Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
  • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/70—Assemblies comprising two or more cells
  • C25B9/73—Assemblies comprising two or more cells of the filter-press type
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0017—Non-aqueous electrolytes
  • H01M2300/0065—Solid electrolytes
  • H01M2300/0082—Organic polymers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• This invention relates generally to proton exchange membrane electrochemical cells.
• this invention relates to a screen assembly that sustains the integrity and structure of the proton exchange membrane, facilitating operation at high pressure and high fluid flow rates with increased reliability.
• Electrochemical cells are energy conversion devices, usually classified as either electrolysis cells or fuel cells, including electrolysis cells having a hydrogen water feed.
• a proton exchange membrane electrolysis cell functions as a hydrogen generator by electrolytically decomposing water to produce hydrogen and oxygen gases.
• process water 102 is reacted at oxygen electrode (anode) 103 to form oxygen gas 104, electrons, and hydrogen ions (protons) 105.
• oxygen gas 104 and a portion of the process water 102' exit cell 101, while protons 105 and water 102" migrate across proton exchange membrane 108 to cathode 107 where hydrogen gas 109, is formed.
• the typical electrochemical cell includes a number of individual cells arranged in a stack with fluid, typically water, forced through the cells at high pressures.
• the cells within the stack are sequentially arranged including a cathode, a proton exchange membrane, and an anode.
• the cathode/membrane/anode assemblies (hereinafter “membrane assembly”) are supported on either side by packs of screen or expanded metal which are in turn surrounded by cell frames and separator plates to form reaction chambers and to seal fluids therein.
• the screen packs establish flow fields within the reaction chambers to facilitate fluid movement and membrane hydration, and to provide mechanical support for the membrane and a means of transporting electrons to and from electrodes.
• the screen packs support the membrane assembly.
• the membrane is typically only about 0.002 - 0.012 inches in thickness, when hydrated, with the electrodes being thin structures (less than about 0.002 inches) of high surface area noble metals pressed or bonded to either side of the membrane and electrically connected to a power source. When properly supported, the membrane serves as a rugged barrier between the hydrogen and oxygen gases.
• the screen packs positioned on both sides of the membrane against the electrodes, impart structural integrity to the membrane assembly. Due to the high pressure differential that exists in an operating cell, however, the membrane and electrode on the low pressure side can be forced into the screen packs.
• existing screen packs comprise multiple layers of screen material formed from 0.007 inches (0.178 millimeters (mm)) - 0.010 inches (0.254 mm) thick metal strands having pattern openings of 0.125 inches (3.17 mm) by 0.053 inches (1.35 mm) to 0.071 inches (1.80 mm) (commonly known as 3/0 screen).
• a pressure differential of about 390 psi forces the membrane assembly into the openings of the first layer of screen on the low pressure side of the cell.
• Carlson et al. teaches the use of a porous plate to attain the desired mass flow characteristics and support of the membrane assembly.
• the porous plate of Carlson et al. allows water access to the electrode, solving the problem of the oxygen blockage of the openings.
• this plate is expensive to produce, difficult to attain repeatability with respect to uniform thickness, porosity, mechanical properties, etc., it is not a viable alternative for a relatively low cost electrochemical system or for a mass production part.
• the electrochemical cell screen assembly comprises: a first screen layer having openings and a second screen layer having openings larger than the first screen layer openings, with the second screen disposed parallel to and in contact with the first screen layer.
• the electrochemical cell of the present invention comprises: an electrolyte membrane; an electrode disposed on each side of the membrane; and a screen assembly disposed adjacent to each of the electrodes, with at least one of the screen assemblies having a first screen layer with openings and a second layer with openings larger than the first layer openings, wherein the second screen layer is disposed parallel to and in contact with the first screen layer.
• FIGURE 1 is a schematic diagram of a prior art electrochemical cell showing an electrochemical reaction
• FIGURE 2 is a cross sectional view of an electrochemical cell showing the relationship of the cell components
• FIGURE 3 is a plan view of a screen assembly of the present invention.
• FIGURE 4 is a partial cross section of an isometric view of a screen assembly according to the present invention shown supporting a membrane.
• FIGURE 5 is a partial cross section of an isometric view of a screen assembly according to the present invention shown supporting a membrane.
• the figures are meant to further illustrate the present invention and not to limit the scope thereof.
• the screen pack of the present invention comprises multilayers of screens assembled such that the layer adjacent the electrode has a smaller opening and/or strand size to provide improved support to the membrane.
• cell 1 includes proton exchange membrane 8 having an anode 3 and a cathode 7 bonded to either side, with the periphery of membrane 3 installed between a pair of cell frames 21.
• Oxygen screen pack 43 is installed inside the active area of the frame assembly between anode 3 and oxygen separator plate 45, while hydrogen screen pack 22 is installed inside of cell frame 21 between hydrogen separator plate 24 and cathode 7.
• process water 2 enters inlet port 25 and a portion of the water is diverted into oxygen screen pack 43.
• a portion of the water 2 not diverted into screen pack 43 continues along conduit 25 formed by axially aligned holes in the components comprising the stack, and enters subsequent cells in the cell stack (not shown) positioned outside of the cell 1.
• the portion of process water 2 diverted through screen pack 43 contacts anode 3 where the water electrochemically converts to oxygen gas and protons.
• the generation of gases in the cell combine with external pressure regulation produces a large pressure differential between the oxygen side and the hydrogen side of the cell. This pressure differential forces membrane 8 and cathode 7 against the opposing screen pack. It should be noted that the direction of the pressure differential, i.e. greater or lower pressure on the cathode side, is dependent upon the application requirements of the electrochemical system.
• a first screen layer 50 and a second screen layer 51 comprise the first two layers of hydrogen screen pack 22.
• Screen layers 50, 51 are preferably comprised of planar screen layers preferably having elongated, such as diamond shaped, openings 52, 53 formed by strands 54, 55 respectively.
• the openings are placed such that the openings and opening in subsequent screens are not in phase or oriented in the same direction, with placing openings 52 of screen layer 50 substantially orthogonal to the diamond shaped openings screen layer 51 such that diamond shaped openings 52 are partially obstructed by strand 55 especially preferred.
• the preferred shape of the openings is dependent upon mass flow characteristics and the structural integrity attained with a screen pack having those openings.
• Diamond shaped openings are shown by way of example, however, other shaped openings are advantageously contemplated by the present invention, such as ovals, circles, and hexagons, among others, with elongated shaped openings preferred. Although diamond openings in adjacent screen layers are preferably oriented orthogonally to one another, other orientations are possible. Furthermore, as is illustrated in FIGURE 5, the openings of the various screen layers 50, 51' can have a different geometry, i.e. diamond and square, respectively, with preferred size and geometry of the screen layers dependent upon mass flow characteristics.
• FIGURES 4 and 5 in conjunction with FIGURE 2, illustrates the ability of the membrane support device to provide structure and integrity to the membrane 8 during operation.
• the pressure differential between the cell halves during operation causes cathode 7 and membrane 8 to press against strands 54 of first screen layer 50, deflected out of plane into diamond shaped perforation 52, where the displacement is arrested by strands 55 of second screen layer 51 (51').
• Screen layer 51 (51') supports screen layer 50, while subsequent layers (not shown) support both screen layers 50 and 51 (51').
• the preferred number of screen layers is dependent upon the side of the cell in which the screen pack will be employed, the pressure differential of the cell, the size of the openings formed by the strands, and the desired mass flow characteristics.
• the low pressure side of the cell has screens 50, 51 (51') and subsequent screens, totaling 9 screens
• the high pressure side of the cell has screens 50, 51 (51') and subsequent screens, totaling 4 screens.
• the screen of subsequent layers is also preferably placed in a pattern having the openings of subsequent layers placed orthogonal to preceding layers.
• the screen layers can be a perforated sheet or a woven mesh, formed from a metal plate or strands or other electrically conductive material.
• the screens are formed from a metal which is inert in the electrochemical cell environment, electrically conductive, and capable of providing sufficient structural integrity to the membrane assembly, such as niobium, zirconium, titanium, or tantalum, among others, and alloys thereof. It is anticipated that the screen can be comprised of expanded metal, stamped sheet, chemically milled sheet, woven screen or any commercially viable embodiment that yields a substantially planar screen member.
• the screens of the present invention preferably employ at least a first thin layer to prevent cutting and rupture of the membrane assembly.
• This thin screen has a strand thickness (t) below about 0.005 inches (0.127 mm) with below 0.004 inches (0.102 mm) preferred and about 0.002 inches (0.051 mm) to about 0.0035 inches (0.089 mm) especially preferred.
• This thin screen layer supports the membrane assembly, preventing extrusion into the screen pack and inhibiting cutting of the membrane assembly by the strands of the screen.
• Subsequent screen layers can have a similar strand thickness, with a strand thickness of about 0.005 inches or greater preferred due to the enhanced structural integrity attained with thicker strands.
• a reduced opening size for at least the first screen layer, with a reduced opening size employed for subsequent screen layers based upon mass flow demands.
• the actual size of the openings is dependent upon the desired mass flow rate and number of screen layers to be employed.
• a diamond size of less than 0.125 inches (3.17 mm), "b” (width), by less than 0.071 inches (1.80 mm), “a” (height) 3/0 can be employed, with a size of about 0.125 inches (3.17 mm) to about 0.050 inches (1.27 mm), “b”, by about 0.071 inches (1.80 mm) to about 0.027 inches (0.686 mm), "a", preferred, i.e.
• Subsequent layers can also employ small opening sizes or can have an opening size larger than the opening size of the screen layer adjacent the electrode to improve mass flow characteristics.
• a 3/0 screen can have a strand thickness of about 0.007 inches (0.178 mm), while a 4/0 or 5/0 screen should have a strand thickness less than 0.005 inches (0.127 mm), with a thickness of about 0.003 inches (0.076 mm) or thinner preferred.
• openings 52 of layer 50 are not unduly obstructed by strands 55.
• the present invention allows for adequate hydration of membrane 8 by facilitating fluid transport through the unobstructed portion of openings 52 by providing for large openings in layer 50, due to the preferred elongated geometry of the strand openings, and by utilizing relatively thin strands 55.
• the membrane support device having the above-described features enables enhanced protection from screen pack induced damage, good flow distribution with high fluid pressures and flow rates, and low cost manufacturing.
• This device is useful all types of electrolysis cells, and particularly beneficial for use on the side of the water feed and/or the low pressure side of the membrane.
• the unsupported length and out of plane displacement of the membrane is reduced.
• the stresses within the membrane assembly are reduced to within an acceptable range for the type of material used.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• General Chemical & Material Sciences (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

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• 1999
  • 1999-06-08 JP JP2000556085A patent/JP2002519508A/ja active Pending
  • 1999-06-08 EP EP99927278A patent/EP1095174A1/de not_active Withdrawn
  • 1999-06-08 WO PCT/US1999/012634 patent/WO1999067447A1/en not_active Application Discontinuation
  • 1999-06-08 AU AU44221/99A patent/AU4422199A/en not_active Abandoned

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