Field of the invention

This invention relates to an electrolyser for the production of gas. One of the main applications is for the production of hydrogen.

Background of the invention

Electrolysers are used in a variety of applications for generating liquid/gas products from various reactants. One of the important applications is the production of hydrogen by electrolysis of water or an aqueous solution. Oxygen or chlorine can be the by-product of this process depending on the electrolyte and the catalysts.

Many commercial processes employ a membrane between the anode and cathode that reduces crosscontamination of the gaseous products resulting from the electrochemical reaction. Conventional commercial processes for water electrolysis include alkaline and polymer electrolyte membrane (PEM) processes.

Membrane-less electrolysers are emerging and overcome some of the drawbacks that membrane based processes may face related to the cost and durability of the membranes employed.

An example of a membrane-less electrolyser under development is described in the article “A membraneless electrolyser with porous walls for high throughput and pure hydrogen production ” Pooria Hadikhani et al., Sustainable Energy & Fuels 2021. In the system proposed in the aforementioned article, the electrolyser comprises a centre channel into which an electrolyte is injected, connected by canals to the first and second side channels, one side channel having a cathode and the other side channel an anode therein. The electrolyte is injected into the cathodic and anodic channels respectively via orifices in the porous walls. The canals are inclined with respect to the direction of flow such that gas bubbles forming on the electrodes are dislodged by fluidic forces in the side channels. Such a construction overcomes the drawbacks associated with electrolyser membranes, while limiting cross-contamination of gaseous products found in earlier membrane-less technologies without a porous separating wall. One of the limitations of this design is the length of the electrolyser in the direction of flow, whereby in order to ensure sufficient flow through the orifices into each of the anodic and cathodic fluidic chambers, the centre inlet chamber should be provided with a gradually reducing cross-sectional area as it progresses from the inlet towards the outlet side. The centre channel configuration flanked by porous walls also increases the distance between electrodes compared to membrane-based technologies, which in conjunction with the insulating material filling the surface area between the pores, increases the voltage required to drive the electrochemical reaction.

Summary of the invention

It is an object of the invention to provide a membrane-less electrolyser for energy efficient and cost effective production of gas that achieves a high purity of the collected gas products.

It is advantageous to provide an electrolyser that is economical to operate and maintain.

It is advantageous to provide an electrolyser that can be easily scaled for high throughput hydrogen production.

It is advantageous to provide an electrolyser that is robust and requires low maintenance.

It is advantageous to provide an electrolyser that is economical to manufacture and assemble.

Objects of this invention have been achieved by providing the electrolyser according to claim 1.

Disclosed herein is an electrolyser including a reactor comprising a housing, fluidic channels within the housing, and electrodes. The electrodes comprise an anode and a cathode, the fluidic channels including an inter-electrode channel arranged between the anode and cathode and connected to an anode channel inlet for injection of an electrolyte into the inter-electrode channel, a cathode channel (6c) separated from the inter-electrode channel by a porous cathode side wall comprising a plurality of canals, and an anode channel separated from the inter-electrode channel by a porous anode side wall comprising a plurality of canals.

Each canal has a tapered shape such that an inlet surface area (Si) of the canal is greater than an outlet surface area (So) of the canal, the inlet surface area being on a side of the porous walls bounding the interelectrode channel.

In an advantageous embodiment, each canal has a centre axis (Cp) arranged at an angle (//) with a centre axis (Ce) of the inter-electrode channel, the angle of inclination being in a range of 30° to 80°, preferably in range of 40° to 70°, for instance between 45° and 65°.

In an embodiment, said angle ( β) of the canal centre axis (Cp) varies between an inlet side and an outlet side of the canal. In an advantageous embodiment, a ratio (Si/ So) of the canal inlet surface area (Si) to the canal outlet surface area (So), is in a range from 1.5 to 8, preferably in a range from 1.5 to 6, for instance in a range from 2 to 4.

In an advantageous embodiment, the canal has a cross-sectional inlet side shape that has a height (Di) equal or greater than a width (di), the width being measured in a direction of fluid flow and the height in the direction orthogonal to the direction of fluid flow.

In an embodiment, the canal has a cross-sectional inlet side shape that has a height (Di) less than a width (di), the width being measured in a direction of fluid flow and the height in the direction orthogonal to the direction of fluid flow.

The inlet cross-sectional shape may for instance be generally oval, for instance generally elliptical.

In an advantageous embodiment, the cross-sectional profde of the canals is generally oval, a height of the profde being greater in a direction orthogonal to the fluid flow than in a direction parallel to a fluid flow in the inter-electrode channel.

In an embodiment, a cross-sectional shape of the canal on the inlet side is different from a cross-sectional shape of the canal on the outlet side, for instance of oval shape on the inlet side and of circular shape on the outlet side.

In an embodiment, said plurality of canals comprise canals with different geometrical shapes or dimensions, for instance having shapes or dimensions that vary as a function of the position of the canal in a direction parallel to a fluid flow in the inter-electrode channel.

In an advantageous embodiment, the cathode fluid channel comprises an inlet connected to a source of electrolyte for injection of electrolyte liquid into the cathode fluid channel.

In an advantageous embodiment, the anode fluid channel comprises an inlet connected to a source of electrolyte for injection of electrolyte liquid into the cathode fluid channel.

In an advantageous embodiment, the electrodes are inserted into the housing from a base side or top side into a corresponding slot within which the corresponding electrode is received within the housing.

In an advantageous embodiment, the electrode is mounted or formed on a dielectric wall forming the porous cathode side wall respectively porous anode side wall comprising the pores. In an advantageous embodiment, the canals are arranged in a single row in a direction of flow, or alternatively wherein the canals are arranged in a plurality of rows at different heights within the interelectrode fluid channel.

Further objects and advantageous aspects of the invention will be apparent from the claims, and from the following detailed description and accompanying figures.

Brief description of the drawings

Figure la is a perspective schematic cross-sectional view of a reactor of an electrolyser according to an embodiment of the invention;

Figure lb is atop plan view of the device of figure la;

Figure 2 is a perspective exploded view of the embodiment of figure 1;

Figure 3a is a perspective schematic view of an electrode device of an electrolyser according to an embodiment of the invention;

Figure 3b is an exploded view of the electrode device of figure 3a;

Figure 4 is a view similar to figure 1 of a variant;

Figure 5a is a schematic cross-sectional view illustrating a canal of a portion of a porous wall of an electrolyser according to an embodiment of the invention;

Figure 5b is a side view of the portion of porous wall of figure 5b;

Figure 6 is a view similar to figure 5a of a variant.

Detailed description of embodiments of the invention

Referring to the figures, an electrolyser includes a reactor 2 comprising a housing 4, fluidic channels 6 (6a, 6b, 6c) and electrodes 16 (16a, 16c). One of the electrodes is an anode 16a and the other electrode a cathode 16c. The electrodes may be mounted in lodgings 12, for instance in the form of slots within the housing, one of the lodgings being an anode receiving slot 12a and the other lodging being a cathode receiving slot 12c. The electrolyser further comprises a pump system (not shown, and a gas collector system (not shown) for collecting the gas products of the electro-chemical reaction. A liquid electrolyte is pumped through the fluidic channels 6 by the pump system and the gas products formed by the electrochemical reaction are collected by the gas collector system coupled to an outlet of the electrolyser reactor 2.

The fluidic channels include an inter-electrode channel 6b arranged between the electrodes 16a, 16c, connected to an inlet 8b coupled to a source of liquid electrolyte that is injected into the inter-electrode channel 6b via the inlet 8b. The fluidic channels further comprise a cathode channel 6c arranged along the cathode 16c, and an anode channel 6a arranged along the anode 16a. The cathode channel 6c is connected at an outlet end to a cathode channel outlet 10c that is coupled to a fluid line connected to the gas collector system (not shown) for collecting the electrolysis gas production from the cathode and re-circulation of the liquid electrolyte back into the circuit. The anode channel 6a is connected at an outlet end to an anode channel outlet 10a that is coupled to a fluid line connected to the gas collector system (not shown) for collecting the electrolysis gas production from the anode and re-circulation of the liquid electrolyte back into the circuit. The anode and cathode channels 6a, 6c are separated from the inter-electrode channel 6b by respective porous walls 14a, 14c each comprising a plurality of canals 20 providing fluidic connection between the inter-electrode channel and the anode and cathode channels 6a, 6c.

In a preferred embodiment, the electrodes 6a, 6c are preferably mounted, deposited or otherwise formed at least partially on or against the porous walls 14a, 14c, and in such embodiments are provided with orifices 18 aligned with the canal outlets on the porous walls 14a, 14c.

The electrodes may however also be arranged fully or partially on other wall portions of the cathode, respectively anode channels, or may comprise a wire, rod or bar (not shown) extending within the anode and cathode channels.

The cathode channel 6c may further comprise a cathode channel inlet 8c and the anode channel 6a may further comprise an anode channel inlet 8a. The anode and cathode channel inlets are connected to a supply of liquid electrolyte and serve to produce a flow of liquid electrolyte in the anode and cathode fluidic channels in order to help collect and dislodge gas bubbles formed on the respective electrodes or porous walls, in particular at the outlet 22 of the canals 20.

The pressure of the electrolyte fluid injected in the inter-electrode channel 6b is higher than the pressure of the electrolytes injected in the cathode channel 6c, respectively in the anode channel 6a, in order to ensure flow of the electrolyte from the inter-electrode channel to the cathode and anode fluidic channels through the porous walls 14a, 14c. The inlets 8a, 8b, 8c may all be connected to a common pump system with pressure regulating means arranged in the supply channels connected to the inlets in order to ensure that the pressure in the inter-electrode channel is higher than in the cathode and anode channels. Alternatively, different pump systems may be connected to the inter-electrode fluid channel and the anode and cathode fluid channels. It may be noted that the flow of electrolyte in the anode and cathode chambers may be configured to be the same, or may be configured to have different flow rates depending on the volume of gas products generated on the anode and cathode respectively. Each canal extending from the canal inlet side 21 to the canal outlet side 22 has a canal centre axis Cp that is inclined at an acute angle p relative to the inter-electrode centre axis Ce. such that any gas bubbles generated are projected in the direction of fluid flow, thus limiting any cross-contamination. In advantageous embodiments, angle P is in a range from 30° to 80°, preferably in a range from 40° to 70°, for instance in a range from 45° and 65°. The angle P can be different for different canal depending on the position of canal in the flow channel 6b.

In the illustrated embodiments, the canals have a substantially linear centre axis Cp, however within the scope of the invention, the centre axis may be curved, at least partially, or over the entire length of the canal. For instance, the angle p at the canal outlet 22 may be greater than it is at the canal inlet 21.

According to an aspect of the invention, a surface area So on the outlet side 22 of the canal 20 is smaller than a surface area Si on an inlet side 21 of the canal. The ratio SUSo of the canal inlet surface area relative to the canal outlet surface is in a range from 1.5 to 8, more preferably in a range from 1.5 to 6, for instance in a range from 2 to 4, to ensure an optimal compromise between the acceleration of the fluid in the canals to dislodge bubbles formed at the canal exit 22, yet ensure a sufficient surface area of electrolyte through the porous wall for the electrical field to pass. Another important advantage of the tapered canal geometry is that it allows the inter-electrode fluid channel 6b to have a length W that is longer in the direction of the inter-electrode centre axis Ce (i.e. the general direction of electrolyte fluid flow through the reactor 2) than the conventional membrane-less design presented in the introductory section of the present disclosure. This can be achieved because: 1) the flow of the liquid electrolyte is uniform among all canals 20 due to its design, 2) the bubbles cannot cross over due to the accelerating flow in the canals 20. A pressure drop from an inlet end of the inter-electrode fluid channel to an outlet end of the inter-electrode channel is minimized compared to a configuration where the canals have a constant cross-sectional area of So.

The length W of the inter-electrode fluid channel in the direction of the inter-electrode centre axis Ce may be further increased by having a height hpi of the canal on the inlet side 21 that is no more than 90%, preferably no more than 80% the height H of the inter-electrode channel (the height H being measured in a direction perpendicular to the liquid flow). The length W can be increased due to the lower pressure drop in larger cross-sectional channels. The rate of flow of the fluid in the inter-electrode channel may thus be kept sufficiently low to ensure an even distribution of the fluid from the inlet and to the outlet end of the fluid channel over a great length with a small pressure drop over the channel length W.

In preferred embodiments, the canals may have a generally circular, elliptic or generally oval cross- sectional profile, the cross-section being considered orthogonal to the canal centre axis Cp. Other shapes such as rectangular, semi-circular and various other shapes may however be provided. The shape of the canal may also vary along its length L from the inlet side 21 to the outlet side 22, for instance going from a generally oval shape at the inlet side to a less oval or circular shape at the outlet side, provided that the change in surface area is configured to increase the mean fluid velocity in a substantially smooth manner, for instance principally maintaining substantially laminar flow in order to avoid higher flow resistance effects due to turbulent flow. Furthermore, the change in the shape can provide higher effective area between electrodes in order to reduce the ohmic resistance.

There may be a single row of canals arranged along the direction of fluid flow through each porous wall, or there may be a plurality of rows of canals, for instance as illustrated schematically in figure 6. The rows of canals 20 may also be offset such that adjacent canals are not aligned along the same orthogonal axis to the flow direction.

For applications of water electrolysis for the production of hydrogen (and oxygen) the canal surface areas at the outlet side 22 may typically be in the range of 40 mm ² to 0.7 mm ² , for instance in a range of 4 mm ² to 1 mm ² .

In an advantageous embodiment, the electrodes may be in the form of thin plates or thin plate structures, that are inserted into the housing 4 in slots 12a, 12c accessible from a top or a bottom of the housing, thus allowing economical manufacturing and assembly of the electrodes and housing. The electrodes 16a, 16c may be in the form of stamped metal sheets, that may be mounted in a holding plate 17 that also forms the porous wall 14 separating the inter-electrode channel 6b from the cathode and anode channels 6a, 6c respectively.

The electrodes may also be made by depositing a conductive material such as a metal on a dielectric surface by various per se known depositing or 3D printing techniques.

The electrodes may also be formed in other manners, for instance by plating or depositing a conductive layer on a dielectric support, which may also form the porous wall separating the inter-electrode channel from the anode or cathode channel.

Within the scope of the invention, the electrodes may be flat or substantially flat electrodes, or may be structured electrodes providing a larger active area and more nucleation points than flat electrodes. Compared to flat electrodes, structured electrodes may allow the produced gas bubbles to detach at smaller sizes and ensure the electrodes surface remains free from bubbles. Furthermore, a larger active electrode area lowers the overpotentials. Within the scope of the invention, the electrodes may be also be assembled or deposited directly on the porous walls and optionally partially within the canals 20 extending thereinto from the outlet end 22, thus bringing the anode and cathode closer together.

The reactor 2 of the electrolyser may be stacked vertically and the inlets 8a, 8b, 8c may be connected to separate supply lines or connected to a common supply line via a manifold (not shown). The electrolyser may thus be formed of a plurality of individual reactor units 2 that may be stacked depending on the production needs and volume of gas products to be produced.

The electrolyser according to embodiments of this invention may also be used for other electrochemical reactions, for instance using brine as the electrolyte liquid to produce chlorine gas, or using other electrolyte liquids to produce various gases, or conducting electrochemical synthesis.

An example of parameters of an electrolyser reactor according to an embodiment of the invention, for illustrative purposes, is provided below.

Range of flow rate and Reynolds number

Aqueous solution with 30 wt. % KOH concentration

Density: 1230 kg/m ³

Viscosity: 0.0016 Pa.s inlet 8b:

Hydraulic diameter: 4.92 mm

Reynolds number at the inlet 8b Re= 165 to 829

Flow rate, inter-electrode channel 6b: 50 ml/min to 250 ml/min

Channel shape: rectangular 4 mm x 1.3 mm

Hydraulic diameter: 1.96 mm

Reynolds number in the inter-electrode channel Re= 416 to 2081

Flow rate, cathode, anode channels 6a, 6c:

O to 150 ml/min

Canals inlet-outlet area relationship

Canal outlet area relationship

The minimum velocity in the outlet side 22 of flow channels should be 7 cm/s. Therefore, the Reynolds number at the outlet of flow channel should be larger than 50. p: density (1230 kg/m ³ : viscosity (0.0016 Pa.s)

Q: flow rate (50 ml/min to 250 ml/min) n _f . number of canals (11)

Re _Omin minimum Reynolds number at the outlet of the canal

D _o : hydraulic diameter of the canal at the outlet

S _o : Area of the canal at the outlet

Canal inlet-outlet area relationship a electrolyte conductivity

D _o : hydraulic diameter of canal outlet

D _i : hydraulic diameter of canal inlet

L length of canal

D : average diameter of the canal over its length n _f . number of canals (11)

W : Length of porous wall (33 mm)

H Height of porous wall (4 mm)

The electrolyte resistance in the canal is

We can specify the average diameter of the canal by comparing this equation with cylindrical canals:

The porous wall open area ratio determines the resistance between the electrodes. We calculate this ratio as follows:

If a canal has an open area larger than 15%. Therefore: From the previous relation, S _o should be smaller than 1.54 mm. Therefore, should be larger than 2.1 mm. List of references in the drawings:

Electrolyser reactor 2

Housing 4

Electrode lodgings (slots) 12

Anode slot 12a

Cathode slot 12c

Fluidic channels 6

Cathode channel 6c

Cathode channel inlet 8c

Cathode channel outlet 10c

Anode channel 6a

Anode channel inlet 8a

Anode channel outlet 10a

Inter-electrode channel 6b

Inlet 8b

Porous cathode-side wall 14c

Porous anode-side wall 14a

Canal 20

Canal inlet side 21

Canal outlet side 22

Electrodes

Anode 16a

Fluid orifices 18

Anode support 17a

Cathode 16c

Fluid orifices 18

Cathode support 17c

Connectors 24a, 24b

Pump system (not shown)

Gas collector system (not shown)

Inter-electrode channel height H

Inter-electrode channel length W

Inter-electrode channel width T

Canal geometry

Canal inlet surface area Si Canal outlet surface area So

Ratio surface areas Canal outlet / inlet Si/ So

Canal centre axis Cp

Canal length on centre axis L Inter-electrode channel centre axis (general flow direction) Ce

Canal centre axis Cp to electrode centre axis Ce angle of inclination β

Canal height/diameter on inlet side Di

Canal width on inlet side di

Canal height/diameter on outlet side Do Canal width on outlet side do