Hydrogen Electrolysis using Pulsed DC Signal

Abstract

An electrolysis system 200 for generating hydrogen and / or oxygen is defined. The system comprising: a first electrolysis apparatus 220, such as an electrolysis stack or cell. The system comprising at

Description

Description The present disclosure relates to an electrolysis system, particularly, but not exclusively, for the production of hydrogen and / or oxygen. The present disclosure further relates to a method of supplying an electrolysis system with electrical power. The process of using electricity to decompose water into oxygen and / or hydrogen gas is known as electrolysis of water. Hydrogen gas produced in this way can be used in various applications and has become widely known as an energy dense option for fuelling vehicles. In other applications, electrolysis of water may be used as a decentralised storage solution storing electrical energy as chemical energy, particularly electrical energy obtained via renewable power. Other hydrogen production methods decompose ammonia into hydrogen and nitrogen by means of electrolysis. In recent years, demand for hydrogen, inter alia, as a fuel for so called hydrogen fuel cells, has increased rapidly. Electrolysers can be grouped into proton exchange membrane (PEM) electrolysers, alkaline electrolysers and solid oxide electrolysers. These different types of electrolysers function in slightly different ways depending on the electrolyte material involved. Yet, some of the most prominent drawbacks of most electrolysers include overall inefficiencies and / or failure to supply hydrogen gas at pressures required for further use. In order to maximize the amount of gas (e.g. oxygen / hydrogen) produced with common electrolysers, it is known to arrange multiple electrodes parallel to each other in a device known as an "electrode stack". Such electrode stacks include multiple electrolyte chambers, each located between neighbouring electrodes, thereby enabling large electrode surface areas to be in contact with the electrolyte solution without requiring large space envelopes. Electrode stacks are useful to combine a plurality of electrolysers in the smallest possible space. Yet, even densely packed electrode stacks require further improvements to be widely applicable, particularly in domestic settings. Large inefficiencies may be created by traditional power supplies. During electrolysis, water molecules are split into hydrogen and oxygen using a DC electrical current. According to Faraday's first law, in electrolysis, the amount of gas produced during the reaction is directly proportional to the current applied to the electrolyte. In the case of hydrogen electrolysis, the current is applied to electrolyte water. It follows that to improve the production of hydrogen, it is necessary to increase the amount of current applied to the electrolysis cell or stack. However, it was found that, if the voltage is increased for this purpose, the so called "double capacitive layer effect" of water, in addition to ohmic losses, lead to a natural limit of productivity achievable by simply increasing the amount of current applied. The double capacitive layer effect appears at the interface between a surface and a fluid. At this boundary, two layers of electric charge with opposing polarity form, one at the surface of the electrode, and one in the electrolyte. Once the double capacitive layer effect of water is reached, additional power will be dissipated as heat due to the internal resistance of the electrolysis apparatus. It is an aim of the present disclosure to solve or at least ameliorate one or more of the problems associated with the prior-art. In particular, it is an object of the present invention to provide an improved electrolysis system exhibiting increased efficiency and hydrogen production. Summary of the invention Aspects and embodiments of the present disclosure provide an electrolysis system for the electrolysis of water, and a method of method of supplying an electrolysis system with electrical power as claimed in the appended claims. Further embodiments are disclosed in the appended, dependent claims. According to a first aspect of the present invention, there is provided an electrolysis system for generating hydrogen and / or oxygen, the system comprising: a first electrolysis apparatus, particularly an electrolysis stack or cell, comprising at least one electrode for the decomposition of electrolyte water; a power supply unit for supplying electric power to the first electrolysis apparatus, wherein the power supply unit comprises a first diode for converting an AC input signal to a first pulsed DC signal, said first pulsed DC signal being a first half wave of the AC input signal, wherein the first electrolysis apparatus is connected to the power supply unit in such a way that the first electrolysis apparatus is supplied with the first pulsed DC signal. "Electrolyte water1' may refer to any type of process fluid used to generate hydrogen. Typically, this may be water with various known electrolytes. However, in some examples, electrolyte-free water, pure water, or distilled water may be employed too. Further examples of "electrolyte water1' that may be used in connection with electrodes and electrolysers of the present disclosure include ammonia, which may be decomposed into hydrogen and nitrogen. The present disclosure suggests using pulsed DC signals to increase the amount of hydrogen / oxygen produced with the electrolysis system. Using pulsed DC currents to supply the electrodes of the electrolysis system may reduce the formation of the electrical double layer, since electrical charges of opposing polarity may be reabsorbed by the electrodes / the electrolyte during low / zero current periods between DC pulses. This may lead to the possibility of supplying the electrodes of the electrolysis system with more electrical power before the "electric double layer" is formed, thereby increasing the amount of process gases (hydrogen / oxygen) produced. Using a diode to convert the AC input signal into a DC output signal represents a particularly simple and effective way of converting existing AC input power, with little loss. The power supply of the present disclosure is also largely maintenance free and requires no human or software control. It was found that providing electrolysis apparatus with pulsed DC signals is particularly beneficial, when using flow-through electrodes. Because flow-through electrodes provide large surface areas that come into contact with the electrolyte water during electrolysis, they are particularly susceptible to the formation of electrical double layers. According to another embodiment, the electrolysis system comprises a second electrolysis apparatus, particularly an electrolysis stack or cell, comprising at least one electrode for the decomposition of electrolyte water, wherein the power supply unit comprises a second diode for converting the AC input signal to a second pulsed DC signal, said second pulsed DC signal being a second half wave of the AC input signal, wherein the second electrolysis apparatus is connected to the power supply unit in such a way that the second electrolysis apparatus is supplied with the second pulsed DC signal. According to another embodiment, the power supply comprises a centre tapped full wave rectifier. According to another embodiment, a negative terminal of the first electrolysis apparatus is connected to a negative terminal of the second electrolysis apparatus and to the centre tap of the power supply. According to another embodiment, the centre tap is earthed, particularly by connecting the centre tap to a chassis of the electrolysis apparatus to ensure safe operation. According to another embodiment, the power supply comprises a centre tapped transformer, said centre tapped transformer comprising a primary winding, a first secondary winding, and a second secondary winding, wherein the first electrolysis apparatus is connected to the first secondary winding via the first diode, and wherein the second electrolysis apparatus is connected to the second secondary winding via the second diode. According to another embodiment, the first secondary winding and the second secondary winding have substantially the same number of windings. According to another embodiment, the primary winding has substantially the same number of windings as the first secondary winding and / or the second secondary winding. According to another embodiment, the at least one electrode of the first electrolysis apparatus is a flow-through electrode, which is permeable to electrolyte water. According to another embodiment, the first electrolysis apparatus comprises a plurality of electrodes stacked in a side-by-side fashion. According to another embodiment, the power supply unit does not comprise a capacitor. According to another aspect of the present disclosure, there is provided a method of supplying an electrolysis system with electrical power, the electrolysis system comprising a first electrolysis apparatus comprising at least one electrode for the decomposition of electrolyte water, wherein the method comprises: providing an AC input signal; converting the AC input signal to a first pulsed DC signal, said first pulsed DC signal being a first half wave of the AC input signal; providing the first electrolysis apparatus with the first pulsed DC signal. According to another embodiment, the electrolysis system comprises a second electrolysis apparatus comprising at least one electrode for the decomposition of electrolyte water, wherein the method further comprises: converting the AC input signal to a second pulsed DC signal, said second pulsed DC signal being a second half wave of the AC input signal; providing the second electrolysis apparatus with the second pulsed DC signal. According to another embodiment, the AC input signal has a frequency of 49Hz to 61Hz. Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, and the claims and / or 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 all features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. Brief description of the drawings The aforementioned and other features and advantages of this disclosure, and the manner of attaining them, will become apparent and the disclosure will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings, wherein: FIG. 1 is a schematic view of a cell type electrolysis apparatus; FIG. 2 is a schematic representation an electrolysis system according to an embodiment of the present disclosure, including a power supply according to a half-wave rectifier principle; FIG. 3A is a schematic representation of an AC input signal; FIG. 3B is a schematic representation of a pulsed DC output signal generated by the power supply according to FIG. 2. FIG. 4 is a schematic representation an electrolysis system according to another embodiment of the present disclosure, including a power supply according to a full-wave rectifier principle; FIG. 5A is a schematic representation of an AC input signal; FIG. 5B is a schematic representation of a first pulsed DC output signal generated by the power supply according to FIG. 4. FIG. 5C is a schematic representation of a second pulsed DC output signal generated by the power supply according to FIG. 4. FIG. 6 is a schematic view of a stack type electrolysis apparatus. Detailed description FIG. 1 shows an exemplary electrolysis apparatus, particularly an electrolysis cell, which may be employed in an electrolysis system according to the present disclosure. In the example of FIG. 1, there is shown an electrolysis apparatus 100 for generating hydrogen, particularly by electrolysis of water. However, as will be appreciated, the electrolysis apparatus 100 shown in FIG. 1 may also be suitable for decomposition of other substances by means of electrolysis. Generally, in this specification, the term "electrolyte water" may encompass water including any type of electrolyte, such as sulphuric acid, sulphate, potassium hydroxide, sodium hydroxide, etc., or in some embodiments water without electrolytes such as tritiated water or purified water. The electrolysis apparatus 100 comprises a housing 102. The housing 102 comprises an electrolyte chamber 104. In one example, the electrolyte chamber is configured to hold electrolyte water under pressure as will be described in more detail below. The electrolyte water may comprise any electrolyte dissolved in water that aids decomposition of water. The housing 102 comprises a first gas collection chamber 106. The first gas collection chamber 106 is separated from the electrolyte chamber 104 by a first electrode 108. The housing 102 comprises a second gas collection chamber 110. The second gas collection chamber 110 is separated from the electrolyte chamber 104 by a second electrode 112. The electrolyte chamber 104 is located between the first and second electrodes 108, 112. The electrolyte chamber 104 is a membrane-less chamber. It will be appreciated that in some embodiments, the electrolysis apparatus may comprise more than two electrodes, e.g. arranged in parallel to each other to form a stack of electrodes, as will be described in more detail with reference to FIG. 6 below. The pair of electrodes 108, 112 of FIG. 1 are thus exemplary for any number of electrodes used in a stack. The housing 102 of FIG. 1 is a multi-part housing. In particular, the housing 102 comprises at least two parts: a first housing part includes the first gas collection chamber 106 and the first electrode 108; a second housing part includes the second gas collection chamber 110 and the second electrode 112. The at least two housing parts are connected to each other such that a gap is formed between first surfaces 114, 118 of the first and second electrodes 108, 112. This gap defines the electrolyte chamber 104, which is thus arranged between the electrodes 108, 112. In the example of FIG. 1, the housing 102 is substantially Fl-shaped as will be described in more detail below. However as will be appreciated, other designs may include a plurality of plate shaped electrodes that typically are flat and similar in construction to a plate heat-exchanger. The first electrode 108 is permeable to gases produced by decomposition of electrolyte water. The first electrode 108 is also generally permeable to electrolyte water. In other words, the first electrode 108 is a so-called "flow-through" electrode in which gases produced by decomposition of electrolyte water as well as the electrolyte water within the electrolyte chamber 104 are able to penetrate the first electrode 108 and thus move from the electrolyte chamber 104 towards the first gas collection chamber 106. To this end, the first electrode 108 is a permeable electrode including a plurality of pores sized to allow permeation of the respective gas, e.g. hydrogen or oxygen, and the electrolyte water through the first electrode 108. The first electrode 108 has a first surface 114 facing the electrolyte chamber and a second, opposite surface 116 facing the first gas collection chamber 106. The first electrode 108 may be made of steel, preferably sintered steel. In some embodiments, the second electrode 112 may also be made of steel, preferably sintered steel. In alternative embodiments, the second electrode 112 may be made of a material different to the first electrode 108. In some embodiments, the first and / or the second electrode 108, 112 may be made of Titanium and / or Nickel. Gases produced by the first electrode 108 may flow into the first gas collection chamber 106. The first gas collection chamber 106 comprises a first gas outlet port 122 for extraction of the gas within the first gas collection chamber 106. As will be described in more detail below, the first gas outlet port 122 may include a pressure control valve, such as a pressure relief valve, configured to set a gas pressure within the first gas collection chamber 106. The second electrode 112 of FIG. 1 is also permeable to gases produced by the decomposition of electrolyte water. The second electrode 112 is also generally permeable to electrolyte water. In other words, the second electrode 112 is also a "flow-through" electrode in which gases produced by decomposition of electrolyte water within the electrolyte chamber 104 are able to penetrate the second electrode 112 and thus move from the electrolyte chamber 104 towards the second gas collection chamber 110. The second electrode 112 has a first surface 118 facing the electrolyte chamber 104 and a second, opposite surface 120 facing the second gas collection chamber 110. Gases produced by the second electrode 112 may flow into the second gas collection chamber 110. The second gas collection chamber 110 comprises a second gas outlet port 124 for extraction of the gas within the second gas collection chamber 110. As will be described in more detail below, the second gas outlet port 124 may include a pressure control valve, such as a pressure relief valve, configured to determine the pressure within the second gas collection chamber 110. The electrolysis apparatus 100 comprises an electrolyte water supply circuit 130 for supplying the electrolyte chamber 104 with electrolyte water. The electrolyte water supply circuit 130 of FIG. 1 is a closed system. Alternatively, the water supply circuit may be an open system including an electrolyte water reservoir. In one example, the electrolyte water supply circuit 130 comprises a pump 134 arranged upstream of an inlet port 126 of the electrolyte chamber 104. The pump 134 may be configured to move electrolyte water through the system and in the direction of the electrolyte chamber 104 at a selectable pressure. The electrolyte supply circuit 130 comprises an electrolyte water supply line 162 for topping up electrolyte water turned into gas by the electrolysis process. As indicated in FIG. 1, the electrolyte water supply line 162 may be connected to the pump 134 via a manually or automatically controlled shut off valve. An expansion vessel 132 is a pressure storage device arranged within the electrolyte water supply circuit 130 and configured to provide expansion derived pressure into the system and configured to enable the pump 134 to have a lower cycle time and maintain a desired pressure range within the circuit 130 / protect the circuit 130 from excessive pressures. The electrolyte chamber 104 comprises a vent port connected to a vent line 105. The vent line 105 is configured to be used to drain the back flushed electrolyte and any associated media. Additionally, the line may be instrumental in sampling and even comprise a collection well for removal of electrolyte in the circulation system either with or without pressure. Additionally, the vent may or may not be instrumental in the purging of air from the system prior to current being applied to the electrodes. Finally, the vent pipe may allow electrolyte flow and recycling from 104 via 105 to 162, the water inlet line or it may discharged / collected. The electrolyte supply circuit 130 may comprise a pressure gauge 134 for monitoring the pressure within the electrolyte chamber 104. As will be appreciated, the pressure gauge 136 may be arranged anywhere downstream of the pump 134. In some embodiments, the pressure gauge 136 may be an integral part of the pump 134. In other embodiments, the pressure gauge may be arranged within the electrolyte chamber 104. In some embodiments, the electrolyte water supply circuit 130 may comprise a pressure storage device, such as an accumulator 138. The accumulator 138 shown in FIG. 1 is arranged downstream of the pump 134. The accumulator 138 may be connected to the pump 134 via a check valve, which, during normal operation of the electrolysis apparatus 100, allows fluid to be pumped into the accumulator 138. As will be appreciated, the check valve will stop fluid from leaving the accumulator 138. The accumulator 138 may also comprise a separate outlet valve for selectively connecting an outlet of the accumulator 138 with the electrolyte chamber 104. In some embodiments, the accumulator 138 may thus comprise a normally-open outlet valve, which is closed during normal operation of the electrolysis apparatus. In other words, during normal operation, pressurized electrolyte water may be pumped into the accumulator 138 but may not leave the accumulator 138, until the outlet valve is opened. As will be described in more detail below, using a normally-open outlet valve enables the accumulator 138 to be used as a safety measure, e.g. during power cuts. The first gas collection chamber 106 comprises a first drain port 142. The second gas collection chamber 110 comprises a second drain port 144. The first drain port 142 is connected to the pump 134 of the electrolyte water supply circuit 130 via a first drain line 146. The second drain port 144 is connected to the pump 134 via a second drain line 148. Electrolyte water permeating the first electrode 108 during operation of the electrolysis apparatus 100 may be drained from the first gas collection chamber 106 via the first drain port 142 and the first drain line 146 respectively. Similarly, electrolyte water permeating the second electrode 112 during operation of the electrolysis apparatus 100 may be drained from the second gas collection chamber 110 via the second drain port 144 and the second drain line 148 respectively. In multicell arrangements any drain port can act for one or more of the cells rather than being required by each cell. In the embodiment of FIG. 1, the first and second drain ports 142, 144 are arranged typically at a bottom end of the first and second gas collection chambers 106, 110. In other words, the drain ports 142, 144 are arranged below the first and second gas outlet ports 122, 124 of the first and second gas collection chambers 106, 110 and below the first and second electrodes 108, 112. In other words, both the first and the second gas collection chambers 106, 110 comprise drain wells 141, 143 arranged typically at a bottom end of the gas collection chambers 106, 110. As can be seen from FIG. 1, the housing 102 is thus substantially H-shaped but does not need to be. It can be multicell or arranged similar to a plate heat exchanger design. The device can be made of multiple electrodes usually arranged in parallel to each other to form a stack of electrodes. During operation of the electrolysis apparatus 100, electrolyte water that has permeated the first or second electrode 108, 112 will collect within the drain well 141, 143 at the bottom of the respective gas collection chambers 106, 110, whereas the gases produced during the electrolysis, will rise and pressurize the gas collection chambers 106, 110. As long as the drain ports 142, 144 are covered with electrolyte water, the drain ports may be opened for drainage of the electrolyte water from the gas collection chambers 106, 110 without inadvertently removing gases via the drain ports 142, 144. In some embodiments, the electrolysis apparatus 100 may comprise electrolyte water level sensors arranged within the gas collection chambers 106, 110 to determine if sufficient levels of electrolyte water are available within the gas chambers 106, 110 in order to safely open one or both of the drain ports 142, 144. These levels may or may not be actively controlled with active movement of electrolyte water to the collection chambers from areas of the electrolyte circulation system with capacity including 138 or as active top up from external water source. The levels may or may not be controlled using active pressure variation and control within the system. The first and second gas collection chambers 106, 110 both comprise gas pressure gauges 150, 152. A first gas pressure gauge 150 is configured to determine the gas pressure within the first gas collection chamber 106. A second gas pressure gauge 152 is configured to determine a second gas pressure within the second gas collection chamber 110. I n some embodiments, the first and second gas gauges may be incorporated into a single device. The electrolysis apparatus 100 comprises a first electrical terminal 154 and a second electrical terminal 156. In the example of FIG. 1, the first terminal 154 is a negative terminal, whereas the second terminal 156 is a positive terminal. However, it will be appreciated that the polarity of the first and second terminals may be swapped, such that the first terminal 154 is a positive terminal and the second terminal 156 is negative. This is because, in some embodiments, the electrolysis apparatus is symmetrical on either side of the electrolyte chamber 104. The terminals 154, 156 are connected to the housing 102 of the electrolysis apparatus 100. In particular, the first terminal 154 is connected to the first gas collection chamber 106. The second terminal is connected to the second gas collection chamber 110. Accordingly, the first terminal 154 is electrically connected to the first electrode 108, which is electrically connected to the first gas collection chamber 106 via its second surface 116. The second terminal 156 is connected to the second gas collection chamber 110, which in turn is connected to the second electrode 112 via the second surface 120 of the second electrode 11 2. Of course, it will be appreciated that the terminals 154, 156 may also be connected to the electrodes 108, 112 directly, rather than via the housing 102 of the electrolysis apparatus 100. The terminals 154, 156 are connectable to a power source or power supply unit, e.g. a direct current power source, to apply a current across the electrodes 108, 112. Examples of power supply units according to the present disclosure will be described in more detail with reference to FIGs. 2 and 4. If the terminals 154, 156 are connected to the power supply unit, current will flow between the first and second electrode 108, 112 via the electrolyte water within the electrolyte chamber 104, thereby activating the electrolysis process for decomposition and separation of electrolyte water into oxygen and hydrogen, as will be explained in more detail below. As mentioned above, in the embodiment of FIG. 1, the first terminal 154 is a negative terminal and the second terminal 156 is a positive terminal. Accordingly, the first electrode 108 of the embodiment in FIG. 1 is the cathode of the electrolysis apparatus 100, whereas the second electrode 112 is the anode of the electrolysis apparatus 100. The first electrode 108 is permeable to gas, particularly hydrogen. The second electrode 112 is permeable to gas, particularly oxygen. In the above example, the first gas collection chamber 106 is configured to receive hydrogen gas, whereas the second gas collection chamber 110 is configured to receive oxygen gas. The electrolysis apparatus 100 further comprises a control unit 160, schematically represented in FIG. 1. The control unit may be connected to the first and / or second gas pressure gauges 150, 152 to receive gas-pressure-data representative of a gas pressure within the first and / or second gas collection chamber 106, 110. The control unit 160 may be connected to the first and second drain valves 142, 144 for controlling operation of the first and second drain valves 142, 144. The control unit may be connected to the first and second gas outlet ports 122, 124 for controlling the operation of the first and second gas outlet ports 122, 124.The control unit 160 may be connected to the power source (not shown) for controlling the supply of electrical power to the first and second electrodes 108, 112. The control unit 160 may be connected to an outlet valve of the accumulator 138. The control unit 160 may be connected to the pump 134 and the electrolyte water pressure gauge 136. The control unit 160 may be connected to any of the above devices via control wires or wirelessly as is well known in the art. The control unit 160 may either be locally arranged together with the housing 102 of the electrolysis apparatus or remotely, e.g. in a centralised control office. The control unit 160 is configured to control a pressure drop across at least one of the permeable electrodes 108, 112. In one embodiment, the control unit 160 is configured to control the electrolyte pressure in the electrolyte chamber 104 relative to a gas pressure in the first or second gas collection chamber 106, 110. The control unit 160 may be configured to control the electrolyte water pressure in the electrolyte chamber 104 to be higher than a gas pressure in the first or second gas collection chambers 106, 110. In other words, the control unit 160 is configured to maintain a pressure drop between the electrolyte chamber 104 and the gas collection chambers 106, 110. In some examples, the control unit 160 is configured to control the electrolyte water pressure in the electrolyte chamber 104 to be at least 5 bar higher than a gas pressure in the first and / or second gas collection chamber 106, 110. Maintaining a pressure drop of at least 5 bar between the electrolyte chamber 104 and the first and / or second gas collection chamber 106, 110 causes electrolyte water to permeate the first electrode 108 and / or the second electrode 112 and thus to flow between the electrolyte chamber 104 and the first and / or second gas collection chamber 106, 110 together with the hydrogen gas produced at the first electrode. Causing the above electrolyte water flow across the first and / or second electrodes 108, 112 significantly increases the efficiency of the electrolysis apparatus 100. In another embodiment, one or both of the gas outlet ports may comprise pressure relief valves configured to open automatically once the gas pressure in the first or second gas collection chamber 106, 110 exceeds a set pressure. In this example, the pressure within the gas collection chambers will be determined by the set pressure of the pressure relief valves of the first and second gas outlet ports 122, 124 respectively. In some embodiments, the set pressure of the pressure relief valves may be adjustable, e.g. via the control unit 160. In both embodiments described above, the control unit 160 may be configured to maintain a gas pressure in the first and second gas collection chamber 106, 110 at lOObar to lOOObar. If the gas pressure within the gas collection chambers 106, 110 is maintained at 100 bar, the control unit may set a desired electrolyte water pressure of 105 bar or more to allow for some electrolyte water to pass through the first and / or second electrode 108, 112 as has been described above. It should be noted that electrolyte water passing through the first and second electrodes 108, 112, due to the pressure drop between the electrolyte chamber 104 and the gas collection chambers 106, 110, may be drained back into the electrolyte water supply circuit 130, e.g. intermittently, via the above drain ports 142, 144. The control unit 160 may be configured to control such electrolyte water drainage operation. The control unit may also be configured to control a power supply unit (see FIGs. 2 and 4) attached to the electrodes 108, 112 via the terminals 154, 156. The operator or controller can alter the amperage according to the type of electrolysis and the type of electrode used and other variables such as cell gap. The control unit may be configured to set the voltage provided by the power source to be set at the desired voltage. The desired voltage may be designated by the operator. The amperage and voltage can be fixed, manually set or variably controlled by the control unit 160. In some embodiments, the control unit may be configured to supply electrical power to the electrodes 108, 112 only once the desired pressure drop across the electrodes 108, 112 has been achieved. In other words, the control unit 160 may monitor a pressure difference between one of the gas collection chambers 106, 110 and the electrolyte chamber 104. Once the pressure difference exceeds a selectable first pressure-threshold, the control unit may activate the power supply to apply a pulsed DC current across the electrodes 108, 112, as will be described in more detail below. The control unit 160 may be configured to de-activate the power supply whenever the pressure difference falls below a second pressurethreshold. The second pressure threshold may be the same as or lower than the first pressure -threshold. Turning to FIG. 2, there is shown an embodiment of the electrolysis system according to the present disclosure. The electrolysis system 200 of FIG. 2 comprises a first electrolysis apparatus 220 and a power supply unit. The power supply unit is configured to provide a pulsed DC voltage / signal to the electrolysis apparatus 220. The power supply unit comprises AC input terminals 202, which are connected to an AC power source 201. The AC input terminals are also connected to a transformer 203. The transformer 203 comprises a primary winding 204 and a secondary winding 206. As is well known in the art, the ratio of the primary winding 204 to the secondary winding 206 defines a voltage increase or decrease in relation to the voltage of the AC input signal. The power supply unit of the embodiment shown in FIG. 2 comprises a half-wave rectifier. To this end, a diode 212 is connected to the secondary winding 206 of the transformer 203. In particular, the diode 212 comprises an anode end 214, which is connected to a first terminal 208 of the secondary winding 206. A cathode end 216 of the diode 212 is connected to a first terminal 218 of an electrolysis apparatus 220. A second terminal 222 of the electrolysis apparatus 220 is connected to a second terminal 210 of the secondary winding 206 of the transformer 203. The electrolysis apparatus 220 may be an electrolysis cell as has been described with reference to FIG. 1 above. Accordingly, the first and second terminals 218, 222 shown in FIG. 2 relate to the first and second terminals 154, 156 of the electrolysis cell 100 described with reference to FIG. 1. Alternatively, and as will be described in more detail with reference to FIG. 6, the electrolysis apparatus 220 may be an electrolysis stack. It will be appreciated that the positive and negative polarities at the secondary winding 206 indicated in FIG. 2 will change continuously at the frequency of the AC input signal. In other words, the first terminal 208 of the secondary winding 206 will only be positive during one half of the AC input wave signal. Similarly, the second terminal 210 of the secondary winding 206 will only be negative during one half of the AC input wave signal. During the second half of the input wave signal, the first terminal 208 will be negative and the second terminal 210 positive. Polarities shown in FIG. 2 may also be referred to as a positive halfwave herein forth. During the positive half-wave, the diode 212 will be conductive, i.e. current will be able to flow from the anode end 214 towards the cathode end 216 and, ultimately, the electrolysis apparatus 220. Conversely, during the negative half-wave, i.e. when the first terminal 208 is of negative polarity, the diode 212 will block the flow of current, such that no power will be supplied to the electrolysis apparatus 220. FIGs. 3A and 3B show exemplary input and output signals of the electrolysis system 200 shown in FIG. 2. In particular, FIG. 3A shows an exemplary AC input signal 300, represented by a sine wave. Each wave of the AC input signal 300 comprises a positive half-wave 302, 306, 310 and a negative half-wave 304, 308. FIG. 3B shows an exemplary output signal created by the power supply unit of FIG. 2, which comprises a half-wave rectifier. Due to the diode 212 of FIG. 2, only the positive half-waves 302, 306, 310 of the AC input signal 300 will be supplied to the electrolysis apparatus 220. The negative half-waves 304, 308 of the AC input signal 300 will be blocked by the diode 212. It follows that in the output signal 312 generated by the power supply unit of FIG. 2 is a pulsed DC signal. The pulsed DC signal 312 only comprises positive half-waves 314, 316, 318 of the AC input signal. The positive half-waves 314, 316, 318 are spaced from each other by a time, which relates to the time period of a half-wave for the AC input signal. In other words, the gap between DC pulses of the output signal 312 correlates to half the period of the AC input signal. At an exemplary AC input signal frequency of 50 Hz (mains frequency in Europe), the gap between DC pulses would thus be 10 ms. It was found that a gap of 5 to 15 ms, preferably 10 ms, is sufficient to avoid the double capacitive layer effect mentioned above. It should also be noted that the DC signal 312 is not smoothed. In other words, the pulses 314, 316, 318 of the DC signal 312 follow the sinus waveform of the AC input signal. As such, the pulsed DC signal 312 suggested by the present disclosure may be generated in a particularly simple and repeatable manner, e.g. by means of a half-wave rectifier. FIG. 4 shows another embodiment of an electrolysis system 400 according to the present disclosure. The electrolysis system 400 differs from the electrolysis system 200 of FIG. 2 mainly in that the power supply unit comprises a full-wave rectifier and that said power supply unit is connected to 2 electrolysis apparatus 420, 428. In more detail, the electrolysis system 400 of FIG. 4 includes an AC input terminal 402, which is connected to the primary windings 404 of a centre-tapped transformer 403. The centre-tapped transformer 403 comprises a first secondary winding 406 and a second secondary winding 407. In some embodiments, the first secondary winding 406 and the second secondary winding 407 may have the same number of windings. In some embodiments, the first and secondary windings 406, 407 may relate to half the number of windings of the primary winding 404. However, as will be appreciated, any number of windings of the primary winding and the first and second secondary winding is feasible, depending on the voltage conversion required. A first terminal 408 of the first secondary winding 406 is connected to an anode end 414 of a first diode 412. A second terminal 410 of the second secondary winding 407 is connected to an anode end 436 of a second diode 434. The centre tap 424 represents a second terminal of the first secondary winding 406 and, at the same time, a first terminal of the second secondary winding 407. A cathode end 416 of the first diode is connected to a first terminal 418 of the first electrolysis apparatus 420. A second terminal 422 of the first electrolysis apparatus 420 is connected to the centre tap 424. The second terminal 422 of the first electrolysis apparatus 420 is connected to a second terminal 426 of the second electrolysis apparatus 428. A cathode end 432 of the second diode 434 is connected to a first terminal 430 of the second electrolysis apparatus 428. The second terminal 426 of the second electrolysis apparatus 428 is connected to the centre tap 424. In other words, a first electrical circuit 440 is established by a serial arrangement of the first secondary winding 406, the first diode 412, the first electrolysis apparatus 420 and the centre tap 424. A second electrical circuit 442 is established by a serial arrangement of the second secondary winding 407, the second diode 434, the second electrolysis apparatus 428, and the centre tap 424. As will be appreciated, during the positive half-wave of the AC input signal, the first diode 412 will be conductive, whereas the second diode 434 will be blocking current flow. In other words, a current may flow in the first circuit 440 of the electrolysis system 400, during the positive half-wave of the AC input signal. During said positive half-wave, no current will flow in the second circuit 442. It follows that, during the positive half-wave of the AC input signal, only the first electrolysis apparatus 420 will be supplied with electrical power, i.e. with a DC pulse. During the negative half-wave of the AC input signal, the first diode 412 will be blocking current flow, whereas the second diode 434 will be conductive. In this scenario, a current may flow in the second circuit 442 of the electrolysis system 400, during the negative half-wave of the AC input signal. During said negative half-wave, no current will flow in the first circuit 440. It follows that, during the negative half-wave of the AC input signal, only the second electrolysis apparatus 428 will be supplied with electrical power, i.e. with a DC pulse. The above is also represented in more detail in FIGs. 5A to 5C. In particular, FIG. 5A shows an exemplary AC input signal 500, which is a sinusoidal wave-signal. The AC input signal comprises alternating positive and negative half-waves, 502, 504, 506, 508, 510. FIG. 5B shows a first DC signal 512, which corresponds to the positive half-waves of the AC input signal 500. First DC signal 512 mostly corresponds to the DC signal 312 of FIG. 3B described above. It follows that the same considerations apply in terms of the time period of the gaps between DC pulses / positive halfwaves 514, 516, 518. FIG. 5C shows a second pulsed DC signal 520, which corresponds to the negative half-waves of the AC input signal 500. The second pulsed DC signal 520 is based on the negative half-waves 504, 508 of the AC input signal, which may pass the second diode 434 of the second circuit 442. The second pulsed DC signal 520 comprises DC pulses 522, 524, which are spaced by the same gap as the DC pulses of the first pulsed DC signal 512. The second pulsed DC signal 520 has the opposite polarity of the first pulsed DC signal 512. A phase shift of n exists between the first pulsed DC signal 512 and the second pulsed DC signal 520. Neither the first DC signal 512 nor the second DC signal 520 is smoothed or otherwise modified compared to the waveform of the AC input signal 500. In particular, it is expressly not intended to include capacitors or any other smoothing component in the first or second circuits 440, 442 of the electrolysis system 400 according to FIG. 4. In conclusion, the power supply unit of the electrolysis system 400 according to the embodiment of FIG. 4 is configured to supply the positive half-waves of the AC input signal 500 to a first electrolysis apparatus 420, in the form of a first pulsed DC signal 512, and the second half-waves of the AC input signal 500 to a second electrolysis apparatus 428, in the form of a second pulsed DC signal 520. In other words, the AC input signal 500 is split between two separate electrolysis apparatus 420, 428. The first and second electrolysis apparatus 420, 428 are provided with pulsed DC power alternatingly, i.e., the first and second electrolysis apparatus 420, 428 are supplied with electrical power, when supply to the respective other is paused. Although the above electrolysis systems have been described in connection with electrolysis cells, such as the electrolysis cell shown in FIG. 1, it will be appreciated that the electrolysis apparatus of the present invention may alternatively comprise electrolysis stacks, such as the stack described in FIG. 6 below. Turning to FIG. 6, there is shown an electrode stack, which may be employed as one or both of the first and / or second electrolysis apparatus described above. The electrode stack 600 comprises a plurality of electrode assemblies 600a to 600h stacked together to form the electrode stack 600. Although FIG. 6 shows a horizontal arrangement of the electrode stack 600, this is for ease of illustration only. In a preferred embodiment, the electrode assemblies of the present invention are stacked in a vertical direction, such that the stack shown in FIG. 6 is indeed turned by 90°. When stacked in a vertical direction, the electric power supply is connected in such a way that the Cathode electrodes will be arranged above adjacent Anode electrodes in the stack. In other words, the top most electrode will be a Cathode electrode. At a first end, the stack 600 is covered by a first end plate 602. At an opposite, second end, the stack is covered by a second end plate 604. In order to connect the electrode assemblies 600a to 600h and the end plates with each other, each of the electrode assemblies 600a to 600h and the end plates 602, 604 include a plurality of mounting holes extending around the circumference of the electrode assemblies 600 and the cover plates 602, 604. Mounting rods 608, 610, for example threaded bolts, extend through the mounting holes to secure the stack and align the individual electrode assemblies 600a to 600h with each other. In the exemplary electrode stack 600 shown in FIG. 6, a first electrode assembly 600a is arranged adjacent to a second electrode assembly 600b. The second electrode assembly 600b is arranged adjacent to a third electrode assembly 600c etc. Each of the electrode assemblies 600a to 600h comprises two flow-through electrodes. Electrodes of adjacent electrode assemblies are spaced from each other by an electrolyte chamber, similar to the electrolyte chamber discussed with reference to FIG. 1. The first electrode assembly 600a is arranged within the stack, such that the first electrode is arranged adjacent to a second electrode of the second electrode assembly 600b. In more detail, the first surface 622 of the first electrode of the first electrode assembly 600a faces the first surface 626 of the second electrode of the second electrode assembly 600b. Electrodes of adjacent electrode assemblies 600a to 600h may be separated by an electrolyte membrane or a diaphragm, which avoids mixing of the hydrogen oxygen produced at the cathode or anode electrodes. The electrode stack 600 shown in FIG. 6 is a bi-polar electrode stack. In other words, the electrode assemblies 600a to 600h of the electrode stack 600 are connected electrically in series, rather than in parallel as is the case for a unipolar stack. In the example of FIG. 6, a first (e.g. positive) terminal of the power supply unit is connected to the first end cover 602, whereas a second (e.g. negative) terminal is connected to the second end cover 604. In this configuration, each of this first electrodes of each electrode assembly 600a to 600h has a positive charge and thus acts as an anode electrode. Similarly, each of the second electrodes of each of the electrode assemblies 600a to 600h is negatively charged and thus acts as a cathode electrode. It follows that in the electrode stack 600 of the present disclosure, each electrode assembly 600a to 600h provides one anode electrode and one cathode electrode separated by a non-permeable divider. FIG. 6 shows two (first) electrolyte water supply galleries 612, 616 extending through the electrode assemblies 600a to 600h. The electrolyte water supply galleries 612, 616 are configured to supply electrolyte water to the first electrodes of each of the electrode assemblies 600a to 600h via respective connection ducts 618, 620. Electrolyte water supplied in this way may enter the first electrodes radially. Preferences and options for a given aspect, feature or parameter of the disclosure should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the disclosure.

Claims

1. An electrolysis system for generating hydrogen and / or oxygen, the system comprising:a first electrolysis apparatus, particularly an electrolysis stack or cell, comprising at least one electrode for the decomposition of electrolyte water;a power supply unit for supplying electric power to the first electrolysis apparatus,wherein the power supply unit comprises a first diode for converting an AC input signal to a first pulsed DC signal, said first pulsed DC signal being a first half wave of the AC input signal, wherein the first electrolysis apparatus is connected to the power supply unit in such a way that the first electrolysis apparatus is supplied with the first pulsed DC signal.

2. The electrolysis system of Claim 1, comprising a second electrolysis apparatus, particularly an electrolysis stack or cell, comprising at least one electrode for the decomposition of electrolyte water, wherein the power supply unit comprises a second diode for converting the AC input signal to a second pulsed DC signal, said second pulsed DC signal being a second half wave of the AC input signal, wherein the second electrolysis apparatus is connected to the power supply unit in such a way that the second electrolysis apparatus is supplied with the second pulsed DC signal.

3. The electrolysis system of Claim 2, wherein the power supply unit comprises a centre tapped full wave rectifier.

4. The electrolysis system of Claim 3, wherein a negative terminal of the first electrolysis apparatus is connected to a negative terminal of the second electrolysis apparatus and to the centre tap of the power supply unit.

5. The electrolysis system of Claim 3 or 4,wherein the centre tap is earthed, particularly by connecting the centre tap to a chassis of the electrolysis apparatus to ensure safe operation.

6. The electrolysis system of any one of Claims 2 to 5, wherein the power supply unit comprises a centre tapped transformer, said centre tapped transformer comprising a primary winding, a first secondary winding, and a second secondary winding, wherein the first electrolysis apparatus is connected to the first secondary winding via the first diode, and wherein the second electrolysis apparatus is connected to the second secondary winding via the second diode.

7. The electrolysis system of Claim 6,wherein the first secondary winding and the second secondary winding have substantially the same number of windings.

8. The electrolysis system of Claim 6 or 7, wherein the primary winding has substantially the same number of windings as the first secondary winding and / or the second secondary winding.

9. The electrolysis system of any one of Claims 1 to 8, wherein the at least one electrode of the first electrolysis apparatus is a flow-through electrode, which is permeable to electrolyte water.

10. The electrolysis system of any one of Claims 1 to 9, wherein the first electrolysis apparatus comprises a plurality of electrodes stacked in a side-by-side fashion.

11. The electrolysis system of any one of Claims 1 to 10, wherein the electrolysis apparatus comprises:a housing comprising an electrolyte chamber;two electrodes for decomposition of electrolyte water, at least one of the electrodes being a flow-through electrode permeable to electrolyte water and gases produced during the electrolysis process, wherein the at least one permeable electrode is arranged between the electrolyte chamber and a first gas collection chamber;an electrolyte supply circuit for supplying electrolyte water to the electrolyte chamber; anda control unit for controlling a pressure drop across the at least one permeable electrode, between the electrolyte chamber and the first gas collection chamber.

12. The electrolysis system of any one of Claims 1 to 11, wherein the power supply unit does not comprise a capacitor.

13. A method of supplying an electrolysis system with electrical power, the electrolysis system comprising a first electrolysis apparatus comprising at least one electrode for the decomposition of electrolyte water, wherein the method comprises:providing an AC input signal;converting the AC input signal to a first pulsed DC signal, said first pulsed DC signal being a first half wave of the AC input signal;providing the first electrolysis apparatus with the first pulsed DC signal.

14. The method of Claim 13, wherein electrolysis system comprises a second electrolysis apparatus comprising at least one electrode for the decomposition of electrolyte water, wherein the method further comprises:- converting the AC input signal to a second pulsed DC signal, said second pulsed DC signal being a second half wave of the AC input signal;- providing the second electrolysis apparatus with the second pulsed DC signal.

15. The method of Claim 13 or 14, wherein the AC input signal has a frequency of 49Hz to 61Hz.

16. Use of an electrolysis system according to any one of Claims 1 to 12 for the decomposition of Ammonia.

17. Use of an electrolysis system according to any one of Claims 1 to 12 for electroplating.

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