GB2604213A - Hydrogen generator - Google Patents

Abstract

An electrolytic device (Figure 5) for the electrolysis of water is described. It comprises a plurality of electrodes 1, 2 arranged in pairs with a membrane (figure 1, 3) which may be an AEM or PEM. Each electrode pair has gas-tight insulation 7 from other pairs of electrodes, in an arrangement which could be called a stack (figure 4). Holes are provided for the supply of water to the electrodes 9. The device also possesses flow collection channels which are arranged to separately direct and collect the hydrogen and oxygen fluids produced from the stack. The electrodes may also have a zigzag or corrugated profile.

Description

Hydrogen generator This invention relates to a hydrogen generator and, in particular, a device for the production of hydrogen by electrolysis of water.

Hydrogen gas is an increasingly important fuel, because when burned with oxygen, it provides carbon-free combustion products. It is therefore one of the few environmentally friendly fuels, as the world deals with climate change. Hydrogen has applications in fuel cells, heating boilers, steam boilers, combined heat and power (CHP) boilers, gas furnaces, and internal combustion engines.

Although hydrogen can be prepared by electrolysis of water, the process is expensive to operate commercially. For that reason, most hydrogen is produced by steam methane reforming, which extracts hydrogen from methane. That process, however, releases carbon dioxide and carbon monoxide into the atmosphere, both of which are greenhouse gases, contributing to climate change.

Thus, there is a need for a more efficient hydrogen-generating electrolysis process to improve its commercial viability and hence the environmental potential of hydrogen as a fuel.

It is also important, from an environmental point of view, to burn hydrogen with pure oxygen, rather than with air. Air contains nitrogen, so that combustion also produces nitrogen oxides, which cause pollution because of their toxicity. Many known devices for the electrolysis of water purify the resulting gases, hydrogen and oxygen by bubbling them through water for purification, either separately or as a mixture of hydrogen and oxygen, known as Brown's gas, or water gas. However, because the filtration water dissolves much of the oxygen, the mixture -2 -has to be supplemented by air to produce a combustible mixture, hence leading to nitrous oxides.

The present invention tackles these dual problems. The electrolytic performance is enhanced by increasing the available surface area of electrodes, yet generating pure hydrogen and oxygen by separating the gases direct from the electrodes.

Attempts have been made to increase the surface area of electrodes. For example Wiley et. Al. ["Alkaline Water Electrolysis at 25 A cm-2 with a Microfibrous Flow-through Electrode" Advanced Energy Materials, Vol 10, Issue 25, 2020, doi.org/10.1002/aenm.202001174] investigated how nano-and micro-structured porous electrodes could improve the productivity of hydrogen generation. The authors studied three nickel electrodes: foam, microfiber felt, and nanowire felt. Although the nanowire felt, having the highest surface area, initially provided the highest performance, this performance quickly decreased as gas bubbles were trapped within the electrode. Furthermore, the nanostructure products may also clog with impurities in the water.

The device of the present invention increases the surface area of the electrodes, while retaining structural integrity, by providing a plurality of electrodes, resulting in a greater potential for electrolytic splitting of water, together with channels to separate the hydrogen and oxygen direct from the electrodes.

Accordingly, the present invention provides a device for the electrolysis of water, which device comprises a plurality of electrodes, the electrodes being arranged in pairs, each pair of electrodes comprising an anode and a cathode, and each pair of electrodes having gas-tight insulation from other pairs of electrodes, each pair of electrodes also having a means to supply water thereto, wherein the device contains a first set of collection channels arranged to direct and collect the hydrogen produced in the electrolytic reaction, and a second set of collection channels arranged to direct and collect the oxygen produced in the electrolytic reaction.

The device may be constructed as a domestic unit for use in a home, or as a larger industrial unit. The number of anode/cathode pairs in the device of may be varied accordingly. Generally, the device comprises at least three pairs of electrodes, typically at least five pairs of electrodes. Suitably, the device may contain from 6 to 50 pairs of electrodes, for example from 7 to 40 pairs, such as from 7 to 10 pairs, or from 10 to 30 pairs of electrodes.

Each electrode contains a terminal to which to apply a direct current voltage across the pair of anode and cathode. Between each anode and cathode, there is suitably a membrane to allow the conduction of ions between the anode and cathode and to separate the released oxygen and hydrogen. Such a membrane may be a proton electrolyte membrane (PEM) or an anion exchange membrane (AEM).

The anode and the cathode present in the device of this invention may be formed of any suitable conductive material, such as platinum, gold, silver, nickel, titanium, stainless steel, copper or aluminium.

The electrodes may be in the form of planar sheets of conductive material. Alternatively, the electrodes may have a zigzag profile.

Thus, in a preferred embodiment the present invention provides a device for the electrolysis of water, which device comprises a plurality of electrodes having a zigzag profile, the electrodes being arranged in pairs, each pair of electrodes comprising an anode and a cathode, and each pair of electrodes having gas-tight insulation from other pairs of electrodes, each pair of electrodes also having a means to supply water thereto, the -4 -device also containing a first set of collection channels arranged to direct and collect the hydrogen produced in the electrolytic reaction, and a second set of collection channels arranged to direct and collect the oxygen produced in the electrolytic reaction.

The zigzag profile of the electrodes significantly increases the available surface area thereof. The term zigzag profile used herein means a profile that alternatively changes direction throughout all or part of its length. Preferably the angles of direction change are substantially equal to each other and may suitably be from 15° to 90°, especially from 15° to 45°, preferably from 200 to 35°, for example from 25° to 30°.

Whatever shape the electrodes have, each pair of electrodes has a gastight insulation from other pairs of electrodes, so that the evolved hydrogen and oxygen is prevented from mixing, thus enabling the gases to be collected separately. The insulation between the pairs of electrodes is formed of a non-conductive material, such as nylon or an inert polymer for example acrylonitrile butadiene styrene (ABS). Advantageously, the insulation material may be coated in a resin material to improve the insulation. Suitably, each pair of electrodes is enclosed within a casing of the insulation material. The casings may then be stacked adjacent each other, with the electrical terminals of the anode and cathode protruding.

Water for the electrolysis reaction is supplied to each electrode. Each pair of electrodes has a means to supply water thereto. Suitably, the water supply means comprises a plurality of holes in each electrode, connected to a conduit supplying water. The holes may be located at the edges of the vertical sides of the electrodes. In that way, the water is contained within each casing around the pairs of electrodes.

The water is conveniently stored an a water tank above the electrodes and fed into the conduits under gravity. The level of the water in the water tank may be maintained by a valve control system, such as a simple float and ball valve, together with a pump which is activated when necessary to add further water. Preferably, the hydrogen and oxygen gases, evolved during the electrolysis reaction, are prevented from dissolving in the water, by means of a valve, such as a mechanical valve.

Before entering the water supply conduits, the water is preferably purified and cleaned, by means of filters, including for example a charcoal filter. The water may optionally be supplemented with electrolytes. Generally, the electrolyte may be an aqueous solution of an inorganic salt, such as sodium chloride, potassium chloride, lithium chloride, ammonium sulphate, sodium sulphate, or an organic salt such as an alkylannine salt. An alkaline solution may also be employed, including sodium hydroxide or potassium hydroxide in solution. Alternatively, simple tap water may be used.

A key feature of the device of this invention is the isolation of substantially pure hydrogen and oxygen produced in the electrolytic reaction, by means of a set of collection channels for each gas.

Preferably, the collection channels are secured to the top of each electrode so that evolved hydrogen is directed into a first set of channels and evolved oxygen is directed into a second set of channels, in such a way that the oxygen and hydrogen do not mix. The channels lead to two separate collection containers to store the gases. The ends of the collection channels adjacent the electrodes preferably terminate in a hood, to capture the evolving gas. Suitably, the channels are gas-tight, for example by coating with a resin material. In a preferred arrangement, each casing that contains a pair of electrodes in a stack of casings is positioned at 180° from the adjacent casing in the stack. In that way, one hood can cover the anodes of two adjacent casings; and a second hood can cover the cathodes of two adjacent casings.

The base of each casing for the electrodes is suitably removable, so that after an electrolysis cycle is complete, the particles that fall off the electrodes during the electrolysis reaction may be removed. This is conveniently achieved by means of a rotating cylinder situated below the electrodes. The upper part of the cylinder forms the base of the casings. At the end of a cycle, the cylinder is moved, to remove the debris, and is rotated to re-seal the casing. It is also advantageous to reverse the polarity at the end of a cycle to allow any accumulated slurry flakes to fall off the plates. The water in the device can then be used to wash most of the flakes that remain on the plates. The water is then filtered and pumped back up to the water tank; and the electrolysis process re-starts.

Both the hydrogen and the oxygen collected in the device of this invention may be used immediately, or stored for future use. Whenever hydrogen is used as a fuel, it needs a source of oxygen, so that the collection and storage of oxygen produced in this device is an aid to the use of hydrogen as a fuel.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a perspective view of a pair of electrodes of the device of this invention; Fig. 2 shows the top view of the electrode pair of Fig. 1; Fig. 3 is a casing into which one pair of electrodes fits; Fig. 4 shows a stack of seven casings, each containing one pair of electrodes; Fig. 5 is a completed device of this invention, incorporating the stack of casings of Fig. 4; Fig. 6 shows the inside view of the water supply and gas collection channel element of the device depicted in Fig. 5; Fig. 7 is a cross-sectional view of one edge of the element shown in Fig. 6; -7 -Fig. 8 shows the element of Fig. 6 fitting on top of the stack of casings containing pairs of electrodes of Fig. 4; and Fig. 9 shows the water supply conduits and the gas collection channels within the element of Fig. 6.

Referring to Fig. 1, two electrodes, 1 and 2, each having a zigzag profile, are aligned with each other and attached to an anion exchange membrane (AEM), 3, running between them. Each electrode, 1 and 2, contains a terminal, 4 and 5, respectively, which protrude laterally from the ends of the electrodes.

The top of the arrangement of Fig. 1 is seen more clearly in Fig. 2, using the same reference numerals.

Fig. 3 shows a casing, 6, comprising side walls, 7, and integral end walls, 8, made of a non-conductive material. The pair of electrodes of Fig. 1 fits into the inside of the casing, 6.

As shown in Fig. 4, seven of the casings of Fig. 3, are then stacked, with their side walls, 7, adjacent each other. Each casing holds a pair of electrodes, 1 and 2, with terminals, 4 and 5, protruding laterally. Along the top edges of the casings are situated a plurality of holes, 9, which provide a means to supply water to the electrodes.

Fig. 5 depicts the assembled device of this embodiment of the invention, having a water storage tank, 10, a water supply and gas collection channel element, 11, an electrolysis section, 12, and a drainage sump, 13. The electrolysis section, 12, comprises the stack of casings and electrodes shown in Fig. 4.

The interior of the water supply and gas collection channel element, 11, is shown in Fig. 6. Water from the water storage tank, 10, enters the central -8 -portion, 14, and flows into cavities, 15, which are connected via conduits to supply water to the electrodes. The outer edges, 16, of the element, 11, also contain the gas collection channels, although not visible in Fig.6. The gas collection channels terminate in gas exit ports, 17. The ports may be rectangular or round.

Fig. 7 is a cross-sectional view of one of the outer edges 16 of the element 11, showing some of the gas collection channels. Gas evolved from the electrolysis reaction, either hydrogen or oxygen, is directed via angled hoods, 18A, into gas collection channels, 19, and thence to gas exit ports, 17A. The set of channels depicted in Fig. 7 are arranged to collect only one gas, either hydrogen or oxygen, by being positioned over the relevant electrodes. The alternate hoods, 18B, extend to the other side of the element, 11, collect the other gas via a second set of channels which terminate at exit port, 17B.

The collection arrangement is shown in more detail in Fig. 8, which depicts the angled hoods, 18, positioned over the stacked casings containing electrodes of Fig. 4. Each hood 18 is secured in gas-tight manner to the membrane 3, to prevent mixing of hydrogen and oxygen. In Fig. 8, each casing each casing that contains a pair of electrodes in a stack of casings is positioned at 180° from the adjacent casing in the stack. Thus, for example, the casing 6A has the anode, 20A, on the left hand side of the casing and the cathode, 20C, on the right hand side of the casing. The adjacent casing, 6B, has the cathode, 21C, on the left hand side of the casing and the anode 21A on the right hand side of the casing. The hood 18A is positioned over the right half of casing 6A (a cathode) and the left part of casing 6B (also a cathode). Thus, the hood 18A collects only hydrogen evolved from the cathodes. Oxygen flows into the alternate hoods 18B and is collected through corresponding channels on the other side of element, 11.

Fig.9 shows the flow of both the water supply conduits and the gas collection channels, within the element 11. Water from the water storage tank flows in the direction of the dotted lines, 22, into the cavities, 15, and thence into the holes 9, which are situated on the upper edges of the casings, 6, to supply water to the electrodes. As the electrolysis proceeds, hydrogen is directed through hoods 18A (in Fig. 8), through the exit port, 17A and into channels in the direction shown by the dotted lines 23, to be collected in a hydrogen storage tank (not shown). On the other side of the element, 11, oxygen is directed through hoods 18B (in Fig. 8), though exit port, 176, and into channels in the direction shown by the dotted lines 24, to be collected in a oxygen storage tank (not shown).

Through the operation of this device, the electrolysis of water is carried out using multiple electrodes having a maximized surface area. In this way, the process achieves an improved performance compared to known methods, and is able to produce substantially pure hydrogen and substantially pure oxygen, which are separately collected and stored for use as fuel materials.

Claims (9)

1. -10 -CLAIMS1. A device for the electrolysis of water, which device comprises a plurality of electrodes, the electrodes being arranged in pairs, each pair of electrodes comprising an anode and a cathode, and each pair of electrodes having gas-tight insulation from other pairs of electrodes, each pair of electrodes also having a means to supply water thereto, wherein the device contains a first set of collection channels arranged to direct and collect the hydrogen produced in the electrolytic reaction, and a second set of collection channels arranged to direct and collect the oxygen produced in the electrolytic reaction.
2. 2. A device as claimed in claim 1, which device comprises a plurality of electrodes having a zigzag profile, the electrodes being arranged in pairs, each pair of electrodes comprising an anode and a cathode, and each pair of electrodes having gas-tight insulation from other pairs of electrodes, each pair of electrodes also having a means to supply water thereto, the device also containing a first set of collection channels arranged to direct and collect the hydrogen produced in the electrolytic reaction, and a second set of collection channels arranged to direct and collect the oxygen produced in the electrolytic reaction.
3. 3. A device as claimed in claim 2 wherein the angle of each zigzag is from 25° to 35°.
4. 4. A device as claimed in any one of claims 1 to 3, wherein the water supply means comprises a plurality of holes in each electrode, connected to a conduit supplying water.
5. 5. A device as claimed in any one of claims 1 to 4, wherein each pair of electrodes is enclosed within a casing of the insulation material.
6. 6. A device as claimed in any one of claims 1 to 5, wherein the collection channels are secured to the top of each electrode so that evolved hydrogen is directed into a first set of channels and evolved oxygen is directed into a second set of channels, in such a way that the oxygen and hydrogen do not mix.
7. 7. A device as claimed in any one of claims 1 to 6, wherein the ends of the collection channels adjacent the electrodes terminate in a hood, to capture the evolving gas.
8. 8. A device as claimed in any one of claims 1 to 7, wherein each casing that contains a pair of electrodes in a stack of casings is positioned at 1800 from the adjacent casing in the stack.
9. 9. A device as claimed in any one of claims 1 to 8 wherein the hydrogen and oxygen collected are stored for future use.