Patent Publication Number: US-2010112396-A1

Title: Field hydrogen generation system

Description:
RELATED APPLICATION 
     This application claims priority of U.S. Provisional patent application Ser. No. 60/909,028 filed Mar. 30, 2007, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention in general relates to a system and process for hydrogen generation and in particular to a system and process for generation of hydrogen for temporary installations or usage remote from infrastructure. 
     BACKGROUND OF THE INVENTION 
     An impediment to the usage of hydrogen as a chemical fuel is the logistics of delivery to a point of usage. Part of the logistics difficulties associated with the use of hydrogen as a chemical fuel is a low energy density per volume, as well as safety concerns associated with the explosive nature of hydrogen. By way of example, hydrogen gas pressurized to 5000 pounds per square inch still requires more than 10 volume equivalents relative to typical aviation jet fuel. This low energy density per volume is exacerbated by concern about a small leak and a stray spark igniting hydrogen in transit whether in a pipeline or pressurized cylinder. 
     Efforts to address the logistics problems of hydrogen transport have included on-site reforming of a fuel feedstock such as methane, ammonia, and gasoline. Unfortunately, on-site hydrogen production with reforming increases the logistics burden in requiring not only fuel feedstock but also electricity, other gases, and utilities in general. An alternative to reforming is electrolysis which while able to form hydrogen from water nonetheless requires considerable inputs of electrical energy that are obtained from line power or inside electrical generation which again increases the logistics burden. As a result of logistics problems associated with hydrogen, this otherwise attractive fuel remains an unattractive option for remote usage from transportation and/or utility infrastructure. 
     Thus, there exists a need for system to generate hydrogen at a site of field usage. 
     SUMMARY OF THE INVENTION 
     A field hydrogen generation system. Includes a flexible housing transparent to visible light and a photoelectrochemical cell adapted to be received within a volume of the housing. A quantity of feedstock liquid within the housing is in contact with said photoelectrochemical cell. A conduit is in fluid communication between the volume of the housing and a hydrogen collection vessel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of an inventive field hydrogen generation system according to the present invention inclusive of several optional components; and 
         FIG. 2  is a schematic of an alternate flexible housing adapted to receive a photoelectrochemical hydrolysis cell in which hydrogen generation is spatially distant from oxygen generation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention has utility in generating hydrogen with a compact and highly transportable system that operates independent of transportation and utility infrastructure. A photoelectrochemical cell (PEC) capable of generating hydrogen from a feedstock such as water, ammonia, and organic compounds inclusive of aliphatics is provided with dimensions suitable to insert within the volume of a flexible housing transparent to visible light. Upon enclosing the PEC in the housing with a quantity of feedstock and exposing the PEC to sunlight, hydrogen is generated. The hydrogen is conveyed to a hydrogen storage vessel by way of a conduit in fluid communication between the interior volume of the housing and the vessel. Since the PEC cell is thin and the flexible housing in the form of a plastic bag is also compact and lightweight, the footprint of an inventive hydrogen generation system for transport into the field is quite small. In instances where the PEC feedstock is water, the water can be transported into the field or collected in the field. The inventive system is particularly well suited in instances where a mobile hydrogen generation source is needed remote from logistical support and is particularly well suited for military field operations, camping, power generation for remote villages and communities, disaster relief, and lunar exploration. 
     Referring now to  FIG. 1 , a schematic of an inventive system is depicted generally at  10 . The system for field hydrogen generation  10  includes a photoelectrochemical cell (PEC) that when in contact with a feedstock upon exposure to a suitable wavelength of light creates a charge that in turn performs electrochemistry on the feedstock so as to produce hydrogen gas. It is appreciated that while one electrode of the PEC generates hydrogen, the other counter electrode generates an oxidation product in the form of a liquid species or gaseous species. Preferably, the PEC includes a light harvester, a nanocrystalline semiconductor that illustratively includes II-VI semiconductors such as cadmium selenide or cadmium sulfide; III-V semiconductors such as binary, ternary, and quaternary materials of gallium arsenide, gallium aluminum arsenide, gallium aluminum indium arsenide; IV semiconductors such as silicon and doped germanium; transition metal oxides and chalcogenides such as titanium dioxide, tungsten oxide, mixed metal oxides containing two or more metals, mixed metal sulfides, mixed metal selenides, and mixed metal sulfides-selenides. Most preferably, the PEC  12  is of a type disclosed in U.S. Pat. Nos. 6,060,026 and 6,361,660. It is appreciated that bulk thin films of the above-detailed semiconductors are also operative herein to harvest solar photons to generate conductive electrons and holes with sufficient energy to produce hydrogen gas. The PEC  12  in addition to a light harvester also includes a cathode electrode and an anode electrode. The PEC  12  regardless of form or composition is provided with a top surface that upon exposure to sunlight generates conductive electrons and holes which are conveyed effectively to one of the two electrodes in contact with a feedstock  14  so as to induce an electrochemical reaction with the feedstock. The feedstock  14  is preferably water, yet it is appreciated that other conventional feedstocks are readily electrolyzed based on conventional chemistries. In addition to water, a feedstock  14  illustratively includes aqueous ammonia and organic compounds. 
     The flexible housing  16  has a top layer  18  that is transparent to the visible light portion of the solar spectrum as denoted by h v. The housing  16  includes a backing layer  20  that is sealed along edges  22  to define a volume within V dimensioned to receive the PEC  12 . The backing layer  20  is optionally formed of a different material than the upper layer  18  and is illustratively of a greater thickness, opaque, compositionally different, or includes a reflective mirrored coating  24 . A conduit  26  is provided in the housing  16  to allow hydrogen gas and counter electrode generated gases to exit the housing  16 . Optionally, the housing  16  is provided with a hydrogen-tight and feedstock-tight reclosable seal  28  such as a ribbon fastener. While the housing  16  is detailed as well suited to surround a PEC  12  in contact with feedstock  14  to generate hydrogen while resting on a level planar substrate S, it is appreciated that the placement of a nonlevel substrate will cause a liquid feedstock  14  to flow to the lowest portion of the housing  16  thereby potentially leaving a portion of the PEC  12  out of contact with feedstock  14  and effectively reducing the surface area of top surface  13  of PEC  12  generating hydrogen. Optionally, to account for a nonlevel surface S, a leveling chamber  30  is provided. While the leveling chamber  30  is depicted as being affixed to backing layer  20 , it is appreciated that a leveling chamber  30  is also provided as an article separate from housing  16 . The leveling chamber  30  is filled with a material capable of flowing to level feedstock  14  so as to preferably completely cover PEC  12 . A fill for leveling chamber  30  illustratively includes air, sand, polymeric beads such as expanded polystyrene, and flowable gels. Optionally, leveling chamber  30  includes a sealable port  32  so as to allow for adjustment of the quantity of fill  31  within the leveling chamber  30 . 
     The conduit  26  extends to a hydrogen collection vessel  34 . Preferably, a one-way check valve  36  is provided intermediate between the collection vessel  34  and the conduit  26  to prevent backflow of hydrogen into the volume V. Typically, duplicate PECs contained within housings are provided to simultaneously feed the collection vessel  34  with a duplicate unit  11  denoted with primed reference numerals relative to unit  11 . The hydrogen collection vessel  34  can be rigid or flexible and is contemplated to be maintained at a low pressure of from 1 to 10 atmospheres. A conduit  40  interconnects the vessel  34  a compressor  38  that functions to increase the pressure of the hydrogen and a possible counter electrode gas, if present in vessel  34 . Optionally, a separator  42  is provided in line with the compressor  38  that is selectively permeable to either the counter electrode gas or hydrogen to create a counter electrode waste gas stream and a hydrogen enriched gas stream  46  with the hydrogen enriched gas stream  46  optionally being passed through a second compressor  50  before entering hydrogen storage  52 . It is appreciated that the hydrogen storage  52  can be in the form of a low pressure tank of less than 200 psi, a high pressure tank of above 200 psi, or a solid hydrogen storage substance. Optionally, a portion of the hydrogen produced is used to generate electricity with a generator  54 , the generator being a fuel cell, turbine, or piston-driven device. The electricity produced by the generator  54  is used to power the compressors  38  and  50 , if present, as well as the separator  42 , if present. Hydrogen from within the hydrogen storage  52  and/or electricity produced by the generator  54 , or a combination thereof, are provided to a consumptive device such as portable electronics or a vehicle. An electrical plug complementary to the electricity consumptive device is preferably provided to facilitate charge transfer. In a simplified embodiment where the hydrogen collection vessel  34  contains hydrogen and oxygen in a stoichiometric ratio of 2:1, this highly explosive mixture is drawn by a compressor on board the end use consumer vehicle or turbine directly into consumer storage or usage. 
     Referring now to  FIG. 2  where like numerals correspond to those detailed with respect to  FIG. 1 , a unit  61  is provided that includes a PEC  64  having spatially separated cathode and anode sections  66  and  68 , respectively. The cathode and anode sections  66  and  68  are electrically coupled together. The housing  70  has a backing layer  20  and an upper layer  72 . The upper layer  72  creates a cathode volume C with the backing layer  20  in fluid communication with conduit  26  for the passage of hydrogen to a hydrogen collection vessel  34  and an anodic volume A from which the counter ion evolved gas is vented to the atmosphere through valve  74 . As a result, hydrogen collection vessel  36  only contains hydrogen thereby simplifying subsequent handling and obviating the need for a separator  42  although one is still optionally used in instances where a higher degree of hydrogen purity is desired. 
     A process for generating hydrogen in the field includes unpacking a unit  11  and filling the housing  16  with feedstock so as to contact the top surface of the PEC  13  or otherwise contact the PEC electrodes. It is appreciated that filling a bladder with feedstock and coupling that bladder to conduits  26  and  26 ′ provides an efficient process for filling multiple housings  16  and  16 ′ simultaneously. The conduits  26  and  26 ′ are then connected to hydrogen collection vessel  34  and upon photons passing through the upper layer  18  and striking the top surface  13  hydrogen is generated that passes into the collection vessel  34 . In instances where the surface on which housing  16  is laid is not level, the leveling chamber  30  is partially filled to self-level the feedstock  14 . Closure  28  is alternately used to charge the volume V with feedstock  14 . Closure  28  is also used to insert PEC  12  that has not been transported within the housing  16 . With exposure to sunlight hydrogen is collected, optionally separated from counter electrode gases and stored for later use or used directly to produce electricity or service a consumer. 
     The present invention allows for a palletized or otherwise small weight and volume hydrogen generation system to be airlifted or carried to a remote location and set up with minimal effort to provide a continual source of hydrogen so long as sunlight and feedstock are available. In instances where the feedstock is water, beyond an initial charge of water delivered with the system, subsequent water requirements can be provided through using the hydrogen so generated to operate a condenser which while lowering the overall energy output of the system renders it independent of a logistics drain and requires only replacement parts and sunlight to operate indefinitely. As a result, a unit in the field is able to establish a forward fueling station in advance of a party advancing to join them and in need of hydrogen or electricity produced therefrom. 
     Patent documents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains. These documents and publications are incorporated herein by reference to the same extent as if each individual document or publication was specifically and individually incorporated herein by reference. 
     The foregoing description is illustrative of particular embodiments of the invention, but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof, are intended to define the scope of the invention.