Patent Publication Number: US-2023136422-A1

Title: Advanced Commercial Electrolysis of Seawater to Produce Hydrogen

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the United States national phase of International Application PCT/AU2021/000032 filed Apr. 12, 2021, and claims priority to Australian Provisional Patent Application No. 2020901163 filed Apr. 12, 2020, the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     INCORPORATION BY REFERENCE 
     The following publications are referred to in the present application and their contents are hereby incorporated by reference in their entirety:
         Australian Patent 2008209322;   United Kingdom Patent GB2460000;   Chinese Patent ZL200880012716;   South African Patent 2011/04916;   Hong Kong Patent HK1137408; and   U.S. Pat. No. 10,316,416.       

     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to the production of hydrogen from seawater. 
     Description of Related Art 
     Hydrogen energy produced from hydrogen and has many uses such as fuel for transport or heating or as a way to store electricity. Hydrogen is an important part of a clean and secure energy future for most countries. 
     Hydrogen can be produced using a number of different processes. Thermochemical processes use heat and chemical reactions to release hydrogen from organic materials such as fossil fuels and biomass. Microorganisms such as bacteria and algae can produce hydrogen through biological processes. Alternatively, water can be split into hydrogen and oxygen using electrolysis or solar energy. 
     The present applicant has previously developed a process that involves the unipolar electrolysis of seawater to produce hydrogen (see, for example, Australian Patent 2008209322). Whilst this technology has been proven to work and hydrogen can be produced from seawater, it can also result in the concurrent production of oxygen and/or chlorine which can be problematic. 
     There is a need to provide an electrolytic system for the production of hydrogen from seawater that minimises the production of chlorine and/or oxygen. 
     SUMMARY OF THE INVENTION 
     According to a first aspect, there is provided an apparatus for electrolysing seawater to produce hydrogen, the apparatus comprising a unipolar electrolytic cell configured to operate in cathode-cathode mode and configured to reduce the production of chlorine and/or oxygen. 
     In certain embodiments, the apparatus is configured to reduce the production of chlorine and/or oxygen by reducing the voltage at the cathode and/or anode. 
     In certain embodiments, the apparatus comprises one or more resistors to reduce the voltage at the cathode and/or anode. 
     In certain embodiments, the apparatus comprises:
         a cathode cell comprising a cathode electrode and a cathode cell solution electrode;   an anode cell comprising an anode electrode and an anode cell solution electrode;   wherein cell gaps between the cathode electrode and a cathode cell solution electrode and the anode electrode and an anode cell solution electrode are set to reduce the voltage at the cathode and/or anode.       

     In certain embodiments, the apparatus comprises:
         multiple anode cells connected in series, each anode cell having a gap between electrodes; and   multiple cathode cells connected in series, each cathode cell having a gap between electrodes   wherein the gap between electrodes in the cathode cell is larger than the gap between electrodes in the anode cell.       

     In certain embodiments, the cathode cells and the anode cells are diaphragm-less electrolytic cells connected in cathode mode. 
     In certain embodiments, the cathode cells and the anode cells are fitted with low electrical resistance electrodes coated with at least one catalyst. 
     In certain embodiments, the apparatus comprises diaphragm-less electrolytic cells where there are more anode cells with smaller gaps between electrodes and less cathode cells with larger gaps between the electrodes. 
     In certain embodiments, the apparatus comprises five anode cells with electrode gaps of 4 mm and four cathode cells with electrode gaps of 6 mm 
     In certain embodiments, the electrodes of the diaphragm-less electrolytic system are made of high electrical conductivity material and coated with a protective coating and/or a catalyst coating. The high electrical conductivity material may be selected from the group consisting of copper and graphene. The catalyst coating may comprise Hastelloy 276c. The protective coating may comprise ruthenium/iridium metal or and oxide thereof. 
     In certain embodiments, the apparatus comprises a cathode cell and an anode cell and a membrane between the anode cell and the cathode cell, the membrane configured to allow only electrons to pass from cathode cell to the anode cell resulting in the cathode electrolyte becoming electrically negative while the anode electrolyte becoming electrically positive and further comprising another set of electrolytic cells through which the electrically negative cathode electrolyte and the electrically positive anode electrolyte can be passed to generate a current and produce hydrogen and oxygen. 
     In certain embodiments, the cathode-cathode mode comprises an electrical connection where the negative of a DC supply is connected to the cathode electrode, the cathode solution electrode connected to the anode electrode and the positive of the DC supply is connected to the anode solution electrode. 
     According to a second aspect, there is provided a process for producing hydrogen from seawater, the process comprising introducing seawater into an apparatus according to the first aspect and producing hydrogen therefrom. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure will be discussed with reference to the accompanying drawings wherein: 
         FIG.  1    is a schematic diagram of a prior art Unipolar electrolysis apparatus as described in, for example, Australian Patent 2008209322; 
         FIG.  2    is a schematic diagram of an electrolysis apparatus according to an embodiment of the present disclosure that can be used to produce hydrogen from seawater; 
         FIG.  3    is a schematic diagram of an electrolysis apparatus according to a further embodiment of the present disclosure that can be used to produce hydrogen from seawater; 
         FIG.  4    is a schematic diagram of an electrolysis apparatus according to an embodiment of the present disclosure that can be used for the commercial production of hydrogen from seawater; 
         FIG.  5    is a schematic diagram of an electrolysis apparatus according to a further embodiment of the present disclosure that can be used for the commercial production of hydrogen from seawater; and 
         FIGS.  6   (A-C) are schematic diagrams of an electrolysis apparatus according to an embodiment of the present disclosure that utilises a membrane cell and can be used for the commercial production of hydrogen from seawater. 
     
    
    
     In the following description, like reference characters designate like or corresponding parts throughout the figures. 
     DESCRIPTION OF THE INVENTION 
     The present applicant has been granted Australian Patent 2008209322, United Kingdom Patent GB2460000, Chinese Patent ZL200880012716, South African Patent 2011/04916 and Hong Kong Patent HK1137408 for a process that involves the Unipolar electrolysis of seawater to produce hydrogen. The apparatus disclosed in these patents is shown in  FIG.  1   . Briefly, the apparatus comprises a DC power supply  10  in electrical connection with a modulator  14 . The modulator is in electrical connection with a cathode cell  22  and an anode cell  38 . The cathode cell  22  comprises a cathode electrode  24  and a solution electrode  32 . The anode cell  38  comprises an anode electrode  36  and a solution electrode  34 . The anode cell  38  acts as a cathode. The components of the apparatus are connected by electrical wires  12 ,  16 ,  28  and  40 . Seawater  30  is introduced into each cell  22 ,  38  and hydrogen  18  and alkaline seawater  20  are produced at the cathode cell  22  and the anode cell  38 . 
     A problem with Unipolar electrolysis apparatus and process depicted in  FIG.  1    is that at the cathode cell  22 , if the cell voltage exceeds 0.828 volts, oxygen and chlorine may be produced and at the anode cell  38 , if the voltage exceeds 0.401 volts, oxygen and chlorine may be produced at the cathode cell  22 . This limitation in voltage reduces the capacity of the system to produce pure hydrogen  18  as shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Projection of voltage in the Unipolar electrolysis of seawater 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 Gap at Anode, mm 4.8675 
               
               
                   
                 Gap at Cathode, mm 10.0506 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Cell Voltage 
                 Anode Volts 
                 Cathode Volts 
                 Total Volts 
                 Overvoltage 
               
               
                   
               
               
                 1.229 
                 0.401 
                 0.828 
                 1.229 
                 0 
               
               
                 1.3 
                 0.424 
                 0.876 
                 1.3 
                 0.071 
               
               
                 1.4 
                 0.457 
                 0.943 
                 1.4 
                 0.171 
               
               
                 1.5 
                 0.489 
                 1.011 
                 1.5 
                 0.271 
               
               
                 1.6 
                 0.522 
                 1.078 
                 1.6 
                 0.371 
               
               
                 1.7 
                 0.555 
                 1.445 
                 1.7 
                 0.471 
               
               
                 1.8 
                 0.587 
                 1.213 
                 1.8 
                 0.571 
               
               
                 1.9 
                 0.620 
                 1.280 
                 1.9 
                 0.671 
               
               
                 2 
                 0.653 
                 1.347 
                 2 
                 0.771 
               
               
                 2.1 
                 0.685 
                 1.415 
                 2.1 
                 0.871 
               
               
                 2.2 
                 0.718 
                 1.482 
                 2.2 
                 0.971 
               
               
                 2.3 
                 0.750 
                 1.550 
                 2.3 
                 1.071 
               
               
                 2.4 
                 0.783 
                 1.617 
                 2.4 
                 1.171 
               
               
                 2.5 
                 0.816 
                 1.684 
                 2.5 
                 1.271 
               
               
                 2.6 
                 0.848 
                 1.752 
                 2.6 
                 1.371 
               
               
                 2.7 
                 0.881 
                 1.819 
                 2.7 
                 1.471 
               
               
                 2.8 
                 0.914 
                 1.886 
                 2.8 
                 1.571 
               
               
                 2.9 
                 0.946 
                 1.954 
                 2.9 
                 1.671 
               
               
                 3 
                 0.979 
                 2.021 
                 3 
                 1.771 
               
               
                   
               
            
           
         
       
     
     There is a need for apparatus and processes that will allow higher rates of production of pure hydrogen  18  from the electrolysis of seawater  30  by allowing a higher cell voltage without producing any substantial amounts of chlorine or oxygen. 
     Disclosed herein is an apparatus for electrolysing seawater  30  to produce hydrogen  18 . The apparatus comprises a unipolar electrolytic cell configured to operate in cathode-cathode mode and configured to reduce the production of chlorine and/or oxygen. 
     In certain embodiments of the present disclosure shown in  FIG.  2   , the apparatus comprises a resistor at the cathode or anode circuit to reduce the voltage at the cathode or anode and prevent chlorine or oxygen being produced. The apparatus comprises a DC power supply  10  in electrical connection with a modulator  14 . The modulator is in electrical connection with a cathode cell  22  and an anode cell  38 . The cathode cell  22  comprises a cathode electrode  24  and a solution electrode  32 . The anode cell  38  comprises an anode electrode  36  and a solution electrode  34 . The components of the apparatus are connected by electrical wires  12 ,  16 ,  28  and  40 . Hydrogen  18  is produced at the cathode cell  22  and the anode cell  38  in the same way as it is produced in the Unipolar electrolysis apparatus shown in  FIG.  1   . In the embodiment shown in  FIG.  2   , resistor  46  is positioned before the cathode cell  22  and resistor  48  is positioned before the anode call  38 . The resistors  46 ,  48  are able to reduce the voltage at the cathode  22  and the anode  38  respectively to minimise or prevent production of chlorine or oxygen at each cell. 
     In the embodiment shown in  FIG.  2    the cell voltage is 2.1 volts but the voltage across the cathode cell  22  is 0.828 volts with resistor  46  taking 0.222 volts based on a current of 100 amperes. At the anode cell  38 , resistor  48  takes 0.65 volts so that the cell voltage across the anode cell  38  is 0.401 volts. The cell gaps  50  and  52  at the cathode  22  and anode  38  respectively are 6 mm. 
     Resistors are inefficient as they consume power without producing hydrogen. Therefore, in certain other embodiments of the present disclosure, the cell gaps at the cathode and the anode are used to reduce the voltage at the cathode or anode and prevent chlorine or oxygen being produced. The voltage across a cell is directly proportional to the gap between the cathode or anode electrode and the corresponding solution electrode. In the prior Unipolar electrolysis apparatus shown in  FIG.  1    and described in, for example, Australian Patent 2008209322, the cell gap at the anode cell is 4.8675 mm and the cell gap at the cathode is 10.0506 mm. It will be appreciated that, as used herein, the term “cell gap” means the spacing between two electrodes in an electrolytic cell, such as the spacing between anode electrode  36  and anode cell solution electrode  34  in anode cell  38  or the spacing between cathode electrode  24  and cathode cell solution electrode  32  in cathode cell  22 . In embodiments of the present disclosure, the cell gaps  50  and  52  at the cathode  22  and anode  38  respectively are 6 mm. It will be appreciated that other cell gaps, such as about 4 mm, about 4.5 mm, about 5 mm, about 5.5 mm, about 6 mm, about 6.5 mm, about 7mm, about 7.5 mm or about 8 mm can be used. It will be appreciated that the best gap for the anode  36  and the cathode  24  electrodes for a particular apparatus can be determined empirically. 
     In certain other embodiments of the present disclosure, a reduction in total cell voltage is achieved without increasing the cell voltages of the anode and the cathode by installing cathode and anode cells in series. This allows a higher total cell voltage without increasing the cathode or anode cell voltage that may result in producing unwanted chlorine or oxygen. This embodiment is shown in  FIG.  3    which shows five anode cells  38  with cell gaps  52  of 4 mm and four cathode cells  22  with cell gaps  50  of 6 mm. As with  FIG.  2   , each anode cell  38  comprises an anode electrode  36  and a solution electrode  34  and each cathode cell  22  comprises a cathode electrode  24  and a solution electrode  32 . The cathode electrodes  24  can be any suitable electrode material such as Pt/Ir (90:10) coated on titanium mesh. The solution electrodes  32  can be any suitable material such as Ir/Ru or Mo/Co/Mn on titanium. The apparatus in  FIG.  3    also comprises a DC power supply  10  in electrical connection with a modulator  14  which, in turn, is in electrical connection with the cathode cells  22  and the anode cells  38 . The components of the apparatus are connected by electrical wires  12 ,  16 ,  28 ,  40  and  54 . 
     Seawater is pumped into each cell at 200 lpm via valves  56  and hydrogen  18  is produced at each cathode cell  22  and each anode cell  38 . 
     With a total cell voltage of  4  volts, the predicted voltage at the anode cells  38  is 0.36 volts while at the cathode cells  22  the predicted cell voltage is 0.545 volts. The predicted voltages are based on the total gaps  52  at the anode cells  38  and the total gaps  50  at the cathode cells  22 . Table 2 shows the cell voltages with the total cell voltage at 4 volts. 
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Voltage with multiple anode and cathode cells 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 Gap at Cathode, mm 6 
               
               
                   
                 Gap at Anode, mm 4 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Cell Voltage 
                 Anode Volts 
                 Cathode Volts 
                 Total Cell V 
               
               
                   
                   
               
               
                   
                 1.229 
                 0.559 
                 0.670 
                 1.229 
               
               
                   
                 1.3 
                 0.591 
                 0.709 
                 1.300 
               
               
                   
                 1.4 
                 0.636 
                 0.764 
                 1.400 
               
               
                   
                 1.5 
                 0.682 
                 0.818 
                 1.500 
               
               
                   
                 1.7 
                 0.773 
                 0.927 
                 1.700 
               
               
                   
                 1.8 
                 0.818 
                 0.982 
                 1.800 
               
               
                   
                 1.9 
                 0.864 
                 1.036 
                 1.900 
               
               
                   
                 2 
                 0.909 
                 1.091 
                 2.000 
               
               
                   
                 2.1 
                 0.955 
                 1.145 
                 2.100 
               
               
                   
                 2.2 
                 1.000 
                 1.200 
                 2.200 
               
               
                   
                 2.3 
                 1.045 
                 1.255 
                 2.300 
               
               
                   
                 2.4 
                 1.091 
                 1.309 
                 2.400 
               
               
                   
                 2.5 
                 1.136 
                 1.364 
                 2.500 
               
               
                   
                 2.6 
                 1.182 
                 1.418 
                 2.600 
               
               
                   
                 2.7 
                 1.227 
                 1.473 
                 2.700 
               
               
                   
                 2.8 
                 1.273 
                 1.527 
                 2.800 
               
               
                   
                 2.9 
                 1.318 
                 1.582 
                 2.900 
               
               
                   
                 4 
                 1.818 
                 2.182 
                 4.000 
               
               
                   
                   
               
               
                   
                 5 Anode and 4 Cathode Cells- no resistors 
               
            
           
         
       
     
     In certain embodiments, the electrode material is made from high electrical conductivity material such as copper or graphene. 
     An arrangement of cells in a commercial plant for electrolysing seawater and producing only pure hydrogen is shown in  FIG.  4   . This technology also produces alkaline seawater that can sequester carbon dioxide. This will assist carbon polluting plants like coal power plants and cement plants using coal or natural gas to sequester their carbon emissions. The apparatus shown in  FIG.  4    comprises three sets of cathode cells  22  and four sets of anode cells  38 . Each set of cathode cells  22  and anode cells  38  is electrically connected to a DC power supply  10  in electrical connection with a modulator  14  which, in turn, is in electrical connection with the cathode cells  22  and the anode cells  38 . In the embodiment illustrated in  FIG.  4    there are eight sets of cathode  22  and anode  38  cells. It will be appreciated that the number of sets of cathode  22  and anode  38  cells can be varied. 
     Seawater  30  is fed into the apparatus of  FIG.  4    via seawater pump  70 . The seawater passes through a filter  72  and into pump box  35 . From pump box  35  the seawater  30  passes via valve  56  and control panel  64  into the bottom of each cathode cell  22  and each anode cell  38 . Hydrogen  18  produced at each cell  22 ,  38  is removed and fed to separation tanks  74  where hydrogen gas is separated from alkaline seawater  20 . Hydrogen  18  is removed from each separation tank  74  by a vacuum pump  60  after which it is purified by passing it through moisture trap  62  and silica gel  79 . The purified hydrogen  18  then passes through a mass flow meter  66  and a % hydrogen meter  68 . 
     A further alternative version of the apparatus shown in  FIG.  4    is shown in  FIG.  5   . This version may be suitable for mounting on a truck or in a shipping container for example. It can be positioned near carbon emitters to demonstrate the production of hydrogen while sequestering their carbon emissions. 
     Again, seawater is fed into the apparatus of  FIG.  5    via seawater pump  70  placed in the ocean  31 . The seawater  30  passes through a screen  83  and into pump box  35  where raw filtered seawater is stored. Excess seawater  33  is allowed to drain away. From pump box  35  the seawater passes via valve  56  into the bottom of each cathode cell  22  and each anode cell  38 . Flow of seawater is controlled by valves  89  and  92 . Hydrogen  18  produced at each cell is removed and flow is controlled by ball valves  80  Alkaline seawater  20  is also removed using ball valves  80 . Pressure valves  82  and Maric valves  84  at 150 lpm are also used to control flow of hydrogen. The pH and Cl content are measured using pH meter  88  and chlorine meter  86  respectively. The hydrogen  18  gas is then fed to separation tank  74  where it is separated from alkaline seawater  20 . Hydrogen  18  is removed from each separation tank  74  by passing an inert gas  76  such as nitrogen through the separation tank  74 . A baffle  78  is used to prevent egress of alkaline seawater  20  from the tank and into the hydrogen off take lines. The hydrogen  18  produced is then removed by a vacuum pump  60  after which it is purified by passing it through moisture trap  62  and dessicant  96 . Gas flow at this point is controlled using valves  94 . The purified hydrogen  18  then passes through a % hydrogen meter  68  and a mass flow meter  66 . The system is powered by a  50  KVA diesel generator  58 . 
     In this embodiment, the cathode electrodes and anode electrodes are copper mesh coated with Hastelloy 276c. The solution electrodes are plate copper or graphene coated with ruthenium-iridium alloy or oxides. 
     To achieve higher hydrogen generation capacity, the current needs to be increased and this requires an increase in the cell voltage. With the diaphragm-less cells described in the above embodiments, increasing the cell voltage above a certain point may result in the production of oxygen and chlorine in the same cell where the hydrogen is produced. To avoid this, membrane type cells as described in U.S. Pat. No. 10,316,416 can be used but instead of an alkaline electrolyte at the anode cell and acid electrolyte at the cathode cell, only alkaline seawater is passed through the anode cell and the cathode cell. The electrodes and the membrane are made of a conductive material such as copper or graphene coated with a catalyst that also acts as protection against corrosion. The conductive membrane allows only electrons to pass so that hydroxide ions accumulate at the cathode and H +  ions accumulate at the anode. Thus, the seawater exiting the cathode cells is electrically negative while the seawater exiting the anode cells is electrically positive. When these seawaters are passed through another set of neutralizing cells, the electrolytes are neutralised and current flows and, according to Faraday, another lot of oxygen and hydrogen are produced. 
     As shown in  FIG.  6 (A) , in membrane cell seawater electrolysis, the seawater is alkaline In this embodiment, the apparatus comprises a cathode cell  22  and an anode cell  38  separated by a membrane  130 . The overall cell potential E 0 =1.229 volts, the anode cell  38  potential E 0 =0.401 volts and the cathode cell  22  potential E 0 =0.828 volts. Hydrogen  18  is produced at the cathode cell  22  and hydroxide ions build up while oxygen  104  is produced at the anode cell  38  and H +  ions build up. The anolyte becomes positive whilst the catholyte becomes negative. 
     After treatment in the charging cells, the electrolytes are de-gassed and then fed to neutralising cells as shown in  FIG.  6 (B) . In the neutralising cell, the electrolyte  118  is positive whilst the electrolyte  120  is negative. Current flows according to Faraday and more hydrogen  18  and oxygen  104  are produced. 
     A system comprising charging cells of  FIG.  6 (A)  and neutralising cells of  FIG.  6 (B)  is shown in  FIG.  6 (C) . Seawater  30  is fed into charging cells comprising anode cells  110  and cathode cells  112 . The anode cells  110  and cathode cells  112  are electrically connected to a DC power supply  10 . Oxygen  104  generated in the anode cells  110  is separated at oxygen off take  108  whilst hydrogen  18  generated in the cathode cells  112  is separated at hydrogen off take  114 . The anolyte  118  and the catholyte  120  then pass to short circuited neutralising cells comprising anode cell  106  and cathode cell  116 . Hydrogen  18  is produced in anode cell  106  and oxygen  104  is produced in cathode cell  116 . Waste seawater  30  is removed from each cell. 
     The apparatus and processes described herein can be used for the commercial production of pure hydrogen from seawater that will be a major boost in the use of hydrogen to replace carbon fuels. It will allow hydrogen to be produced in many parts of the world so long as there is seawater available. 
     It will be understood that the terms “comprise” and “include” and any of their derivatives (eg comprises, comprising, includes, including) as used in this specification is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied 
     The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. 
     It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims