Electrolysis system and method for exfoliating graphite

Abstract

An electrolysis system 100 for generating graphite oxide and / or graphene oxide is described. The system 100 comprises: a housing 102 with a liquid chamber 104; two electrodes 108,112 for decomposition

Description

BACKGROUND OF THE INVENTION The present disclosure relates to an electrolysis system for generating graphite oxide and / or graphene oxide. Other aspects of the present disclosure relate to a method for generating graphite oxide and / or graphene oxide. For more than two decades, one of the most highly praised materials has been a two-dimensional carbon layer known as "graphene". Graphene is a two-dimensional layer of carbon atoms which form hexagonal rings and is expected to transform a range of sectors such as microelectronics, energy creation and storage, as well as health and construction. This single atom layer of carbon exhibits remarkable properties, such as an electric conductivity that is higher than copper and a strength that is 200 times the strength of steel. Pure graphene is also highly transparent making it a particularly non-intrusive alternative to many other electric conductors. In view of the above, researchers around the world have been trying to establish new ways of isolating high purity graphene more effectively, so as to be able to manufacture the carbon layers at a competitive price. Since graphene was first isolated in the lab by Nobel Prize winners Prof. Andre Geim and Konstantin Novoselov at the University of Manchester in 2004, graphene production methods have improved drastically. Yet, the process still requires significant improvements to render the use of graphene as a replacement for other well established materials, such as silicone wavers or steel structures, commercially viable. It is an aim of the present disclosure to solve or at least ameliorate one or more problems of the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the present disclosure relate to an electrolysis system and a method for generating graphite oxide and / or graphene oxide as claimed in the appended claims. In one aspect of the present disclosure, there is provided an electrolysis system for generating graphite oxide and / or graphene oxide, said system, comprising: • a housing comprising a liquid chamber; • two electrodes for decomposition of water or electrolyte water, wherein at least an anode-electrode is a flow-through electrode comprising graphite; • a liquid supply for supplying water or electrolyte water to the liquid chamber. In one embodiment, the liquid supply is configured for supplying electrolyte-free water. In another embodiment, the electrolyte-free water is purified water, preferably deionised or distilled water. In another embodiment, the liquid chamber comprises a gap located between the two electrodes, wherein the gap has a width smaller than a Debye-length of purified water. In another embodiment, the graphite part of the flow-through electrode has a porosity that will allow the electrolyte-free water to permeate through said electrode. In another embodiment, both electrodes comprise graphite. In another embodiment, both electrodes are flow-through electrodes. In another embodiment, the electrolysis system comprises an electric supply circuit for supplying electric power to the electrodes. In another embodiment, the electric supply circuit is configured to supply electric power at a voltage that enables current to flow through electrolyte-free water between the anode-electrode and the cathode-electrode. In another embodiment, the electric supply circuit comprises a rectifier for supplying the electric power as a pulsed direct current, preferably by full-wave rectification of an alternating current supply. In another embodiment, the electric supply circuit comprises a transformer comprising primary windings and center tapped secondary windings connected to the rectifier. In another embodiment, the electrolysis system comprises a control unit for controlling a pressure within the liquid chamber. In another embodiment, the control unit is configured to control a pressure drop across the flow-through anode-electrode. In another aspect of the present disclosure, there is provided a method of generating graphite oxide and / or graphene oxide by electrolysis comprising: • supplying water or electrolyte water to electrodes of an electrolyser, said electrolyser comprising two electrodes, wherein at least an anodeelectrode is a flow-through electrode comprising graphite; • suppling electric power to the electrodes. In one embodiment, the method comprises supplying electrolyte-free water to the electrodes. In another embodiment, the electrolyte free water comprises purified water, particularly deionized water or distilled water. In another embodiment, the flow-through electrode has a porosity that will allow the water or electrolyte water to permeate through the electrode. In another embodiment, the method comprises supplying the electric power at a voltage that enables current to flow through electrolyte-free water between the two electrodes. In another embodiment, the method comprises supplying the electric power as a pulsed direct current, preferably by full-wave rectification of an alternating current supply. In another embodiment, the method comprises supplying the water or electrolyte water to the electrodes at a pressure, preferably at a pressure of more than 1 bar. 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 more 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: Figure 1 shows a schematic illustration of an electrolysis system according to an embodiment of the present invention; Figure 2 shows a schematic cross-section of an electrode structure; Figure 3 shows a schematic cross-section of an electrode stack; Figure 4 shows a schematic illustration of an electric power supply; Figure 5 shows a flow diagram of a method according to an embodiment of the present disclosure. Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the disclosure, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner. DETAILED DESCRIPTION FIG. 1 shows an electrolysis system 100 according to an embodiment of the present disclosure. In the example of FIG. 1, there is shown an electrolysis system 100 for generating graphite, particularly by electrolysis of water or electrolyte water. However, as will be appreciated, the electrolysis system 100 shown in FIG. 1 may also be suitable for generating graphite via electrolysis utilising other substances. Generally, in this specification, the term "water" may encompass tap water including that with no added electrolytes. In this specification, the term "electrolyte water" may encompass water including any added electrolyte suitable for water electrolysis. In some parts of this specification "electrolyte water" may also be referred to as electrolyte solution. Electrolyte water may contain any type of electrolyte additive, such as sulphuric acid, sulphate, potassium hydroxide, sodium hydroxide, etc. The term "electrolyte-free water" refers to tap water with reduced electrolyte content. As will be appreciated, even tap water will typically include natural levels of electrolytes. "Electrolyte-free water", therefore, relates to treated tap water that has a reduced, and preferably (to the extent possible) no electrolyte content. Although electrolyte will be removed from "electrolyte-free water" it should be understood that "electrolyte-free water" may still include various other non-water impurities, such as organic molecules. Examples of "electrolyte-free water" include purified water, such as deionised water and distilled water. The electrolysis system 100 comprises a housing 102. The housing 102 comprises a liquid chamber 104. In one example, the liquid chamber is configured to hold water or electrolyte water (hereinafter collectively referred to as reaction liquid) under pressure as will be described in more detail below. The housing 102 comprises a first gas collection chamber 106. The first gas collection chamber 106 is separated from the liquid 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 liquid chamber 104 by a second electrode 112. The liquid chamber 104 is located between the first and second electrodes 108, 112. The liquid chamber 104 is a membrane-less chamber. It will be appreciated that in some embodiments, the electrolyser may comprise more than two electrodes, e.g. arranged in parallel to each other to form a stack of electrodes. The pair of electrodes 108, 112 of Figure 1 are thus exemplary for any number of electrodes used in a stack. One possible arrangement of electrodes in a stack will be described in more detail with reference to Fig. 3. The housing 102 of Figure 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 liquid chamber 104, which is thus arranged between the electrodes 108, 112. In the example of Figure 1, the housing 102 is substantially H-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, as will be discussed with reference to Fig. 3. The first electrode 108 is permeable to gases produced by decomposition of reaction liquid. The first electrode 108 is also permeable to the reaction liquid. In other words, the first electrode 108 is a so-called "flow-through" electrode in which gases produced by decomposition of water (and the reaction liquid) within the liquid chamber 104 are able to penetrate the first electrode 108 and thus move from the liquid 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, through the first electrode 108. The first electrode 108 has a first surface 114 facing the liquid chamber and a second, opposite surface 116 facing the first gas collection chamber 106. The first electrode 108 may be made of graphite. In some embodiments, the second electrode 112 may also be made of graphite. In alternative embodiments, the first electrode 108 may be made of a different as the second electrode 108. For example, the second electrode may be made of titanium, nickel, steel, or any other suitable metal. 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 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 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 Figure 1 is also permeable to gases produced by the decomposition of reaction liquid. The second electrode 112 is also generally permeable to reaction liquid depending on a pressure within the liquid chamber 104 as will be explained in more detail below. In other words, the second electrode 112 is also a "flow-through" electrode in which gases produced by decomposition of the reaction liquid within the liquid chamber 104 are able to penetrate the second electrode 112 and thus move from the liquid chamber 104 towards the second gas collection chamber 110. The second electrode 112 has a first surface 118 facing the liquid 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 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 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 system 100 comprises a liquid supply, particularly a liquid supply circuit 130, for supplying the liquid chamber 104 with reaction liquid. The liquid supply circuit 130 of Figure 1 is a semi-closed system. "Semi-closed system" refers to the supply circuit 130 being closed via a drain port 142 of the first gas collection chamber 106, but open a second drain port 144 of the second gas collection chamber 144, as will be described in more detail below. Alternatively, the liquid supply circuit may be an open system including a reaction liquid reservoir. In one example, the liquid supply circuit 130 comprises a pump 134 arranged upstream of an inlet port 126 of the liquid chamber 104. The pump 134 may be configured to move reaction liquid through the system and in the direction of the liquid chamber 104 at a selectable pressure. The electrolyte supply circuit 130 comprises a liquid supply line 162 for topping up reaction liquid turned into gas by the electrolysis process. As indicated in Figure 1, the liquid supply line 162 may be connected to the pump 134 via a manually or automatically controlled shut off valve 164. Depending on the type of reaction liquid used, the liquid supply line 162 may be connected to either a water supply line, a reaction liquid tank or any other suitable reaction liquid source. An expansion vessel 132 is a pressure storage device arranged within the reaction liquid supply circuit 130. The expansion vessel 132 is configured to provide expansion derived pressure into the system and to enable 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 liquid chamber 104 may comprise a vent port connected to a vent line 105. The vent line 105 is configured to be used to drain back flushed electrolyte and any associated media. Additionally, the vent line 105 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 136 for monitoring the pressure within the liquid 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 liquid chamber 104. In some embodiments, the reaction liquid 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 system 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 liquid chamber 104. In some embodiments, the accumulator 138 may thus comprise a normally-open outlet valve, which is closed during normal operation of the electrolyser. In other words, during normal operation, pressurized reaction liquid 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 reaction liquid supply circuit 130 via a first drain line 146. The second drain port 144 is connected to a gaphite solution tank 166 via a second drain line 148. Reaction liquid permeating the first electrode 108 during operation of the electrolysis system 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, reaction liquid permeating the second electrode 112 during operation of the electrolysis system 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 (e.g. electrode stacks) any drain port can act for one or more of the cells rather than being required by each cell. In the embodiment of Figure 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 outlets 122, 124 of the first and second gas collection chambers 106, 110. In this embodiment, the drain ports 142, 144 are also arranged below the first and second electrodes 108, 112 but this may not always be the case. 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 Figure 1, the housing 102 is thus substantially H-shaped but does not need to be, it can be a 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 as will be described with reference to Figures 2 and 3. During operation of the electrolysis system 100, reaction liquid that has permeated the first electrode 108 will collect within the drain well 141 at the bottom of the first gas collection chamber 106, whereas the gases produced during the electrolysis, will rise and pressurize the first gas collection chamber 106. Reaction liquid that is drained via the first drain port 142 will be returned into the semi-closed liquid supply circuit 130 via first drain line 146, e.g. upstream of pump 134, and may thus be redirected towards the liquid chamber 104. Reaction liquid that has permeated the second electrode 112 will collect within the drain well 143 at the bottom of the second gas collection chamber 110, whereas the gases produced during the electrolysis, will rise and pressurize the second gas collection chamber 112. Reaction liquid that is drained via the second drain port 144 will be directed towards the graphite solution tank 166. It was found that the permeation of reaction liquid through the pores of the second electrode 112, i.e. a graphite flow-through electrode, will result in exfoliation of graphite from the second electrode 122 (anode-electrode), such that the drain well 143 of the second gas collection chamber 110 will collect a graphite solution, e.g. a solution of graphite particles in the reaction liquid that penetrated the second electrode 112. This graphite solution may then be drained via the second drain line 148 into the graphite solution tank 166 for later separation of graphite or even graphene from the reaction liquid. The reaction liquid that penetrated the first electrode 108 may be collected for use and not recycled back to the liquid chamber 104, depending on the properties it has aquired by passing through the Cathode. 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. In some embodiments, the first and second gas gauges may be incorporated into a single device. The electrolysis system 100 comprises a first electrical terminal 154 and a second electrical terminal 156. In the example of Figure 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 electrolyser is symmetrical on either side of the liquid chamber 104. In some embodiments, the first and the second electrodes 108, 112 are flow-through graphite electrodes. In such embodiments, the terminals may be swapped to change the polarity after some time. This swap will turn the first electrode 108 into an anode-electrode and the second electrode into a cathode-electrode. This embodiment is beneficial in that both graphite electrodes may be exfoliated by simply swapping the polarity of the terminals 154, 156. The terminals 154, 156 are connected to the housing 102 of the electrolysis system 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 112. 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 system 100. The terminals 154, 156 are connectable to a power source, e.g. a direct current power source, to apply a current across the electrodes 108, 112. If the terminals 154, 156 are connected to the power source, current will flow between the first and second electrode 108, 112 via the reaction liquid within the liquid chamber 104, thereby activating the electrolysis process for decomposition and separation of reaction liquid into oxygen and hydrogen, as will be explained in more detail below. As mentioned above, in the embodiment of Figure 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 Figure 1 is the cathode of the electrolysis system 100, whereas the second electrode 112 is the anode of the electrolysis system 100. The first electrode 108 is permeable to gas, particularly hydrogen. The second electrode 112 is permeable to gas, particularly oxygen. In one example, the first and second electrodes 108, 112 comprise different porosities. In some embodiments, the porosity of the first electrode 108 may be about half of the second electrode 112. 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 system 100 further comprises a control unit 160, schematically represented in Figure 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 outlets 122, 124 for controlling the operation of the first and second gas outlets 122, 124. The control unit 160 may be connected to a 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 reaction liquid pressure gauge 136. The control unit may be connected to any of the above devices via control wires or wirelessly as is well known in the art. The control unit may either be locally arranged together with the housing 102 of the electrolyser 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 liquid 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 reaction liquid pressure in the liquid chamber 104 to be higher than a gas pressure in the first and / or second gas collection chambers 106, 110. In other words, the control unit 160 is configured to maintain a pressure drop between the liquid chamber 104 and the gas collection chambers 106, 110. In some examples, the control unit 160 is configured to control the reaction liquid pressure in the liquid chamber 104 to be at least 1 bar higher than a gas pressure in the first and / or second gas collection chamber 106, 110. Maintaining a pressure drop of at least 1 bar between the liquid chamber 104 and the first and / or second gas collection chamber 106, 110 may increase the amount of reaction liquid permeating the first electrode 108 and / or the second electrode 112 and thus causes flow between the liquid chamber 104 and the first and / or second gas collection chamber 106, 110. As will be described in more detail below, it may be beneficial to increase reaction liquid flowthrough the second electrode 112 to increase production of graphite solution. The control unit 160 may be configured to maintain a pressure drop of at least 1 bar, preferably at least 5 bar, across the second electrode 112 to increase flow of reaction liquid through the second electrode 112. In order to maintain the required pressure drop across one or both of the electrodes 108, 112, the control unit 160 of Figure 1 is configured to receive gas-pressure-data representative of a gas pressure within the first or second gas collection chambers 106, 110 respectively. In the example of Figure 1, the gas-pressure-data may be pressure readings supplied by the first and / or second gas pressure gauges 150, 152. On the basis of the gas-pressure-data, the control unit will determine a desired reaction liquid pressure within the liquid chamber 104. In some examples, the control unit may add a preselected amount of pressure to the gas pressure indicated by the gas-pressure-data in order to determine the desired reaction liquid pressure. In some embodiments, the control unit 160 may determine a desired reaction liquid pressure that is at least 1 bar higher than the gas pressure within the second gas collection chamber 110. The control unit may then control the reaction liquid supply circuit 130 to supply reaction liquid to the liquid chamber 104 until the desired reaction liquid pressure is reached. In the example of Figure 1, the control unit 160 may be configured to activate the pump 134 to supply reaction liquid to the control chamber 104 until the desired reaction liquid pressure has been reached. To this end, the control unit may receive liquid-pressure-data representative of a pressure of reaction liquid within the liquid chamber 104. In the embodiment of Figure 1, the liquid-pressure-data comprises pressure readings supplied by the pressure gauge 136 arranged downstream of the pump 134. The control unit may control activation of the pump 134 via a control loop, based on the liquid-pressure-data provided by the pressure gauge 136. For example, the control unit may control the reaction liquid pressure within the control chamber 104, represented by the pressure readings of the pressure gauge 136, via a PID control loop. It should be appreciated that a pressure drop between the liquid chamber 104 and the gas collection chambers 106, 110 will vary continuously as the electrolysis system 100 is operated. This is because, during operation of the electrolysis system, i.e. when pressurised reaction liquid is available in the liquid chamber 104 and a current is applied across the two electrodes 108, 112, hydrogen and oxygen gases are produced and added to the first and second gas collection chambers 106, 110 continuously. Accordingly, in this example, as long as the first and second gas outlets 122, 124 remain closed, the gas pressure within the gas collection chambers 106, 110 will continue to rise. This exemplary rise in gas pressure will be determined by the control unit 160 on the basis of the gas-pressure-data. The control unit 160 will then determine a new, higher, desired reaction liquid pressure and control the pump 134 to increase the reaction liquid pressure within the liquid chamber 104 and match said increased desired reaction liquid pressure. The control unit 160 may continuously adjust the pressure within the liquid chamber 104 as long as the gas pressure within the first or second gas collection chamber 106, 110 rises. The control unit 160 may also control the gas pressure within the first and / or second gas collection chamber 106, 110. In the example of Figure 1, the control unit may be configured to control an operation of the first and / or second gas outlet 122, 124. The control unit 160 may open and close the first gas outlet 122 to control the (hydrogen) gas pressure within the first gas collection chamber 106. The control unit 160 may open and close the second gas outlet 124 to control the (oxygen) gas pressure within the second gas collection chamber 110. In some embodiments, the control unit 160 may receive a first desired gas pressure for the first gas collection chamber 106 and a second desired gas pressure for the second gas collection chamber 110. The first and second desired gas pressures may be selected by an operator. In some examples, the desired gas pressures may be determined directly by apparatus using the hydrogen and oxygen gases provided by the electrolysis system 100. In another embodiment, one or both of the gas outlets 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 outlets 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 reaction liquid pressure of 101 bar or more to allow for some reaction liquid to pass through the first and / or second electrode 108, 112 as has been described above. The control unit may also be configured to control a power source (not shown) attached to the electrodes 108, 112 via the terminals 154, 156. The operator or controller can alter the voltage 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 at a 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 liquid chamber 104. Once the pressure difference exceeds a selectable first pressurethreshold, the control unit may activate the power supply to apply a DC current across the electrodes 108, 112 and the reaction liquid within the liquid chamber 104 to start operation of the electrolysis system 100. The control unit 160 may be configured to de-activate the power supply whenever the pressure difference falls below a second pressure-threshold. The second pressure threshold may be the same as or lower than the first pressure-threshold. The application is not limited to the electrolysis system comprising an H-shaped housing shown in FIG. 1. Rather, the present invention is applicable to any type of electrolysis system, in which at least the anode-electrode is constructed as a graphite flow-through electrode. At least the anode-electrode(s), and preferably also the cathode-electrode(s), may comprise any type of graphite that can be exfoliated. Another example of suitable flow-through electrodes shall be discussed with reference to FIGs. 2 and 3. FIG. 2 shows a flow-through electrode 200. The flow-through electrode 200 is made of a porous structure that is permeable to gases produced during electrolysis and reaction liquids. The electrode layout shown in FIG. 2 may be used for both an anodeelectrode and a cathode-electrode in an electrolysis system for exfoliating graphite. However, it is feasible to construct the anode-electrode and the cathode-electrode of different materials. While the anode-electrode will be constructed of porous graphite, the cathode-electrode may be constructed of any suitable porous structure that is electrically conductive, such as graphite, titanium, nickel, or steel. The porous electrode 200 shown in FIG. 2 may be sintered into the structure shown, so as to provide suitable pore sizes. The electrode 200 comprises a first surface 202 and an opposite second surface 204. Both the first and second surfaces 202, 204 are made of the flow-through material (e.g., graphite, titanium, nickel, or steel). A gas collection chamber 206 is located between the first and second surfaces 202, 204 of the electrode 200. In other words, the electrode 200 comprises a first porous wall 203 comprising the first surface 202 and a second porous wall 205 comprising the second surface 204. The gas collection chamber 206 extends between the first and second walls 203, 205. As will be appreciated, the electrode shown in FIG. 2 differs from the electrodes shown in the embodiment of FIG. 1 in that the electrode 200 includes an integral gas collection chamber. The gas collection chamber 206 is arranged on the inside of the electrode 200. By contrast, the gas collection chambers of FIG. 1 were provided as a part of the housing 102 and are thus separate parts that may be disconnected from the electrodes. Due to the arrangement of the gas collection chamber 206 on the inside of the electrode 200, the electrode 200 comprises two flow-through surfaces, namely the first and the second surfaces 202, 204. In other words, the electrode 200 of FIG. 2 may be provided with reaction liquid on both sides of the electrode, i.e., on both surfaces 202, 204, such that electrolysis may occur when reaction liquid penetrates the first wall 203 and / or the second wall 205. As has been described with reference to FIG. 1 above, during the electrolysis process, reaction liquid and gases produced by the decomposition of the reaction liquid will penetrate the flow-through electrode 200 and flow into the gas collection chamber 206. If the electrode 200 is provided with electrical power of a positive polarity, the electrode will be an anode-electrode and reaction liquid penetrating the first and / or second walls 203, 205 will act to exfoliate graphite from the porous graphite structure of the walls 203, 205 during electrolysis. At the same time, the anode-electrode will decompose some of the reaction liquid into oxygen. Accordingly, during the electrolysis process, oxygen and a graphite solution will enter the gas collection chamber 206 of the electrode 200. The so collected oxygen and graphite solution may be extracted from the electrode 200 via corresponding extraction openings. In particular, the oxygen gas may be extracted via a gas collection opening 208, whereas the graphite solution may be extracted via a liquid collection opening 210. The functionality of the gas collection opening 208 is comparable to the gas outlet 124 of FIG. 1, whereas the functionality of the liquid collection opening 210 is comparable to the drain port 144 of FIG. 1. The way in which the gases and liquid are removed from the gas collection chamber 206 is, however, not the subject of this invention. If the electrode 200 is provided with electrical power of a negative polarity, it will act as a cathode-electrode for the production of hydrogen. The cathode-electrode may be made of any conductive material, such as graphite or steel. The structure of the cathode-electrode may, however, be identical to the structure of the anode-electrode, i.e., the structure of the electrode 200 shown in FIG. 2. During the electrolysis process at the cathode-electrode, no exfoliation of graphite occurs at the cathode-electrode, even if the cathode-electrode is a graphite flow-through electrode. Turning to FIG. 3, there is shown an electrode stack 300 comprising three electrodes of FIG. 2 arranged adjacent to each other. A first electrode 300a is a first anodeelectrode. The first electrode 300a is connected to a positive pole of an electric power supply. A second electrode 300b is arranged in parallel and adjacent to the first electrode 300a. The second electrode 300b is connected to a negative pole of the electric power supply of the electrolysis system. A third electrode 300c is arranged in parallel and adjacent to the second electrode 300b. The third electrode 300c is connected to a positive terminal of the electric power supply of the electrolysis system. Each of the electrodes 300a, 300b, 300c of the electrode stack 300 has a structure that is identical to the structure of the electrode 200 discussed with reference to FIG. 2. Accordingly, the first electrode 300a has a first surface 302 defined by a first porous wall and a second surface 304, which is arranged opposite to the first surface 302 and defined by a second porous wall. A gas collection chamber 306 is arranged between the first and second surfaces 302, 304 of the first and third electrodes 300a, 300c. The first and third electrodes 300a, 300c comprise gas collection openings 308 and reaction liquid collection openings 310. As discussed above, the gas collection openings 308 are preferably arranged at an upper region of the electrodes, whereas the reaction liquid collection openings 310 are arranged at a bottom end of the electrodes. The second electrode 300b of the electrode stack 300 shown in FIG. 3 is arranged between the first and third electrodes 300a, 300c. The second electrode 300b comprises a first surface 314 and an opposite second surface 316. A gas collection chamber 318 is arranged between the first surface 314 and the second surface 316 of the second electrode 300b. The second electrode 300b comprises a gas collection opening 320, which is arranged at an upper end of the electrode 300b. The second electrode 300b further comprises a reaction fluid collection opening 320, which is arranged at a lower end of the second electrode 300b. The electrode stack 300 comprises a first liquid chamber 330 arranged between the first electrode 300a and the second electrode 300b. The electrode stack 300 also comprises a second liquid chamber 332 arranged between the second electrode 300b and the third electrode 300c. The first liquid chamber 330 is arranged between the second surface 304 of the first electrode 300a and the first surface 314 of the second electrode 300b. The second liquid chamber 332 is arranged between the second surface 316 of the second electrode 300b and the first surface 302 of the third electrode 300c. The first and second liquid chambers 330, 332 are connected to each other via a reaction liquid channel 324 extending through the second electrode 300b, i.e., between the first surface 314 and the second surface 316. Accordingly, in the electrode stack 300 shown in FIG. 3, reaction liquid within the first and second liquid chambers 330, 332 will have the same pressure, which is then applied to the second surface 304 of the first electrode 300a, the first and second surfaces 314, 316 of the second electrode 300b, and the first surface 302 of the third electrode 300c. The first and third electrodes 300a, 300c are anode-electrodes, such that, during the electrolysis process, oxygen is generated at the first and third electrodes 300a, 300c. At the same time, reaction liquid in the first and second liquid chambers 330, 332 will enter the gas collection chambers 306 of the first and third electrodes 300a, 300c. Since the porous structure of the first and third anode-electrodes 300a, 300c is made of graphite, the reaction liquid permeating the porous structure of the first and third electrodes 300a, 300c will act to exfoliate some of the graphite of the flow-through electrodes, such that a graphite solution will be received within the gas collection chambers 306 of the anode-electrodes. This graphite solution may be drained from the gas collection chambers 306 of the anode-electrodes 300a, 300c via their respective liquid collection openings 310. Reaction liquid within the first and second liquid chambers 330, 332 will be decomposed into hydrogen gases at the cathode-electrode, i.e., the second electrode 300b of FIG. 3. Accordingly, hydrogen produced via the flow-through porous structure of the second electrode 300b will enter the gas collection chamber 318 of the second electrode 300b. Since the porous walls of the second electrode 300b may also be permeable to reaction liquid, the gas collection chamber 318 may receive some of the reaction liquid of both liquid chambers 330, 332 during the electrolysis process. Such reaction liquid may be drained from the second electrode 300b via the liquid collection opening, whereas hydrogen gas may be collected via the gas collection opening 320. It will be understood that the electrode stack 300 may extend further on either side of the first and third electrodes 300a, 300c. In particular, in such an electrode stack, further electrodes would be arranged adjacent to each other in an alternating fashion. In other words, another cathode-electrode would be arranged next to the first electrode 300a (i.e., on the left of the first electrode 300a). Similarly, a third cathodeelectrode would be arranged in parallel with and adjacent to the third electrode 300c (i.e., on the right side of the third electrode 300c). The so created, additional liquid chambers would be connected to the first and second liquid chambers 330, 332 via channels 312 extending through the first and third electrodes 300a, 300b. FIGs. 1 to 3 describe various ways of arranging flow-through electrodes in an electrolysis system. The present invention is, however, not restricted to any particular type of electrode arrangement. Rather, it has been found that using graphite flow-through electrodes, at least on the anode side of the electrolysis system, leads to a significant production of graphite solution as reaction liquid flows through the anodeelectrode. At the same time, the electrolysis process on the cathode side, i.e., at the cathode-electrodes, produces hydrogen, which may conventionally be used to power various different machines. Accordingly, it should be understood that although the present disclosure suggests using a flow-through anode-electrode made of graphite, this is not necessarily the case for the cathode-electrodes, which may be made of any other suitable material for decomposing water into hydrogen. In view of the above, the present invention provides an electrolysis system and electrolysis method, which provides a dual functionality, i.e. to produce hydrogen gas at the cathode side and, at the same time, produce graphite solution at the anode side. The graphite solution may be stored until graphite or graphene is extracted from the graphite solution in a subsequent step. In one embodiment, the reaction liquid supply discussed above will provide electrolyte-free water to the one or more liquid chambers of the electrolysis system. The electrolyte-free water may be any type of water from which naturally occurring electrolytes have substantially been removed. In some examples, the electrolyte-free water may be purified water, preferably deionized or distilled water. Using electrolyte-free water within the electrolysis system of the present invention, further increases the amount of graphite solution produced at the anode side. This is particularly the case if the liquid chamber comprises a gap between the adjacent surfaces of the cathode and anode-electrodes, that has a width smaller than a Debye-length of purified water. By reducing the gap between the electrodes to a width smaller than the Debye-length, the electrolyte-free water will be decomposed without the need for electrolyte additives typically used for electrolysis. Such small gap sizes ensure that OH- ions may travel from the cathode-electrode to the anode-electrode. At the anodeelectrode, some of the OH- ions will be converted to oxygen, which will penetrate the anode-electrodes. Other parts of the OH’ ions will combine with graphite exfoliated by the reaction liquid when permeating through the porous structure of the flow-through anode-electrodes. The so created graphite particles surrounded by OH’ ions may in some circumstances be two-dimensional layers, i.e. graphene flakes that are collected within the gas collection chambers of the anode-electrodes. Turning back to the porous structure of the anode-electrode / electrodes of the present electrolysis system, these flow-through electrodes should have a pore size that allows the electrolyte-free water to permeate through the anode-electrodes. In some embodiments, the pore size of the anode-electrode flow-through structures may be larger than the pore size of the cathode-electrodes, such that more reaction liquid will penetrate the anode-electrodes more than the cathode-electrodes. Increasing the size of the pores of the anode-electrodes, will increase the amount of graphite solution harvested at the anode-electrodes. The electrolysis system of the present invention comprises an electric supply circuit for supplying electric power to the electrodes, e.g., via the terminals 154, 156 shown in FIG. 1. An embodiment of an electric supply circuit 400 is shown schematically in FIG. 4. The electric supply circuit 400 is configured to supply electric power at a voltage that enables current to flow through electrolyte-free water between the anode electrode and the cathode electrode. As will be appreciated, electrolyte-free water has a very low electrical conductivity due to the absence of electrolytes. Yet, due to self-ionization of water, in which some water molecules deprotonate to form hydroxide ions (OH ), whereas the hydrogen ions (H+) immediately protonate another water molecule to form hydronium (H3O+). Although even electrolyte-free water shows some electrical conductivity, due to the self-ionization effect, a comparatively high voltage needs to be applied between the electrodes of the electrolysis system to achieve a flow current and thus start the electrolysis process. In the embodiment of FIG. 4, the electric supply circuit comprises a transformer 403 connected to a rectifier for supplying electric power as pulsed direct current to the electrodes 416, 418 of the electrolysis system. The transformer 403 is connected to the full-wave rectifier. In particular, the transformer comprises primary windings 404 and secondary windings 406. The secondary windings 406 are connected to the rectifier. In particular, the secondary windings are center tapped secondary windings connected to the rectifier. The rectifier comprises a first diode 408 connected to a first (positive) terminal of the secondary windings 406 of the transformer 403. The rectifier comprises a second diode 410 connected to a second (negative) terminal of the secondary windings 406 of the transformer 403. The first and second diodes 408, 410 are connected in parallel and face the same direction. In other words, both the first and second diodes 408, 410 are connected to the secondary windings 406 of the transformer 403 via their respective anode ends. The two diodes are connected to each other and an anode electrode 416 of the electrolysis system via their opposite cathode end. The cathode electrode 418 is connected to ground 420. As schematically shown in FIG. 4, an AC input waveform 402 will be stepped down in voltage by the transformer 403 and rectified by the full-wave rectifier thereafter. The result is a pulsed DC waveform 414, which is then applied across the electrodes of the electrolysis system. FIG. 5 shows a schematic flow chart of a method of generating graphite oxide and / or graphene oxide by electrolysis according to the present disclosure. In a first step 502, the method comprises providing an electrolysis system with a flow-through graphite anode-electrode. Such a flow-through anode-electrode may have a porosity that will allow the electrolyte water to permeate through the electrode. In a next step 504, water or electrolyte water is supplied to the electrodes of the electrolysis system 100, such system 100 described in FIG. 1. In some embodiments, the water supply to the electrodes may be electrolyte-free water, particularly purified water such as deionized water or distilled water. Once the system has been supplied with water or electrolyte water, electric power is supplied to the electrodes of the electrolysis system, thereby starting the electrolysis process. During the electrolysis, the water or electrolyte water supplied to the electrodes will partly be decomposed by the flow-through graphite anode electrode to provide oxygen. At the same time, parts of the reaction liquids supplied to the electrodes will penetrate the flow-through anode-electrode, thereby exfoliating some of the graphite from the flow-through electrode. It has been found that using electrolyte-free water, particularly purified water for the electrolysis process will enhance the amount of graphite being exfoliated from the flow-through electrode. As a result of the exfoliation process, a graphite solution will be obtained behind the porous graphite flow-through electrode structure. In another step (not shown), this graphite solution may be stored for further use. In one example, the reaction liquid may be removed from the solution to obtain high purity graphite, particularly in two-dimensional layers also known as graphene. 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. It will be appreciated that although, in the embodiments described above, a single control unit was mentioned for the control of various aspects of the electrolyser of the present disclosure, the electrolysis system may also include a plurality of control units controlling some of the aforementioned aspects and, preferably, communicating with each other. In some embodiments, the water or electrolyte water may contain chemicals to enhance the graphene oxide, so that when it is processed to form a 2D layer of carbon, it has been doped to have special properties.

Claims

228 Amended claims1. An electrolysis system for generating graphite oxide and / or graphene oxide and / or graphene, said system comprising:• a housing comprising a liquid chamber;• two electrodes for decomposition of water or electrolyte water, wherein at least an anode-electrode is a flow-through electrode comprising graphite;• a liquid supply for supplying water or electrolyte water to the liquid chamber.

2. The electrolysis system of Claim 1, wherein the liquid supply is configured for supplying electrolyte-free water.

3. The electrolysis system of Claim 2, wherein the electrolyte-free water is purified water.

4. The electrolysis system of any one of Claims 1 to 3, wherein the liquid chamber comprises a gap located between the two electrodes, wherein the gap has a width smaller than a Debye-length of purified water.

5. The electrolysis system of any one of Claims 1 to 4, wherein the graphite part of the flow-through electrode has a porosity that will allow the electrolyte water to permeate through said electrode.

6. The electrolysis system of any one of Claims 1 to 5, wherein both electrodes comprise graphite.

7. The electrolysis system of any one of Claims 1 to 6, wherein both electrodes are flow-through electrodes.

8. The electrolysis system of any one of Claims 1 to 7, comprising an electric supply circuit for supplying electric power to the electrodes.

9. The electrolysis system of Claim 8, wherein the electric supply circuit is configured to supply electric power at a voltage that enables current to flow through electrolyte-free water between the anode-electrode and the cathode-electrode.08 08 2210. The electrolysis system of Claim 8 or 9, wherein the electric supply circuit comprises a rectifier for supplying the electric power as a pulsed direct current11. The electrolysis system of Claim 10, wherein the electric supply circuit comprises a transformer comprising primary windings and center tapped secondary windings connected to the rectifier.

12. The electrolysis system of any one of Claims 1 to 11, comprising a control unit for controlling a pressure within the liquid chamber.

13. The electrolysis system of Claim 12, wherein the control unit is configured to control a pressure drop across the flow-through anode-electrode.

14. A method of generating graphite oxide and / or graphene oxide and / or graphene by electrolysis comprising:• supplying water or electrolyte water to electrodes of an electrolyser, said electrolyser comprising two electrodes, wherein at least an anodeelectrode is a flow-through electrode comprising graphite;• suppling electric power to the electrodes.

15. The method of Claim 14, comprising supplying electrolyte-free water to the electrodes.

16. The method of Claim 15, wherein the electrolyte free water comprises purified water.

17. The method of any one of Claims 14 to 17, wherein the flow-through electrode has a porosity that will allow the water or electrolyte water to permeate through the electrode.

18. The method of any one of Claims 14 to 17, comprising supplying the electric power at a voltage that enables current to flow through electrolyte-free water between the two electrodes.08 22co19. The method of any one of Claims 14 to 18, supplying the electric power as a pulsed direct current.

20. The method of any one of Claims 14 to 19, comprising supplying the water or electrolyte water to the electrodes at a pressure.

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