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WO2010148198A1 - Pile à combustible sans membrane multipassage - Google Patents

Pile à combustible sans membrane multipassage Download PDF

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Publication number
WO2010148198A1
WO2010148198A1 PCT/US2010/038990 US2010038990W WO2010148198A1 WO 2010148198 A1 WO2010148198 A1 WO 2010148198A1 US 2010038990 W US2010038990 W US 2010038990W WO 2010148198 A1 WO2010148198 A1 WO 2010148198A1
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WIPO (PCT)
Prior art keywords
stream
fuel
fuel cell
electrolyte
oxidizer
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English (en)
Inventor
Jonathan Posner
Kamil Salloum
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University of Arizona
Arizona State University ASU
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University of Arizona
Arizona State University ASU
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Publication of WO2010148198A1 publication Critical patent/WO2010148198A1/fr
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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
    • H01M8/04—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
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • 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
    • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
    • 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

  • the present application relates to a fuel cell, and more particularly to a multipass membraneless microfluidic fuel cell, in which liquid fuel and liquid oxidant are interfaced multiple times through a flow system.
  • U.S. Patent Publication Nos. 2003/0165727 and 2004/0058203 disclose mixed reactant fuel cells where the fuel, oxidant, and electrolyte are mixed together and then flow through the anode and cathode.
  • the anode is allegedly, or otherwise purported to be, selective for fuel oxidation
  • the cathode is allegedly, or otherwise purported to be, selective for oxidizer reduction.
  • the respective designs in these publications have significant shortcomings.
  • the amount of some oxidizers that can be typically carried by an electrolyte is relatively low (e.g., the oxygen solubility in an electrolyte is typically quite low relative to fuel solubility).
  • the present application addresses the aforementioned challenges without the use of a proton exchange membrane.
  • a fuel cell comprising a first fluid passageway, a second fluid passageway, and an electrolyte passageway positioned at a first reaction zone between the first and second fluid passageways.
  • the first fluid passageway comprises at least one anode and the second fluid passageway comprises at least one cathode.
  • the fuel cell further comprises a port for a reducing agent (such as fuel) in fluid communication with the first fluid passageway for supplying a fuel stream to the first fluid passageway, and an oxidizing agent (or oxidizer) port in fluid communication with the second fluid passageway for supplying an oxidizer stream to the second fluid passageway.
  • the electrolyte passageway comprises an electrolyte stream providing fluidic and ionic communication with the fuel stream and the oxidizer stream.
  • the electrolyte stream can be non-reacting and can maintain a separated fluidic interface between the fuel stream and the oxidizer stream.
  • the electrolyte stream maintains substantially laminar flow.
  • the fuel cell further defines a plurality of reaction zones between the fuel stream, the oxidizer stream, and the electrolyte stream.
  • the electrolyte stream creates and maintains a separated fluidic and ionic interface between the fuel stream and the oxidizer stream.
  • the electrolyte stream of each reaction zone can be a common or a dedicated electrolyte stream. Thus, the electrolyte stream can be varied in each of the reaction zones.
  • Fig. 1 is a schematic view of one aspect of a reaction zone in a membraneless microfluidic fuel cell.
  • Fig. 2 is a schematic view of one aspect of the fuel cell of Fig. 1, showing a plurality of reaction zones.
  • FIG. 3 is a schematic view of the fuel cell of Fig. 2, showing a scheme for interconnections between the reaction zones connected to a load, according to one aspect.
  • Fig. 4 is a cross-sectional view of one aspect of a membraneless microfluidic fuel cell.
  • FIG. 5 is a perspective view of a prototype of one aspect of a membraneless microfluidic fuel cell.
  • FIG. 6 is a schematic view of a multi-pass fuel cell, according to one aspect.
  • Figs. 7A, 7B, and 7C graphically illustrate polarization data for the multi-pass fuel cell of Fig. 6 operating at varied reactant and/or electrolyte flow rates.
  • Fig. 8 graphically illustrates and compares polarization and power density curves for a single cell and the multi-pass fuel cell of Fig. 6.
  • Fig. 9 graphically illustrates the overall fuel utilization for a first cell (Cell 1) of the multi-pass fuel cell of Fig. 6 and both cells of the multi-pass fuel cell at varying reactant flow rates.
  • Fig. 1OA graphically illustrates the thermodynamic losses of a conventional fuel cell.
  • Fig. 1OB graphically illustrates the thermodynamic losses of a multi-pass fuel cell, according to one aspect.
  • an and the include plural referents unless the context clearly dictates otherwise.
  • reference to “an anode” includes two or more such anodes, and the like.
  • Ranges can be expressed herein as from “about” one particular value, and/or to
  • a fuel cell comprising a first fluid passageway 100, a second fluid passageway 200, and an electrolyte passageway 300 positioned at a reaction zone 20 between the first and second fluid passageways.
  • the first fluid passageway 100 comprises at least one anode 110 and the second fluid passageway 200 comprises at least one cathode 210.
  • the fuel cell further comprises a fuel port 120 in fluid communication with the first fluid passageway 100 for supplying a fuel stream 105 to the first fluid passageway, and an oxidizer port 220 in fluid communication with the second fluid passageway 200 for supplying an oxidizer stream 205 to the second fluid passageway 200.
  • the electrolyte passageway 300 comprises an electrolyte stream 305 in fluid communication with the fuel stream 105 and the oxidizer stream 205.
  • the electrolyte stream 305 creates and maintains a separated interface between the fuel stream 105 and oxidizer stream 205.
  • the electrolyte that enters the electrolyte port 320 and the fuel that enters the fuel port 120 interface with each other and flow through the remainder of the fuel passageway 100, and similarly the electrolyte from electrolyte port 320 and oxidizer from oxidizer port 220 interface and flow through the remainder of the oxidizer passageway 200.
  • the interaction between the respective reactant (fuel or oxidizer) and the electrolyte primarily serves to maintain a separated interface where the fuel and oxidizer do not mix.
  • the electrolyte mixes with the respective reactant (fuel or oxidant), therefore enhancing the conductivity of the fluid passing through the first and second fluid passageways 100 and 200.
  • the fuel and oxidizer already exhibit high conductivities, in which case the electrolyte stream still serves the function of maintaining sufficient conductivity for ion exchange through the reaction zone 20.
  • all of the streams maintain substantially laminar flow.
  • the fuel cell further defines a plurality of reaction zones 20 between the fuel stream, the oxidizer stream, and the electrolyte stream.
  • the electrolyte stream 305 creates and maintains separated interfaces between the fuel stream 105 and the oxidizer stream 205.
  • each consecutive reaction zone is in a downstream direction with respect to the fuel stream and each consecutive reaction zone is in a downstream direction with respect to the oxidizer stream. That is to say, the second reaction zone is downstream from the first reaction zone.
  • the first fluid passageway comprises an anode and the second fluid passageway comprises a cathode.
  • FIG. 3 is a schematic view of the fuel cell 10 showing a plurality of anodes
  • the anodes 110 can be made out of a supported electrocatalyst material so that when the fuel comes into contact with the anodes 110, the anodes 110 oxidize fuel and generate electrons for conduction to the load and oxidation products, hi this aspect, the electrocatalyst serves as the catalyst while the support can serve as the main pathway for electron conduction.
  • at least one anode 110 can be embedded in at least a portion of the first fluid passageway 100.
  • anode could be embedded in a porous medium and/or a packed bed in the first fluid passageway, and electron shuttling can occur through this embedded electrocatalyst to the substrate contact or to an electrical interconnect 115, described more fully below.
  • an "oxidation product” is an ionic or molecular byproduct of the fuel's oxidation that has donated at least one electron.
  • An "oxidation product” can also be referred to as a cation because the loss of an electron can result in a positive charge.
  • the cations can be supported in the electrolyte by negative ions.
  • Figure 3 also shows a plurality of cathodes 210 that are each connectable to the external load.
  • the cathodes 210 can be made out of a catalyst material so that when the cathodes 210 are connected to the anodes 110 via the load, the cathodes reduce the oxidizer.
  • the cathodes 210 are configured to receive electrons from the load to reduce an oxidizer (oxidant) when the oxidizer comes into contact with the cathodes 210 to form reduction products and complete an electrochemical circuit.
  • at least one cathode 210 can be embedded in at least a portion of the second fluid passageway 200.
  • the cathode could be embedded in a porous medium and/or a packed bed in the second fluid passageway, and electron shuttling can occur through this embedded electrocatalyst from the substrate contact or to an electrical interconnect 115, described more fully below.
  • a "reduction product” is an ionic or molecular byproduct of the oxidizer that has gained at least one electron.
  • a "reduction product” can also be referred to as an anion because the gain of an electron can result in a negative charge.
  • the anions can be supported in the electrolyte by positive ions.
  • the fuel cell 10 further comprises a plurality of electrical interconnects 115 to electrically couple adjacent reaction zones 20, as illustrated in Figure 3.
  • the electrical interconnects can be conductive material configured to transfer electrons from the anode 110 of a first reaction zone to the cathode 210 of an adjacent reaction zone, minimizing resistive losses. Therefore, the electrons produced from an anode can be transferred to an adjacent cathode for consumption there without external connections.
  • the electrical interconnects 115 can be catalytic as the electrocatalyst can be embedded in the fluid passageways 100, 200, 300, and coupled to the interconnects.
  • a single common electrical "pad" can connect each anode 110 of the plurality of anodes, and a similar pad can connect each cathode 210 of the plurality of cathodes. In this aspect, neither pad would cross a reaction zone 20, and the two pads would only be coupled through the load.
  • Reaction zone 1 represents the schematic shown in Figure 1, in which the outlets for each of the fuel stream and the oxidant stream, which each contain electrolyte and the unreacted portion of the reactant, are used in the next reaction zone.
  • the unreacted fuel and oxidant from reaction zone 1 flow to reaction zone 2, which operates on the same principals as shown in Figure 1. It is contemplated that this sequential recycling can be repeated multiple times.
  • Figure 2 shows seven reaction zones, but more or fewer zones are contemplated. In this manner both high thermodynamic and coulombic efficiencies can be maintained through appropriate loading.
  • thermodynamic efficiency Ej
  • V/V R increases when a fuel cell is operated at a higher voltage V with respect to a maximum theoretical reversible voltage V R .
  • Figure 4 illustrates one possible embodiment of a multipass separated flow micro fluidic fuel cell which has a radial flow pattern.
  • the reaction zones are substantially along a single axis.
  • the advantage to the illustrated radial design is to maximize an ion transfer zone area in a small volume without jeopardizing the laminar flow feature.
  • the electrolyte stream 305 interfaces between the fuel stream 105 and oxidizer stream 205 at each reaction zone 20.
  • the fuel, electrolyte, and/or the oxidant comprise a reactant with high conductivity.
  • the illustrated embodiment is not intended to be limiting in any way.
  • the electrolyte passageway 300 comprises an insulating porous bed 310, such that the first fluid passageway 100 and the second fluid passageway 200 are electrically insulated from one another so as not to cause any short-circuits within the fuel cell and maintain a laminar flow even at higher flow rates.
  • the fuel cell comprises a fuel port 120, an oxidizer port
  • Each of the ports 120, 220, and 320 can be in the form of an aperture, which can be circular in shape as illustrated, or can have any other suitable shape. Although all of the ports 120, 220, 320 are illustrated as being the same size and shape, they do not necessarily have to have the same size and shape.
  • the fuel port can be larger or smaller than the oxidizer port, depending on the desired flow rates and pressures to be realized within the fuel cell.
  • the ports 120, 220, 320 can be created by micromachining, etching, lithography, or any other suitable technique.
  • each passageway can be individually configured to have the desired width and shape so that the desired flow rates and pressures can be realized within the fuel cell.
  • the fluid passageways in one aspect, are designed so that the flow of the fuel, electrolyte(s), and oxidizer is a laminar flow.
  • the passageways can be created by stacking a plurality of routing plates 400, each defining various bores or slots which, when stacked, create the fluid passageways, hi this aspect, the anodes and cathodes are sandwiched between each layer. In the aspect shown in Figure 4, the anodes are radially inward of the cathodes, but other configurations are contemplated.
  • the fluid passageways 100, 200, 300 can span the microfluidic to millifluidic range, i.e., the smallest dimension, such as the diameter of the passageway, can be in the range of about 1 ⁇ m to about 10 mm.
  • the lengths of the passageways can be designed so that the most efficient reactant utilization can be achieved, and can depend on the concentrations of the particular reactants in the fuel and the oxidant.
  • the anode 110 can comprise any electrically conductive material that supports a suitable electrocatalyst for oxidizing the fuel as the fuel passes over the anode 110.
  • the anode 110 can at least partially comprise a porous material that is the catalyst itself.
  • catalysts that can be used include platinum, ruthenium, palladium, nickel, gold, and carbon or alloys of the aforementioned and the like.
  • the porous material can be, for example, a catalyst coated carbon cloth, a porous foam, a packed bed of catalyst particles, colloidal crystal, or reverse opal that allows the fuel to pass therethrough and oxidizes the fuel as it passes.
  • the cathode 210 can comprise any electrically conductive material that supports a suitable electrocatalyst for reducing the oxidizer as the oxidizer passes over the cathode 210.
  • catalysts that can be used include platinum, ruthenium, palladium, nickel, gold, and carbon or alloys of the aforementioned and the like.
  • the cathode 210 can at least partially comprise a porous material that is the catalyst itself.
  • the porous material can be, for example, a catalyst coated carbon cloth, a porous foam, a packed bed of catalyst particles, colloidal crystals, or reverse opal that allows the oxidizer to pass therethrough and reduces the oxidizer as it passes.
  • the fuel port 120 can be fluidly connected to a fuel source.
  • the oxidizer port 220 can be fluidly connected to an oxidizer source and the electrolyte port 320 can be fluidly connected to an electrolyte source.
  • the fuel, oxidizer, and electrolyte can be fed to their respective ports 120,
  • suitable flow generators such as pumps or pressurized sources, can be used to generate the flows of the fuel, oxidizer, and electrolyte through their respective ports 120, 220, 320 and into the respective fluid passageway.
  • each electrode can be made up of any electrically conductive material that is coated with a suitable catalyst.
  • each electrode comprises a porous material that is the catalyst itself, including but not limited to a catalyst coated carbon cloth, a porous foam, a packed bed of catalyst particles, and/or colloidal crystals and the like.
  • the electrical current can be carried from the anode 110, through the external load, and to the cathode 210 with wires or conductive traces that are patterned on to one or more of the fuel cell substrates.
  • the substrate's circuitry can be configured to directly route electrons from an anode zone, to a cathode zone in a separate reaction zone, as opposed to extracting and conveying the electrons from each anode 110 and cathode 210 through external means, which in some exemplary aspects increases resistance losses.
  • the anode of reaction zone 4 sends electrons to the cathode of reaction zone 6, anode of reaction zone 2 to cathode of reaction zone 4, anode of reaction zone 1 to cathode of reaction zone 2, anode of reaction zone 3 to cathode of reaction zone 1, and so on.
  • the remaining anode of reaction zone 6 and cathode of reaction zone 7 can be used to reduce Ohmic losses and reduce the system's circuit complexity, e.g. a hydrogen PEM fuel cell stack with bipolar graphite plates.
  • the fuel cell 10 can be a membraneless microfluidic fuel cell that reuses a reactant, in contrast to conventional multi-channel systems that employ common manifolds for inlets and outlets.
  • Electrodes/Catalysts Platinum, Platinum black, Platonized metal (any),
  • Nickel, Nickel Hydroxide, Manganese, Manganese Oxides (all states), Palladium, Platinum Ruthenium alloys, Nickel Zinc alloys, Nickel Copper alloys, Gold, Platinum black supported on metal oxides, Platinum Molybdenum alloys, Platinum Chromium alloys, Platinum Nickel alloys, Platinum Cobalt alloys, Platinum Titanium alloys, Platinum Copper alloys, Platinum Selenium alloys, Platinum Iron alloys, Platinum Manganese alloys, Platinum Tin alloys, Platinum Tantalum alloys, Platinum Vanadium alloys, Platinum Tungsten alloys, Platinum Zinc alloys, Platinum Zirconium alloys, Silver, Silver/Tungsten Carbide, Iron tetramethoxyphenyl porphorin, Carbon or Carbon Black.
  • Fuels Formic acid, Methanol, Ethanol, 1-proponal, 2-propoanl,
  • Oxidants Air, Oxygen gas, Dissolved Oxygen, Hydrogen Peroxide,
  • Electrolytes Potassium Hydroxide, Sodium Hydroxide, Sulfuric acid, Nitric acid, Formic acid, Phosphoric acid, Trifluoromethanesulfonic acid (TFMSA), Ionic liquids (all types), Acetimide, Fluoroalcohol emulsions, and Perflourocarbon emulsions ⁇ e.g., Flourinert®).
  • a membraneless micro fluidic fuel cell 10 was created that integrated two reaction zones 20 into a single fuel cell.
  • each reaction zone can be treated as an individual electrochemical cell (i.e., Cell 1 and Cell 2) with its own porous anode 110 and cathode 210, and external contact for current sourcing.
  • Figure 6 illustrates the flow pattern in the multipass micro fluidic fuel cell 10 of this example.
  • the fuel stream 105 and the oxidant stream 205 were introduced through a porous electrocatalyst.
  • an electrolyte stream 305 directs the fuel through the first fluid passageway 100 and the oxidant through the second fluid passageway 200 channels leading from Cell 1 to Cell 2.
  • the flow pattern was repeated in Cell 2, and terminated with the fuel and oxidant flowing to independent outlets.
  • the membraneless micro fluidic fuel cell 10 of this example was comprised of three PMMA layers fabricated using a carbon dioxide laser ablation system (M360, Universal Laser Systems, Scottsdale, AZ).
  • the bottom layer had holes cut out for inserting 0.127 mm sections of platinum wire (SPPL-010, Omega Engineering, Stamford, CT) that served as current collectors.
  • the wires came in contact with the electrodes which were 1 mm tall and 8 mm long stacked sheets of Toray carbon paper (E-TEK, Somerset, NJ) housed in the middle layer.
  • the spacing between the electrodes (where the electrolyte stream 305 is introduced) was 1 mm.
  • the active top projected electrode area in the cell was 0.08 cm 2 , and all absolute current and power numbers were normalized by this area.
  • the top layer of the fuel cell sealed the assembly with holes cut out for fluidic access. Liquids were delivered to the cell using 1.5 mm TygonTM tubing (EW-06418-02, Cole Parmer, Vernon Hills, IL) bonded to the ports with quick dry epoxy. The three PMMA layers were adhered using double sided adhesive Mylar (3M, St. Paul, MN).
  • the electrolyte 305 and both reactants 105, 205 were delivered to the fuel cell 10 by two independent programmable syringe pumps (KDS200, KD Scientific, Holliston, MA). Reactant flow rates ranged from 50 to 500 ⁇ l/min, and electrolyte flow rates ranged from 0 to 250 ⁇ l/min.
  • the fuel cell leads were connected to a source meter (Model 2410, Keithley Instruments, Cleveland, OH) operating in galvanostatic mode. Polarization data for Cell 1 and Cell 2 was recorded with a source meter (Model 2410, Keithley Instruments, Cleveland, OH) and a potentiostat (VersaSTAT 4, Princeton Applied Research, Oak Ridge, TN) respectively.
  • Cell 1 was held at a fixed current density, and Cell 2 was then completely polarized by galvanostatic steps. After every step, the voltage in Cell 2 required 10- 15 seconds to reach steady state. The steady state voltage was then time averaged and reported for 10 seconds. Then Cell 1 was held at another current density, and the polarization for Cell 2 was repeated.
  • Vanadium redox species in acidic media V 2+ AV 3+ at the anode 110 and
  • VO 2 VvO 2+ at the cathode 210) were used to characterize the fuel cell 10. Vanadium on bare carbon was chosen because of its relatively high activity and its relatively high open circuit potential. 50 mM V 2+ and VO 2 + in 1 M sulfuric acid were prepared through electrolysis of VO 2+ .
  • Reactants for the cell were obtained by preparing 50 mM vanadium(IV) oxide sulfate hydrate (CAS 123334-20-3, Sigma Aldrich, St. Louis, MO) in sulfuric acid (CAS 7664-93-9, EMD Chemicals, Hibbstown, NJ) diluted to 1 M in 18.3 M ⁇ deionized water (Millipore, Billerica, MA). After mixing, a clear blue solution indicated the presence of the vanadium(IV) ion.
  • An in-house electrolytic cell was fabricated using PMMA for the housing, Toray paper for the electrodes, and a Nafion membrane (NRE212, Fuel Cell Store, Boulder, CO) as the ion exchange medium. The electrolytic cell generated the oxidation states vanadium(II) and vanadium(V) from the stock vanadium(IV).
  • NRE212 Nafion membrane
  • Cell 2 as a function of the operating conditions of Cell 1 condition was studied. As can be appreciated, cell to cell variations can be observed for stacked cells that reuse reactants. In this case, Cell 2 was downstream of Cell 1 and its potential was dependent on the local reactant concentration and flow conditions which can be modified by the operation of Cell 1.
  • FIGS 7 A, 7B, and 7C show polarization data for the multi-pass fuel cell 10 operating at reactant/electrolyte flow rate ratios (in ⁇ l/min) of 50/25, 500/250, and 500/25, respectively.
  • the open circuit potential (OCP) for Cell 1 was approximately 1.2 V for all flow rate cases.
  • the OCP for Cell 2 decreased with increasing Cell 1 current density. This behavior can be more pronounced at low reactant and electrolyte flow rates. Additionally, interfaces with lower flow rates can be more susceptible to reactant crossover. Reactants at their counter electrodes can also reduce the average OCP of the cell, where the magnitude of this voltage loss can be dependent on the sourced current.
  • Figures 7B and 7C show similar Cell 1 polarization at varying separating electrolyte flow rates (250 and 25 ⁇ l/min, respectively). As can be seen, the flow rate of the separating electrolyte had negligible effects on the polarization of Cell 1. For Cell 2, and at the same reactant flow rate, lower maximum current densities at higher separating electrolyte flow rates were observed. Again with reference to Figures 7B and 7C, higher electrolyte flow rates appear to be detrimental to the performance of Cell 2, and therefore the losses due to reactant dilution were more dominant.
  • the multi-pass fuel cell 10 allows for on-chip reactant recycling and can be analyzed as a single microfluidic fuel cell.
  • Cell 1 and Cell 2 were electrically connected in parallel, i.e. Cell 1 and Cell 2 had a common anode 110 and common cathode 210.
  • Figure 8 compares polarization and power density curves between a single and the multi-pass microfluidic fuel cells electrically connected in parallel.
  • the reactant and the separating electrolyte flow rates are 500 and 25 ⁇ l/min, respectively.
  • the Ohmic loss differences were distinct between the two cases, where the slope of the linear region of the stacked cell was approximately half that of the single cell. Curvature in the polarization curves that would typically be associated with activation or mass transport losses was not readily observed. As vanadium redox species exhibit fast electrode kinetics on bare carbon, and at 500 ⁇ l/min mass transport losses were delayed, the majority of the polarization curve reflected the Ohmic losses.
  • ⁇ (6) nFCQ
  • i the maximum measured current density
  • A the top projected electrode area
  • n the number of electrons transferred
  • F Faraday's constant
  • C the concentration of the fuel
  • Q the fuel flow rate
  • Equation (6) describes the fuel utilization calculated from the maximum current density from a single polarization curve. However, the overall fuel utilization given independent polarization curves from Cell 1 and Cell 2 is calculated by:
  • Figure 9 plots the overall fuel utilization using equation (7) for the flow rate cases of 50/25 and 500/25, shown in filled circle and square symbols respectively.
  • the open symbols reflect the first term of equation (7) and are shown for comparison.
  • the value of ⁇ o also increased when ij increased.
  • Both the applied voltage and current density define the efficiency of the fuel cell, where Vop is the fuel cell voltage, and V R is the reversible voltage.
  • the first term in equation (8) is the thermodynamic efficiency, and the losses due to this term are demonstrated by the shaded areas in Figures 1OA and 1OB.
  • ⁇ is maximized at peak fuel cell power, as shown in Figure 1OA.
  • the overall efficiency remains at about 50%.
  • fuel utilization must be sacrificed due to a low value of i j li max -
  • the multipass fuel cell 10 offers a microfluidic solution to this compromise by extracting z, from each pass and therefore having the overall efficiency:
  • Equation (9) The summation in equation (9) is over the total number of passes in the design, each pass designated by the subscripty.
  • the multi-pass architecture decouples the thermodynamic and Faradaic efficiencies. This allows the designer or engineer to independently set the operating fuel cell voltage and current by simply tuning the number of passes the reactants flow through.
  • Parallel flow based laminar flow fuel cells suffer from complications in mass transport boundary layer growth over flat plate electrodes and diffusive broadening at the reaction zone of fuel and oxidant.
  • Previous microfluidic fuel cell designs used porous electrocatalysts to maximize reaction surface area and brief ionic reaction zone zones where advection occurs in the direction of reactant concentration gradients.
  • the multi-pass fuel cell 10 of this application successfully recycles reactants from one cell to the other through the use of multiple reaction zones 20, which increases both the overall fuel cell power and efficiency of the fuel cell. The influence of one reaction zone on the next is prominent at low reactant flow rates and high current densities.
  • the multi-pass fuel cell 10 separates of the reactants throughout the device.
  • a high conductivity ionic exchange reaction zone reduces reactant diffusive mixing.
  • porous electrocatalysts increase available reactions surface area. This multi-pass fuel cell results in an effective increase in the ionic exchange cross sectional area by repeating reaction zones exhibiting reduced diffusive mixing as opposed to a single extended diffusive reaction zone, reducing Ohmic losses in the fuel cell.

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Abstract

L'invention porte sur une pile à combustible ayant un premier circuit fluide, un second circuit fluidique et un circuit électrolytique positionné au niveau d'une première zone de réaction entre les premier et second circuits fluidiques. Le premier circuit fluidique a au moins une anode et le second circuit fluidique a au moins une cathode. La pile à combustible a également un orifice de combustible en communication fluidique avec le premier circuit fluidique pour diriger un flux de combustible dans le premier circuit fluidique, et un orifice d'oxydant en communication fluidique avec le second circuit fluidique pour diriger un flux d'oxydant dans le second circuit fluidique. Le circuit électrolytique a également un flux d'électrolyte en communication fluidique avec le flux de combustible et le flux d'oxydant qui crée et maintient une interface séparée entre le flux de combustible et le flux d'oxydant.
PCT/US2010/038990 2009-06-17 2010-06-17 Pile à combustible sans membrane multipassage Ceased WO2010148198A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120247979A1 (en) * 2010-06-17 2012-10-04 Massachusetts Institute Of Technology Method for Enhancing Current Throughput in an Electrochemical System

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