Patent Publication Number: US-2023143168-A1

Title: Direct Coupling Device for Generating Hydrogen from Concentrated Sunlight

Description:
The invention is a device to collect and concentrate sunlight, convert concentrated sunlight into electrical and thermal energy and use this energy to power a single proton membrane water electrolyser with several individualized anodic and cathodic catalyst coated zones, with direct coupling to generate hydrogen gas with better performance and service life. 
     STATE OF THE ART 
     The Chinese patent application CN 105483745 concerns a concentrated solar energy module and an electrolysis hydrogen production module, however, the application we intend to protect differs substantially from the Chinese patent application in that it is a single direct coupling device, which produces hydrogen from sunlight and water and only uses liquid water avoiding the use of water vapour. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG.  1    illustrates the operating concept of the device, showing that sunlight is collected and concentrated at a factor of 200× or more using a Fresnel lens  30 , for the direct coupling device  31 , comprised of a solar concentrator  32  and a water electrolyser  33 . 
     The sunlight is further concentrated at a factor of 1× or more using the Solar Concentrator  32 , which converts the concentrated sunlight into electrical and thermal energy, and which also transfers the energy to the water electrolyser  33 , where thermal energy raises the temperature of the water circulating through the water electrolyser  33  and where electrical energy feeds the electrochemical electrolysis of the water, resulting in the generation of hydrogen and oxygen. 
     The direct coupling device  31  comprises a proton exchange membrane  2 , such as Nafion® or another ionomer, copolymer or polymer mixture, with several anodic individualized zones ( 6 ) coated with catalyst on one side of the membrane suitable to facilitate the oxidation of water, and several cathodic individualized zones ( 12 ) coated with catalyst on the opposite side suitable to facilitate/allow the reduction of protons to hydrogen gas, several cathode single-polar plates (UPP)  3  and several anode UPPs  5 , each with a pair of cathode and anode UPPs enclosing the proton exchange membrane  2  and adjacent to the individualized areas coated with catalyst  12  and  6  on the cathode side and the anode side respectively. 
     The direct coupling device  31  also comprises several regeneration electrodes  1 , enclosing the proton exchange membrane  2  and arranged towards the edge of the individualized zones coated with catalyst  6  and  12 , so that they are adjacent to the coated zones on both sides of the proton exchange membrane  2 , several floating flow guide plates  7  on both sides, enclosing the UPPs  5  and  3  and the proton exchange membrane  2  between them, several elastic compression elements  8  on both sides, enclosing the flow guide plates  7 , the UPPs  5  and  3  and the proton exchange membrane  2  between them. 
     The device also has a casing consisting of an upper part  9  and a lower part  10 , sealed together and enclosing the elastic compression elements  8 , the floating flow guide plates  7 , the UPPs  5  and  3 , the regeneration electrodes  1  and the proton exchange membrane  2  between them, a source of electrical and thermal energy and the concentrator converter  32  connected to the top  9  of the casing. 
     As illustrated in  FIG.  2   , the concentrator converter  32  has an optical concentration element  15  glued to a photovoltaic cell  14  coupled with a heat exchanger  13 . The optical concentration element  15  is made of glass with suitable optical composition, such as borosilicate glass which, by refraction and/or total internal reflection, redirects and further concentrates the sunlight falling on its upper surface in a multiple junction type photovoltaic cell  14 , such as a triple-junction structure of GaInP/GaInAs/Ge or similar high-efficiency solar cell. The solar energy that is not directly converted into electrical energy by photovoltaic cell  14  is absorbed as thermal energy by the heat exchanger  13 , made of an aluminium, copper or copper alloy, and which has several closed channels where water can circulate and be heated by the thermal energy. 
     The casing, which consists of an upper part  9  and a lower part  10 , provides mechanical support for the other parts of the water electrolyser  33 . The casing is typically made of a thermoplastic or thermoset polymer, with or without reinforcing additives or other similar material with appropriate electrical insulation properties and chemical and mechanical resistance. 
     The elastic compression element  8  can be made of, among other materials, a polymer material, a metal, an elastomer foam, or other materials with a suitable elasticity module, typically in the shape of a solid rectangular block, but which may also be hollow and may also include round or rectangular holes. 
     The floating flow guide plates  7  are typically made of a polymer, or polymer mixture, or any other suitable rigid material that is not electrically conductive, including metal alloys coated with electrically insulating layers. There are several open channels on their main surface facing the anode  5  or cathode  3  UPPs respectively. When assembled, and by the action of the elastic compression elements  8 , the floating flow guide plates  7  press against the main cooperating surfaces of the single-polar plates  5  and  3  to allow the inlet of water and outlet of water and oxygen, and the outlet water and hydrogen respectively. The elastic compression elements  8  also provide the necessary contact force to allow close contact between the UPPs  5  and  3  and their individualized zones coated with catalyst  6  and  12  so that the electrical contact resistance between them can be kept to a minimum, thus lowering the operating voltage of the electrolysis reaction. 
     Anode  5  UPPs are typically made of titanium or a titanium alloy, with several round or rectangular holes, arranged on their main surface, serving as a combination of a gas diffusion layer and a current collector. Anode  5  UPPs are typically coated with a thin film of platinum or a platinum alloy. 
     Cathode  3  UPPs are typically made of a stainless-steel alloy with several round or rectangular holes, arranged on their main surface, serving as a combination of a gas diffusion layer and a current collector, usually with a thin coating of gold. 
     Regarding  FIG.  3   , it can be seen that the cathode UPPs  3  are arranged side by side against the proton exchange membrane  2 , with some space separating them from each other and the regeneration electrodes  1 , so that they are all physically separated from each other. 
       FIG.  4    illustrates the electrical circuitry that conducts the electrolysis reaction. A cathode UPP ( 3 ) in contact with an individualized zone coated with a catalyst ( 12 ) of the proton exchange membrane  2  and facing an anode UPP  5  in contact with an individualized zone coated with catalyst  6  constitutes an electrochemical cell ( 4 ), the cathode UPP  3  is negatively polarized and the anode UPP  5  is positively polarized. Each electrochemical cell ( 4 ) is connected in series to the next, as illustrated in the circuit diagram, and all share the same proton exchange membrane  2 . 
     The Vd voltage needed to ensure the electrolysis of the water is provided by the concentrator converter  32 , illustrated in  FIG.  2   . 
     The direct coupling device  31  should use very pure water free of ionic contaminants. The quality of deionized water is generally measured by its resistivity, which should be as high as possible (up to &gt;18 MΩ cm) to avoid contaminating the proton exchange membrane with unwanted cations during operation and that accumulate over time impairing the electrolyser&#39;s performance and lifespan. However, in practice, and for economic reasons, it is desirable to use less pure water with resistivity &gt;4 MΩ cm. To allow the use of less pure water, it is necessary to greatly reduce the accumulation of ionic contaminants in the proton exchange membrane and therefore the water electrolyser  33 , as illustrated in  FIG.  2   , has several regeneration electrodes  1 , enclosing the proton exchange membrane  2 . 
     Concerning  FIG.  5   , when the device is not in operation, for example at night or if it is overcast, the control voltage for electrolysis is V =0V. Under these conditions, an external circuit connected to regeneration electrodes  1  provides a Vr voltage of about 2 to 25 V, thereby establishing an electrical field that causes the cations accumulated on the proton exchange membrane  2  to move towards the enclosed zone between the negatively charged regeneration electrodes and out of the enclosed zones between the UPPs, thereby removing contamination in the active zones of the electrolyser and significantly extending the life of the proton exchange membrane  2 . 
     This invention also has a method for generating hydrogen by the direct coupling device  31  with the following steps:
         establish the water supply circuit for electrolysis, where the flow enters the heat exchanger  13 , exiting towards the water inlet from the top of the casing  9 , through which it enters, to be distributed on the floating flow guide plates  7  to bathe the anode UPPs  5 , the regeneration electrodes  1 , the catalyst coated areas  6  and the proton exchange membrane  2 ;   establish the hydrogen and water sampling circuit, in which a flow of hydrogen and water is led out of the cavity at the bottom of the liner  10  towards a suitable container;   point the direct coupling device  31  towards the sun to capture the electrical and thermal energy needed to sustain the electrolysis of the water;   close the electrical circuit to polarize the UPP  3  and  5  with the operating voltage Vd supplied by the photovoltaic cell  14 , initiating the electrolysis of the water, which was heated during its passage through the heat exchanger  13 ;   keep the assembly pointed at the sun as mentioned in step ( 3 ) for as long as the hydrogen generation is desired;       

     When no more hydrogen is required, stop the production by no longer pointing the assembly at the sun as referred to in step ( 3 ) and opening the electric circuit referred to in step ( 4 ). 
     Carry out the regeneration of the active zones of the proton exchange membrane  2  by closing the external circuit connecting the source of a voltage Vr to the regeneration electrodes  1  periodically at appropriate intervals and for an appropriate time when the production of hydrogen is interrupted (or it is not possible to produce directly from solar energy, especially at night or when it is overcast). 
     Figure Key 
       1 —Regeneration electrodes
 
 2 —Proton exchange membrane
 
 3 —Single-polar cathode plate (UPP)
 
 4 —Electrochemical cell
 
 5 —Single-polar anode plate (UPP)
 
 6 —Individualized anodic zone coated with a catalyst
 
 7 —Floating flow guide plate
 
 8 —Elastic compression element
 
 9 —Upper part of the casing
 
 10 —Lower part of the casing
 
 12 —Individualized cathodic area coated with a catalyst
 
 13 —Heat exchanger
 
 14 —Photovoltaic cell
 
 15 —Optical concentration element
 
 31 —Direct coupling device
 
 32 —concentrator converter
 
 33 —water electrolyser