WO2014066130A1 - Piles à combustibles à tourbillons en écoulement taylor mettant en œuvre des suspensions électrolytiques - Google Patents

Piles à combustibles à tourbillons en écoulement taylor mettant en œuvre des suspensions électrolytiques Download PDF

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Publication number
WO2014066130A1
WO2014066130A1 PCT/US2013/065401 US2013065401W WO2014066130A1 WO 2014066130 A1 WO2014066130 A1 WO 2014066130A1 US 2013065401 W US2013065401 W US 2013065401W WO 2014066130 A1 WO2014066130 A1 WO 2014066130A1
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Prior art keywords
electrolyte
fuel cell
particles
current collector
ctp
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PCT/US2013/065401
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English (en)
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Halbert P. FISCHEL
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Global Energy Science, Llc
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Publication of WO2014066130A1 publication Critical patent/WO2014066130A1/fr

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    • 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
    • H01M8/08—Fuel cells with aqueous electrolytes
    • H01M8/083—Alkaline fuel cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9091—Unsupported catalytic particles; loose particulate catalytic materials, e.g. in fluidised state
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04276—Arrangements for managing the electrolyte stream, e.g. heat exchange
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04701—Temperature
    • H01M8/04731—Temperature of other components of a fuel cell or fuel cell stacks
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04746—Pressure; Flow
    • 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 is in the field of galvanic electrochemical fuel cells used to convert chemical energy of hydrogen-containing fuels (e.g., hydrogen, methane, methanol, borohydride) into electrical energy and having means to provide relative motion between an element and an electrolyte containing galvanic particles - including means for creating Taylor Vortex Flows (TVF) and Circular Couette Flows (CCF) in the electrolyte (U.S. Class 429/7, 50, 51, 67, 69, 72, 408 ; Int. Class H01M-14/00, 10/44, 2/38, 2/36 8/06) to promote generation of electricity.
  • hydrogen-containing fuels e.g., hydrogen, methane, methanol, borohydride
  • TVF Circular Couette Flows
  • two methods of converting chemical energy into electrical energy are a) burning fuel (e.g., coal, natural gas, liquid hydrocarbons) with oxygen to create heat in an engine used to provide mechanical power to an electrical generator or alternator and b) promoting a reduction-oxidation (redox) reaction in a chemical cell that generates an electrical current in a circuit external to the cell.
  • the former method can provide direct current (DC) or alternating current (AC); however, the process is Carnot ⁇ temperature-limited by materials and therefore efficiency of burning fuel for electrical energy is low in accordance with the Second Law of Thermodynamics.
  • Fuel cells are galvanic cells used to convert chemical energy into electrical energy - usually through use of catalysts that support reduction-oxidation (redox) chemical reactions. They are distinguished from batteries and flow cells that depend on faradaic reactions, can be electrically recharged and cannot react with hydrogen-based fuels. They are also distinguished from electrolytic electrochemical cells that require electrical energy to initiate and sustain electrochemical reactions (e.g., electro winning), which are usually irreversible. Also, electrolytic cell electrodes do not contain catalytic or faradaic materials.
  • galvanic materials includes catalytic materials that support redox reactions but are not chemically altered as a result. Some examples include metals from Group 10 of the Periodic Table of the Elements, some alloys, such as Pt-Ru, and some molecules including a metal, such as Mn0 2 .
  • fuel cells exploit three-phase (catalyst - fluid - electrolyte) electrochemical reactions where the fluid is selected from a set consisting of fuel and oxidizer. These reactions separate electrons from atoms or molecules, which then become energized ions (e.g., protons, hydroxides). The electrons travel from one electrode to the other electrode through an external electrical circuit where work is performed while the ions travel through a fluid electrolyte between the electrodes.
  • ions e.g., protons, hydroxides
  • TVF also known as Taylor -Couette Flows
  • enhance reaction rates in electrochemical cells by a) reducing mass-transport losses, b) preventing fuel and oxidizer crossover, c) capturing reaction products that can degrade catalysts and electrolytes and d) eliminating those degrading reaction products from the cells, e) increasing temperature to reduce electrode overpotentials and raise reaction rates and f) permitting higher pressures and concentrations to accelerate reactions at both electrodes.
  • TVF has a unique property of keeping fuel and oxygen gases separated so long as they are present only as gases. That is because each unreacted gas is trapped within bubbles at its respective vortex center. Thus, TVF eliminate any need for membranes used in conventional fuel cells.
  • U.S. Patent No. 8,017,261 provides a description of TVF.
  • This invention is a class of TVF galvanic electrochemical cells (e.g., U.S. Patent Nos. 8,187,737 and 8,394,518) with improved electrolytes containing suspensions of particles with galvanic materials for generating electricity. These are flowable electrolyte suspensions where particles are free to move with and within a carrier electrolyte fluid - as distinguished from particles that are fixed to an electrode or otherwise unable to move.
  • An important concept of this invention is the novel use of fluid dynamics in galvanic cells.
  • Conventional battery cells and flow cells not utilizing TVF; but, comprising electrolytes containing a variety of suspended particles, are known in the art (e.g., Patent Publication No. US2011/0200848 of 18 AUG 2011 for a High Energy Density Redox Flow Device to Chiang et al).
  • TVF fuel cells of this invention can outperform conventional fuel cells is that it utilizes fluid dynamics to configure components that improve how particulate suspensions interact with current collectors in electrolyte chambers.
  • catalytic materials are affixed to electrically-conducting structures (e.g., electrodes, current collectors) of finite dimensions.
  • the electrode structure is porous so that the amount of catalytic material per unit area of structure or electrolyte flow can be increased.
  • SA specific activity
  • ion diffusion path length through electrolyte to the complementary electrode limit current and power density. This is true even though all spatially distributed catalytic material can participate in simultaneous redox reactions.
  • catalyst SA depends upon catalyst surface access to dissolved gas (e.g., fuel or oxidizer and redox reaction products) mass transport through a thin electrolyte layer.
  • dissolved gas e.g., fuel or oxidizer and redox reaction products
  • Catalyst porous substrates e.g., carbon
  • hydrophobic e.g., coated with PTFE
  • Hydrophobicity limits the ability of the carbon substrate to participate in ion exchange current or capacitive charge storage. Liquid electrolyte must penetrate the porous substrate to provide an electrolyte coating to the catalyst surface for a redox reaction. Hydrophobic catalyst porous substrates severely limit the amount of active catalyst surface that can participate in a redox reaction.
  • the electrically-conducting component structure containing galvanic material is divided into small particles - each resembling a small element of the typical galvanic electrically-conducting structure. These particles are called charge transfer particles (CTP).
  • CTP charge transfer particles
  • the CTP are mixed with the electrolyte (e.g., KOH) to form a suspension, which may be a non-Newtonian (e.g., thixotropic) fluid.
  • Thixotropy is the property of certain non-Newtonian fluids that are thick or viscous under normal conditions; but, become less viscous over time when shaken, agitated, spun in TVF or otherwise stressed. They then take a fixed time to return to a more viscous state.
  • Newtonian fluids e.g., aqueous KOH as used in prior art fuel cells and batteries
  • a thixotropic fluid e.g., aqueous KOH containing suspended CTP
  • a thixotropic fluid is a non- Newtonian fluid that requires a finite time to attain equilibrium viscosity or shear stress when introduced to a step change in shear rate.
  • Novel configurations of fuel cells of this invention generate dynamic forces in the fluid that accelerate CTP in the electrolyte suspension, where galvanic reactions take place, to make low-electrical-impedance, brief contact with the cell's current collectors. At any given instant, there are some CTP approaching the current collectors, some in contact with the current collectors and some departing from the current collectors. Not all CTP are simultaneously in contact with the current collectors to participate in the current-producing reaction at a given moment; but, those that have been charged and make momentary contact with the current collector surface contribute to the cell's electrical current. Novel structures are provided to assure that population and frequency of such contact is sufficient to support high current and power density.
  • Standard art battery architecture incorporates faradaic material into a thin paste wrapped under pressure or compressed into a porous cake or briquette where faradaic material is physically attached to metal current collectors or electrodes.
  • a conducting additive usually carbon
  • Another architecture physically attaches faradaic particles to porous electrode scaffolding.
  • Faradaic particles in so-called semi-solid electrochemically active suspensions of prior art faradaic battery cells cannot, because of their very nature, provide that connection. Galvanic particle electrolyte suspensions containing catalyst have not been found in fuel cells.
  • U.S. Patent No. 4,126,733 of 21 NOV 1978 to Doniat teaches a faradaic battery cell incorporating an electrolyte containing low-density glass or plastic balls that are coated with zinc and have diameters in the range of 0.2 to 2.0-mm. While not expressly taught by Doniat, electrolyte suspension flow through the anode electrolyte chamber would have to be laminar (not turbulent) in order to limit pump power loss.
  • Doniat' s '733 battery patent seeks to overcome low current density limitations by teaching Advantageously, the transverse dimension of the compartment A (anode electrolyte particulate suspension chamber) is small in order to authorize (sic) as many impacts of the (low density) balls 18 on the (current) collectorl4, for the sake of obtaining a yield of electrochemical oxidation as high as possible.
  • reduction of the transverse dimension of the anode compartment reduces the number of balls available to complete a galvanic reaction and this also limits current density.
  • a second example of a battery cell incorporating electrolyte with suspended particles is taught by Chiang et al in Patent Publication No. US2010/0047671 of 25 FEB 2010 for a High Energy Density Redox Flow Device.
  • Chiang et al teach faradaic cells employing fine particles of 2.5-to-lO-micron suspended in electrolytes - such as slurries, particle suspensions, colloidal suspensions (sols), emulsions, gels, or micelles where particles suspended in electrolyte act as electrodes that participate in faradaic redox reactions adjacent to non-reactive current collectors.
  • Chiang et al ('671 at Paragraph [0115]) also teach:
  • the rate of charge or discharge of the redox flow battery is increased by adjusting the interparticle interactions or colloid chemistry of the semisolid to increase particle contact and the formation of percolating networks of the ion-storage material particles.
  • the percolating networks are formed in the vicinity of the current collectors.
  • the semi-solid is shear-thinning so that it flows more easily where desired.
  • the semi-solid is shear thickening, for example so that it forms percolating networks at high shear rates such as those encountered in the vicinity of the current collector.
  • a liquid that is percolating is, by definition, moving slowly or gradually - especially as compared to a liquid in a TVF cell (e.g., U.S. Patent Nos. 8,187,737 and 8,394,518) that is propelled by convective flow.
  • a particle in percolating flow has a velocity vector component orthogonal to the collector surface that must approach zero, which means that current density must be low - on the order of a few milliamperes per square centimeter of projected current collector area.
  • TVF cells of this invention do not use fine particles; but instead, contain bigger particles having greater densities than the particles taught by Chiang et al. Therefore, these particles can be launched with greater energy available to penetrate laminar flows created by CCF at the current collector surface.
  • the larger CTP are integrated structures that comprise finely divided particulate matter for greater chemical reactivity.
  • a Ni(OH) 2 particle (density of 4.10 g/cm 3 ) colliding with a current collector (in a battery undergoing charging) will release protons (H + ) and undergo crystalline realignment to become a NiO(OH) particle (density of 3.97 g/cm 3 ), which differs not only in density but also the amount of intercalation of water and cations such as K + .
  • the particle transforms into a different species. Fluid dynamics have little effect on these species transformations in conventional galvanic cells, such as the Chiang et al cells; however, consequences are different in TVF galvanic cells.
  • Chiang el al also teach that heating and cooling will produce convective vortices rising normally from cell walls in accordance with the Rayleigh - Benard theory of vortex flows; however, these flows will drive particles away from, not toward, the current collector surfaces because they also create current collector surface boundary layers.
  • Nano-size particles can be used in TVF providing they are accompanied by large metal conducting particles. These large metal hydrophilic particles, coated with galvanic suspension, act as sledgehammers that drive the faradaic or galvanic particles into a current collector.
  • a better particle suspension alternative comprises finely divided nano-size faradaic or galvanic particles attached to the large micron-size metal particles.
  • ions e.g., H + , OH "
  • protons move slowly along paths orthogonal to the current collector surfaces toward the opposite current collector. Only small diffusion, concentration and migration gradient forces slowly propel these ions through the electrolyte to complete the cell's internal chemical circuit.
  • electrolyte is pumped through the cell, then the ions must move across the cell along paths that are orthogonal to electrolyte convection flows, which do not provide any acceleration to the ions toward an opposing electrode.
  • the ions in Chiang et al cells must permeate an ion permeable separator, such as a NAFIONTM membrane, that increases the cell's internal resistance.
  • the ions can pass through the filter and enter the CCF on the opposite side for transport to the opposite current collector or they can combine with other ions near the filter to produce a reaction product (e.g., H 2 0) in the electrolyte.
  • a reaction product e.g., H 2 0
  • TVF cells do not require ion permeable separators such as NAFIONTM proton exchange membranes.
  • TVF cells have unique flow properties that are exploited to increase mechanical forces that aid in charge transfer by particles not taught in the prior art for use in galvanic cells. As described above, the Chiang et al particles flow tangentially past the current collector as an isotropic suspension. This can also occur in a TVF vector field.
  • a particle has particular size, shape, mass and density ratio with respect to its suspending fluid, then it will not have a stable position within a TVF vortex and will be thrust radially (not axially as in a Chiang et al cell) toward a collision with a current collector.
  • the Chiang et al suspensions of finely divided faradaic particles in liquid electrolyte are to be used in a TVF galvanic cell, then they require an addition of larger conducting particles acting as sledgehammers in order to effectively transfer charges to the TVF current collectors. These larger particles must be of a volume fraction that would not exceed the faradaic or galvanic material. Even higher current densities can be obtained by attaching the faradaic or galvanic materials directly to the large conducting particles.
  • These particles will have a mass of ⁇ 1 to 20 xl0 "6 -grams depending upon shape selected from a range extending from spherical to flake. Their forces at impact can be estimated.
  • particle sizes in the range 30-75 microns and masses in the range or 0.5 - 1.0 x 10 "6 grams are useful.
  • the impulse interval is thus about 1.25 to 6.25 ⁇ sec for 1 to 2-mm gaps, respectively.
  • the size and shape of the particle limits the contact area to about a 25 -micron radius circle for a contact area of 76 xlO "8 square inches, assuming some particle deformation at contact with a suitably roughened surface. Therefore, the contact pressure is greater than 690-psi (47-atm) and less than 3,450-psi (235-atm) for TVF gaps in the range of 1 to 2 mm and 3600 RPM. That pressure is both far greater than the contact pressure attainable with the Chiang et al 10 micrometer (also referred to as micron and ⁇ ) or smaller, fine particles and more than adequate to secure complete charge transfer.
  • prior art 1 to 10-micron or smaller galvanic particles have a mass of ⁇ 4 to 200 xl0 ⁇ 8 -grams, depending upon material and shape selected. Because of their small sizes, these particles are enclosed by surface layers of electrolyte that have relatively high surface tensions, so the particles remain in isotropic suspension or settle out very slowly.
  • the electrode active materials do not include materials that are added to facilitate the transport of electrons from an electrode current collector to the electrode active material (i.e., additional materials that increase the electronic conductivity).
  • a first advantage of the present invention provides an improvement over earlier galvanic cells by providing galvanic TVF cells comprising catalytic CTP in electrolyte suspensions that are especially configured for use with TVF.
  • a second advantage of the present invention provides an improvement over earlier galvanic cells through use of particles in electrolyte suspensions that have 35 to 100- micron diameter (enclosing sphere) particles.
  • a third advantage of the present invention provides an improvement over earlier galvanic cells through use of particles in electrolyte suspensions that have mass of at least 1 x 10 ⁇ 6 -grams per particle.
  • FIG. 1 is a cross section drawing of a TVF fuel cell of this invention.
  • FIG. 2A is a conceptual cross-section view of a fuel cell pore taken from the prior art.
  • FIG. 2B is a conceptual cross-section view of a fuel cell pore of this invention.
  • FIG. 3A is a conceptual cross-sectional illustration of a charge transfer particle decorated with catalyst particles.
  • FIG. 3B is a conceptual cross-section drawing of a catalyst particle for attachment to a charge transfer particle of FIG. 3A.
  • FIG. 4 is a conceptual illustration of how an electron is transferred from a charge transfer particle in TVF to a current collector and how a proton cation is propelled by CCF toward a hydroxide anion at a rotating filter.
  • FIG. 5 is a conceptual illustration of an alternative current collector incorporating a surface of galvanic material.
  • FIG. 1 is a cross-sectional view of essential features of a preferred embodiment of an electrochemical cell 100 comprising a fuel cell 102.
  • the fuel cell 102 is similar to the fuel cell 602 of U.S. Patent No. 8,187,737, with some important improvements that are to be described.
  • the fuel cell 102 is contained within a case 104 and comprises a cylinder-like outer current collector 106 that is secured to the case 104 and a cylinder- like inner current collector 108 that is also fixed to the case 104.
  • the outer current collector 106 is connected by positive terminal 110 (CATHODE) and the inner current collector 108 is connected to the negative terminal 112 (ANODE), respectively, to external electrical circuit 114 by conductors 116.
  • Both of the current collectors 106, 108 have a very large number of very fine pores extending radially from their outer to their inner surfaces; however, open-cell metal foams and other electrically-conducting porous materials also can be used.
  • the outer current collector 106 forms a coaxial right- circular cylinder as shown in FIG. 1; however, this attribute is not a requirement and other cylinder-like geometries (e.g. elliptical, conical, hyperbolic, irregular, different axes) may be employed.
  • inner current collector 108 A prerequisite is that there are two electrolyte chambers separated by a filter that is permeable to flow of electrolyte; but, not particles entrained in the electrolyte. Additionally, there must be means for rotating the filter to create a vortex in the electrolyte in one of the electrolyte chambers.
  • a gap 118 between the outer current collector 106 and the inner current collector 108 is divided by a filter 120 into an outer electrolyte chamber 122 and an inner electrolyte chamber 124.
  • the filter 120 in this embodiment is also a right-circular cylinder that is coaxial with the current collectors 106, 108; however, the filter 120 may be cylinderlike and it need only be approximately coaxial with the outer current collector 106 and the inner current collector 108.
  • the inner surface of the current collector 106 and the outer surface of the current collector 108 are electrolyte-facing surfaces of these porous current collectors (106, 108).
  • the filter 120 is permeable to the flow of electrolyte, water and ions; but not to particles. This feature distinguishes the filter 120 from ion-permeable membrane 208 (e.g. NAFIONTM and LISICONTM ion-exchange or ion-conducting membranes) that is shown in FIG. 5 of U.S. Patent No. 7,964,301. and that is impermeable to electrolyte, water and particles. Those membranes are popular choices for use in prior art aqueous fuel cells.
  • ion-permeable membrane 208 e.g. NAFIONTM and LISICONTM ion-exchange or ion-conducting membranes
  • NAFIONTM membranes only transport cations (e.g., protons) and limit the chemistries that can be employed to only those using acidic electrolytes.
  • the filter 120 in the TVF fuel cell 102 is compatible with both acid and alkaline chemistries, tolerates higher operating temperatures and facilitates water balance between the cathode and anode sections of the fuel cell 102
  • a catholyte flows in the outer electrolyte chamber 122, which is in the gap 118 between the filter 120 and the outer current collector 106.
  • An anolyte flows in the inner electrolyte chamber 124, which is in the gap 118 between the filter 120 and the inner current collectors 108. If another chemistry is selected, then the electrolyte chambers 122, 124 can be exchanged for anolyte and catholyte, respectively.
  • an oxidizer chamber 126 is formed between the case 104 and the outer current collector 106.
  • a fuel chamber 128 fills the interior of the inner current collector 108. If another chemistry is selected, then the oxidizer chamber 126 and the fuel chamber 128 can be exchanged for fuel and oxidizer, respectively.
  • Catholyte flowing in the outer electrolyte chamber 122 comprises a non- Newtonian or thixotropic fluid mixture of an electrolyte such as KOH (an alkaline electrolyte) and catholyte catalyst particles (e.g., containing Mn0 2 ).
  • an anolyte flowing in the inner electrolyte chamber 124 comprises a thixotropic mixture of the same electrolyte and anolyte catalyst particles (e.g., containing Ni, NiO or noble metal catalysts).
  • the filter 120 is porous to the electrolyte; but, impermeable to both types of particles.
  • the catholyte and the anolyte particles also called charge transfer particles (CTP)
  • CTP charge transfer particles
  • the CTP also transfer charges when CTP make momentary electrical contact with metal current collectors 106 and 108.
  • Both anolyte and catholyte suspensions may include dispersion or wetting agents (e.g., etidronic acid, also known as HEDP, lignin sulfonic acid, etc.) and particles that facilitate electron charge transfer at metal electrode surfaces (e.g., cobalt, Co(OH) 2 , BaS0 4 etc.).
  • dispersion or wetting agents e.g., etidronic acid, also known as HEDP, lignin sulfonic acid, etc.
  • particles that facilitate electron charge transfer at metal electrode surfaces e.g., cobalt, Co(OH) 2 , BaS0 4 etc.
  • the term galvanic materials include catalytic materials.
  • the galvanic fuel cell 102 comprises, in one case, three-phase (catalyst - fuel or oxidizer -electrolyte) electrochemical reactions that separate electrons or ions (e.g., protons) from atoms or molecules.
  • the electrons travel from one electrode 108 to the other electrode 106 through the external electrical circuit 114 where work is performed while the ions travel through a fluid electrolyte between the electrodes 106, 108.
  • the filter 120 is journaled for rotational movement within the gap 118 between the current collectors 106 and 108 to generate Taylor Vortex Flows and Circular Couette Flows in at least one of the electrolyte chambers 122, 124.
  • the top of the filter 120 is secured to hub 130 that is fixed to the axle 132 of motor 134.
  • the motor may be connected in parallel to the external electrical circuit 114 by conductors 116.
  • the catholyte from a balance of plant, BOP enters the outer electrolyte chamber 122 through input orifice 136 and returns to the BOP after exiting through catholyte output orifice 138.
  • the anolyte from BOP enters the inner electrolyte chamber 124 through anolyte input orifice 140 and returns to the BOP after exiting through anolyte output orifice 142.
  • the BOP may contain pumps (not shown) to accelerate electrolyte flows and may provide reservoirs of large volumes of catholyte and anolyte.
  • the filter 120 serves two principal functions. First, it prevents catholyte and anolyte particles from intermingling and neutralizing their charges by preventing crossover through the filter. Second, the filter 120 rotates between the outer electrolyte chamber 122 and the inner electrolyte chamber 124 to generate outer electrolyte chamber 122 flows, such as TVF 144, and inner electrolyte chamber 124 flows, such as TVF 146. Where TVF 144, 146 are generated, outer electrolyte chamber CCF 148 and inner electrolyte chamber CCF 150 can be generated, as described in U.S. Patent Nos. 8,017,261 and 8,394,518. Third, the filter 120 facilitates water balance and accelerates inter-electrode ion exchange by permitting cross filter flows.
  • the filter 120 should have particular, if not especially unique, properties. It should contain a dielectric material (e.g., PTFE) that prevents electrical shorting of the outer and the inner electrolyte chambers 122, 124 to each other.
  • the filter 120 should be porous to the fluid component of the electrolyte suspension and it should be wettable (hydrophilic) in that fluid.
  • the filter 120 should be smooth on both its faces. This means that surface pits and protuberances should be substantially smaller than the smallest particles 300, 402 in suspension.
  • the filter 120 is provides dynamic surface rejection to prevent suspended particles 300, 402 from attaching to its surface or penetrating its pores.
  • Dynamic surface rejection requires a moving filter 120 surface as in TVF 144, 146, 404.
  • the filter 120 surfaces are intended to wet and drag the fluid phase - not suspended particles 300, 402 that are carried in the fluid phase flow. For this reason, the current collector 106, 108, 406 surfaces are deliberately roughened to catch particles and transfer charge, even if only momentarily.
  • the fuel cell 102 is operated to produce electricity for transmission to the external electrical circuit 114 by a process comprising:
  • anolyte flows, such as TVF 146 and CCF 150, to form in the inner electrolyte chamber 124 anolyte.
  • the filter 120 can be rotated at a speed that will not produce TVF 146 or CCF 150; however, the fuel cell 102 will generate less electrical current.
  • charge transfer occurs within electrode pores and is primarily restricted to a narrow band of electrolyte within a meniscus where the meniscus is approximately 10-nanometers thick and in contact with catalyst on interior walls of the pores - as shown in Bockris et al Figs 13.12 & 13.13.
  • FIG. 2A taken from Bockris el at Fig. 13.12, is a schematic representation of a three-phase interface in a single pore when the meniscus contact angle is a few degrees.
  • Pore 200 in a fuel cell Metal Electrode contains both electrolyte and a fluid selected from a set consisting of fuel and oxidizer. A portion of the pore 200 wall is coated with or holds a catalyst.
  • a meniscus 202 separates the electrolyte from the fuel or oxidizer gas.
  • the meniscus' surface tension regulates the amount of gas penetrating into the electrolyte.
  • the total catalyst surface area for a cell's electrode can increase; however, the surface tension of the meniscus also increases and less gas is able to penetrate the meniscus 202 and dissolve into the electrolyte. Therefore, a tradeoff between total catalyst surface area and the amount of gas penetration to the catalyst surface can exist.
  • Zone 204 illustrates where optimum results (e.g., highest current) can be obtained for a three-phase redox reaction of gas dissolved in electrolyte adjacent to catalyst.
  • optimum results e.g., highest current
  • the distance is too high, then there is a large increase in limiting diffusion current. If the distance is too low, then there will be too much resistance to the flow of reaction products (e.g., H 3 0 + ions) back to bulk electrolyte.
  • reaction products e.g., H 3 0 + ions
  • the volume of gas solvated in electrolyte of a PEM fuel cell can be increased by raising gas pressure; however, raising the pressure will require more accurate regulation to prevent an escalation in both the amounts of wasted fuel and mechanical stress on the PEM.
  • the process of solvating gas in the electrolyte also can be accelerated by increasing temperature both to increase solubility and to lower meniscus surface tension; however, temperature is limited by a need to preserve structural integrity of the PEM.
  • surface tension of the meniscus can be reduced by raising humidity of the gas (e.g., 80%); however, adding water will reduce the electrolyte's ability to transport of ions.
  • reaction products must diffuse to accommodate fresh fuel or oxygen.
  • the requirement is difficult to satisfy for conventional cells containing PEM where only the margins of polymer electrolyte on catalyst bring the three phases together across a short diffusion path because only diffusion, concentration and migration gradient forces are available to remove the reaction products.
  • the complementary oxygen reduction reaction catalyst (ORR) density is usually higher, at 0.5 mgm of platinum catalyst per cm 2 of projected electrode area or 500 cm 2 of platinum catalyst surface area platinum per cm 2 of projected electrode area. At 1 mA/cm 2 of platinum catalyst surface area, the oxygen cathode operates at about 1 % of theoretical catalyst efficiency.
  • the total volume of platinum catalyst particles in the static catalyst structure examples is only 0.3% of the volume of a typically 30 ⁇ thick active porous electrode layer adjacent the electrolyte or PEM. This means that the Pt particles only sparsely cover the electrode and the distance between particles is greater than the diameter of a virtual sphere enclosing a particle. Gas molecules diffusing through such a sparsely-seeded structure must waste a substantial portion of residence time while migrating to and react with catalyst particles.
  • porous electrodes of the conventional fuel cells contribute to the internal impedance of the cells and limit electric current density for the following reasons:
  • ⁇ Static catalyst structures are inherently limited to low current densities (e.g., decreasing pore sizes increases electrolyte meniscus surface tension - thereby decreasing gas solubility).
  • ⁇ Narrow diameters of the pores impede the purging of reaction products moving outward from the pores and retard movement of electrolyte with dissolved gas inward to redox sites.
  • Ions e.g., protons, hydroxides
  • Electrolyte pressures and levels must be precisely monitored to prevent flooding of electrode pores, which would block gas access to the catalyst.
  • the electrode comprises catalyst supported on porous carbon and the porous carbon serves both as a diffuser of gas reaching the catalyst and an electrical double layer (EDL), then electrolyte necessary for charging the EDL restricts the flow of gas necessary for the redox reaction at the catalyst.
  • EDL electrical double layer
  • FIG. 2B is cross-sectional view of a fuel cell pore 210 in a Metal Current Collector (e.g., 106, 108) of this invention.
  • a Metal Current Collector e.g., 106, 108
  • the pore 210 of FIG. 2B contains only fuel or oxidizer gas.
  • electrolyte may be hydrophilic with respect to the pore 210 walls, it does not form an internal meniscus similar to the meniscus 202 of FIG. 2A because gas pressure creates an external electrolyte meniscus dome 212 outside of the pore.
  • the gas and electrolyte pressures need only be regulated to assure that electrolyte does not flood the pores and that the meniscus dome 212 does not become an ejected bubble that allows gas to escape into the electrolyte.
  • the pores 200 occupy only 15-25% of the current collector 106, 108, 406 volumes, which can be very strong mechanical structures and only 10-15% open area on the current collector surface.
  • the gas meniscus domes 212 cover much of the current collector 106, 108, 406 surfaces. Because the CCF 148, 150, 410 boundary layers cover static current collector surfaces, the gas does not leave the current collector 106, 108, 406 surfaces unless forced by excessive gas pressure.
  • a typical CTP 300 comprises a metal core 302 surrounded by a rough-surfaced skin 304 of electrically- conducting material, such as carbon (e.g., particles, graphene, graphite, nano-tubes), to which catalyst particles 306 are attached.
  • electrically- conducting material such as carbon (e.g., particles, graphene, graphite, nano-tubes)
  • Each of the CTP 300 should have a mass of at least 1 x 10 ⁇ 6 grams and a density of at least 4 grams/cm "3 in order to escape the TVF 144, 146, 404.
  • each of the cores 302 should be a metal having a density of at least 8 grams per cm "3 so that the CTP have densities of at least 4 grams/cm "3 .
  • the cores 302 may contain tungsten, nickel, nickel alloys (e.g., INCONELTM alloy), stainless steels or similar metals.
  • the CTP 300 is entrained in electrolyte 308 that contains an Inner Helmholtz Layer (IHL) and an Outer Helmholtz Layer (OHL).
  • IHL Inner Helmholtz Layer
  • OHL Outer Helmholtz Layer
  • the IHL and the OHL form the EDL on supported catalyst surfaces in the electrolyte that encapsulates the CTP 300.
  • the EDL refers to two parallel layers of charge surrounding the CTP 300 that form a capacitive electrical energy store.
  • the IHL is an electrical surface charge (either positive or negative) comprising ions adsorbed directly onto or into catalyst surfaces fully or partly covering the CTP 300 due to chemical interactions.
  • the OHL is composed of ions attracted to the surface charge because of the coulomb force electrically screening the IHL.
  • the OHL is loosely associated with the CTP 300, because the OHL is made of free ions that move in the electrolyte 308 under the influence of electric attraction and thermal motion rather than being firmly anchored.
  • the EDLs are the sites of electrical charge that are subsequently transferred to the current collectors 106, 108.
  • the catalyst particle 306 contains a catalytic metal core 310 of a first metal (e.g., platinum) that supports admetal islands 312 created by depositing a second metal (e.g., ruthenium) on the core 306 with a process that displaces surface atoms of the core 306 with atoms of the deposition metal to create the islands 312.
  • a first metal e.g., platinum
  • a second metal e.g., ruthenium
  • One of the metals can contain an element selected from Group 10 of the Periodic Table of the Elements.
  • the admetal islands 312 have a bimetallic structure that is distinct from that of their component metals and can preferentially absorb OH " ions.
  • hydrocarbon fuels e.g., methanol
  • CO is also produced.
  • the CO would poison the surface of the catalytic core 310; however, the OH " ions can oxidize CO to C0 2 and resist CO poisoning.
  • the oxidation of CO to C0 2 provides an additional benefit of widening the choice of electrolytes to include both acid and alkaline solutions because CO poisoning is no longer a primary concern.
  • the catalyst particle may also comprise an inert heavy metal core metal selected from a set containing densities of at least 8 grams per milliliter (e.g., tungsten) covered by carbon (e.g., CNT).
  • the carbon can support catalyst (e.g. NiOOH, Ni, Mn0 2 , one of the metals can contain an element selected from Group 10 of the Periodic Table of the Elements etc.).
  • FIG. 4 illustrates how an electron (e " ) 400 is created on a CTP 402 in TVF 404 and then delivered to current collector 406 and how a cation (H + ) 408 is released and propelled by high-shear-rate CCF 410 toward an anion (e.g., OH " ) 412 at rotating filter 414.
  • e " electron
  • H + cation
  • anion e.g., OH "
  • the CTP 402 initially is trapped near the swirling center of TVF 404 at position 402a because its hydrodynamics are different from those of the electrolyte. After the CTP 402 collides with another similar particle (not shown) and acquires some of the other particle's kinetic energy, CTP 402 is accelerated to position 402b where centrifugal force and the velocity of the TVF 404 accelerate it to positions 402c and 402cl before it enters high shear rate CCF 410 and collides with the current collector 406 at position 402e.
  • the collision with the current collector 406 causes the CTP 402 to lose momentum and get drawn back into the TVF 404 to the position 402a.
  • the collision with the current collector 406 also causes the CTP 402 to become coated with the electrolyte-fuel solution and the presence of fuel, electrolyte and catalyst initiates a three-phase redox reaction that charges the CTP 402.
  • the CTP 402 has the benefit of a long interval as it returns to the center of the TVF 404 many times where it regains sufficient momentum to escape. This interval is sufficient for the redox reaction to convert almost all of the fuel chemical energy to electrical charge energy.
  • the electron (e " ) 400 is transferred to the current collector 406 for passage to the External Electrical Circuit.
  • ORR oxidizer reduction reaction
  • the fuel cell CTP 300, 402 continuously move from the TVF 404 to the current collector 106, 108, 406 surfaces and back again.
  • the CTP 300, 402 contact the current collectorl06, 108, 406 surfaces, the CTP 300, 402 are replenished with gas liberated from the meniscus dome 416 that dissolves within the electrolyte 308 covering and attached to the CTP and enters the redox reaction.
  • the solute gas at the CTP 300, 402 catalyst surfaces is reacted, it is replenished by solute gas previously stored in the EDL. This reaction is a continuous process during the transit time between CTP 300, 402 collisions with the current collector 106, 108, 406 surfaces.
  • FIG. 5 An alternative to the current collector 406 of FIG. 4 is shown in FIG. 5.
  • Electron (e " ) 500 has been created on a CTP 502e that has collided with current collector 506 and meniscus domes 516.
  • the current collector 406 of FIG. 4 has no galvanic properties and cannot participate in a redox reaction
  • the current collector 506 of FIG. 4 is a composite that contains a galvanic material coating 518 that is decorated with galvanic flakes.
  • the galvanic material cover 518 may comprise several layers of graphene or another active carbon, such as carbon nanotubes (CNT) or those used to construct supercapacitors.
  • the coating 518 covers the metal current collector 506; but, not its microscopic pores.
  • the layers serve as a substrate for catalyst (e.g., anode - Ni, NiO, etc.; cathode - Mn0 2 , etc.).
  • the CTP 502 may have the galvanic properties of the CTP 402.
  • the CTP 502 may be replaced by a metal particle (not shown) with similar mass and size; but, without galvanic properties. Gas will form meniscus domes 516 at the surface of the galvanic material cover 518 and the redox reaction will proceed as described for FIGS. 1-4.
  • the alternative structure of FIG. 5 may be preferred in some applications because processing of the anolyte and catholyte in the BOP may be simpler - especially if simple metal particles are substituted for the CTP 502.
  • the structure of FIG. 4 may be chosen because it is easier to replace CTP 402 than it is to exchange the current collector 506 with its galvanic material cover 518.
  • Time or spatial variation of electrolyte suspension viscosity as a function of local shear rate is an important factor for TVF galvanic cells.
  • the local shear rate can be estimated as S ⁇ -d /dmmr 2 , where,
  • SL is local angular momentum of a fluid mass element, m
  • r is the radial position of the fluid element, dm, with respect to the vortex spin axis
  • ⁇ is the angular velocity of the fluid element, dm.
  • ⁇ is maximum at the center of the vortex where viscosity is at a minimum with respect to the value in the boundary layer adjacent the current collector metal surface.
  • any two adjacent vortices 404 in a galvanic TVF cell share a peripheral electrolyte flow vector pointing alternately in axial sequence toward or away from the current collector 406 or the filter 414.
  • CTP 402 contained within these flow vectors may collide with the current collector 406 surface if they penetrate the CCF 410 boundary layer, travel a short distance (about the diameter of the vortex) along the current collector surface and leave that surface.
  • Contact with the current collector 406 surface is enhanced if the surface is substantially roughened with protuberances approximately the size of the CCF 410 boundary layer covering the surface. The protuberances will further strengthen the local vortices at the current collector 406 surface that lie outside the TVF 404.
  • the local vortices continuously arrive carrying charged CTP 402 and depart carrying discharged CTP 402.
  • CTP 402 contact with the current collector 406 surface is enhanced by action of local vortices and eddies.
  • the CTP 300, 402 are hydrophilic and completely encased in a fluid boundary layer containing dissolved or solvated gas (fuel or oxidizer). Within that layer and adjacent the solid surfaces of the CTP 300, 402 is the IHL, of about 1 to 2-nanometer (nm) thickness, enclosed by the OHL.
  • the IHL is intimately associated with the CTP 300, 402 crystal structure and is the locus of the EDL, which is classically defined as the location where electrons can be exchanged across it to the current collector 406 surface.
  • the rate of exchange per unit of current collector 406 surface is the exchange current density.
  • Centers of ions or charged molecules that are absorbed at the surface of the CTP lie within the OHL, of about 10-nanometers thickness. It is the locus of the centers of solvated ions at their distance of closest approach to the CTP 402, 300 surfaces. Both loci are adjacent to the point of contact of CTP 300, 402 and the current collector 406 surface where charge transfer between them takes place. It is the ability of the CTP 300, 402 to compress IHL and OHL against the metal current collector 406 surface that causes charge transfer. Charge 400 transfer is virtually instantaneous once the CTP 402 makes solid contact with the current collector 406 surface. The cell's current is the integral over the current collector 406 surface of charge transfer with respect to time.
  • capacitive anolyte particles capable of EDL charge storage can be manufactured with existing carbon technology adapted to discrete particle architecture where carbon and redox catalyst are joined as coatings of a dense metal core to form large discrete particles of 35-micron or greater enclosing sphere diameters containing finely divided (i.e., highly dispersed) catalyst material.
  • Coatings of carbon nanotubes (CNT) or other forms of graphene with nanoscale catalyst (metals such as Pt, Ni, Mn0 2 etc.) have been demonstrated (Patent Publication US 2010/0105834 of 29 APR 2010 to Tour et al). The use of CNT and graphene as
  • supercapacitor material has also been taught (Patent Publication US 2012/0134072 of 31 MAY 2012 to Bac et al).
  • other forms of carbon such as aerogel, activated polymer and metalloid carbides in micron-size particle form are candidates for use in galvanic cells.
  • Current technology can decorate CNT, carbon fibers or other carbon forms on metal substrates with nano-size catalyst particles.
  • These micron-size capacitive charge transfer particles (CCTP) have very large capacitive values due to the nature of the materials comprising them.
  • fuel is fed as a high-temperature gas through the sub- micron to nanoscale porous, anolyte facing, surface of a negative current collector 108.
  • the fuel is metered at a rate to meet RMS load demand - not the transient or instantaneous current.
  • the CCTP strikes the porous current collector, the CCTP picks up fuel in the form of solvated gas molecules that become attached to the CCTP's highly -jagged surface. If the CCTP contains a charged EDL from prior redox reactions after previous contact with the fuel rich current collector surface, then the CCTP can transfer its charge during the present contact. Charge transfer is virtually instantaneous; but, the capacitive EDL dipole charge takes longer to create.
  • CCTP Charge transfer from the CCTP, such as the CTP 300, to the current collector 106, 108 surface depletes the EDL charge; but, the rate of depletion depends upon several factors. External electric circuit load impedance determines the rate at which CCTP will actually transfer charge. At open circuit, there can be no transfer of charge to the current collector. Similarly, internal ionic circuit impedance will also affect charge transfer. Thus, a CCTP will be prevented from delivering a charge to the current collector 106, 108 surface if the EDL cannot simultaneously release an ion for exchange with the catholyte because, as previous explained, ionic current within a galvanic cell must balance the electric current in the external electric circuit.
  • a CCTP When a CCTP contacts the anolyte current collector (alkaline electrolyte) and does not transfer an electron (e.g., the AC waveform is at null), it is still eligible to add charge to its EDL to the point of saturation. That process takes place as though the CCTP were a supercapacitor - even after the CCTP leaves the current collector surface to follow a recirculating path into and out of TVF.
  • anolyte current collector alkaline electrolyte
  • Fuel attached to the CCTP catalyst surfaces can undergo a series of chemical reactions. Some are merely rearrangement of atoms and ions, such as dehydrogenation of methanol. These do not require electron exchange or ion release. Other steps in the reaction will move electrons and ions with respect to the carbon substrate EDL which essentially adds charge potential. Even if the chemical charging redox process is slow, it is repetitive, continuous and does not require continuous contact with the current collector 108 surface.
  • the CTP 402 must make solid contact with the current collector 406 in order to transfer charges 400. In order to attain the cell's desired current density, there must be a sufficient number of particle collisions per unit time. These two conditions cannot be attained solely with the 10-micron or smaller particles of the prior art. However, there are two alternatives that can be employed for use with the larger CTP 402.
  • the first option for using the 10-micron or smaller galvanic particles to create CTP 402 in a galvanic TVF cell is to mix substantially denser and larger, 100-micron-size metal particles with the micro and nano-size faradaic particles.
  • the galvanic particles may be supported by carbon particles or carbon nanotubes.
  • the larger, 100-micon-size particles need not be faradaic or catalytic and may comprise tungsten, alloys of stainless steel or other metals that are corrosion resistant and hydrophilic.
  • the smaller galvanic particles will be attracted to the larger particles and held there by electrolyte surface tension and charge attraction as the larger particles are accelerated toward collisions with the current collector 406.
  • the second option for using the 10-micron or smaller galvanic particles to create CTP 402 is to decorate or attach (e.g., sinter, electroplate, coat, deposit) highly dispersed the 10-micron or smaller galvanic particles to the denser and larger 35 to 100- micron-size metal particles.
  • carbon nanotubes (CNT) or other forms of graphene can be grown (i.e., electroplated or vacuum oven deposited) onto tungsten, stainless steel or RANEYTM nickel surfaces of 100 -micron-size particles that are then coated these with galvanic fine particles.
  • These 35 to 100-micro-size particles will have both the density and mass needed for use in TVF galvanic cells.
  • the second of the two options is generally preferred. Examples of depositing galvanic materials on fine particles have been described in the prior art as improvements in conventional batteries. There are descriptions of depositing catalyst onto cragged, RANEY nickel surfaces that could be used for applying faradaic materials to particles. Deposition of galvanic materials onto porous metal scaffolds used as current collectors or sintering these materials to achieve porous electrodes is common in practice. However, it is easier, less expensive and far more practical in application to deposit galvanic materials onto dispersed metal particles than to fabricate them into electrodes. Additionally, replacing particle suspensions is easier and more economical than replacing electrodes in galvanic cells.
  • CTP 402 used in galvanic TVF cells is aided by defining specifications for a hypothetical CTP.
  • the CTP 402 need not be of a particular shape; but, its virtual enclosing sphere must have a diameter that is approximately one-half that of the full thickness of the nominal CCF 410 boundary layer.
  • the CTP 402 composite density should be in a range of 2-to-6 (preferably about 4) times the mean density of their electrolyte-particle suspension.
  • the electrically conductive core of the composite CTP 402 may occupy approximately 10% (in the range of 5 to 20%) of the CTP 402 virtual enclosing sphere. Small tungsten cores are useful because they can be fabricated to desired sizes with appropriate mean densities.
  • the CTP 300, 402 whether or not decorated with admetal islands 312 or catalyst particles 306, is many times the size of the catalyst particle 306 (in the range of 30 to 300 or more) and must be hydrophilic. These specifications are the consequence of calculation and experiment as briefly described below. [0141] The following calculations are based on Eckhardt et al, Scaling of global momentum transport in Taylor-Couette and pipe flow, Eur. Phys. J. B 18, 541-544 (2000) and Eckhardt et al, Torque scaling in turbulent Taylor-Couette flow between independently rotating cylinders, J. Fluid Mech. (2007), vol. 581, 221-250 (2007). These papers and their references only describe isotropic Newtonian fluids; but, they may provide mathematical criteria for obtaining a first-order approximation of the motion of discrete particles in TVF.
  • Fig. 5 of Taylor, p. 323, illustrates laminar streamlines defined by a parameter, ⁇ ⁇ , which is related to radial velocity of fluid flow in TVF.
  • these laminar streamlines can be considered cross-sections of three-dimensional cylinder -like surfaces.
  • the electrolytes in these surfaces also have an angular momentum, L, which is largely preserved. If torque (e.g., shear stress, friction) is not considered, then a first-order approximation of L can be calculated. The calculation can be based on an assumption that the square-like ⁇ turn surface profiles are circles, without significantly affecting the estimate.
  • torque e.g., shear stress, friction
  • L ( ⁇ ) ⁇ that is conserved in the absence of shear stress friction. is a measure of the accumulation of angular momentum of a fluid element as a function of increasing r inside the shearing Taylor vortex fluid that controls the value of tangential velocity at position, r.
  • a fluid element is not a solid body for which a moment of inertia about a fixed axis can be calculated.
  • TVF there is an analogous exchange between kinetic and potential energy - as described next.
  • Fine particles in a fluid suspension within TVF and away from boundary layers at walls defining a chamber are believed to follow streamline flow vectors (as shown in Taylor, Fig. 5 at p. 323) until they are expelled from the vortex.
  • Net centrifugal force on a particle is estimated to be CF ⁇ L" 2 /mr 5 where is an approximately conserved (constant) value of angular momentum, , and m is an expression for mass density relative to the mean density of the fluid suspension where bubbles are buoyant and have negative mass density.
  • both shear and CF act together to drive bubbles quickly to the vortex rotational axis where they become trapped until the vortex is released to the BOP through an exit port (e.g., orifices 138, 142 of FIG. 1) under axial or longitudinal flow.
  • an exit port e.g., orifices 138, 142 of FIG. 1
  • viscous and centrifugal forces are in opposition so that the particles remain within the TVF until they attain sufficient angular momentum, , to escape.
  • the shear force is due to TVF vortex fluid shear where and m are conserved quantities (constants) so the expression describes how shear force is related to distance, r from the TVF vortex axis.
  • Shear force, SF is always in a direction toward the vortex rotation axis, as indicated by the negative sign, ⁇ is a parameter that is related, in part, to particle size, shape and other factors.
  • the viscosity, ⁇ of thixotropic suspensions used here tends to diminish with increasing shear rate, S. Therefore it would normally be lowest near the vortex spin axis where S is the highest. But the latter parameter is very high (in excess of several thousand inverse seconds) everywhere in energetic TVF, so the variation of ⁇ with r is not a significant factor.
  • Particle centrifugal force CF
  • shear force SF
  • the forces have different magnitudes that are functions of the distance of a particle from the center of the vortex.
  • Particle centrifugal force, CF varies as L" 2 /mr 5 while shear force, SF, an opposing force, varies as - ⁇ / ⁇ 3 .
  • individual 75-micron diameter spherical Ni or 100-micron square by 50-micron-thick stainless steel flake or smaller tungsten particles have masses of ⁇ 4 xlO "6 grams, which can vary depending upon internal structural factors. This mass is fairly typical of CTP 402 suitable for use in TVF 404.
  • a powerful effect can be illustrated for a TVF fuel cell with a gap 118 at radius R 0 , width in the range of l-to-2 mm and a spin rate, ⁇ 0 , of 3600-RPM (377-rad./sec).
  • the following analysis can describe functional relationships without actually calculating the tangential velocity, ⁇ 0 at ⁇ nic of the outermost vortex envelope. This can be approximated using momenta and energy scaling as described in the Eckhardt et al references.
  • the filter diameter may be 30-mm and the TVF gap may be in the range of 1 to 2-mm.
  • the filter surface speed is 565.5-cm/sec.at 3600-RPM, which is the speed of a 60-Hz alternating current synchronous motor. That is also the peripheral tangential velocity of the vortex regardless of gap width.
  • the ⁇ ⁇ spin rate becomes 1,800-Hz for a 1-mm gap or 900-Hz for a 2-mm gap. Particles entrained within this flow at the vortex periphery and moving at its velocity will be ejected from the vortex and impact the current collector with considerable force that depends upon how much of the particle momentum is lost upon each impact.
  • a CTP will travel during the interval (t 2 — ti) a distance that is estimated to be approximately the center distance between protuberances on the metal current collector, which is about 50-microns. If the CTP velocity is greater than 500 cm/sec, then the impact interval at first or subsequent strikes would have to be less than 10 5 seconds. There is sufficient impact force to penetrate the Helmholtz planes and any solid-electrolyte interface (SEI) surface deposits.
  • SEI solid-electrolyte interface
  • TVF gaps and rotational velocities used in this invention are extremely energetic compared to the multi-cm gaps and low RPM commonly found in prior art fuel cells. These differences contribute to the high current, power and energy densities of fuel cells taught here.
  • Charging of a fuel cell CTP 300, 402 is equivalent to catalyzed redox (oxygen to the cathode and fuel to the anode) charging of a fuel cell with no load or overvoltage at its exchange current density, j 0 . It also includes charging an EDL, as in a supercapacitor.
  • Fuel cell catalysis is optimized when it proceeds continuously at the typically low exchange current density, ⁇ j 0 , with respect to specific catalyst surface area.
  • the maximum load should be only a very little more than j 0 .
  • Transient increases should be met with current drawn from the EDL.
  • j 0 can continue to charge the EDL to full capacity. That will permit a smoother adjustment of stoichiometric gas supply. Because charge transfer to and from the EDL is fast, the EDL associated with the CTP 300, 402 supports much higher fuel cell efficiency.
  • the amount of charge carried by the EDL can be greatly increased if the carbon is finely divided (e.g., graphene, CNT), as in the
  • a fuel cell CTP 300, 402 built around a dense core coated with finely divided carbon is preferred because it significantly increases the surface area for storage of charge held by a polarized EDL. That charge is fed by an exchange current density, j 0 , to the limit of the fuel cell's Gibbs free energy, zero-current potential, V e .
  • V Ve - Vo - (RT/2aF)ln(j/jo)
  • V net fuel cell voltage
  • V 0 an activation overvoltage that tends to 0 with temperatures above 250 °C;
  • T temperature in °K
  • a charge transfer coefficient (usually about 0.5 at 60 ° C);
  • Fuel cells should be sized to operate so that the maximum catalyst-specific supply current, j, is as close to j 0 as possible so that the operating voltage V is as close to V e as possible.
  • Typical values of V e for many fuels e.g., hydrogen, methane, methanol, gasoline and kerosene
  • This voltage is a safe potential for storing charge in an EDL using carbon.
  • Values of j 0 can vary by orders of magnitude among catalysts, temperatures and fuel and oxidizer chemistries. Fast reactions at low temperatures ( ⁇ 60 °C) are limited almost exclusively to hydrogen fuel on platinum catalyst and yield electrode current densities that are substantially less than 1.0 A/cm 2 . Above 250 °C and when gas molecular mass transport and solvation is substantially accelerated as earlier described, Ni is nearly as active as the noble metals for fuel oxidation and NiO or Mn0 2 are equally active for the ORR.
  • Each of the millions to billions of catalyst particles on a CTP 300, 402 adds charge to the CTP's EDL.
  • Each of the millions to billions of CTPs colliding with and transferring charge to the current collector 106, 108, 406 represents a parallel addition of j 0 to the cell's overall current density and a corresponding reduction in functional internal impedance of the cell.
  • the TVF fuel cells 102 utilize CCF 148, 150 and TVF 144, 146 to achieve high ion velocities.
  • the TVF 144, 146 also sweep reaction products (primarily gases) away from the catalyst surfaces into vortex centers so that fresh fuel or oxygen-saturated electrolyte can replace them near the current collector 106, 108, 406 surfaces. This is especially important when hydrocarbon fuels (e.g., methane, methanol, ethanol) create CO and other reaction products that can poison catalysts.
  • TVF capture the reaction products and move them to the BOP, where they can be exhausted or recycled.
  • Current density is not limited to the SA of conventional static catalyst contained within a narrow band of porous electrode surface adjacent the electrolyte.
  • a TVF fuel cell 102 with the CTP 300, 402 taught here there is a much higher concentration of catalyst surface available to a unit area or cm 2 of current collector 106, 108, 406 surface than for a conventional cell's electrode.
  • Current density is a function of the frequency of CTP 300, 402 impacts with the current collector.
  • the current density at the current collectors 106, 108, 406 is several orders of magnitude higher that the current density of electrodes in conventional fuel cells.
  • the CTP 300, 402 taught here eliminate any need for temperature-sensitive membrane electrode assemblies and facilitate higher temperatures that permit use of much less expensive catalysts while achieving still higher current density.
  • the TVF cell dynamic catalyst suspension carries 3 or 4-orders of magnitude more catalyst surface area servicing the projected area of a current collector equal to surface area of a conventional electrode.
  • a 1-mm TVF suspension gap is 30 to 40-times thicker than the conventional 30- ⁇ thick porous electrode (where thickness is measured by penetration of electrolyte) and the TVF fuel cell 102 catalyst concentration is 30 to 40% instead of 0.2 to 0.3% by volume for the conventional fuel cell.
  • the combination of these two features favor the TVF fuel cell 102 by a factor of 3000 to 4000.
  • the TVF fuel cell 102 advantage is further enhanced by the treatment of catalyst. In the conventional cells, catalyst is fixed in place within narrow pores of the electrodes.
  • each current collector 106, 108, 406 surface is continuously bombarded by CTP 300, 402 which discharges accumulated EDL capacity.
  • the charge in the EDL is being continuously replenished by a large amount of finely divided nanoscale catalyst particles covering and contained within the CTP 300, 402 structure.
  • a CTP 300, 402 remains in contact with the current collector 106, 108, 406 only briefly; but, EDL charge transfer is very rapid. Once a given CTP 300, 402 rebounds from the current collector 106, 108, 406 surface, it is quickly replaced by another CTP that will repeat the process.
  • Embodiment 1 A fuel cell (102) containing a flowable electrolyte suspension comprising: electrolyte; and particles (300, 402) including a galvanic material that are entrained in the electrolyte.
  • Embodiment 2 The fuel cell (102) of Embodiment 1, wherein the electrolyte suspension is thixotropic.
  • Embodiment 3 The fuel cell (102) of any of Embodiments 1 - 2, wherein the particles (300, 402) have a diameter of at least 30 micrometers.
  • Embodiment 4 The fuel cell (102) of any of Embodiments 1 - 3, wherein the particles (300, 402) have a mass of at least 0.5 x 10 "6 grams.
  • Embodiment 5 The fuel cell (102) of any of Embodiments 1 - 4, wherein the particles (300, 402) have a composite density in a range of 2 to 6 times the mean density of their electrolyte-particle suspension.
  • Embodiment 6 The fuel cell (102) of any of Embodiments 1 - 5, wherein the particles (300, 402) are decorated with catalytic particles (306).
  • Embodiment 7 The fuel cell (102) of Embodiment 6, wherein the catalytic particles (306) are attached to a skin (304) of electrically-conducting material covering a metal core (302) to form a charge transfer particle (300).
  • Embodiment 8 The fuel cell (102) of Embodiment 7, wherein the electrically-conducting material is carbon.
  • Embodiment 9 The fuel cell (102) of Embodiment 8, wherein the skin (304) of carbon electrically-conducting material is decorated with nanoscale catalyst particles (306).
  • Embodiment 10 The fuel cell (102) of any of Embodiments 6 - 9 wherein the catalyst particles (306) are nanoscale deposits of a metal selected from a set containing NiOOH, Ni, Mn0 2 and a metal containing an element selected from Group 10 of the Periodic Table of the Elements.
  • Embodiment 11 The fuel cell (102) of any of Embodiments 7 - 10, wherein the core (302) is a metal having a density of at least 8 grams per cm "3 .
  • Embodiment 12 The fuel cell (102) of Embodiment 6, wherein the catalytic particles (306) have a core (310) of a first metal that supports islands (312) created by depositing a second metal in a process that displaces surface atoms of the first metal.
  • Embodiment 13 The fuel cell (102) of Embodiment 12, wherein one of the metals contains an element selected from Group 10 of the Periodic Table of the Elements.
  • Embodiment 14 The fuel cell (102) of any of Embodiments 1 - 13, comprising in addition means for creating Taylor Vortex Flows (144, 146) in the electrolyte.
  • Embodiment 15 The fuel cell (102) of any of Embodiments 1 - 14, comprising in addition means for creating Circular Couette Flows (148, 150) in the electrolyte.
  • Embodiment 16 The fuel cell (102) of any of Embodiments 1 - 15, comprising in addition: first and second current collectors (106, 108) separated by a gap (118); a filter (120) within the gap (118) and dividing the gap (118) into an outer electrolyte chamber (122) and an inner electrolyte chamber (124); electrolyte in at least one of the electrolyte chambers (122, 124); and means for moving the filter (120) within the gap (118) to generate Taylor Vortex Flows (144, 146) in the electrolyte in at least one of the electrolyte chambers (122, 124).
  • Embodiment 17 The fuel cell (102) of Embodiment 16, comprising in addition means for moving the filter (120) within the gap (118) to generate Circular Couette Flows (148, 150) in the electrolyte in at least one of the electrolyte chambers (122, 124).
  • Embodiment 18 The fuel cell (102) of any of Embodiments 16 - 17, wherein at least one of the current collectors (106, 108) is porous.
  • Embodiment 19 The fuel cell (102) of any of Embodiments 16 - 18, comprising in addition means for pumping a fluid selected from a set consisting fuel and oxidizer through one of the porous current collectors (106, 108) toward one of the electrolyte chambers (122, 124).
  • Embodiment 20 The fuel cell (102) of any of Embodiments 16 - 19, comprising in addition means for regulating temperature and pressure of the fluid to convert it into a gas that can create an external electrolyte meniscus gas dome (212) in the electrolyte outside of the electrolyte-facing surface of the porous current collector (106, 108).
  • Embodiment 21 The fuel cell (102) of any of Embodiments 16 - 20, where one of the current collectors (106, 108) is decorated with galvanic flakes.
  • Embodiment 22 The fuel cell (102) of any of Embodiments 16 - 21, wherein one of the current collectors (106, 108) is a composite that contains a galvanic material coating (518).
  • Embodiment 23 The fuel cell (102) of any of Embodiments 1 - 22, comprising in addition two electrolyte chambers (122, 124) separated by a filter (120) that is permeable to flow of the electrolyte in the electrolyte chambers (122, 124); but, not the particles (300, 402) entrained in the electrolyte.
  • Embodiment 24 The fuel cell (102) of Embodiment 23 comprising in addition means for rotating the filter (120) to create a vortex (144, 146, 404) in the electrolyte in one of the electrolyte chambers (122, 124).
  • the galvanic fuel cells of this invention offer structures that provide improved fluid dynamics (e.g., TVF, CCF) for use with flowable electrolyte suspensions that contain galvanic charge transfer particles acting as electrodes in coordination with current collectors that need not contain galvanic materials.
  • fluid dynamics e.g., TVF, CCF
  • the charge transfer particles in the fuel cells of this invention are plentiful and can be easily replaced by simply replacing the electrolyte suspension.

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Abstract

La présente invention concerne des piles à combustibles à tourbillons en écoulement Taylor (102) pour la conversion d'énergie chimique en énergie électrique, qui comportent un filtre particulaire rotatif (120) de forme cylindrique entre des collecteurs de courant (106, 108) de forme cylindrique utilisables avec des électrolytes contenant des particules de matière galvanique chargées circulant entre les collecteurs de courant (106, 108) de forme cylindrique et le filtre (120).
PCT/US2013/065401 2012-10-23 2013-10-17 Piles à combustibles à tourbillons en écoulement taylor mettant en œuvre des suspensions électrolytiques WO2014066130A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3553861A4 (fr) * 2016-12-06 2020-07-29 Showa Denko K.K. Plaque collectrice et batterie à flux redox
EP3553859A4 (fr) * 2016-12-06 2020-07-29 Showa Denko K.K. Plaque collectrice et pile rédox

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Publication number Priority date Publication date Assignee Title
US4016338A (en) * 1975-09-06 1977-04-05 Varta Batterie Aktiengesellschaft Galvanic element
US20060024564A1 (en) * 2004-07-06 2006-02-02 Manclaw Ronald R Manclaw-Harrison fuel cell
US20070141440A1 (en) * 2005-12-21 2007-06-21 General Electric Company Cylindrical structure fuel cell
US20070141456A1 (en) * 2005-12-21 2007-06-21 General Electric Company Bipolar membrane
US20120003518A1 (en) * 2009-06-26 2012-01-05 Halbert Fischel Galvanic electrochemical cells utilizing taylor vortex flows

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Publication number Priority date Publication date Assignee Title
US4016338A (en) * 1975-09-06 1977-04-05 Varta Batterie Aktiengesellschaft Galvanic element
US20060024564A1 (en) * 2004-07-06 2006-02-02 Manclaw Ronald R Manclaw-Harrison fuel cell
US20070141440A1 (en) * 2005-12-21 2007-06-21 General Electric Company Cylindrical structure fuel cell
US20070141456A1 (en) * 2005-12-21 2007-06-21 General Electric Company Bipolar membrane
US20120003518A1 (en) * 2009-06-26 2012-01-05 Halbert Fischel Galvanic electrochemical cells utilizing taylor vortex flows

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3553861A4 (fr) * 2016-12-06 2020-07-29 Showa Denko K.K. Plaque collectrice et batterie à flux redox
EP3553859A4 (fr) * 2016-12-06 2020-07-29 Showa Denko K.K. Plaque collectrice et pile rédox
US10790531B2 (en) 2016-12-06 2020-09-29 Showa Denko K.K. Collector plate and redox flow battery

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