NL2036327B1

NL2036327B1 - Plane parallel converging gas flow electrolyzer, cell and use thereof

Info

Publication number: NL2036327B1
Application number: NL2036327A
Authority: NL
Inventors: Pieters Rudi
Original assignee: Elyser B V
Priority date: 2023-11-22
Filing date: 2023-11-22
Publication date: 2025-06-02
Also published as: WO2025110878A1

Abstract

An electrolyzer for generating hydrogen from water comprising electrodes and an electrically non—conductive separator layer extending in a substantially vertical plane comprising macroscopic through holes, and wherein the electrodes themselves comprise an anode and a cathode, characterized in that the electrodes are each furnished at opposite faces of the separator, and that the electrodes each comprise a plurality fins and wherein each fin of the plurality of fins projects outwardly from the layer for restricting the upward movement of electrode generated. bubbles to a bubble stream that is substantially parallel to the vertical plane. [Fig. 2]

Description

Plane parallel converging gas flow electrolyzer, cell and use thereof

The present invention relates to an electrolyzer for generating hydrogen from water comprising electrodes and an electrically non-conductive separator layer extending in a substantially vertical plane, wherein the electrodes themselves comprise an anode and a cathode.

Renewable energy sources such as solar and wind power are an increasingly important of the energy mix. A significant problem related to renewable sources is that these sources are often stranded (in remote locations) and not dispatchable (availability is not synchronized with demand). The time scale of the dispatch mismatch ranges from minutes to hours as a consequence of the diurnal cycle in the case of solar energy, to several months due to seasonal variance of production and consumption.

A way to address this is to convert the collected energy into chemical energy for transport and storage. Photovoltaics and wind turbines both generate electricity. With electrolysis this electricity can be used to split water into hydrogen and oxygen. The hydrogen can be transported via pipeline and stored for later use or can be converted into other substances (such as ammonia) for transport and storage.

An impediment for wide-spread use of this approach is the high cost of electrolyser equipment, which is currently in the order of € 1,000 per kW of installed capacity. Important drivers for the high cost are the use of (semi)precious metals as catalyst and the requirement to separate the product gases after they evolve on the electrodes of the electrolytic cells.

For the gas separation, three approaches are described in literature: 1. Use of a semi-permeable membrane

In this approach, a membrane of a suitable material (e.g. Nafion®&) is placed between the electrodes to keep the gas bubbles that evolve on the electrodes separated. A disadvantage of this approach is the high cost and limited lifetime of the membranes. It also adds to the complexity of cell construction. 2. Force the electrolyte through porous electrodes

In this approach, a pumping system is used to force the electrolyte through the electrodes which have been made porous. The flow carries the gas bubbles through the electrode on which they evolved and away from the opposite electrode. Disadvantages of this approach are the added cost of the pumping system, added complexity and the energy required to maintain an adequate flow rate. 3. Use of hydrodynamic forces

In this approach, the gas bubbles are kept separate separated by confining them to an area close to the electrode on which they evolved. Disadvantages of this approach are the need to maintain adequate velocity of the electrolyte flow, adding cost and complexity to the system. It also requires a minimum separation between the electrodes, which reduces the efficiency of the cell.

At current cost levels, adding electrolysis to renewable energy system to make the collected energy transportable and storable would at least double the cost of the entire system.

A more economical method for electrolysis would enable renewable energy to cover a larger part of the energy mix.

Patent no. US 2010213052 Al, by Roy E. McAlister hereinafter,

US'052 in particular teaches an alternative in which an

- 3 = electrolyzer makes use of buoyancy forces to separate the generated gases. In US'’052, the buoyant forces are employed to direct the flow of the gas bubbles ‘distal’ to the opposing electrode. However, notably, paragraph [0056] of US'052 gives much reason to believe that this solution requires constructing separators from numerous components, which appears challenging to do in a cost-effective way.

Another issue with the embodiment of US’052 depicted in FIG. 4 thereof is mixing of the product gases, wherein some of the bubbles formed near the inner edges of the electrode compo- nents will rise through the central opening and are likely to coalesce, causing flow disturbances.

As such, it is a purpose of this invention to propose a cost effective alternative electrolyzer to semi-permeable membranes, porous electrodes and confining bubbles while maintaining an adequate electrolyte flow.

Accordingly, the present invention is characterized in that the electrodes are each furnished at opposite faces of the separator layer, such as a plate, and that the electrodes each comprise a plurality of fins and wherein each fin of the plurality of fins projects outwardly from the separator layer for restricting the upward movement of electrode generated bubbles to a bubble stream that is substantially parallel to the vertical plane.

The electrolyzer can typically be used in a cell comprising a housing, an electrolyte water solution within the housing, wherein the electrolyzer is arranged within said housing such that the anode and cathode are at least partially submerged in sald water solution.

The simplicity of the cell design presents an opportunity to increase the operating temperature of the electrolyser stack while maintaining stack lifetime. A higher operating tempera- ture increase the effectivity of the catalyst which makes it practical to replace precious metals with semi-precious metals while still achieving limited cell overpotential at reasonable current densities.

More specifically the electrodes comprise an electrode plate and the plurality of fins protruding therefrom. These elec- trode plates would extend in planes that are substantially parallel to the plane of the separator layer. In the case of parallel planar electrodes as described in this disclosure, this implies that the flow direction is parallel to the plane of the electrodes. In this disclosure, in contrast to US’052, the bodies of electrolyte in contact with the opposing elec- trodes would beneficially be separated by an impermeable boundary with macroscopic through holes, such as 1mm-200mm in width, and optionally forming slits the length of a proximal fin. The macroscopic through holes may themselves comprise a permeable membrane, optionally of the same material as the separator layer, but porous. In such a case the permeable mem- brane can be integral with the layer. Alternatively, the through holes can be provided with a membrane material that is different from the separator layer. In either case the remain- der of the separator layer is designed to be non-permeable to electrolytes. The through holes may be interrupted or uninter- rupted along the length of a slit. The dimensions of the through holes can be taken separate from any other feature in this portion of the description and are combinable with all embodiments of the invention. Beneficially buoyancy forces are by grace of the design according to the invention used to di- rect the flow of the gas bubbles to a path parallel to the plane of the electrodes which takes the bubbles around these openings as they rise. The approach of this disclosure allows for a cell design which is more compact and much easier to fabricate.

In the arrangement according to the invention, the anode and cathode electrodes are, as it were, placed back-to-back with an electrical insulation in between. Here the separator layer is a plate providing such insulation. The ions, that is to say electrolytes, in use, may in one example travel between the electrodes through holes which are distributed across the electrode plates. To prevent gas bubbles travelling through these through holes and mixing, a barrier may be replaced di- rectly beneath each opening to deflect the rising gas bubbles around the opening. The fins may be arranged so as to form said barrier. As such, more in general, the separator plate may be provided with through holes between vertically spaced fins of the plurality of fins, wherein said fins are provided as a barrier to prevent rising gasses from being exchanged through the separator plate.

To reduce stagnant bubbles which could otherwise form at the electrodes and in doing so improve contact between the electrode and the water, the plurality of {fins of each electrode may form pairs of upwardly converging fins. These fins of each pair of fins converge without meeting for, in use, merging and releasing the bubble streams of the fins as one upward stream. In use, is also separately from this option is a term that refers to a state wherein the electrolyzer is provided with an electrical current while at least partially submerged in water for actively separating water into hydrogen

Hz and oxygen Oz. By presenting the bubbles with a converging flow path a gaseous displacement of water is kept very close to the separator plate. The buoyancy effect of the rising bubbles draws in a preferential flow along the fins through the separator while gaseous exchange from one side of the separator plate to another side remains low. This allows for rapid electrolyte regeneration which in turn improves the efficacy of the electrolyzer.

In one example the through holes are macroscopic, that is to say 1mm-200mm in width, optionally designed as slits with a substantially equal upward angle compared to the converging fins. This arrangement adds to the electrical resistance of the cell, but with these suitable dimensions this additional resistance is less than the typical resistance of semi- permeable membrane and the efficiency penalty is believed to be comparable to the penalty of pumped electrolyte solutions.

In some embodiments, the electrodes are partially integrated into the separator plate. In other examples the electrodes are fixed to an outer surface of the separator plate.

Optionally, the electrodes comprise a metal plate, wherein the fins are provided on such plate and project outwardly from the separator plate by projecting outwardly from said metal plate.

The barriers, which may be the fins, should be positioned in such a way that, in use, the bubble stream is deflected to areas or channels where the bubbles can subsequently rise to the top of the electrode plates unimpeded. This arrangement reduces the local density of bubbles along the fins, wherein density should not be confused with mass density, but is simply given to mean the local volume ratio of gas over liquid. Also, the turbulence in the vicinity of the openings nearer to the top of the electrode plates is reduced. This reduces the mixing of the product gasses due to cross-over of bubbles between the sides of the back-to-back electrodes.

In one example any surface of the electrodes, such as the fins, which is directly below an opening or facing the opposite electrode is covered with a suitable material to prevent evolution of gas bubbles in these areas. As an example, polytetrafluorethylene (PTFE) can be used to cover these areas for its qualities as an electrical insulator and its resistance to corrosion. However, the person skilled in the art will understand that other materials may also be used.

The electrolyzer, as mentioned, may find an increased production performance in cell designs wherein the plate partitions the inner volume between the anode and cathode respectively and wherein the inner walls of the housing of each partition of the cell comprise electrical conductors optionally covered with catalyst which are electrically conductively connected to the anode and cathode respectively, for improving the efficacy of the cell. In more general terms an upper surface of the plurality of fins of each electrode may be electrically isolated, such as by a non-conductive coating.

In one embodiment the fins of adjacent pairs are integrally formed as a V-shaped ridge. This prevents bubbles form coalescing to form a separate diffuse column of rising bubbles which may cause disturbances in the larger fluid flow in a cell.

In vet another embodiment multiple pairs of fins are vertically spaced apart from each other so that, in use, an upward bubble stream of one pair adds to an upward bubble stream of another pair of the multiple pairs, and wherein the space between pair forming fins defines a vertical bubble path parallel to the vertical plane. This further improves efficacy.

The drawings show embodiments of the disclosed subject matter for the purpose of illustrating the invention. However, it should be understood that the present application is not limited to the precise arrangements and instrumentalities shown in the schematical drawings:

FIG. 1 shows a cross-section of a sample arrangement of the back-to-back anode and cathode with openings and barriers.

FIG. 2 shows a sample arrangement of openings, barriers, and channels where the bubbles are collected, and the direction of bubble flow resulting from this arrangement.

FIG. 3 shows a sample arrangement of the overall collector plate, including barriers to conduct the product gases to opposite sides of the electrolyzer stack.

FIG. 4 shows a sample arrangement of a part of the stack of collector plates, including the gas separation barrier.

FIG. 5 shows the cross-section of an electrolyzer cell with example sizes.

In Figure 1 an electrolyzer 100 is shown in cross-section. The electrolyzer serves for generating hydrogen from water comprising electrodes and an electrically non-conductive separator plate 3 extending in a substantially vertical plane comprising macroscopic through holes 7. In this example these through holes are 2 mm in width, but these dimensions are not set in stone and the person skilled in the art know that these may vary depending on the size of the cell that one intends to assemble. The electrodes themselves comprise an anode 1 and a cathode 2, characterized in that the electrodes 1, 2 are each furnished at opposite faces of the separator 3. The electrodes 1, 2 each have a plurality fins 4, 5 and wherein each fin of the plurality of fins projects outwardly from the plate 3 for restricting the upward movement of electrode generated bubbles to a bubble stream that is substantially parallel to the vertical plane. The electrolyzer is also shown as applied in a electrolyzer cell 1000. Also separately from this example the plurality of fins are designed to extend to inner wall of a housing of a cell. The fins thus form barriers by a protruding from a plate of the electrode itself. The electrode 1, 2 can

- Gg - be formed by a lanced metal sheet. The through holes 7 are shown to be provided to the separator plate 3 between the vertically spaced of fins 4, 5. The upper surface of each fin is, in this example at least, covered with an electrically insulating coating to prevent bubbles from forming on them. A suitable material for this coating is Polytetrafluoroethylene (PTFE) or Perfluoroalkoxy alkane (PFA) as those materials combine excellent corrosion resistance with good electrical insulation. The coating can be applied using the powder coating technique with parts of the electrodes masked while applying the powder. This arrangement deflects the flow of bubbles away {from the openings towards the top of the electrode plate. This reduces the amount of cross-over of bubbles to the other side of the anode-cathode assembly and hence improves the separation of the product gases.

The space between the electrode plates is occupied by the separator plate 3 which is an electrical insulator completely covering the areas of the plates facing each other. The electrode plates are themselves interrupted in places where through holes extend between the separator plate 3. The exposed parts of the separator plate 3 are covered with a coating to protect it from corrosion. If PTFE or PFA is used for the insulation of the ridge x1, then enamel is a suitable material for the insulation of the separator plate 3as it can withstand the temperature needed to bake the PTFE/PFA coating and can easily be applied to metals. Also separately from the above and compatible with all embodiments a plate of each electrode comprises a ridge x1 which protrudes outwardly from the plate for, in use, directing rising bubbles from the plurality of fins 4, 5 of said electrode to an outlet. The ridge may further be at least partially curved along the plane of said electrode.

Figure 2 shows one side of one of the electrodes 1, 2 of the electrolyzer 100. Here it is shown that “the electrode comprises a plate which itself also comprises through holes 7.1 which correspond to the through holes 7 of the separator plate”. It is noted that the quoted portion may be introduced into the claimed separately as a feature as it is compatible with all embodiments of the invention. In a more detailed example the fins 4, 5 are lanced from the electrode plate.

Each fin is integral with an adjacent fin forming the shape of a shallow V with a rounded angle. The upward angle of both fins 4, 5 deflects the flow of the bubbles to the side and around the openings between other fins of the plurality also forming a V towards the top of the plate. The rounded angle is intended to limit the stretch of the material when lancing the barrier. Shallow here means an angle between 100-170 degrees between integral fins.

Referring to FIG 3, in some embodiments a plurality fins 4,5 forming pairs 45 and V-shaped fins, as depicted in detail in

FIG 2. The space between V-shaped fins define channels in which generate bubbles rise upwards. A ridge xl, formed by bending a part of the electrode plate deflects the rising bubble flow sidewards x2 so all gas evolving on the electrode plate is expelled at one side of the plate. In the assembled stack, these ridges are pressed against the flat plates separating the cells. The opposing electrode has a similar ridge which deflects the bubble flow to the opposing side of the electrode plate. This arrangement allows for the product gases to be collected separately on the opposing sides of the cell stack. The product gases can be further kept separate by a barrier x3 between the top of the cell stack and the containing vessel. Supports x7 keep the cell stack isolated from the containing vessel.

Through the lanced protrusions, also referred to as fins 4,5 and ridges x1 described previously, each separator plate is in electrical contact with the adjacent anode and cathode. The electrical insulation between the anode and cathode provides the electrical insulation between successive cells, which obviates the need for separate gaskets, further simplifying the fabrication of the stack. The cell stack can be fabricated by alternating stacking of a combined anode/cathode plate and a separator plate between two end plates which are connected with tensions rods or springs.

Referring to FIG. 4, a lateral stack yl of collector and separator plates is seen in cross-section. A gas separation barrier y2 is placed at the top of the stack. The barrier is formed of a single piece of a material with sufficient elasticity to secure a gas-tight fit with the top of the stacked plates. Protrusions y3 of the barrier fit in the gaps formed by ridges which deflect the gas bubbles sideways as indicated in FIG. 3, label x1.

Referring to FIG. 5, with the dimensions shown therein the contribution to the cell overpotential by the resistivity of the electrolyte (35%-weight KOH at 50 °C and a current density of 0.5 A/cm2) is about 0.6 V, which is the same magnitude as for a standard cell with a gap of 4 mm between the electrodes and a semi-permeable membrane. For approached based on forced electrolyte flow, the overpotential of a standard cell with a gap of 4 mm is in the order of 0.4 V. When the operating temperature is increased to 150 °C (which would be impractical when a membrane is used) the contribution of the electrolyte resistivity is reduced to 0.3 V. So, the overpotential penalty of the arrangement in the current disclosure is at most limited and can be avoided altogether by choosing a higher operating temperature.

Concludingly, the invention is described herein according to the following aspects: 1. An electrolyzer {100} for generating hydrogen from water comprising electrodes (1, 2) and an electrically non- conductive separator layer (3), such as a plate, extending in a substantially vertical plane comprising macroscopic through holes (7), such as 1lmm-200mm in width, and wherein the electrodes themselves comprise an anode (1) and a cathode (2), characterized in that the electrodes (1, 2) are each furnished at opposite faces of the separator (3), and that the electrodes (1, 2) each comprise a plurality fins (4, 5) and wherein each fin of the plurality of fins projects outwardly from the separator layer (3) for, in use, restricting the upward movement of electrode generated bubbles to a bubble stream that is substantially parallel to the vertical plane. 2. The electrolyzer according to aspect 1, wherein the electrodes each comprise a single plate, such as integral with the plurality of fins of said electrode, which extends in a plane parallel to the plane the vertical plane of the separator layer (3). 3. The electrolyzer according to aspect 2, wherein the plate of each electrode comprises a ridge {x1) which protrudes outwardly from the plate for, in use, directing rising bubbles from the plurality of fins (4, 5) of said electrode to an outlet. 4. The electrolyzer according to aspect 1, 2 or 3, wherein the plurality of fins (4, 5) of each electrode form pairs of upwardly converging fins (45), and wherein the fins of each pair of fins converge without meeting for, in use, merging and releasing the bubble streams of the fins as one upward stream. 5. The electrolyzer according to aspect 4, wherein the fins of adjacent pairs (45) are integrally formed as a V- shaped ridge (V) forming a shallow angle between pairs between 100-170 degrees, preferable 120-150 degrees. 6. The electrolyzer according to any one of aspects 4 or 5, wherein multiple pairs of fins are vertically spaced apart from each other so that, in use, an upward bubble stream of one pair adds to an upward bubble stream of another pair of the multiple pairs, and wherein the space between pair forming fins defines a vertical bubble path parallel to the vertical plane.

7. The electrolyzer according to any one of aspects 1-6, wherein an upper surface of the plurality of fins of each electrode is electrically isolated, such as by an electrically non-conductive coating.

8. The electrolyzer according to aspect 7, wherein,

the through holes are provided (7) between vertically spaced fins of the plurality of fins, directly above and along each fin of the plurality of fins, wherein said fins are provided as a barrier to prevent rising gases from being exchanged through the separator layer (3).

9. An electrolyzer cell comprising:

- a housing defining an internal volume;

- an electrolyte water solution within the housing; and

— the electrolyzer (100) according to any one of aspects 1- 8 arranged within said housing.

10. The cell according to aspect 9, wherein lateral sides of said housing are fluid impermeable and wherein said lateral walls {facing the inner volume are provided with electrical conductors associated with the electrodes to increase the total active surface area of the electrodes of the electrolyzer.

11. A stack arrangement of electrolyzer cells, comprising laterally and vertically adjacent cells, wherein said cells are cells according to aspect 2 or 10.

12. The use of an electrolyzer cell according to aspect 9 or 10.

Claims

CONCLUSIONS

1. An electrolyser (100) for generating hydrogen from water comprising electrodes (1, 2) and an electrically non-conductive separation layer (3), such as a plate, extending into a substantially vertical plane comprising macroscopic holes (7), such as Imm - 200 mm wide, and wherein the electrodes themselves comprise an anode (1) and a cathode (2), the electrodes (1, 2) each being disposed on opposite faces of the separator (3), the electrodes (1, 2) each comprising a plurality of fins (4, 5), and each fin of the plurality of fins extending outwardly relative to the separation layer (3) so as, in use, to confine the upward movement of bubbles generated by the electrode to a bubble stream substantially parallel to the vertical plane.

2. The electrolyzer of claim 1, wherein the electrodes each comprise a single plate, such as integral with the plurality of fins of said electrode, said single plate extending in a plane parallel to the vertical plane of the separating layer (3).

3. The electrolyzer of claim 2, wherein the plate of each electrode includes a ridge (x1) extending outwardly from the plate to direct bubbles rising from the plurality of fins (4, 5) of that electrode during use to an outlet.

4. The electrolyzer of claim 1, 2 or 3, wherein the plurality of fins (4, 5) of each electrode form pairs of upwardly converging fins (45), and wherein the fins of each pair of fins converge without meeting to, in use, merge and release the bubble streams from the fins as one upward stream.

5. The electrolyzer of claim 4, wherein the fins of adjacent pairs (45) are integrally formed as a V-shaped ridge (V) forming a shallow angle between pairs between 100-170 degrees, preferably 120-150 degrees.

6. The electrolyzer of claim 4 or 5, wherein a plurality of pairs of fins are vertically spaced apart such that, in use, an upward bubble flow from one pair contributes to an upward bubble flow from another pair of the plurality of pairs, and wherein the space between pair-forming fins defines a vertical bubble path parallel to the vertical plane.

7. The electrolyzer of any one of claims 1 to 6, wherein an upper surface of the plurality of fins of each electrode is electrically insulated, for example by an electrically non-conductive coating.

8. The electrolyzer of claim 7, wherein the holes are provided (7) between vertically spaced fins of the plurality of fins, directly above and along each fin of the plurality of fins, the fins being configured as a barrier to prevent rising gases from being exchanged through the separation layer (3).

9. An electrolytic cell comprising: — a housing defining an internal volume; - an electrolyte-water solution within the housing; and — the electrolyzer (100) according to any one of claims 1 to 8, arranged within the housing.

10. The cell of claim 9, wherein the sides of the housing are liquid-impermeable and the side walls facing the inner volume are provided with electrical conductors connected to the electrodes to increase the total active surface area of the electrodes of the electrolyzer.

11. Stacking device of electrolysis cells comprising laterally and vertically adjacent cells, said cells being cells according to claim 9 or 10.

12. Use of an electrolysis cell according to claim 9 or 10.