WO2015118073A1

WO2015118073A1 - A separator plate for an electrolyser, an electrolyser for generating two separate gasses from a fluid

Info

Publication number: WO2015118073A1
Application number: PCT/EP2015/052425
Authority: WO
Inventors: Nigel WILLIAMSON
Original assignee: Clean Power Hydrogen Limited
Priority date: 2014-02-05
Filing date: 2015-02-05
Publication date: 2015-08-13
Also published as: GB201401993D0

Abstract

A separator plate (1) for mounting between two electrode plates (20) of a fluid electrolyser comprises a first face (2) having a central part (5) and a peripheral part (4), a second face (3) opposite the first face and having a central part and a peripheral part, and two pairs of spaced-apart apertures extending from the first face to the second face of the plate, each pair of spaced-apart apertures comprising an inlet aperture (7, 8) and an outlet aperture (9, 10). A first recess (12, 5) is provided extending substantially across the first face (2) of the plate from a first inlet aperture (7) to a first outlet aperture (9) of the first pair of apertures and adapted to guide a fluid from the first inlet aperture to the first outlet aperture. A second recess (13, 5) is provided extending substantially across the second face (3) of the plate from a second inlet aperture (8) to a second outlet aperture (10) of the second pair of apertures and adapted to guide a fluid from the second inlet aperture to the second outlet aperture. The central parts of the first and second faces comprises a membrane that is permeable to ions and resistant to permeation by gases.

Description

TITLE

A separator plate for an electrolyser, an electrolyser for generating two separate gasses from a fluid

BACKGROUND TO THE INVENTION

There are numerous systems in production throughout the World which are mixed gas (hydrogen and oxygen in stoichiometric proportions) generation systems for use in automotive aftermarket environments, where the gas is added to the incoming air to aid in the combustion reaction in a typical ICE (Internal Combustion Engine) vehicle. These systems are designed and installed with a view to making the combustion reaction more efficient, thereby reducing fuel consumption and associated exhaust pollutants.

There are numerous drawbacks, however, to the use of such systems on more modern vehicles which have complex and sophisticated electronic control systems to ensure optimum efficiency and pollution control. As sophisticated as they are, these systems struggle to prove themselves capable of refining the exhaust emissions to legislated levels, and there is considerable, growing interest in the use of hydrogen gas to contribute to the purification process. The drawbacks mentioned above include those associated with the oxygen content of the mixed gas, which is seen by the oxygen sensors in the on-board control system as indicating a lean mixture. The control system compensates for this by the provision of extra fuel to the engine, which is, of course, completely counter-productive.

A further undesirable effect arising from the supply of extra oxygen to the engine is in the generation of oxides of nitrogen, known as NOx (NO and NO2). NOx is typically generated during the combustion reaction by combination of air-borne nitrogen with any oxygen left over from the combustion reaction, at the typical elevated temperatures and pressures encountered in the reaction. NOx gases react to form smog and acid rain as well as being central to the formation of tropospheric ozone, and are now the primary target of governments in their drive to reduce pollution, particularly in cities. Further, the leaner a mixture, and therefore the more economical, the hotter the combustion and associated NOx generation. It is therefore difficult to beneficially affect fuel economy without deleteriously affecting NOx generation, and vice- versa.

A rich mixture gives rise not only to reduced fuel efficiency, but will generate a greater mass of particulates as a result of incomplete combustion of the fuel molecules. These particulates are also targeted for reduction in many countries and communities, as they are also a major pollutant, and give rise to numerous ailments in city populations. Addition of hydrogen as a single gas can help these issues to resolve to a large extent, by essentially 'enriching' the parent fuel (Petrol, Diesel, LPG or LNG), thereby making the combustion reaction more efficient. An efficient combustion will allow an engine to run cooler, thereby producing fewer NOx molecules. Additionally, it will reduce the generation of particulates which are, as already described, the product of incomplete combustion.

However, other pollutants generated in the combustion reaction include carbon monoxide (CO), carbon dioxide (C02) and hydrocarbons (HC), of which the CO is the most undesirable when considering ground-level pollution and its effect on human health. Generation of CO is higher when the oxygen in the air induced to an engine is substantially consumed in the combustion reaction. This is another issue when attempting to clean up exhaust emissions.

It is, therefore, advantageous to provide some oxygen, at a lower concentration than the stoichiometric ratio of 2: 1, to the engine along with the hydrogen. Each engine, fuel type and control system will give rise to different exhaust emissions characteristics, which will potentially require different ratios of hydrogen and oxygen addition to the incoming air to attain the optimum result when all economy and pollution requirements are considered.

It is an object of the invention to overcome at least one of the above-referenced problems.

STATEMENTS OF INVENTION

In a first aspect, the invention provides an integrated flow-field plate (hereafter referred to as a "separator plate") for mounting between two electrode plates of a water electrolyser, the separator plate comprising:

a first face having a central part and a peripheral part; a second face opposite the first face and having a central part and a peripheral part;

two pairs of spaced-apart apertures extending from the first face to the second face of the plate, each pair of spaced-apart apertures comprising an inlet aperture and an outlet aperture;

- a first recess extending substantially across the first face of the plate from a first inlet aperture to a first outlet aperture of the first pair of apertures and adapted to guide a fluid from the first inlet aperture to the first outlet aperture; and

a second recess extending substantially across the second face of the plate from a second inlet aperture to a second outlet aperture of the second pair of apertures and adapted to guide a fluid from the second inlet aperture to the second outlet aperture;

wherein the central parts of the first and second faces comprises a membrane that is permeable to ions and resistant to the passage of gases.

The separator plate of the invention, by virtue of its arrangement of holes and recesses, provides on its first face a flow chamber to conduct flow from a first inlet orifice to a first outlet orifice, and on its second face a flow chamber to conduct flow from a second inlet orifice to a second outlet orifice, and separate fluid circulation circuits supplying the first face and the second face.

Thus, when one side of the separator faces an anode and the other side faces a cathode, and an aqueous fluid is separately supplied to each face through the first and second inlet apertures, oxygen gas will generated on one side of the cell and hydrogen gas will be generated on the other side, prevented from recombining by the separator. The separate outlet apertures ensure that the oxygen and hydrogen containing fluids will be kept separate.

Preferably, the two pairs of apertures are mounted in the peripheral part, and wherein the central membrane part is recessed relative to the peripheral part.

Suitably, the central recessed part comprises the membrane, typically a polymeric or woven fabric membrane. Ideally, the inlet and outlet apertures of each pair of apertures are diagonally spaced-apart across the plate. Suitably, the inlet apertures are disposed towards a base of the plate and the outlet apertures are disposed towards a top of the plate.

Ideally, the inlet apertures are smaller than the outlet apertures.

The invention also provides a reactor stack for an electrolyser and comprising at least one electrolysis cell, the at least one electrolysis cell comprising a separator plate according to the invention and two electrode plates, each electrode plate having first and second inlet apertures and first and second outlet apertures corresponding to the first and second inlet and and first and second outlet apertures of the separator plate, wherein the separator plate is sandwiched between the two electrode plates such that the first inlet apertures of the electrode and separator plates form a first fluid inlet manifold, the second inlet apertures of the electrode and separator plates form a second fluid inlet manifold, the first outlet apertures of the electrode and separator plates form a first fluid outlet manifold, and the second outlet apertures of the electrode and separator plates form a second fluid outlet manifold.

Preferably, the reactor stack comprises a plurality of electrolysis cells, suitably between 4 and 100. The invention also provides an electrolyser system for performing electrolysis on a fluid and comprising:

- at least one reactor stack of the invention;

- a first degassing unit adapted to receive liquid electrolyte bearing gas in suspension, and to separate at least a portion of said gas from said electrolyte by gravity;

- a first return conduit adapted to return the electrolyte to a fluid inlet manifold of the reactor stack;

- a second degassing unit adapted to receive gas-bearing electrolyte from the second outlet manifold of the reactor stack and to separate at least a portion of said gas from said electrolyte by gravity;

- a second return conduit adapted to return the electrolyte to a fluid inlet manifold of the reactor stack; and

- pump means for pumping fluid through the inlet and outlet manifolds of the reactor stack. Suitably, the first return conduit is adapted to return the fluid phase to the first inlet manifold, and the second return conduit is ideally adapted to return the fluid phase to the second fluid inlet manifold. Typically, the system comprises a first gas conduit adapted to receive the first gas from the first degassing unit and a second gas conduit adapted to receive the second gas from the second degassing unit.

Ideally, the reactor stack comprises a plurality of electrolysis cells, each cell comprising a separator plate sandwiched between polar plates, one side of which would be the anode for one cell, and the other the cathode for its neighbouring cell, whereby each cell has an anode and a cathode. When the fluid is aqueous (i.e. water + electrolyte), this arrangement provides a stoichimetric amount of hydrogen and oxygen (2: 1).

Typically, a reactor stack will comprise of a number of groups of cells, each of which has a mono-polar plate at each end, one being the anode for the group and the other the cathode, with a number of bi-polar plates spaced therebetween, of which one side is the anode for a cell, and the other a cathode. The number of bi-polar plates in a group of cells is determined by the voltage to be applied to the group, in such a way as to ensure that each cell has an optimal operational voltage.

In one embodiment, the stack comprises a plurality of electrolysis cells, wherein at least one of the cells comprises a separator plate sandwiched between an anode and a cathode and an least one of the electrolysis cells comprises a separator plate sandwiched between an anode and a cathode plate of opposite polarity, wherein the flow to the cathode side of the predominating cells is mixed with that of the anode side of the reversed polarity cell(s). When the fluid is aqueous (i.e. water + electrolyte), this arrangement provides a non- stoichimetric amount of hydrogen and oxygen (2: 1), and can be adapted to increase the amount of oxygen relative to hydrogen. Electrode plates are bi-polar plates or mono-polar plates, dependent upon their location in the reactor stack relative to (a.) other plates, (b.) points of electrical connection within the stack and (c.) orientation or 'handing' of cell separator/membrane plates. Examples of such plates are shown in the figures section. Typically, the electrolyser system comprises an electrical supply means in electrical comunication with the electrode plates, being connected to mono- polar plates throughout the stack. Preferably, the electrical supply means comprises electrical generation means.

Suitably, the electrical supply means comprises control means for controlling the electrical supply to the reactor stack.

The invention also relates to a machine comprising: an internal combustion engine; an electrolyser system of the invention, and means for conveying the first and/or second gas generated by the electrolyser system to the internal combustion engine. The use of hydrogen, as a separate gas for cleaning exhaust emissions, is also potentially significant, where failure to meet increasingly stringent emission legislation is contributing to significant cost in the automotive, trucking and off -road vehicle manufacture, and ongoing maintenance.

This can be accomplished by injection of hydrogen directly into the exhaust system, immediately after the exhaust manifold of an engine, to react with particulates and other constituents of the exhaust gases in the same way as expensive urea systems (Ad-Blue systems) are used.

The invention also provides a method of performing electrolysis on a fluid to generate first and second separate gasses, which method employs an electrolyser system of the invention, the method comprising the steps of: charging the electrodes; pumping the fluid into the first inlet manifold and out of the first outlet manifold whereby electrolysis of the fluid generates a first mixture comprising fluid and a first gas; pumping the fluid into the second inlet manifold and out of the second outlet manifold whereby electrolysis of the fluid generates a second mixture comprising fluid and a second gas; separating the first mixture in the first degassing unit to provide liquid and the first gas; separating the second mixture in the second degassing unit to provide liquid and the second gas; and return the liquid from the degassing units to the inlet manifolds.

Typically, the fluid from the first degassing unit is returned to the first inlet manifold, and the fluid from the second degassing unit is returned to the second inlet manifold.

Suitably, the fluid is aqueous and the first gas is hydrogen and the second gas is oxygen. Preferably, each separator plate is sandwiched between a cathode and an anode, wherein the hydrogen and oxygen are produced in stoichimetric amounts.

Typically, one or more of the cells may be orientated with the opposite polarity to the rest of the cells within the stack, wherein the hydrogen and oxygen generated by the stack are produced in non- stoichimetric amounts.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be described in more detail with reference to the accompanying figures in which:

Figs. 1 and 2 are front and rear plan views, respectively, of a separator plate of the invention;

Fig. 3 is a perspective view of the front face of the separator plate of Fig. 2;

Fig. 4 is an expanded perspective view of a reactor stack according to the invention showing two separator plates of the invention sandwiched between electrode plates;

Fig. 5 is a perspective view of the reactor stack of Fig. 4 taken from the opposite side;

Fig. 6 is a perspective view of a separator plate according to the invention; Fig. 7 is a perspecive view of a reactor stack according to the invention comprising a plurality of electrolysis cells and end plates;

Fig. 8 is a perspective view of an electrolyser system according to the invention and comprising a reactor stack of the invention; and

Figs. 9 and 10 are perspective views of separator plates according to the invention having deflection supports. Figs. 11, 12 and 13 are frontal views of separator plates with optional possible designs of moulded-in deflection suports for the membrane

Figs. 14 and 15 are perspective exterior and sectioned views respectively of a 'bubbler' type flash-back arrestor

Fig. 15 is a perspective view of a typical cylindrical flash-back arrestor

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, and initially to Figs. 1 to 3, there is illustrated a separator plate of the invention indicated generally by the reference numeral 1. The plate 1 is planar and circular in shape, has a first face 2 and a rear face 3, a peripheral section 4 and a recessed central portion 5 formed by a membrane. A first fluid inlet aperture 7 and a second fluid inlet aperture 8 are formed in the peripheral section 4, towards a base of the plate 1. A first fluid oulet aperture 9 and a second fluid outlet aperture 10 are formed in the peripheral section 4, towards a top of the plate 1. The inlet apertures 7, 8 are smaller than the outlet apertures 9, 10. The front face 2 of the plate 1 comprises a recessed portions 12A, 12B that together with the recessed central portion 5 forms a flow path for fluid from the first inlet aperture 7 to the first outlet aperture 9. Thus, fluid supplied through the inlet aperture 7 can flow across the face of the plate 1 to the outlet aperture 9. Likewise, the rear face 3 of the plate 1 comprises a recessed portions 13A, 13B that together with the recessed central portion 5 forms a flow path for fluid from the second inlet aperture 8 to the second outlet aperture 10. Thus, fluid supplied through the inlet aperture 8 can flow across the face of the plate 1 to the outlet aperture 10. The separator plate defines first and second fluid circuits and keep the fluid in each circuit separate.

The separator plate 1 comprises a number of formations 15 on its periphery adapted to receive screws or other fixing means for the purpose of fixing the plate to adjacent electrode plates. In this embodiment, the plate 1 has dimensions of 160mm dia for the main portion and is formed from a compliant plastic material. As described above, the plate comprises a peripheral border that is thicker than the central membrane portion. The purpose of this is to provide a flow-field for the electrolyte. Likewise, parts of the peripheral portion of the plate may be cut-away or recessed as shown in Fig. 6, thus using less material than the plates of Figs. 1 to 3. In another embodiment of the invention, the separator plate 1 comprises support means 17 disposed on the recessed portions that are designed to prevent bending or deflection of the recessed portions due to uneven water pressure one side to the other. In Fig. 9, the supports comprise raised ribs 18 and in Fig. 10 the supports comprise short columns 19.

Referring to Figs 4 and 5, these is illustrated an arrangement of electrodes 20 and separator plates 1 in an expanded view, in which each separator plate 1 is disposed between two electrode plates 20. In this embodiment, the electrode plates are bipolar electrodes having a cathode side 21 (Fig. 4) and an anode side 22 (Fig. 5). The electrode plates 20 each comprise first and second fluid inlet apertures 27, 28 and first and second fluid outlet apertures 29, 30 that correspond with the inlet and outlet apertures of the separator plates 1. When the plates 1, 20 are sandwiched tightly together to form an electrolysis cell, the apertures align such that the first fluid inlet apertures 7, 27 form a first fluid inlet manifold (see 33 in Fig. 7), the second fluid inlet apertures 8, 28 form a second fluid inlet manifold (see 34 in Fig.7), the first fluid outlet apertures 9, 29 form a first fluid outlet manifold (see 35 in Fig.7), and the second fluid outlet apertures 10, 30 form a second fluid outlet manifold (see 36 in Fig.7).

Referring to Fig. 7, there is illustrated a reactor stack according to the invention indicated generally by the reference numeral 37 and comprising a plurality of electrolysis cells of Figs 4 and 5 sandwiched together between end plates 31 A and 3 IB. The end plates have inlet apertures and outlet apertures that together with the inlet and outlet apertures of the separator and electrode plates to form first and second fluid inlet manifolds 33, 34 and first and second fluid outlet manifolds 35, 36. Referring to Fig. 8, there is illustrated an electrolyser unit of the invention in which parts identified with reference to the previous embodiments are assigned the same reference numerals. The electrolyser unit, indicated generally by the reference numeral 40, comprises a reactor stack 37, a first fluid degassing vessel 41 disposed on a first side of the reactor stack 37 and in fluid communication with the first fluid outlet manifold, a second degassing vessel 42 disposed on a second side of the reactor stack 37 and in fluid communication with the second fluid outlet manifold, a first return conduit (not shown) for returning degassed fluid from the first degassing vessel 41 to the fluid inlet manifold (not shown), and a second return conduit (not shown) for returning degassed fluid from the second degassing vessel 42 to the fluid inlet manifold (not shown). Pumps 43 are provided to pump the fluid around the two separate circuits.

Referring to figures 11, 12 and 13, raised portions of plastic, moulded on the material of the membranes are shown as a mesh (44) in Fig. 11, straight raised strips (45) in Fig. 12, and raised dots or columns (46) in Fig 13, and are designed to prevent excessive deflection of the material of the membrane in the presence of differntial pressure, side-to-side. These raised portions are not limited to the three forms shown, as numerous other designs could be used to perform the same beneficial function. In use, an aqueous electrolyte fluid is pumped by means of the pump to the first fluid inlet manifold, and is distributed and passed over the first faces of the separator plates where it comes into contact with the cathode side of the metal electrode plates where hydrogen is generated. The mixture of electrolyte fluid and hydrogen passes into the first fluid outlet aperture where it is pumped to the first degassing unit where the hydrogen is separated from the liquid and removed. The electrolyte fluid is then recycled to the first fluid inlet manifold. This is the first fluid circuit, which produces hydrogen. Likewise, an aqueous electrolyte fluid is pumped by means of the pump to the second fluid inlet manifold, and is distributed and passed over the second faces of the separator plates where it comes into contact with the anode side of the metal electrode plates where oxygen is generated. The mixture of electrolyte fluid and oxygen passes into the second fluid outlet aperture where it is pumped to the second degassing unit where the oxygen is separated from the electrolyte liquid and removed. The electrolyte liquid is then recycled to the second fluid inlet manifold. This is the second fluid circuit, which produces oxygen. By reversing the polarity of a cell, it is possible to generate hydrogen in the oxygen stream and oxygen in the hydrogen stream. This, though never done in the industry at present, could provide for a metred volume of oxygen in the hydrogen stream to facilitate improved fuel combustion in an internal combustion engine to which such a system is attached.

There are two possible ways of achieving this:

1. where left and right-handed cell membrane/separator plates are used within a stack, placing a left-handed unit in a run of right-handed units would provide the appropriate result, and

2. should all cells be made up of one-handed units, a group of cells may be connected up with the opposite polarity to give the same effect. The present invention comprises a number of novel aspects, including:

Moulded membrane/flow-field plate which, in a single moulding, accomplishes a.) separation of the electrolyte streams (anode stream carries oxygen, cathode stream carries hydrogen); b.) accurately spaces monopolar and bi-polar plates apart for optimum efficiency of electrolysis, c.) organises and conducts the flow across the cell- plates, while accommodating the generated gas in the electrolyte stream and thereby avoiding pressure build-up and electrolyte displacement due to the presence of the gases, and d.) seals the cell, in cooperation with the metal electrode plates (mono-polar and bi-polar),both from external and internal (fluid stream to fluid stream) leakage. The multiple functionality of this component allows for the construction of exceptionally simple reactor stacks, without the need for gaskets and spacers

Pumped electrolyte flows to each side of the cells, facilitating improved gas removal from the surface of the metal electrodes (mono-polar and bi-polar plates) on which it is generated.

Incorporation of a thermal management system (radiator, thermal switch, fan and pump) which maintains optimum operating temperature

The ability to change to the opposite handed membrane/flow-field plate in order to change the polarity of a cell within a group of cells in order to incorporate a proportion of oxygen into the hydrogen stream, and vice-versa

The ability to change the polarity of a cell, by electrical isolation, to the opposite polarity from the main stack in order to accomplish a similar resultant ratio of oxygen to hydrogen in the gas stream.

This invention relates to a system for the generation of hydrogen and oxygen from water in such a way as to be capable of assembly or modification to vary the amount of oxygen supplied with the hydrogen gas between zero and a stoichiometric 33%.

The system comprises of twin circulation systems with reservoirs and pumps for each circuit, and a reactor stack in which the gases are generated. The reactor stack is comprised of a number of individual cells, defined by metal plates. Each cell is split into two portions by a strategically positioned separator plate (membrane) which maintains separation of one flow circuit from the other, while allowing the reaction to take place each side of it. One side of a cell will be positively charged, being the anode, and the other negatively charged, being the cathode. Hydrogen is generated at the cathode and Oxygen at the anode. Metal plates, therefore, are in most cases through a stack, bi-polar, having an anode and a cathode side. Occasionally through the stack, where required by supply Voltage, an electrical contact plate will be provided which is mono-polar, being either anode or cathode on both sides. By this means, large (long length) stacks can be constructed for optimisation of the volume of gas produced.

The separator plate (membrane support component) incorporates a flow-field each side which guides the electrolyte and the generated gases which are carried on the flow, from the inlet manifold, across the reactive area of the metal plates and out through the exit manifold to return to the gas separator/reservoir in which the electrolyte is contained. The gas in each flow- stream separates out from the electrolyte in its reservoir by gravity.

This separator (integrated flow-field/membrane) plate component is specifically designed to optimise the velocity of the flow across it, and to guide the flow to the appropriate manifold for removal of each gas, in such a way as the oxygen generated within the stack is conducted (typically) to the oxygen gas/electrolyte flow manifold, and similarly for the hydrogen gas/electrolyte flow.

Ideally, reactor stacks will be built of both left and right-hand membrane/flow-field plates, so that the polarity change through the stack (at every specified number of cells down the stack) can be accommodated without any additional components being required.

Should there be a requirement for a proportion of the oxygen gas to be generated in the hydrogen gas stream, it is possible, by incorporation of the other-handed membrane/flow-field plate in a section of the stack. By this means, it would be possible, by incorporation of a single, or multiple wrong-handed plates, to generate hydrogen with a variety of oxygen concentration ratios.

For example, in a 32-cell stack, were a single cell to be wrong-handed, there would be (l/32)X33%(stoichiometric % 02 content in water) = 1.031% 02. Similarly, 2, 3, and 4 cells would add 2.063%, 3.094% and 4.125% 02 respectively.

This could be done to vary the 02 content from 0%, by any proportion in increments of 1.031%, right up to a stoichiometric (2: 1) ratio.

It is also possible to accomplish this with a single (one-handed) moulding, where the proportions would be in relationship to the number of groups in a stack, with reversed polarity electrical supply.

Further, it would be possible, whether experimentally or as demanded throughout an engine's duty-cycle, to vary the ratio of oxygen in the hydrogen by electrically isolating or reversing the polarity of individual cells within a pre-constructed, ratio-defined stack. The reactor stack cells

The reactor stack, as already described, is comprised of a number of cells in which the internal volume is divided by a membrane/flow-field plate, which is designed to guide the electrolyte and the gases carried by it to its appropriate flow manifold.

In the preferred embodiment, this is done by use of a moulded, compliant plastic component with two identical sides, separated by the membrane material. These sides have a substantially diagonal flow-field which takes electrolyte in at the bottom and out at the top, where the bottom orifice (which forms, in cooperation with neighbouring cell plates, the inlet manifold) is located towards one side of the plate, guiding the electrolyte across the face of the metal plate on which gas is generated, to the outlet orifice (which forms, in cooperation with neighbouring cell plates, the outlet manifold) located at the top of the membrane/flow-field plate, towards the opposite side. Each side of the membrane/flow-field plate is identical, thereby conducting the flow at each side to and from opposite inlet and outlet orifices. By this means, oxygen gas, as generated on one side of the cell is kept separate from the hydrogen gas generated on the opposite side, being conducted, carried on the electrolyte streams, to separate manifolds through the stack.

Figs 1 and 2 show a typical membrane/flow-field plate of the invention, showing that the rear face is identical to the front face. The hydrogen flow-path, being generated at the cathode, is shown in Fig. 2, and the oxygen (anode) flow-path in Fig. 1. An isometric view is also given to show that the flow-field portion of the plate is recessed to allow flow across it.

Figs 4 and 5 show how the separator (membrane/flow-field) plate cooperates with the metal bi-polar plates on each side. The two views are from opposite oblique angles, with the plates shown separated (exploded view). As can be seen, in the above graphic, both sides of the assembly look the same, but each side guides its flow to and from opposed orifices.

Dependent upon differential pressure from the hydrogen flow circuit to the oxygen circuit, it may be necessary to provide deflection supports to the recessed portion of the plates in order to avoid flow from one side crossing to the other due to deflection of the thinner portion away from the metal bi-polar and mono-polar plates. Figs 9 and 10 show two methods of support, one having elongated raised ribs in the reduced thickness area of the plate, which are designed to hold the membrane/flow-field plate against the metal plate to which it should form a sealing contact, and the other having raised diameter columns, which allow flow around and past. Other methods may be used, also, dependent upon designer and toolmaker preferences (e.g. conical, domed, pyramid, etc.). Similarly, in order to prevent the material of the membrane deflecting in the presence of a differential pressure from one side to the other, and, as a result, potentially touching the surface of the metal electrode plates, it may be desirable to provide standing ribs or columns, moulded or otherwise located onto the material of the membrane to ensure minimum deflection.

It is also possible to reduce the volume of raw material used in the moulding of this plate, by coring out or recessing the larger portions of the plate. This will contribute to lower material content and associated cost and weight, increase the unit loading on seals by reducing the area over which the axial force is applied during assembly, and avoid the 'slumping' that can occur during the moulding process in large material-content portions of mouldings (Fig. 6).

The assembled stack

The cells as described are assembled together with end-plates to form a complete reactor stack, the length of which is determined by the required gas output. Each cell will draw a certain current and Voltage, which, in turn, will generate a given volume of hydrogen and oxygen gases. This being the case, it is relatively straightforward to determine the number of cells required for any given gas output volume, and, therefrom, calculate the length of the reactor stack required.

Fig. 7 shows a stack with back- to-back identical end-plates which are designed to conduct the flow through the stack in separate circuits, for which the separation is maintained by the form of the membrane/flow-field plate design already described.

The Balance of Plant (BOP)

As already highlighted, it is necessary to have a different flow circuit for the anode (oxygen side) from that for the cathode (hydrogen side). Each side requires, therefore, a reservoir for the electrolyte, in which the gases are separated out by gravity, and a pump to maintain circulation.

As a by-product of the electrolysis reaction is thermal energy, there will also be required a cooling system. This, however, may only be required on the anode, oxygen generation circuit, as it is the oxygen release reaction (ORR) which is the least efficient, leading to the generation of the greatest proportion of the thermal energy generated throughout the stack.

A typical system may look like that shown in Fig. 8:

In such a system, the electrolyte contained in the anode circuit reservoir passes from the reservoir, through the pump and the cooling system before passing through the stack and back to the reservoir. The electrolyte in the cathode circuit passes from its reservoir, through the pump and the stack, then back to the reservoir.

Flame propagation protection technology

In order to prevent a gas ignition event propagating backwards through the system, it is advisable to incorporate a flame propagation protection device, commenly referred to as a flash-back arrestor.

Such devices can take numerous forms, two of which are shown in figures 14, 15 and 16. Figures 14 and 15 show one configuration of a 'bubbler' device 50, which is comprised of head 51 and substantially cylindrical container body 52. Head 51 has inlet 53 and outlet 54 connections for the gas stream. Inlet 53 is fluidly connected to tube 55, down which gas passes into the cylindrical body 52. The fluid (typically water) level in cylindrical body 52 is maintained at a level substantially above tube outlet 57, at a depth approximately indicated by arrow 56.

In such a device, gas passes from the inlet connection 53, down tube 55, and bubbles through the water into head space 58 and out of the head through outlet connection 54.

The device 60 shown in Fig. 16 is of a type commonly found in the gas industry for use with explosive gases, and typically comprises of a metal 'wool' or mesh filled cylindrical body 61 with inlet hose connector 62 and outlet connector 63 at the ends. Gas passes through orifice 64 in the end of inlet hose connector 62, through the resitrictive internal media in body 61, and out of the outlet hose connector 63.

Should ignition of the downstream gas flow occur, the resulting flame is prevented by such technologies from further propagation. The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail without departing from the spirit of the invention.

Claims

1. A separator plate ( 1 ) for mounting between two electrode plates (20) of a fluid electrolyser, the plate comprising:

a first face (2) having a central part (5) and a peripheral part (4);

a second face (3) opposite the first face and having a central part and a peripheral part; two pairs of spaced-apart apertures extending from the first face to the second face of the plate, each pair of spaced-apart apertures comprising an inlet aperture (7, 8) and an outlet aperture (9, 10);

a first recess (12, 5) extending substantially across the first face (2) of the plate from a first inlet aperture (7) to a first outlet aperture (9) of the first pair of apertures and adapted to guide a fluid from the first inlet aperture to the first outlet aperture; and

a second recess (13, 5) extending substantially across the second face (3) of the plate from a second inlet aperture (8) to a second outlet aperture (10) of the second pair of apertures and adapted to guide a fluid from the second inlet aperture to the second outlet aperture; wherein the central part of the first and second faces comprises a membrane that is permeable to ions and resistant to permeation by gases.

2. A separator plate as claimed in Claim 1 in which the two pairs of apertures are mounted in the peripheral part (4), and wherein the central part (5) is recessed relative to the peripheral part.

3. A separator as claimed in any preceding Claim in which the central recessed part (5) comprises a polymeric membrane.

4. A separator as claimed in any preceding claim in which the central recessed part (5) comprises a fabric membrane.

5. A separator plate as claimed in any preceding Claim in which the inlet and outlet apertures of each pair of apertures are diagonally spaced-apart across the plate.

6. A separator as claimed in any preceding Claim in which the inlet apertures (7, 8) are disposed towards a base of the plate and the outlet apertures (9, 10) are disposed towards a top of the plate.

7. A separator as claimed in any preceding Claim in which the inlet apertures (7, 8) are smaller than the outlet apertures (9, 10).

8. A reactor stack (37) for an electrolyser and comprising at least one electrolysis cell, the at least one electrolysis cell comprising a separator plate (1) of any of Claims 1 to 7 and two electrode plates (20), each electrode plate having first and second inlet apertures (27, 28) and first and second outlet apertures (29, 30) corresponding to the first and second inlet and and first and second outlet apertures of the separator plate, wherein the separator plate is sandwiched between the two electrode plates such that the first inlet apertures of the electrode and separator plates form a first fluid inlet manifold (33), the second inlet apertures of the electrode and separator plates form a second fluid inlet manifold (34), the first outlet apertures of the electrode and separator plates form a first fluid outlet manifold (35), and the second outlet apertures of the electrode and separator plates form a second fluid outlet manifold (36).

9. A reactor stack as claimed in Claim 8 and comprising a plurality of electrolysis cells.

10. An electrolyser system (40) for performing electrolysis on a fluid comprising: at least one reactor stack of Claim 8 or 9;

a first degassing unit (41) adapted to receive liquid electrolyte bearing gas in suspension, and to separate at least a portion of said gas from said electrolyte by gravity;

a first return conduit adapted to return the electrolyte to a fluid inlet manifold of the reactor stack;

a second degassing unit adapted to receive gas-bearing electrolyte from the second outlet manifold of the reactor stack and to separate at least a portion of said gas from said electrolyte by gravity; a second return conduit adapted to return the electrolyte to a fluid inlet manifold of the reactor stack; and

pump means for pumping fluid through the inlet and outlet manifolds of the reactor stack.

11. An electrolyer system as claimed in Claim 10 in which the first return conduit is adapted to return the fluid phase to the first inlet manifold (33), and the second return conduit is adapted to return the fluid phase to the second fluid inlet manifold (34).

12. An electrolyser system as claimed in Claim 10 or 11 including a first gas conduit adapted to receive the first gas from the first degassing unit (41) and a second gas conduit adapted to receive the second gas from the second degassing unit (42).

13. An electrolyser system as claimed in any of Claims 10 to 11 comprising a plurality of electrolysis cells, each cell comprising a separator (1) plate sandwiched between an anode (22) and a cathode (21).

14. An electrolyser system as claimed in any of Claims 10 to 13 comprising a plurality of electrolysis cells, wherein at least one of the cells comprises a separator plate (1) sandwiched between an anode (22) and a cathode (21) and at least one of the electrolysis cells comprises a separator plate sandwiched between an anode and an anode, or a cathode or a cathode, or a charged electrode plate and a non-charged electrode plate.

15. An electrolyser system as claimed in any of Claims 10 to 14 in which the electrode plates are bi-polar plates or mono-polar plates.

16. An electrolyser system as claimed in any of Claims 10 to 15, including an electrical supply means in electrical comunication with the electrode plates.

17. An electrolyser system as claimed in Claim 16, in which the electrical supply means comprises electrical generation means.

18. An electrolyser system as claimed in 16 or 17, in which the electrical supply means comprises control means for controlling the electrical supply to individual plates.

19. A machine comprising: an internal combustion engine; an electrolyser system of any of Claims 10 to 18, and means for conveying the first and/or second gas generated by the electrolyser system to the internal combustion engine.

20. A machine as claimed in Claim 19 including means for metering the relative amounts of the first and second gasses into the internal combustion engine.

21. A machine as claimed in any of Claims 19 or 20 and including a fuel tank, wherein the means for conveying the first and/or second gas generated by the electrolyser system to the internal combustion engine comprises a mixing chamber for mixing the or each gas with fuel from the fuel tank.

22. A machine as claimed in any of Claims 19 to 21, in which the electrolyser system is adapted to generate hydrogen and oxygen gasses, and including means for conveying hydrogen gas generated by the electrolyser system to an exhaust of the combusion engine.

23. A method of performing electrolysis on a fluid to generate first and second separate gasses, which method employs an electrolyser system of any of Claims 10 to 18, the method comprising the steps of: charging the electrodes; pumping the fluid into the first inlet manifold and out of the first outlet manifold whereby electrolysis of the fluid generates a first mixture comprising fluid and a first gas; pumping the fluid into the second inlet manifold and out of the second outlet manifold whereby electrolysis of the fluid generates a second mixture comprising fluid and a second gas; separating the first mixture in the first degassing unit to provide fluid and the first gas; separating the second mixture in the second degassing unit to provide fluid and the second gas; and return the fluid from the degassing units to the inlet manifolds.

24. A method as claimed in Claim 23 in which the fluid from the first degassing unit is returned to the first inlet manifold, and the fluid from the second degassing unit is returned to the second inlet manifold.

25. A method as claimed in Claim 23 or 24 in which the fluid is aqueous and the first gas is hydrogen and the second gas is oxygen.

26. A method as claimed in Claim 225 in which each separator plate is sandwiched between a cathode and an anode, wherein the hydrogen and oxygen are produced in stoichimetric amounts.

27. A method as claimed in Claim 25 or 26 in which one of the separator plates is sandwiched between an anode and an anode, or a cathode or a cathode, or a charged electrode plate and a non-charged electrode plate, wherein the hydrogen and oxygen are produced in non- stoichimetric amounts.