TECHNICAL FIELD

The present disclosure relates to a system and method of regeneration of one or more electrodes of an electrolyser. In particular, the present disclosure relates to regeneration of one or more electrodes while the electrodes remain in situ within the electrolyser.

BACKGROUND

It has long been known that hydrogen is a highly effective energy carrier which results in no CO2 emissions when energy is released. It can be readily stored and transported making it a truly viable alternative to fossil fuels such as petrol, coal and diesel. However, hydrogen production via water electrolysis, requires a tremendous amount of electricity thereby potentially reducing the positive environmental impact of moving to hydrogen-based fuel.

Hydrogen produced by renewable energy sources such as wind or solar power is the environmental ideal since no fossil fuels are used in its production. Hydrogen produced in this way is known as green hydrogen. However, because wind and solar power production is dependent on ever changing environmental conditions, it is difficult in practice to produce hydrogen efficiently directly from such power sources. One of the reasons for this is that wind turbine generators and solar farms tend to be located in relatively inaccessible and remote locations such as at the top of mountains, in deserts or offshore, making maintenance of colocated water electrolysis equipment difficult and expensive.

During the use of water electrolysis equipment, such as an electrolyser comprising a stack of electrolysis cells, a major component of efficiency loss is the degeneration of the electrodes. Existing alkaline electrolysers are well optimised for performance with catalytic coatings being used on the anode and cathode of the electrolysis cells to reduce cell overpotential. However, the catalysts are developed and optimised for continuous stable condition operation or shortterm operation, and have not been proved for extended periods with multiple start-stop operation under variable conditions such as would be experienced by an electrolyser operated directly by a wind turbine or solar power source which can only produce power in suitable atmospheric conditions. It is a concern in the field that the electrodes and/or catalysts will not tolerate such a mode of operation well.

It is against this background that the present invention has been developed. SUMMARY OF THE INVENTION

The present invention provides a method of regenerating one or more electrodes of an electrolyser when the one or more electrodes are located in-situ within the electrolyser, the method comprising providing at the one or more electrodes in-situ in the electrolyser a first salt solution and reacting the first salt solution with the one or more electrodes to cause regeneration of the one or more electrodes.

The method of the present invention is advantageous as it provides for the regeneration of the electrodes of an electrolyser without having to disassemble the electrolyser thereby saving time and cost of electrolyser maintenance.

Optionally the first salt solution comprises a plurality of different metal ions so that different materials of the electrodes may be regenerated depending on their specific chemistry.

The one or more electrodes optionally comprise a catalyst material and wherein reacting the first salt solution with the one or more electrodes to cause regeneration of the one or more electrodes comprises causing regeneration of the catalyst material. Catalysts help to reduce cell overpotential and regeneration of the catalyst material helps to restore cell efficiency which typically deteriorates over time.

Reacting the first salt solution with the one or more electrodes may comprise: providing a potential difference between the electrodes of the electrolyser to cause an electrochemical reaction between the first salt solution and the one or more electrodes; and/or heating the first salt solution to cause a reaction between the first salt solution and the one or more electrodes.

In one example the method may comprise mixing one or more salts and/or one or more second salt solutions with a water source upstream of the electrolyser to form the first salt solution. This is beneficial as the pipe system supplying reactant to the electrolyser may also be used to supply the salt solution to the electrodes.

Advantageously the water source may comprise a water source that is also used to supply the electrolyser during normal operation of the electrolyser.

The method may optionally comprise: evacuating alkaline reactant from the electrolyser before providing the first salt solution at the one or more electrodes in-situ in the electrolyser; and/or using water to flush out the electrolyser before providing the first salt solution at the one or more electrodes in-situ in the electrolyser; and/or introducing a cleaning solution into the electrolyser before providing the first salt solution at the one or more electrodes in-situ in the electrolyser; and/or evacuating the first salt solution from the electrolyser before using water to flush out the electrolyser. Cleaning the electrodes before regeneration helps to ensure a more complete regeneration of the electrode material, and flushing out the electrolyser between process steps helps ensure that only the desired chemistry exists inside the electrolyser for any given process step.

The electrolyser may be powered directly by a renewable energy source in normal operation, wherein the method is utilised: during maintenance of the renewable energy source; or when the realisable power production of the renewable energy source is less than or equal to a predetermined amount. Conveniently, the method may be used when the electrolyser is unable to be run in its normal operational mode of full production capacity.

In one example the method may comprise: obtaining a weather forecast; using the weather forecast to predict the realisable power production of the renewable energy source in a predetermined time window; and initiating the method if the realisable power production of the renewable energy source is predicted to be less than or equal to a predetermined amount for greater than a predetermined length of time. Advantageously the method may be used during periods of low wind in the case of a wind turbine supplied electrolyser, or overnight is the case of an electrolyser powered by photovoltaic cells.

Optionally the method comprises disconnecting the electrolyser from a connection to at least one supply essential to the normal operation of the electrolyser. For example, the water supply or power supply. If desired, the electrolyser may be physically moved from its normal operational location to another location for electrode regeneration. However, even if this is done, the electrodes remain in-situ during the regeneration process.

The method optionally comprises initiating and/or controlling the method from a location remote from the location of the electrolyser. This is convenient as an operator or control system need not be located at the same locations as the electrolyser containing the electrodes to be regenerated.

In another aspect the present invention provides a system for regenerating one or more electrodes of an electrolyser, the system comprising: an electrolyser comprising a plurality of electrodes; a water supply pipe connected to a water inlet of the electrolyser; a product outlet pipe connected to an outlet of the electrolyser; and a storage container containing a salt or a salt solution, wherein the salt or salt solution comprises one or more salts selected from a group of salts capable of causing regeneration of the material of one or more of the plurality of electrodes when mixed with water to form a treatment salt solution, wherein the storage container is in selective fluidic communication with the water supply pipe via one or more valves which are configured so that at least a portion of the contents of the storage container can enter the water supply pipe when the one or more valves are suitably operated. By providing a supply of salt or salt solution at the location of the electrolyser, the regeneration process can be initiated at any time without having to provide a supply of salts before the regeneration can take place. This is particularly advantageous for electrolysers located in remote or inaccessible locations. The system may optionally be located in the nacelle of a wind turbine. This aspect of the invention therefore also concerns a wind turbine which comprises a nacelle and the system for regenerating one or more electrodes of an electrolyser, wherein the system is located in the nacelle.

Optionally the one or more salts are selected from a group consisting of Nickel (II) nitrate hexahydrate (Ni(NOs)2) and Iron (II) sulfate heptahydrate (FeSO4), Sodium molybdate (Na2MoO4) and Ammonium thiocyanate (CH4N2S), Nickel sulfate (NiSO4), Iron sulfate (FeSO4), Trisodium citrate (CeHsOyNas) and boric acid (H3BO3).

In a further aspect, the present invention provides a controller for implementing the method of regenerating one or more electrodes, wherein the controller is configured to receive an initiation control signal comprising an instruction to initiate an electrode regeneration cycle, wherein the initiation control signal comprises an indication that: the realisable power production of a renewable energy source which supplies power to the electrolyser in normal use is, or is forecast to be, less than or equal to a predetermined amount for greater than a predetermined period of time; or maintenance of the renewable energy source is in progress, or is scheduled, and will last for greater than a predetermined period of time; or the electrolyser is otherwise unable to be operated, or is scheduled to be inoperable, for greater than a predetermined period of time, wherein, upon receipt of the initiation control signal, the controller is configured to: request a signal indicative of the availability of a power supply capable of supplying sufficient power, for a sufficient period of time, to successfully complete every step of the method; receive a signal indicative of the availability of said power supply in response to the request, and: if the signal indicates availability of power for a sufficient period of time: issue a control signal comprising an instruction to shut down normal operation of the electrolyser; issue a control signal comprising an instruction to provide a first salt solution to the electrodes of the electrolyser in-situ in the electrolyser; and issue a control signal comprising an instruction to re-start normal operation of the electrolyser or: if the signal indicates no availability of power, or availability of power for an insufficient period of time: ignore the instruction to initiate the electrode regeneration cycle.

Optionally, if the signal indicates availability of a power for a sufficient period of time, the controller may be configured to: issue a first drain control signal comprising an instruction to drain the electrolyser of liquid before issuing the control signal to provide a first salt solution to the electrodes; and/or issue a second drain control signal comprising an instruction to drain the electrolyser of liquid after issuing the control signal to provide a first salt solution to the electrodes; and/or issue a control signal comprising an instruction to fill the electrolyser with reactant before issuing the control signal to re-start normal operation of the electrolyser.

The controller may optionally be configured to issue the second drain control signal after: receipt of an electrolyser status signal confirming that the electrolyser is substantially full of liquid; and a predetermined period of time has elapsed since receipt of the electrolyser status signal.

If the signal indicates availability of a power for a sufficient period of time, the controller may be configured to issue a control signal to heat the first salt solution to a predetermined temperature.

In one example, if the signal indicates availability of a power for a sufficient period of time, the controller may be configured to issue a control signal to apply a potential difference across the electrodes of the electrolyser after issuance of the control signal to provide the first salt solution to the electrodes.

Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic drawing of an electrolysis system.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawing that shows, by way of illustration, specific details and an embodiment in which the invention may be practiced. Embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice the invention. Other embodiments may be utilised, and structural changes may be made without departing from the scope of the invention as defined in the appended claims.

Figure 1 shows a schematic drawing of an electrolysis system comprising an electrolyser 1 which has a plurality of electrolysis cells arranged in a stack (not shown). The electrolyser 1 comprises a first side 2 and a second side 3. The first side 2 comprises a first inlet 4 for receiving a flow of reactant into the electrolyser 1 , and a first outlet 5 for allowing removal of a first product flow stream 10 from the electrolyser 1. Similarly, the second side 3 of the electrolyser 1 comprises a second inlet 6 for receiving a flow of reactant into the electrolyser 1 , and a second outlet 7 for allowing removal of a second product flow stream 11 from the electrolyser 1.

In normal use, when an electrical potential difference is applied across the electrodes of the electrolyser 1 , and the reactant supplied to the electrolyser 1 comprises water, the first side 2 of the electrolyser 1 produces hydrogen as the first product flow stream 10, and the second side 3 of the electrolyser 1 produces oxygen as the second product flow stream 11 . The first side 2 of the electrolyser 1 may therefore be referred to as the hydrogen side 2, and the second side 3 may therefore be referred to as the oxygen side 3. In the examples that follow the reactant streams are alkaline water based. However, it will be understood by those skilled in the art that electrolysers may be used to split other water-based reactants in order to produce hydrogen.

In normal use, the first inlet 4 of the electrolyser 1 is supplied with alkaline water reactant via water supply pipe 15 and first branch supply pipe 16, and the second inlet 6 of the electrolyser 1 is supplied with reactant via water supply pipe 15 and second branch supply pipe 17. It is well known in the art to add potassium hydroxide and/or potassium carbonate to water supplied to the electrolyser 1 to form the alkaline water reactant. This may be achieved by providing a dosing system 35 in selective fluid communication with the water supply pipe 15 upstream of the first and second branch supply pipes 16, 17. The dosing system is configured to supply potassium hydroxide and/or potassium carbonate to water flowing from a water supply 25 to the inlets 4, 6 of the electrolyser 1 via water supply pipe 15. The first product flow stream 10 is carried away from the first outlet 5 of the electrolyser 1 by a first product outlet pipe 18, and the second product flow stream 11 is carried away from the second outlet 7 of the electrolyser 1 by a second product outlet pipe 19. The first product flow stream 10 comprises a flow of reactant containing gaseous and/or dissolved hydrogen, and the second product flow stream 11 comprises a flow of reactant containing gaseous and/or dissolved oxygen. The product flow streams are taken to two separate tanks, so as not to mix the hydrogen and oxygen, where the gases are separated from the liquid reactant. The reactant is then returned to the inlets 4, 6 of the electrolyser 1 via water supply pipe 15 or branch supply pipes 16, 17. Consequently, the reactant flows in a circuit around a loop comprising the electrolyser 1 and a series of pipes 15, 16, 17, 18, 19. Nonetheless, the upstream side of the electrolyser 1 is the inlet side comprising first and second inlets 4, 6, and the downstream side of the electrolyser 1 is the outlet side comprising first and second outlets 5, 7. Hence water and/or reactant flow streams in the water supply pipe 15, and/or the branch supply pipes 16, 17, are upstream flows, and product flows in the first and second product outlet pipes 18. 19 are downstream flows.

Each electrolysis cell in the electrolyser 1 has an anode and a cathode forming a pair of electrodes. Each electrode typically comprises a catalytic coating which is optimised to reduce cell overpotential and thereby increase efficiency of the electrolyser 1. During use of the electrolyser 1 , a major cause of efficiency loss is the degradation of the materials forming the electrodes, particularly the catalysts. There are significant costs associated with the decommissioning and replacement of the electrodes, especially when the electrolyser 1 is located in a place which is difficult to reach either geographically and/or in situ within a complicated electrolysis system.

Surprisingly, the inventor found a method to regenerate the electrodes in situ and hence without the need to decommission or disassemble the electrolyser. The method concerns regenerating the electrodes without the need to decommission and disassemble the electrolyser 1 and comprises providing, at the electrodes in situ, a salt solution and reacting the salt solution with the electrodes in situ to cause regeneration of materials forming the electrodes.

Example 1

In an example method of in situ electrode regeneration, the electrolyser 1 may be supplied with a salt solution formed using water from the water supply 25. In this example a salt storage container 30 containing one or more salts suitable for the regeneration of the electrodes is provided. A diverter valve 31 is located in the water supply pipe 15 for diverting at least a part of the flow of water from the water supply 25 to the salt storage container 30 via a first diverter pipe 32. A second diverter pipe 33 is provided for delivering salt solution back to the water supply pipe 15.

In use, when electrode regeneration is required, the diverter valve 31 may be operated to divert some or all of the flow of water from the water supply 25 into the salt storage container 30 so that the salt contained in the salt container dissolves in the water to form a salt solution. The flow of salt solution from the storage container 30 to the water supply pipe 15 is controlled by valve 34. The salt solution is delivered to the water supply pipe 15 upstream of the electrolyser 1 from where it is delivered to the electrolyser 1 via the water supply pipe 15, the branch supply pipes 16, 17 and the electrolyser inlets 4, 6. An example salt solution suitable for regeneration of the catalytic material of the electrodes comprises 0.15 M of Ni(NOs)2 (Nickel (II) nitrate hexahydrate) and 0.15 M of FeSC Oron (II) sulfate heptahydrate). Preferably 22.5 litres of such salt solution are used per square meter of electrode within the electrolyser 1 .

The amount of salt and the volume of the storage container 30 is selected so that when the storage container is filled with water from the water supply 25 a salt solution of the desired concentration results. Typically, salts which are suitable for regeneration of the catalytic material of the electrodes dissolve readily in water. If desired, the water may reside in the storage container for approximately 5 minutes to ensure complete dissolution before valve 34 is opened. The storage container may optionally comprise a paddle or other agitation device for agitating the liquid in the storage container 30 to assist with the rate dissolution of the salt(s) and the homogeneity of the resulting salt solution. The paddle (or other agitation device) may be driven by an electric motor or similar. Alternatively, the salts may be provided as premixed salt solutions, however, this would require transport I storage of larger volumes and weights of reactants as compared with preparation of salt solutions at the site of application using water already present as a reactant of the electrolyser. This would also risk the decomposition of the solution or chemical reaction with the container.

The salt solution is transported into the electrolyser 1 via the inlets 4, 6 and the water supply pipe 15 and/or the branch supply pipes 16, 17. The electrolyser 1 is filled with the salt solution so that the salt solution is provided at the electrodes in situ in the electrolyser 1 to cause regeneration of the one or more electrodes.

In this first example, a 10 mA/cm ² galvanostatic current is induced in the electrodes for 120 seconds to induce the electrodeposition of metal ions from the salt solution onto the cathodes of the electrochemical cells in the electrolyser 1. Next, a -10 mA/cm ² galvanostatic current is induced in the electrodes for a further 120 seconds to induce the electrodeposition of metal ions from the salt solution onto the anodes of the electrochemical cells in the electrolyser 1. The electrodeposition process leaves a coating of 5-7 mg/cm ² of deposited material on the electrodes. Preferably the electrolyser 1 is flushed with water before and after the electrodeposition steps to clean residual potassium hydroxide and/or potassium carbonate and salts from the system.

Example 2

In an alternative example method, the salt solution may be heated before it enters the electrolyser 1 or when it is in the electrolyser 1. For example, the salt solution may be heated using the heat exchanger of the electrolyser 1 or an electric heater. In this case the deposition of metal ions from the salt solution onto the electrodes is thermally rather than electrically activated. In this example 0.1 kg of Sodium molybdate (Na2MoO4) and 0.3 kg of Ammonium thiocyanate (CH4N2S) is dissolved in 22.5 litres of water per square meter of electrode. The solution is heated to 200° C and kept within the electrolysis stack for twelve hours. After which the formation of Molybdenum disulphide (M0S2) on Nickle Sulphide (NisS2) grown on the Nickle Foam electrode will leave a coating of 3-8 mg/ cm ² . After this regeneration step the chamber is flushed with water to remove excess Sulphides.

Example 3

A third example method uses chemical, rather than electrochemical reduction, to regenerate the electrodes. By introducing into the electrolyser 1 405 grams of Nickel sulfate (NiSC ), 45 grams of Iron sulfate (FeSC ), 1350 grams of Trisodium citrate (CeHsOyNas) and 675 grams of (boric acid) H3BO3 to be dissolved in 22.16 litres of water with 344 ml of the electrolyte used in the electrolyser at concentration of 20 wt% Potassium hydroxide and introduced to the system after being heated to 82° C and left to react with the electrodes for 1500 min. The salt solution is heated to the required temperature by a heater (not shown) located in the water supply pipe 15 upstream of electrolyser 1 and downstream of the storage container 30. Once the regeneration reaction is satisfactorily complete, the electrolyser is flushed with water to remove residual salts. The electrolyser 1 is then re-filled with reactant and re-started for normal operation (i.e. the production of hydrogen and oxygen).

In an alternative example to the examples given above, instead of using water to dissolve solid salt(s) stored in the storage container, the salt solution may be pre-prepared and introduced into the electrolyser 1 from the storage container 30 via the valve 34 and water inlet pipe 15. In a further alternative example, the salt solution stored in the storage container 30 may be of a higher concentration than that required to regenerate the electrodes. In this case water may be user to dilute the salt solution in the storage container 30 in the same way as described above for the dissolution of solid salt(s).

The application of a potential difference (and therefore a current) across the electrodes of the electrolyser 1 during the regeneration process and the heating of the salt solution before or during the regeneration process are not mutually exclusive and a regeneration process in which the salt solution is heated, and a potential difference is applied across the electrodes is envisaged.

Before any electrode regeneration process (such as those described above) is carried out, the electrolyser 1 may be isolated from the reactant supply by closing a shut-off valve 20 located in the water supply pipe 15 (or alternatively by closing shut-off valves located in the first and second branch supply pipes 16, 17). Reactant in the electrolyser 1 may then be evacuated via the product outlet pipes 18, 19. Once the reactant has been substantially evacuated from the electrolyser 1 , the valve 20 may be re-opened so that the electrolyser 1 may be flushed with water before further treatment. Water from the water supply 25 may be used for this purpose providing that the dosing system 35 is isolated from the water supply pipe 15 by closing of shut-off valve 36. The electrolyser may comprise a sensor (not shown) for sensing when the electrolyser 1 is substantially full of liquid and/or when the electrolyser 1 is substantially drained of liquid. The sensor may issue an electrolyser status signal to a controller as will be described in greater detail below.

In order to better ensure conductivity of the electrodes during the regeneration reaction, the stack may be flushed with a 1 M hydrochloric acid solution before the electrode regeneration process is started to clean the electrodes by reduction of any oxide layers which have built up on the electrodes during use. A second dosing system 37 may be provided for this purpose, wherein the second dosing system 37 comprises a storage tank 38 for storing hydrochloric acid. The stored hydrochloric acid may be at a concentration greater than that required to clean the electrodes. For example, the stored hydrochloric acid may be a 2 M solution of hydrochloric acid which is diluted with water to form a 1 M solution of hydrochloric acid when required. The diluting water may be provided from the water supply 25. A valve 39 is provided for enabling fluidic communication between the interior of the storage tank 38 and the water supply pipe 15.

In order to secure substantially complete reduction of the electrodes, 22.5 litres of 1 M hydrochloric acid solution is required per meter square of electrode surface. The hydrochloric acid solution is preferably provided at the electrodes of the electrolyser via the inlets 4, 6 and the water supply pipe 15 and/or the branch supply pipes 16, 17 and allowed to react with the electrodes for 600 seconds. After the electrodes have been sufficiently cleaned by the hydrochloric acid reduction, the electrolyser 1 may be flushed with water, which may come from the water supply 25, to remove any residual hydrochloric acid form the electrolyser 1 .

Once the cleaning process, if used, is complete an electrode regeneration process (such as those described above) may be carried out. Once complete, the electrolyser 1 may be flushed with water once more before being re-filled with reactant and put back into normal operation (after any required re-start process has taken place if required).

The advantage of the electrode regeneration process described above is that it can be carried out while the electrolyser 1 remains in situ within an electrolysis system. This significantly reduces the downtime and costs required to repair degenerated electrodes which would otherwise have to be replaced.

A diverter valve or valves (not shown) may be provided in the product outlet pipes 18, 19 so that the used salt solution or hydrochloric acid solution may be diverted to a storage tank to treatment or collection for disposal. Separate storage tanks and separate diverter valves mat be provided for the salt solution and hydrochloric acid respectively.

As shown in Figure 1 , the electrolyser 1 is connected to a fluctuating or transient power supply 29. In Figure 1 the fluctuating power supply 29 is schematically represented as a wind turbine 50 which comprises a rotor 51 which is configured to drive a generator 53 via a gearbox 52. Electrical power generated by the generator 53 is converted from and AC power supply to a DC power supply by a rectifier 54. DC current is supplied to the electrolyser 1 directly from the rectifier 54.

It will be understood that the fluctuating power supply 29 may be provided to the electrolyser 1 by any power supply apparatus which typically produces a variable output which is dependent on some environmental condition such as wind power, solar power or wave power. It will also be understood that the power supply to the electrolyser may be provided from a plurality of such devices either directly or through a local or national grid. In addition, a number of power sources may be used to supply the electrolyser 1 and it is not necessary that only one form of renewable energy is employed. For example, wind power may be used together with solar power.

Although the electrolyser regeneration process described hereinabove may be effected at any time, it is preferable that the regeneration of the electrodes takes place when the prevailing weather conditions are such that the fluctuating power supply 29 is unable to produce power, or is unable to produce enough power to allow operation of the electrolyser 1. In one example, a weather forecast may be used to predict how much power the fluctuating power supply 29 will be able to produce in a given period of time. If the prediction indicates that the fluctuating power supply 29 will not be able to consistently produce sufficient power to allow operation of the electrolyser 1 , the regeneration process may be scheduled to take place during said time period. In one example, the regeneration process may be initiated from a location remote from the electrolyser 1 .

Although it is preferred that the electrolyser 1 remains in situ in the electrolysis system during the regeneration process, this is not essential and optionally the electrolyser 1 may be disconnected from the water supply 25 and/or fluctuating power supply 29 (both essential to the normal operation of the electrolyser) and physically removed from the system before the regeneration process takes place. The regeneration process may be carried out on the isolated electrolyser 1 before being re-installed in the electrolysis system. However, even if the electrolyser 1 is physically isolated from power supply and/or water supply, the cells and electrodes remain in situ in the electrolyser 1 during the regeneration process. For the avoidance of doubt, the supplies essential to the normal operation of the electrolyser 1 are a supply of electrical power and a supply of reactant.

The operations necessary to effect the processes described above may manually initiated and controlled by operatives physically located at the site of the electrolyser system. Alternatively, the various processes may be automated by the use of appropriate valves, switches, actuators, pumps and heaters etc. A fully automated system may be controlled remotely via a communications system such as a telecommunications system or the internet.

The system may be controlled by a controller, which may be an electronic controller, configured to issue a series of control signals in response to one or more inputs. For example, the controller may be configured to receive an input comprising an initiation control signal comprising an instruction to initiate an electrode regeneration cycle. The initiation control signal may be instigated locally by a system operator or control program or may be transmitted from a remote location when instigated by an operator at the remote location or by a control program at the remote location.

The initiation control signal may comprise an indication that the realisable power production of a renewable energy source (29) which supplies power to the electrolyser (1) in normal use is, or is forecast to be, less than or equal to a predetermined amount for greater than a predetermined period of time, or that maintenance of the renewable energy source (29) is in progress, or is scheduled, and will last for greater than a predetermined period of time, or that the electrolyser (1) is otherwise unable to be operated, or is scheduled to be inoperable, for greater than a predetermined period of time. For example, a component or system essential to the operation of the electrolyser 1 may require maintenance.

Upon receipt of the initiation control signal, the controller may be configured to request a signal indicative of the availability of a power supply capable of supplying sufficient power, for a sufficient period of time, to successfully complete every step of the method. For example, a back-up power supply in the event that the renewable energy source (29) is unavailable due to lack of wind, lack or sunlight (for example overnight) or scheduled or unscheduled maintenance shut down.

The controller may be configured to receive a signal indicative of the availability of a power supply capable of supplying sufficient power, for a sufficient period of time to complete the regeneration of the electrodes in response to the request. If the signal indicates no availability of power, or availability of power for an insufficient period of time, the controller may be configured to ignore the instruction to initiate the electrode regeneration cycle.

If the signal indicates availability of power for a sufficient period of time, issue a control signal comprising an instruction to shut down normal operation of the electrolyser 1. The controller may be configured to then issue a control signal to drain the electrolyser 1 and/or flush the electrolyser with water to remove residual reactant from the electrolyser 1 . The controller may be configured to next issue a control signal to fill the electrolyser 1 with a hydrochloric acid solution (or other reducing solution) to clean the electrodes in situ in the electrolyser 1 by reduction of oxides which have built up on the electrodes during normal use of the electrolyser (i.e. normal use to produce hydrogen and oxygen). The controller may be configured to require that the hydrochloric acid solution remain in the electrolyser 1 for a predetermined period of time to ensure thorough cleaning of oxides from the electrodes. The controller may be configured to then issue a control signal to drain and/or flush the electrolyser 1 to remove any residual hydrochloric acid.

The controller may be configured to next issue a control signal comprising an instruction to provide a first salt solution to the electrodes of the electrolyser (1) in-situ in the electrolyser (1). The controller may also be configured to issue control signals to cause water to be directed into the storage container 30, to reside in the storage container 30 for a predetermined period of time, to activate an agitation paddle (or other device) if present, and to cause salt solution to be delivered from the storage container 30 into the water supply pipe 15 and or the branch supply pipes 16, 17. Once the salt solution has been provided at the electrodes in situ in the electrolyser 1 , the controller may be configured to require that the salt solution reside in the electrolyser 1 for a predetermined period of time sufficient to allow regeneration of the material of the electrodes. The controller may be configured to issue a control signal to apply a potential difference across the electrodes to induce an electrochemical reaction. The controller may be configured to issue a control signal to apply a reverse polarity potential difference across the electrodes of the electrolyser 1 after the first potential difference has been applied across the electrodes. The controller may be configured to issue a control signal to heat the salt solution to a predetermined temperature.

The controller may be configured to issue a control signal to drain and/or flush the electrolyser with water to remove any residual salt solution. The controller may be configured to then issue a control signal to re-fill the electrolyser 1 with reactant. The controller may be configured to issue a control signal to re-start normal operation of the electrolyser 1 .

As mentioned above, the electrolyser 1 may comprise a sensor configured to sense if the electrolyser is substantially full or empty of liquid. The controller may be configured to receive inputs from the sensor and to only move onto the next operational step if the signal from the sensor indicates that the electrolyser is in an appropriate condition for the next process to begin. For example, the controller may be configured to issue a control signal to apply a potential difference across the electrodes of the electrolyser when the sensor signal indicates that the electrolyser is substantially filled with liquid.

The controller may be part of a computer system configured to control operation of the electrolyser 1 in normal operating conditions when the electrolyser is operated to produce hydrogen and oxygen.

In the above examples each of the electrode treatment processes (reduction/regeneration) take place with the treatment liquid (hydrochloric acid or salt solution) resident in the electrolyser 1 for a period of time. However, it is not essential that the treatment liquids be resident in the electrolyser for a set period of time. In alternative examples, the treatment liquids may continuously flow through the electrolyser 1 to a set period of time such that the reduction and/or regeneration reactions take place as the treatment liquids flow past the electrodes.