WO2005112176A1 - Apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell - Google Patents

Apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell Download PDF

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Publication number
WO2005112176A1
WO2005112176A1 PCT/KR2005/000340 KR2005000340W WO2005112176A1 WO 2005112176 A1 WO2005112176 A1 WO 2005112176A1 KR 2005000340 W KR2005000340 W KR 2005000340W WO 2005112176 A1 WO2005112176 A1 WO 2005112176A1
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Prior art keywords
anode
cathode
polymer electrolyte
reference electrode
electrolyte membrane
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PCT/KR2005/000340
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French (fr)
Inventor
Eun-Sook Lee
Back-Kyun Kho
Won Shim
Jong-Wook Lee
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Hyupjin I & C Co., Ltd.
Skc Co., Ltd.
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Application filed by Hyupjin I & C Co., Ltd., Skc Co., Ltd. filed Critical Hyupjin I & C Co., Ltd.
Publication of WO2005112176A1 publication Critical patent/WO2005112176A1/en

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    • D—TEXTILES; PAPER
    • D03—WEAVING
    • D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
    • D03D15/00—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used
    • D03D15/50—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the properties of the yarns or threads
    • D03D15/56—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the properties of the yarns or threads elastic
    • 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
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04544—Voltage
    • D—TEXTILES; PAPER
    • D03—WEAVING
    • D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
    • D03D13/00—Woven fabrics characterised by the special disposition of the warp or weft threads, e.g. with curved weft threads, with discontinuous warp threads, with diagonal warp or weft
    • D03D13/004—Woven fabrics characterised by the special disposition of the warp or weft threads, e.g. with curved weft threads, with discontinuous warp threads, with diagonal warp or weft with weave pattern being non-standard or providing special effects
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/382—Arrangements for monitoring battery or accumulator variables, e.g. SoC
    • 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
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04537—Electric variables
    • H01M8/04544—Voltage
    • H01M8/04552—Voltage of the individual fuel cell
    • 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
    • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
    • 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 invention relates to an apparatus for determining electropotential properties of a membrane electrode assembly, more particularly for determining the electropotential property of each of the two electrodes of a polymer electrolyte membrane fuel cell in a separate, independent manner.
  • Polymer electrolyte membrane fuel cells have a common structural feature that comprises a membrane electrode assembly (MEA) which consists of a cathode, an anode and a polymer electrolyte membrane disposed between the electrodes, and conductive anode and cathode bipolar plates having channels for the passage of a fuel and an air or oxygen for the anode and cathode, respectively, which encase MEA.
  • MEA membrane electrode assembly
  • the MEA essentially controls the output performance of a PEMFC, and in order to accurately analyze and predict such output performance, many studies have been carried out to independently measure and monitor electropotential properties of the anode and cathode using a reference electrode.
  • 1998- 116622 discloses a method for determining the electropotential properties of a PEMFC using a platinum reference electrode disposed between an anode and an anode bipolar plate.
  • this method has problems in that the reference electrode is affected by the electric field of the anode, and therefore, it is not possible to independently measure the electropotential properties of two electrodes, and the reference electrode causes an increase in the ohmic resistance.
  • a system for determining the voltages of electrodes relative to a reference electrode by way of bringing an extended part of the polymer electrolyte membrane of MEA into contact with a sulfuric acid solution in a separate vessel, and then, dipping the reference electrode in the sulfuric acid solution (see [S. Sarangapani, Journal of Power Sources, 29(1990), 355-364]), as shown in FIG. 1.
  • this system requires a cumbersome equipment and the position of the reference electrode affects the voltage measurement, resulting in poor reproducibility.
  • an apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell which comprises; (A) a membrane electrode assembly accommodation part into which a membrane electrode assembly is installed, said assembly comprising a cathode, an anode and a polymer electrolyte membrane disposed therebetween, the polymer electrolyte membrane having an exposed part which extends beyond the ends of the electrodes; (B) anode bipolar and cathode bipolar plates disposed in line and contact with the anode and cathode of the installed assembly, respectively, each having a predesigned channel in the region in contact with the electrode; (C) a reference electrode which projects from the side of the exposed part of the extended polymer
  • FIG. 1 a schematic diagram of a conventional apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell
  • FIG. 2A a schematic diagram of the apparatus used in Example 1 in accordance with the present invention for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell
  • FIGs. 2B and 2C front views of the anode bipolar and cathode bipolar plates of the apparatus, respectively;
  • FIG. 1 a schematic diagram of a conventional apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell
  • FIG. 2A a schematic diagram of the apparatus used in Example 1 in accordance with the present invention for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell
  • FIGs. 2B and 2C front views of the anode bipolar and cathode bipolar plates of the apparatus, respectively;
  • FIG. 1 a schematic diagram of a conventional apparatus
  • FIG 3 A a schematic diagram of the apparatus used in Example 2 in accordance with the present invention for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell
  • FIGs. 3B and 3C front views of the anode bipolar and cathode bipolar plates of the apparatus, respectively
  • FIGs. 4 and 5 variations in the cell voltage, the respective voltages of the anode and the cathode relative to a reference electrode, and the voltage difference therebetween, measured in Examples 1 and 2, respectively, as function of the current density.
  • reference electrode 2 moisture-feeding means 3 : polymer electrolyte membrane 4 : anode 5 : cathode 6 : anode bipolar plate 7 : cathode bipolar plate 8 : anode end plate 9 : cathode end plate 10 : gasket 11, 12, 13 : volameters 14 : hole to which a reference electrode is inserted 15 : hole to which a moisture-feeding means is inserted 16 : fuel inlet 17 : fuel outlet 18 : air outlet 19 : air inlet
  • FIGs. 2A and 3A are schematic diagrams of two representative embodiments of the inventive apparatus for determining the individual electropotential properties of the anode and cathode of a membrane electrode assembly (MEA) for a polymer electrolyte membrane fuel cell (PEMFC).
  • MEA membrane electrode assembly
  • PEMFC polymer electrolyte membrane fuel cell
  • An MEA for a PEMFC comprising an anode (4), a cathode (5) and a polymer electrolyte membrane (3) disposed between the electrodes is formed by preparing each of the anode (4) and cathode (5), placing the polymer electrolyte membrane (3) between the electrodes, and heat-pressing them together.
  • the polymer electrolyte membrane (3) is formed in such a way that it has an exposed part which extends beyond the ends of the electrodes.
  • the MEA thus prepared is installed in a unit cell evaluation apparatus comprising a reference electrode (1) as shown in FIGs. 2A and 3 A.
  • the inventive unit cell evaluation apparatus comprises a membrane electrode assembly accommodation part into which the MEA is installed; an anode bipolar plate (6) and cathode bipolar plate (7) each having a predesigned channel which is formed on both sides of the accommodation part; and an anode end plate (8) and cathode end plate (9), respectively, located outside of the respective bipolar plates.
  • the MEA is installed into the membrane electrode assembly accommodation part such that its anode (4) and cathode (5) face the anode bipolar plate (6) and cathode bipolar plate (7), respectively.
  • the reference electrode (1) is attached to the exposed part of the polymer electrolyte membrane (3) of the installed assembly such that it vertically projects outward across the bipolar plate and end plate, through a region of the bipolar plate where the channel is not formed.
  • the reference electrode (1) may be disposed on either the anode or cathode side, or both sides, and brought in contact with a site of the exposed part of the polymer electrolyte membrane.
  • the reference electrode (1) is preferably disposed at 10 to 200% of a diagonal length of the anode or cathode away from a periphery of the anode or cathode.
  • the reference electrode (1) is installed on the anode (4) side.
  • the inventive apparatus may comprise a moisture-feeding means (2) which is in contact with the polymer electrolyte membrane (3) at a site (the cathode (5) side) opposite to the reference electrode (1). This moisture-feeding means (2) prevents the drying of the electrolyte membrane at a unit cell temperature of 50 ° C or higher.
  • the anode bipolar plate (6) and cathode bipolar plate (7) face in line with the anode and cathode of the installed assembly, respectively, and each has a predesigned channel in the contact region.
  • the channel may be of any suitable form, and a fuel (hydrogen (H 2 ) or methanol) and air are introduced into and discharged from the channels of the anode bipolar and cathode bipolar plates, respectively.
  • the anode bipolar and cathode bipolar plates (6 and 7) also serve as terminals for measuring currents and voltages generated during the operation of MEA. FIGs.
  • FIG. 2B and 2C depict the front views of the anode bipolar and cathode bipolar plates of the inventive apparatus, respectively, wherein the anode bipolar plate (6) contains a channel which extends from a fuel inlet (16) to a fuel outlet (17) as well as a hole (14) through which the reference electrode is inserted; and the cathode bipolar plate (7), a channel which extends from an air inlet (19) to an air outlet (18) and a hole (15) through which the moisture-feeding means is inserted.
  • the reference electrode (1) is installed on the cathode (5) side and the fuel may be introduced into or discharged from the anode (4) side opposite to the reference electrode (1). As shown in FIG.
  • the channel of the anode bipolar plate (6) extends to a site opposite to the reference electrode (1).
  • the channel of the cathode bipolar plate (7) which extends from an air inlet (19) to an air outlet (18) should be confined into the region in contact with the cathode (see FIG. 3C).
  • a cell voltage (an MEA voltage) and respective voltages of the anode and cathode against the reference electrode may be independently obtained at the same time by feeding a fuel and air to the anode and cathode, respectively, after an electric loader is connected to the anode bipolar and cathode bipolar plates.
  • the cell voltage and the respective voltages of the anode and cathode against the reference electrode are measured by three voltameters (11, 12 and 13) connected between the anode bipolar plate and the cathode bipolar plates, the anode bipolar plate and the reference electrode, and the cathode bipolar plate and the reference electrode, respectively.
  • the reference electrode used in the present invention may be a hydrogen, calomel, silver-silver chloride, mercury-mercuric oxide, mercury- mercuric sulfate or platinum electrode.
  • the anode, cathode, polymer electrolyte membrane, end plate and bipolar plate used in the present invention may be any one of conventional materials which are used for the manufacture of the PEMFC.
  • the apparatus of the present invention provides a simple and accurate means for determining electropotential properties of the anode and cathode of an MEA for a PEMFC such as a direct methanol, formic acid and hydrogen ion conductive fuel cell.
  • a PEMFC such as a direct methanol, formic acid and hydrogen ion conductive fuel cell.
  • a catalyst composition containing 5mg/cm 2 of Pt-Ru black (Johnson- Meti) and 15% by weight of Nafion ionomer (Dupont) based on the total weight of the composition was coated on a carbon paper (Toray) and dried to prepare an anode.
  • Another catalyst composition containing 5mg/cm 2 of Pt black (Johnson-Meti) and 10% by weight of Nafion ionomer (Dupont) based on the total weight of the composition was coated on a carbon paper (Toray) and dried to prepare a cathode.
  • a Nafion 117 hydrogen ion electrolyte membrane (Dupont) was placed between the anode and cathode, and heat- pressed at 130 ° C under a pressure of 100kg/cm 2 for 3 min to prepare a membrane electrode assembly (MEA) (size of each of anode and cathode : 3cm X 3cm).
  • MEA membrane electrode assembly
  • the MEA thus prepared was installed into the membrane electrode assembly accommodation part of the inventive unit cell evaluation apparatus in the way as shown in FIG. 2A, wherein the polymer electrolyte membrane (3) extended beyond the electrodes, and 2M aqueous methanol and air were fed to the anode (4) and cathode (5), respectively.
  • a calomel electrode was used as a reference electrode (1) and a moisture-feeding means (2) was installed such that it contacted with the polymer electrolyte membrane (3) at a site opposite to the reference electrode (1).
  • Anode bipolar and cathode bipolar plates (6 and 7) shown in FIGs. 2B and 2C, respectively, were employed, wherein the hole (14) to which the reference electrode was inserted was positioned at 15 mm from the fuel inlet (16) at a periphery region of the anode, while the hole (15) to which the moisture-feeding means was inserted was positioned at a site opposite to the reference electrode.
  • the cell voltage, and respective voltages of the anode and cathode against the reference electrode as function of the current density were independently measured after an electric loader was connected to the anode and cathode bipolar plate terminals.
  • the measurement result is shown in FIG. 4.
  • the difference between the measured voltages of the anode and cathode to the reference electrode is practically identical to the cell voltage, i.e., the potential between the anode and cathode.
  • the membrane electrode assembly (MEA) prepared by the same method as in Example 1 was installed into the membrane electrode assembly accommodation part of the inventive unit cell evaluation apparatus in the way as shown in FIG. 3 A, wherein the polymer electrolyte membrane (3) extended beyond the electrodes, and 2M aqueous methanol and air were fed to the anode (4) and cathode (5), respectively.
  • a calomel electrode was used as a reference electrode (1) and no moisture-feeding means (2) was used.
  • 3B and 3C were employed in such a way that the hole (14) to which the reference electrode was inserted was positioned at 15 mm from the air outlet (18) at a periphery region of the cathode, and the channel for the fuel was extended to a site opposite to the reference electrode (1).
  • the cell voltage, and respective voltages of the anode and cathode against the reference electrode as function of the current density were independently measured after an electric loader was connected to the anode and cathode bipolar plate terminals. The measurement result is shown in FIG. 5.
  • the difference between the measured voltages of the anode and cathode to the reference electrode is practically identical to the cell voltage, i.e., the potential between the anode and cathode.
  • Comparative Example A membrane electrode assembly (MEA) having a polymer electrolyte membrane extended longer than the length of the unit cell was prepared by the method of Example 1, and it was installed into a conventional unit cell evaluation apparatus.
  • the extended portion of the polymer electrolyte membrane was brought into contact with 0.5M sulfuric acid in a vessel positioned outside and a calomel reference electrode was dipped in the sulfuric acid solution as shown in FIG. 1.
  • the respective voltages of the anode and cathode against the reference electrode as function of the current density were independently measured by the method of Example 1.
  • the anode and cathode voltages with respect to the reference electrode depended on the position of the reference electrode, leading to unaccurate evaluation of the output performance of the PEMFC, in contrast to Examples 1 and 2.
  • the apparatus of the present invention provide a simple and accurate means for determining the electropotential properties of the anode and cathode of an MEA for a PEMFC.

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Abstract

Described in the present invention is an apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell comprising a reference electrode which projects from a side of an exposed part of a polymer electrolyte membrane of the assembly vertically toward the outside.

Description

APPARATUS FOR DETERMINING ELECTROPOTENTIAL PROPERTIES OF A MEMBRANE ELECTRODE ASSEMBLY FOR A POLYMER ELECTROLYTE MEMBRANE FUEL CELL
FIELD OF THE INVENTION
The present invention relates to an apparatus for determining electropotential properties of a membrane electrode assembly, more particularly for determining the electropotential property of each of the two electrodes of a polymer electrolyte membrane fuel cell in a separate, independent manner.
BACKGROUND OF THE INVENTION Polymer electrolyte membrane fuel cells (PEMFCs) have a common structural feature that comprises a membrane electrode assembly (MEA) which consists of a cathode, an anode and a polymer electrolyte membrane disposed between the electrodes, and conductive anode and cathode bipolar plates having channels for the passage of a fuel and an air or oxygen for the anode and cathode, respectively, which encase MEA. The MEA essentially controls the output performance of a PEMFC, and in order to accurately analyze and predict such output performance, many studies have been carried out to independently measure and monitor electropotential properties of the anode and cathode using a reference electrode. For example, Japanese Patent Publication No. 1998- 116622 discloses a method for determining the electropotential properties of a PEMFC using a platinum reference electrode disposed between an anode and an anode bipolar plate. However, this method has problems in that the reference electrode is affected by the electric field of the anode, and therefore, it is not possible to independently measure the electropotential properties of two electrodes, and the reference electrode causes an increase in the ohmic resistance. In addition, there has been reported a system for determining the voltages of electrodes relative to a reference electrode by way of bringing an extended part of the polymer electrolyte membrane of MEA into contact with a sulfuric acid solution in a separate vessel, and then, dipping the reference electrode in the sulfuric acid solution (see [S. Sarangapani, Journal of Power Sources, 29(1990), 355-364]), as shown in FIG. 1. However, this system requires a cumbersome equipment and the position of the reference electrode affects the voltage measurement, resulting in poor reproducibility.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a simple apparatus which can be advantageously used to accurately determine the individual electropotential properties of the anode and cathode of a membrane electrode assembly for a polymer electrolyte membrane fuel cell. In accordance with one aspect of the present invention, there is provided an apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell, which comprises; (A) a membrane electrode assembly accommodation part into which a membrane electrode assembly is installed, said assembly comprising a cathode, an anode and a polymer electrolyte membrane disposed therebetween, the polymer electrolyte membrane having an exposed part which extends beyond the ends of the electrodes; (B) anode bipolar and cathode bipolar plates disposed in line and contact with the anode and cathode of the installed assembly, respectively, each having a predesigned channel in the region in contact with the electrode; (C) a reference electrode which projects from the side of the exposed part of the extended polymer electrolyte membrane of the installed assembly vertically toward the outside and is disposed on either the anode or cathode side, or both sides; (D) an electric loader connected between the anode bipolar and cathode bipolar plates which induces a fuel cell reaction at a constant current density or voltage; and (E) three voltameters connected between the anode bipolar plate and the cathode bipolar plate, the anode bipolar plate and the reference electrode, and the cathode bipolar plate and the reference electrode, respectively, for measuring potential differences therebetween.
BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and features of the present invention will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, which respectively show: FIG. 1 : a schematic diagram of a conventional apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell; FIG. 2A : a schematic diagram of the apparatus used in Example 1 in accordance with the present invention for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell; and FIGs. 2B and 2C : front views of the anode bipolar and cathode bipolar plates of the apparatus, respectively; FIG. 3 A : a schematic diagram of the apparatus used in Example 2 in accordance with the present invention for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell; and FIGs. 3B and 3C : front views of the anode bipolar and cathode bipolar plates of the apparatus, respectively; and FIGs. 4 and 5 : variations in the cell voltage, the respective voltages of the anode and the cathode relative to a reference electrode, and the voltage difference therebetween, measured in Examples 1 and 2, respectively, as function of the current density. 1 : reference electrode 2 : moisture-feeding means 3 : polymer electrolyte membrane 4 : anode 5 : cathode 6 : anode bipolar plate 7 : cathode bipolar plate 8 : anode end plate 9 : cathode end plate 10 : gasket 11, 12, 13 : volameters 14 : hole to which a reference electrode is inserted 15 : hole to which a moisture-feeding means is inserted 16 : fuel inlet 17 : fuel outlet 18 : air outlet 19 : air inlet
DETAILED DESCRIPTION OF THE INVENTION FIGs. 2A and 3A are schematic diagrams of two representative embodiments of the inventive apparatus for determining the individual electropotential properties of the anode and cathode of a membrane electrode assembly (MEA) for a polymer electrolyte membrane fuel cell (PEMFC). An MEA for a PEMFC comprising an anode (4), a cathode (5) and a polymer electrolyte membrane (3) disposed between the electrodes is formed by preparing each of the anode (4) and cathode (5), placing the polymer electrolyte membrane (3) between the electrodes, and heat-pressing them together. The polymer electrolyte membrane (3) is formed in such a way that it has an exposed part which extends beyond the ends of the electrodes. The MEA thus prepared is installed in a unit cell evaluation apparatus comprising a reference electrode (1) as shown in FIGs. 2A and 3 A. The inventive unit cell evaluation apparatus comprises a membrane electrode assembly accommodation part into which the MEA is installed; an anode bipolar plate (6) and cathode bipolar plate (7) each having a predesigned channel which is formed on both sides of the accommodation part; and an anode end plate (8) and cathode end plate (9), respectively, located outside of the respective bipolar plates. The MEA is installed into the membrane electrode assembly accommodation part such that its anode (4) and cathode (5) face the anode bipolar plate (6) and cathode bipolar plate (7), respectively. The reference electrode (1) is attached to the exposed part of the polymer electrolyte membrane (3) of the installed assembly such that it vertically projects outward across the bipolar plate and end plate, through a region of the bipolar plate where the channel is not formed. The reference electrode (1) may be disposed on either the anode or cathode side, or both sides, and brought in contact with a site of the exposed part of the polymer electrolyte membrane. The reference electrode (1) is preferably disposed at 10 to 200% of a diagonal length of the anode or cathode away from a periphery of the anode or cathode. In one embodiment of the inventive apparatus shown in FIG. 2A, the reference electrode (1) is installed on the anode (4) side. For the purpose of providing the polymer electrolyte membrane (3) with moisture, the inventive apparatus may comprise a moisture-feeding means (2) which is in contact with the polymer electrolyte membrane (3) at a site (the cathode (5) side) opposite to the reference electrode (1). This moisture-feeding means (2) prevents the drying of the electrolyte membrane at a unit cell temperature of 50 °C or higher. The anode bipolar plate (6) and cathode bipolar plate (7) face in line with the anode and cathode of the installed assembly, respectively, and each has a predesigned channel in the contact region. The channel may be of any suitable form, and a fuel (hydrogen (H2) or methanol) and air are introduced into and discharged from the channels of the anode bipolar and cathode bipolar plates, respectively. The anode bipolar and cathode bipolar plates (6 and 7) also serve as terminals for measuring currents and voltages generated during the operation of MEA. FIGs. 2B and 2C depict the front views of the anode bipolar and cathode bipolar plates of the inventive apparatus, respectively, wherein the anode bipolar plate (6) contains a channel which extends from a fuel inlet (16) to a fuel outlet (17) as well as a hole (14) through which the reference electrode is inserted; and the cathode bipolar plate (7), a channel which extends from an air inlet (19) to an air outlet (18) and a hole (15) through which the moisture-feeding means is inserted. In another embodiment of the inventive apparatus shown in FIG. 3 A, the reference electrode (1) is installed on the cathode (5) side and the fuel may be introduced into or discharged from the anode (4) side opposite to the reference electrode (1). As shown in FIG. 3B, the channel of the anode bipolar plate (6) extends to a site opposite to the reference electrode (1). In this case, the channel of the cathode bipolar plate (7) which extends from an air inlet (19) to an air outlet (18) should be confined into the region in contact with the cathode (see FIG. 3C). In the inventive apparatus, a cell voltage (an MEA voltage) and respective voltages of the anode and cathode against the reference electrode may be independently obtained at the same time by feeding a fuel and air to the anode and cathode, respectively, after an electric loader is connected to the anode bipolar and cathode bipolar plates. The cell voltage and the respective voltages of the anode and cathode against the reference electrode are measured by three voltameters (11, 12 and 13) connected between the anode bipolar plate and the cathode bipolar plates, the anode bipolar plate and the reference electrode, and the cathode bipolar plate and the reference electrode, respectively. The reference electrode used in the present invention may be a hydrogen, calomel, silver-silver chloride, mercury-mercuric oxide, mercury- mercuric sulfate or platinum electrode. The anode, cathode, polymer electrolyte membrane, end plate and bipolar plate used in the present invention may be any one of conventional materials which are used for the manufacture of the PEMFC. In accordance with the inventive apparatus, the difference between the voltages of the anode and cathode to the reference electrode is practically identical to the cell voltage. As described above, the apparatus of the present invention provides a simple and accurate means for determining electropotential properties of the anode and cathode of an MEA for a PEMFC such as a direct methanol, formic acid and hydrogen ion conductive fuel cell. The following Examples and Comparative Example are given for the purpose of illustration only, and are not intended to limit the scope of the invention. Example 1
A catalyst composition containing 5mg/cm2 of Pt-Ru black (Johnson- Meti) and 15% by weight of Nafion ionomer (Dupont) based on the total weight of the composition was coated on a carbon paper (Toray) and dried to prepare an anode. Another catalyst composition containing 5mg/cm2 of Pt black (Johnson-Meti) and 10% by weight of Nafion ionomer (Dupont) based on the total weight of the composition was coated on a carbon paper (Toray) and dried to prepare a cathode. A Nafion 117 hydrogen ion electrolyte membrane (Dupont) was placed between the anode and cathode, and heat- pressed at 130°C under a pressure of 100kg/cm2 for 3 min to prepare a membrane electrode assembly (MEA) (size of each of anode and cathode : 3cm X 3cm). The MEA thus prepared was installed into the membrane electrode assembly accommodation part of the inventive unit cell evaluation apparatus in the way as shown in FIG. 2A, wherein the polymer electrolyte membrane (3) extended beyond the electrodes, and 2M aqueous methanol and air were fed to the anode (4) and cathode (5), respectively. A calomel electrode was used as a reference electrode (1) and a moisture-feeding means (2) was installed such that it contacted with the polymer electrolyte membrane (3) at a site opposite to the reference electrode (1). Anode bipolar and cathode bipolar plates (6 and 7) shown in FIGs. 2B and 2C, respectively, were employed, wherein the hole (14) to which the reference electrode was inserted was positioned at 15 mm from the fuel inlet (16) at a periphery region of the anode, while the hole (15) to which the moisture-feeding means was inserted was positioned at a site opposite to the reference electrode. The cell voltage, and respective voltages of the anode and cathode against the reference electrode as function of the current density were independently measured after an electric loader was connected to the anode and cathode bipolar plate terminals. The measurement result is shown in FIG. 4. As can be seen in FIG. 4, the difference between the measured voltages of the anode and cathode to the reference electrode is practically identical to the cell voltage, i.e., the potential between the anode and cathode. Example 2
The membrane electrode assembly (MEA) prepared by the same method as in Example 1 was installed into the membrane electrode assembly accommodation part of the inventive unit cell evaluation apparatus in the way as shown in FIG. 3 A, wherein the polymer electrolyte membrane (3) extended beyond the electrodes, and 2M aqueous methanol and air were fed to the anode (4) and cathode (5), respectively. A calomel electrode was used as a reference electrode (1) and no moisture-feeding means (2) was used. Such anode bipolar and cathode bipolar plates (6 and 7) shown in FIGs. 3B and 3C, respectively, were employed in such a way that the hole (14) to which the reference electrode was inserted was positioned at 15 mm from the air outlet (18) at a periphery region of the cathode, and the channel for the fuel was extended to a site opposite to the reference electrode (1). The cell voltage, and respective voltages of the anode and cathode against the reference electrode as function of the current density were independently measured after an electric loader was connected to the anode and cathode bipolar plate terminals. The measurement result is shown in FIG. 5. As can be seen in FIG. 5, the difference between the measured voltages of the anode and cathode to the reference electrode is practically identical to the cell voltage, i.e., the potential between the anode and cathode.
Comparative Example A membrane electrode assembly (MEA) having a polymer electrolyte membrane extended longer than the length of the unit cell was prepared by the method of Example 1, and it was installed into a conventional unit cell evaluation apparatus. The extended portion of the polymer electrolyte membrane was brought into contact with 0.5M sulfuric acid in a vessel positioned outside and a calomel reference electrode was dipped in the sulfuric acid solution as shown in FIG. 1. Then, the respective voltages of the anode and cathode against the reference electrode as function of the current density were independently measured by the method of Example 1. In this apparatus, the anode and cathode voltages with respect to the reference electrode depended on the position of the reference electrode, leading to unaccurate evaluation of the output performance of the PEMFC, in contrast to Examples 1 and 2.
As described above, the apparatus of the present invention provide a simple and accurate means for determining the electropotential properties of the anode and cathode of an MEA for a PEMFC. While the invention has been described with respect to the above specific embodiments, it should be recognized that various modifications and changes may be made to the invention by those skilled in the art which also fall within the scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS :
1. An apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell, which comprises;
(A) a membrane electrode assembly accommodation part into which a membrane electrode assembly is installed, said assembly comprising a cathode, an anode and a polymer electrolyte membrane disposed therebetween, the polymer electrolyte membrane having an exposed part which extends beyond the ends of the electrodes;
(B) anode bipolar and cathode bipolar plates disposed in line and contact with the anode and cathode of the installed assembly, respectively, each having a predesigned channel in the region in contact with the electrode;
(C) a reference electrode which projects from the side of the exposed part of the extended polymer electrolyte membrane of the installed assembly vertically toward the outside and is disposed on either the anode or cathode side, or both sides;
(D) an electric loader connected between the anode bipolar and cathode bipolar plates which induces a fuel cell reaction at a constant current density or voltage; and
(E) three voltameters connected between the anode bipolar plate and the cathode bipolar plate, the anode bipolar plate and the reference electrode, and the cathode bipolar plate and the reference electrode, respectively, for measuring potential differences therebetween.
2. The apparatus of claim 1, wherein the reference electrode is disposed at 10 to 200% of a diagonal length of the anode or cathode away from a periphery of the anode or cathode.
3. The apparatus of claim 1, wherein the reference electrode is a hydrogen, calomel, silver-silver chloride, mercury-mercuric oxide, mercury-mercuric sulfate or platinum electrode.
4. The apparatus of claim 1, wherein the reference elecfrode is positioned on the side of the anode.
5. The apparatus of claim 1, wherein the reference elecfrode is positioned on the side of the cathode.
6. The apparatus of claim 4, wherein a moisture-feeding means is placed in contact with the polymer electrolyte membrane at a site opposite to the reference elecfrode.
7. The apparatus of claim 5, wherein a fuel is introduced into or discharged from a site opposite to the reference electrode.
8. The apparatus of claim 7, wherein the channel of the anode bipolar plate extends to a site opposite to the reference electrode.
9. The apparatus of claim 1, wherein the membrane elecfrode assembly is used for a direct methanol, formic acid or hydrogen ion conductive fuel cell.
PCT/KR2005/000340 2004-05-18 2005-02-04 Apparatus for determining electropotential properties of a membrane electrode assembly for a polymer electrolyte membrane fuel cell WO2005112176A1 (en)

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KR1020040035038A KR100618233B1 (en) 2004-05-18 2004-05-18 System for determining polarization property of a membrane electrode assembly for a polymer electrolyte membrane fuel cell

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