Framing Structure For An Electrolyser

The present invention relates to a framing structure for an electrolyser subject to internal pressure, able to withstand corrosive environments and radial pressure forces. The present invention also relates to an electrolytic cell and electrolyser equipped with said framing structure, as well as its use in high-pressure water electrolysis applications.

FIELD OF THE INVENTION

The present invention relates to the field of framing structures for electrolysers.

BACKGROUND OF THE INVENTION

Depending on their industrial application, electrolysers may be operated at varying pressures and are therefore required to withstand the consequent mechanical stress exerted on the individual components as well as the overall structure. Pressure conditions may be dictated by chemistry, components, dimensions, and industry served. Examples of high-pressure electrolysers may be found, for example, in the field of proton exchange membrane (PEM) electrolysis and alkaline water electrolysis (AWE), where operating pressures may exceed 5 bars.

In the past, cell frames of high-pressure electrolysers in AWE applications, for instance, have been entirely made of carbon steel or stainless steel, which provided good mechanical resistance. However, due to the corrosion rate of these metals when immersed into strong alkaline solutions, they were also negatively impacting on the overall performance of the electrolyser and affecting its working life. The corrosion of carbon or stainless steels adversely affects the electrolyte purity and causes sludge formation, which in turn may obstruct the electrolyte flow and cause pressure losses as well as safety concerns.

Conversely, in modern high-pressure AWE electrolysers, the cell frame is made of high-grade engineering plastic such as PSU (polysulfone), PPS (Polyphenylene sulfide) or PEEK (polyether ether ketone), optionally reinforced with glass fiber. These materials are almost chemically inert to the electrolyte but their mechanical properties do not match those of steel. Their Young's modulus, for instance, is 15 to 100 times lower than steel at room temperature.

Engineering plastics can be used to manufacture cell frames of small, pressurized electrolysers, where mechanical stresses and deformation are limited due to the cell frame dimensions. However, in larger and/or high-pressure electrolysers, cell frames made of these materials require a considerable thickness to withstand mechanical stress and keeping mechanical deformations in an acceptable range. This approach is disadvantageous since it considerably increases the costs, dimensions, and weight of the electrolyser.

Purpose of the present invention is to provide a framing structure for electrolysers subject to internal pressure, regardless of their dimensions and of the industry served, able to combine the chemical resistance to corrosive environments of engineering plastics with the robust mechanical properties of steel, while limiting the cell frame costs, the dimensions of its components and their weight.

Additional purpose of the present invention is to provide an electrochemical cell and an electrolyser equipped with the framing structure according to the invention, in particular for use in high-pressure water electrolysis applications.

DETAILED DESCRIPTION OF THE INVENTION

Under a first aspect, the present invention relates to a framing structure, optionally stackable, and suitable to be used in an electrolyser.

The framing structure according to the invention comprises:

Each support structure typically has two major opposite surfaces and an outer border of overall thickness Ts.

The term “outer border” indicates the area connecting the two major opposite surfaces of the support structure and may be flat, rounded, concave or convex, and/or provided with ridges, nooks, slopes or indentations.

The first and a second support structures are placed facing each other, even if other elements may be interposed between them, so that their major opposite surfaces are essentially parallel to each other.

Typically, the major opposite surfaces of the support structures are substantially flat or exhibit slight concave or convex profiles. The specific shapes, however, shall be chosen by the skilled person according to practice. Analogously, the overall geometry of the support structures may vary, both in size and shape. Typically, they either exhibit a circular/oval section or a polygonal shape, though any shape may in principle be used. The support structures may be provided with a housing suitable to accommodate any elements that may be lodged within an electrolytic cell, either alone or in combination, such as: electrodes, separators, elastic elements, bipolar plates and/or current collectors. The housing can be situated on at least one of the two major opposite surfaces of each support structure. The housing may be an empty space with appropriate contouring around its edges to suitably hold the electrode and/or the other elements. The housing may be a through hole to expose the electrode surface, and foster the electrochemical reaction, on both sides.

Preferably, the support structures are made of an electrochemically inert material, such as plastic, to avoid the formation of sludge. The choice of material will also depend on the application. In corrosive environments, such as those of alkaline water electrolysis, the support structures according to the invention can be advantageously made of high-grade engineering plastics, preferably polysulfone, polyphenylene sulfide or polyether ether ketone, and optionally reinforced with glass fibers.

In less demanding electrochemical applications, supporting structures in polypropylene or other less expensive plastics may be satisfactorily used.

The first and second containment structures are respectively positioned around the outer border of the first and second support structures, wrapping the exposed surface of said border completely or in part.

It is noted that, during the operation of a pressurized electrolyser, the support structures are subject to a hydrostatic pressure equal to the stack operating pressure, which will deform radially towards the containment structures. Because of their mutual positioning, upon direct or indirect contact of the internal support structure with the corresponding containment structure(s), most of the mechanical stress will be transferred to the latter. Therefore, the containment structure(s) may be chosen of a more mechanically robust material than the support structures and suffer less or negligible deformation.

Indeed, unlike the support structures (which are in contact with the electrolyte and shall, as discussed, be advantageously chosen of a compatible, corrosion resistant material), the containment structures are preferably not in contact with the electrolyte and serve as mechanical reinforcement of the support structure under pressure. In order to further reduce possible deformations of the internal support structure, and to keep the containment structures removed from the electrolyte, the latter may be advantageously shaped to minimize, and preferably avoid, any overlap with either of the two major opposite surfaces of each support structure.

According to the present invention, each containment structure is not a continuous unit, but is composed by at least two separate segments, and each segment is provided with at least two engageable elements.

The engageable elements are means to allow connecting, securing and/or pressing the two containment structures together, fixing them in place. For instance, the engageable elements may be through holes, contactable via tie-rods, screws, bolts or rivets. They may, less preferably, be fashioned into female/male shapes or other interlocking shapes (or any other mechanisms, mechanical or otherwise) suitable to be create a mutual and reliable connection with each other.

The segments within each containment structure are preferably placed substantially adjacent and consecutive to each other along the border of the support structure. Each containment structure may be composed of any number of segments equal or greater than two, but a number between 2-8 segments for each containment structure is preferable for practical reasons.

Since each containment structure is composed of a plurality of distinct segments not necessarily connected with each other, to ensure mechanical stability of the framing structure the segments of the first and second containment structures are mutually oriented in such a way that at least two engageable elements present in one same segment of the first containment structure face two engageable elements present into two separate segments of the second containment structure.

This ensures that once the engageable means of the first containment structure are connected with the opposite ones of the second containment structure, the two containment structures acquire a rigid and mechanically stable set up.

The segmented design of the external containment structure allows to dramatically reduce the amount of manufacturing scraps, and to make these structures easier to transport and less cumbersome to manage/mount.

According to one embodiment, the containment structure overlaps with the outer border of the support structure for a width (i.e. along the z axis in the figures) which is at least 50% of the outer border thickness Ts, preferably at least 70%. The higher the pressure within the electrolyser and/or the higher its size, the higher should be the border percentage covered by the containment structure.

The partial or complete adherence of the containment structures with the support structure has the effect of counteracting the radial pressure force that is generated within the cell during the electrolytic reaction. Indeed, during operation of an enclosed electrochemical cell, the gas evolution reaction increases the pressure within the cell enclosure and thus inside the cell. Typically, terminal flanges are used to counteract the pressure force acting perpendicularly to the electrode surface. The framing structure according to the invention effectively addresses the radial pressure that is directed outwardly in the electrode plane.

According to another embodiment, the containment structure overlaps with the outer border of the support structure for a width which is less than 100% of the border thickness Ts, thus avoiding a complete coverage of the border and a possible direct contact between adjacent containment structures. This may prevent the containment structures from discharging the tightening force on each other, as they may be made of materials that are unsuitable to this effect. Suitable spacers may be inserted between them. Additionally, leaving some space between adjacent containment structures allows room for inserting useful devices for monitoring cell voltage parameters.

According to another embodiment, when the number of support structures is greater than two, at least one containment structure may be situated around the outer border of at least two adjacent support structures at once. This allows to reduce the number of pieces required for the assembly of an electrolyser and facilitates its installation.

In the framing structure according to the invention, at least two support structures may be placed adjacent to one another other and may be optionally separated by gaskets. The gaskets may be housed within suitable grooves situated on the major surfaces of the support structure. In other embodiments the gaskets may be placed externally to the surface area of the support structure and sandwiched between two adjacent support structures.

In the framing structure according to the invention, the first and second containment structures may be mutually separated by spacers, optionally made of rubber. This helps maintaining the correct mutual position of the elements. It also ensures that the pressure from the electrolyser tightening system is mainly transferred to the support structures and their gasketing systems.

According to another embodiment, the outer border of each support structure has a protruding ridge along at least one of its perimetral edges to facilitate the accommodation of the respective containment structure within the resulting nook.

The containment structures according to the invention are preferably made of a material having a greater mechanical resistance of the internal support structures, such as metal, for example. Even more preferably they are made of steel, particularly carbon steel or stainless steel. Alternatively, they may also be made of a composite material. For instance they can be made of carbon fibers, or constituted of a metal core covered by a plastic outer surface which prevents corrosion.

All the above-mentioned materials impart enough robustness to the external containment structures to effectively counteract the radial forces that the pressurized electrolyser is subject to.

The skilled person easily recognizes that the framing structure according to the above embodiments may exhibit a greatly reduced overall dimension compared to cell frames entirely made of engineering plastic of the prior art, thanks to the mechanical properties of the external containment structure. This also results in an overall lesser quantity of expensive engineering plastic employed, with a positive impact on costs.

Under a further embodiment, in the framing structure according to the invention, the support structures are of substantially circular shape having a maximum external diameter DF, and the containment structures have an annular shape divided into a plurality of arc-shaped segments. Each annular-shaped containment structure has an internal and external diameter Di and De, where Di<DF<De or DF<Di<De. Depending on whether the support structure has a protruding ridge or not, the former or the latter condition respectively apply.

Under a second aspect, the invention relates to an electrochemical cell comprising the framing structure hereinbefore described, where the at least first support structure houses an anode, the at least second support structure houses a cathode, said anode and said cathode being placed facing each other and being optionally separated by a separator element such as a diaphragm or a membrane.

Under a third aspect, the invention relates to an electrolyser comprising a plurality of electrochemical cells wherein each cell is equipped with the framing structure hereinbefore described and the containment structures are mutually connected via tie rods engaging with the at least two engageable elements of each segment, which are preferably through holes.

In a further embodiment of the electrolyser according to the invention, each framing structure may advantageously comprise two internal support structures placed between the first and second containment structure, and additional two support structures are placed externally with respect to the peripheral containment structures and are closed by two opposite terminal flanges.

It is preferable that the latter are not placed in direct contact with the containment structures, to avoid discharging the pressure force along the electrolyser axial direction (i.e. the direction perpendicular to the electrodes) directly on the more rigid elements of the stack.

Under a fourth aspect, the invention relates to the use of the above electrolyser for high pressure (>5 bar) water electrolysis, preferably alkaline water electrolysis.

A number of embodiments of the invention are described by way of example below with reference to the appended drawings, the purpose of which is solely to illustrate the mutual arrangement of the various elements relating to said embodiments of the invention. The drawings are not to scale. Identical numbers are used to indicate features having the same purpose/effect. The coordinate axis x, y, z, are used in the same fashion throughout all figures. The xy plane is substantially parallel to the two major surfaces of the internal support structures, whereas z is perpendicular to such plane and identifies the main longitudinal axis of the electrolyser according to the invention.

In this embodiment, each containment structure covers two support structures at a time (such as (120) covering (220, 220)). The support structures have ridges (221, 222, 223) that create a receded space to accommodate the containment structure. In this embodiment the containment structures have an individual thickness Tc roughly equal to 1.6·Ts, and each one covers around 80% of the support structure individual thickness Ts.

The containment structures are mutually separated by spacers (701, 702, 703). While the containment structures address the pressure forces exerted in the xy plane, the terminal flanges (800, 850) counteract the pressure in the z direction. It is preferable to assemble the framing structures of the electrolyser in such way as to avoid having the containment structures, which may be advantageously made of steel, in direct contact with the metallic terminal flanges.

FIG. 5 is the same view of FIG. 2(b) for a rectangular rather than circular geometry and shows a first and second containment structure (110, 120) placed with respect to a same set of coordinates, in the xy plane. The second containment structure (120) is identical to the first containment structure but is rotated at an angle in the xy plane (in this specific instance 180°) so that the points of discontinuity (01, 02, 03, 04, 05, 06) in the first and second containment structures are offset with respect to each other. This allows to have at least two engageable elements (010, 011) of one same segment (111) of the first containment structure (110) facing two engageable elements (020, 028) present in two separate segments (127, 125) of the second containment structure. The same concept applies for each segment of each containment structure.

In the description and the claims in this application the words “comprise” and its variations such as “comprising” and “comprises” do not rule out the presence of other additional elements, components, or stages.

The discussion of documents, deeds, materials, apparatus, articles and the like is included in the text solely for the purpose of providing context for this invention; it should not however be understood that this material or part thereof constitutes general knowledge in the field relating to the invention prior to the priority date of each of the claims appended to this application.