure and the respective contact bodies, which spaces are configured to contain a pressurized hydraulic fluid, and wherein the contact bodies are movably embedded within the enclosure such that the volume of the spaces between the enclosure and the respective contact bodies changes upon movement of the contact bodies relative to the enclosure.

4. A solid state compressor according to claim 3, wherein the spaces between the enclosure and the respective contact bodies are hydraulically connected to each other.

5. A solid state compressor according to any one of claims 1 to 4, wherein the opposing flanges are connected together by at least one bolted assembly, and wherein one or more Belleville washers are positioned between at least one of the flanges and a bolt head or nut of the bolted assembly.

6. An assembly of an enclosure and at least one contact body for a solid state compressor according to any preceding claim, wherein a space is contained between the enclosure and the contact body, which space is configured to contain a hy- pressure hydraulics

7. A pressure adjustment mechanism for adjusting the pressure of a hydraulic fluid contained in a space contained between an enclosure and a contact body of a solid-state compressor according to any one of claims 1 to 5, the mechanism being provided for adjusting the pressure in the hydraulic fluid based on the pressure prevailing on a cathode side of the at least one membrane electrode assembly, and wherein a fixed ratio is maintained between the pressure prevailing on the cathode side of the at least one membrane electrode assembly and the pressure in the hydraulic fluid, and wherein the pressure in the hydraulic fluid is maintained greater, preferably between 1.1 times and 2.5 times greater, and more preferably 2 times greater than the pressure prevailing on the cathode side of the at least one membrane electrode assembly.

8. A method for operating a solid-state compressor according to any one of claims 1 to 5, comprising introducing a pressurized hydraulic fluid into the space between the enclosure and the contact body, and wherein the method further comprises adjusting the pressure in the hydraulic fluid, and wherein the pressure in the hydraulic fluid is adjusted based on the pressure prevailing on a cathode side of the at least one membrane electrode assembly, and wherein a fixed ratio is maintained between the pressure prevailing on the cathode side of the at least one membrane electrode assembly and the pressure in the hydraulic fluid, and wherein the pressure in the hydraulic fluid is maintained greater, preferably between 1.1 times and 2.5 times greater, and more preferably 2 times greater than the pressure prevailing on the cathode side of the at least one membrane electrode assembly.

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