Nanofiber membrane-electrode-assembly and method of fabricating same

Abstract

In one aspect of the present invention, a method of fabricating a fuel cell membrane-electrode-assembly (MEA) having an anode electrode, a cathode electrode, and a membrane disposed between the anode electrode and the cathode electrode, includes fabricating each of the anode electrode, the cathode electrode, and the membrane separately by electrospinning; and placing the membrane between the anode electrode and the cathode electrode, and pressing then together to form the fuel cell MEA.

Claims

1. A method of fabricating a fuel cell membrane-electrode-assembly (MEA) having an anode electrode, a cathode electrode, and a membrane disposed between the anode electrode and the cathode electrode, comprising: fabricating each of the anode electrode, the cathode electrode, and the membrane separately by electrospinning; and placing the membrane between the anode electrode and the cathode electrode, and pressing them together to form the fuel cell MEA, wherein the step of fabricating the membrane comprises: forming one or more first-type polymer solutions from one or more first-type polymers and one or more second-type polymer solutions from one or more second-type polymers, respectively, wherein each of the one or more first-type polymers comprises a charged polymer and each of the one or more second-type polymers comprises a uncharged (or minimally charged) polymer; electrospinning, separately and simultaneously, the one or more first-type polymer solutions and the one or more second-type polymer solutions to form a dual or multi fiber mat of one or more first-type polymer fibers and one or more second-type polymer fibers; and processing the dual or multi fiber mat by softening and flowing at least one of the one or more first-type polymer fibers to fill in the void space between the one or more second-types polymer fibers, or by softening and flowing at least one of the one or more second-type polymer fibers to fill in the void space between the one or more first-types polymer fibers, so as to form the membrane.

2. The method of claim 1, wherein the one or more first-type polymer fibers comprise ionically conducting polymer fibers, and the one or more second-type polymer fibers comprise uncharged (or minimally charged) polymer fibers.

3. The method of claim 2, wherein the uncharged (or minimally charged) polymer is polyphenylsulfone, and the ionically conducting polymer is a perfluorosulfonic acid polymer.

4. The method of claim 1, wherein the step of processing the dual or multi fiber mat by softening and flowing at least one of the one or more first-type polymer fibers comprises: compressing the dual or multi fiber mat; and thermal annealing the dual or multi fiber mat to soften and flow at least one of the one or more first-type polymer fibers to fill in the void space between the one or more second-type polymer fibers.

5. The method of claim 1, wherein the step of processing the dual or multi fiber mat by softening and flowing at least one of the one or more second-type polymer fibers comprises: compressing the dual or multi fiber mat; and exposing the dual or multi fiber mat to solvent vapor to soften and flow at least one of the one or more second-type polymer fibers to fill in the void space between the one or more first-type polymer fibers.

6. The method of claim 5, wherein the step of processing the dual or multi fiber mat by softening and flowing the at least one of the one or more second-type polymer fibers further comprises: thermal annealing the dual or multi fiber mat.

7. The method of claim 1, wherein the step of fabricating each of the anode electrode and the cathode electrode comprises: forming a polymer solution containing a catalyst and an ionomer or an uncharged (or minimally charged) polymer; electrospinning the polymer solution to generate electrospun fibers so as to form a nanofiber mat; and pressing the nanofiber mat to fabricate the electrode.

8. The method of claim 7, wherein the catalyst comprises platinum-supported carbon (Pt/C).

9. The method of claim 7, wherein the ionomer or uncharged polymer comprises Nafion.

10. A method of fabricating a fuel cell membrane-electrode-assembly (MEA), comprising: fabricating a first nanofiber electrode by electrospinning; sequentially fabricating a nanofiber membrane on the first nanofiber electrode by electrospinning; and sequentially fabricating a second nanofiber electrode on the nanofiber membrane by electrospinning to form the fuel cell MEA, wherein one of the first and second nanofiber electrodes is an anode electrode, and the other of the first and second nanofiber electrodes is a cathode electrode, wherein the step of fabricating the nanofiber membrane comprises: forming one or more first-type polymer solutions from one or more first-type polymers and one or more second-type polymer solutions from one or more second-type polymers, respectively, wherein each of the one or more first-type polymers comprises a charged polymer and each of the one or more second-type polymers comprises a uncharged (or minimally charged) polymer; electrospinning, separately and simultaneously, the one or more first-type polymer solutions and the one or more second-type polymer solutions to form a dual or multi fiber mat of one or more first-type polymer fibers and one or more second-type polymer fibers; and processing the dual or multi fiber mat by softening and flowing at least one of the one or more first-type polymer fibers to fill in the void space between the one or more second-types polymer fibers, or by softening and flowing at least one of the one or more second-type polymer fibers to fill in the void space between the one or more first-types polymer fibers, so as to form the membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings illustrate one or more embodiments of the invention and, together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment.

(2) FIG. 1 schematically shows a membrane-electrode-assembly (MEA) formed according to one embodiment of the present invention.

(3) FIG. 2 shows H.sub.2-air fuel cell performance at about 80 C., 100% relative humidity for an entirely electrospun MEA (E-MEA) compared to a standard MEA (Nafion 212 membrane with decal electrodes). (.square-solid.) E-MEA voltage, () E-MEA power density, (.circle-solid.) Nafion/decal voltage, and () Nafion/decal power density. The H.sub.2 flow rate was about 125 mL/min and the air flow rate was about 500 mL/min. The E-MEA was composed of an about 30 m thick Nafion/polyphenylsulfone electrospun membrane in which Nafion was reinforced by polyphenylsulfone nanofibers and the Nafion loading was about 65 vol %. The E-MEA anode and cathode were electrospun nanofiber mats having about 72 wt % Pt/C, about 13 wt % Nafion, about 15 wt % PAA. Each electrode had a Pt loading of about 0.15 mg/cm.sup.2. The Nafion/decal MEA was a Nafion 212 membrane (51 m thick) with decal electrodes (about 0.15 mg/cm.sup.2 Pt loading and was about 77 wt % Pt/C and about 23 wt % Nafion binder).

DETAILED DESCRIPTION OF THE INVENTION

(4) The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.

(5) The terms used in this specification generally have their ordinary meanings in the art, within the context of the invention, and in the specific context where each term is used. Certain terms that are used to describe the invention are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner regarding the description of the invention. For convenience, certain terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; the scope and meaning of a term are the same, in the same context, whether or not it is highlighted. It will be appreciated that the same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.

(6) It will be understood that when an element is referred to as being on another element, it can be directly on the other element or intervening elements may be present there between. In contrast, when an element is referred to as being directly on another element, there are no intervening elements present. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

(7) It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the invention.

(8) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises and/or comprising, or includes and/or including or has and/or having when used in this specification specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

(9) Furthermore, relative terms, such as lower or bottom and upper or top, may be used herein to describe one element's relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the lower side of other elements would then be oriented on upper sides of the other elements. The exemplary term lower can, therefore, encompass both an orientation of lower and upper, depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as below or beneath other elements would then be oriented above the other elements. The exemplary terms below or beneath can, therefore, encompass both an orientation of above and below.

(10) Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

(11) As used herein, around, about, substantially or approximately shall generally mean within 20 percent, preferably within 10 percent, and more preferably within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term around, about, substantially or approximately can be inferred if not expressly stated.

(12) As used herein, the terms comprise or comprising, include or including, carry or carrying, has/have or having, contain or containing, involve or involving and the like are to be understood to be open-ended, i.e., to mean including but not limited to.

(13) The terms proton exchange membrane or its abbreviation PEM, as used herein, refer to a membrane generally made from ionomers and designed to conduct protons. The terms proton exchange membrane fuel cell or PEM fuel cell, or its abbreviation PEMFC, refer to a fuel cell using the PEM.

(14) The terms anion exchange membrane or its abbreviation AEM, as used herein, refer to a membrane generally made from ionomers and designed to conduct anions. The terms anion exchange membrane fuel cell or AEM fuel cell, or its abbreviation AEMFC, refer to a fuel cell using the AEM.

(15) As used herein, the term conducting polymer or ionomer generally refers to a polymer that conducts ions. More precisely, the ionomer refers to a polymer that includes repeat units of at least a fraction of ionized units. As used herein, the term polyelectrolyte generally refers to a type of ionomer, and particularly a polymer whose repeating units bear an electrolyte group, which will dissociate when the polymer is exposed to aqueous solutions (such as water), making the polymer charged. The conducting polymers, ionomers and polyelectrolytes may be generally referred to as charged polymers. As used herein, the terms polyelectrolyte fiber or charged polymer fiber generally refer to the polymer fiber formed by polyelectrolytes or the likes. As used herein, polyelectrolyte, ionomer, and charged polymer can be used interchangeably.

(16) As used herein, the terms uncharged polymer or uncharged (or minimally charged) polymer generally refer to the polymer that does not effectively conduct ions, particularly to the polymer whose repeating units do not bear an electrolyte group or bear a small number of electrolyte groups, and thus the polymer will not be charged or will have a very small charge when being exposed to aqueous solutions. As used herein, the terms uncharged polymer fiber or uncharged (or minimally charged) polymer fiber generally refer to the polymer fiber formed by the uncharged/uncharged (or minimally charged) polymer.

(17) As used herein, nanoscopic-scale, nanoscopic, nanometer-scale, nanoscale, nanocomposites, nanoparticles, the nano- prefix, and nanostructure generally refers to elements or articles having widths or diameters of less than about 1 m. In all embodiments, specified widths can be smallest width (i.e. a width as specified where, at that location, the article can have a larger width in a different dimension), or largest width (i.e. where, at that location, the article's width is no wider than as specified, but can have a length that is greater). In describing nanostructures, the sizes of the nanostructures refer to the number of dimensions on the nanoscale. For example, nanotextured surfaces have one dimension on the nanoscale, i.e., only the thickness of the surface of an object is between 1.0 and 1000.0 nm. Nanowires have two dimensions on the nanoscale, i.e., the diameter of the tube is between 1.0 and 1000.0 nm; its length could be much greater. Finally, sphere-like nanoparticles have three dimensions on the nanoscale, i.e., the particle is between 1.0 and 1000.0 nm in each spatial dimension. A list of nanostructures includes, but not limited to, nanoparticle, nanocomposite, quantum dot, nanofilm, nanoshell, nanofiber, nanowire, nanotree, nanobrush, nanotube, nanorod, and so on.

(18) The description is now made as to the embodiments of the invention in conjunction with the accompanying drawings. Although various exemplary embodiments of the present invention disclosed herein may be described in the context of fuel cells, it should be appreciated that aspects of the present invention disclosed herein are not limited to being used in connection with one particular type of fuel cell such as a proton exchange membrane (PEM) fuel cell and may be practiced in connection with other types of fuel cells or other types of electrochemical devices such as capacitors and/or batteries without departing from the scope of the present invention disclosed herein.

(19) In accordance with the purposes of this invention, as embodied and broadly described herein, this invention relates to an integration/combination of nanofiber electrodes with a nanofiber-based membrane to create a fuel cell membrane-electrode-assembly (MEA) for an electrochemical device, where each of the nanofiber electrodes and the nanofiber membrane is fabricated by an electrospinning process. Those skilled in the art will recognize that the electrospinning process typically involves applying a high voltage electric field to a spinneret needle containing a polymer solution or polymer melt. Mutual charge repulsion on the surface of the solution overcomes the surface tension such as to produce and eject a thin liquid jet of the solution from the tip of the spinneret needle. As the jet of electrified solution travels towards a collector with a different electric potential, electrostatic repulsion from surface charges causes the diameter of the jet to narrow. The jet may enter a whipping mode and thereby be stretched and further narrowed due to instabilities in the electric field. Solid fibers are produced as the jet dries and the fibers accumulate on the collector to form a non-woven material.

(20) Referring to FIG. 1, an MEA 100 is shown according to one embodiment of the present invention. The MEA 100 in use may be incorporated into an electrochemical device, for example, a proton exchange membrane (PEM) fuel cell. The MEA 100 has an anode electrode 110, a cathode electrode 120, and a membrane 130, where the anode electrode 110 and the cathode electrode 120 are respectively attached to the opposing surfaces of the membrane 130. In the MEA, one or both electrodes 110 and/or 120 are formed of electrospun nanofibers, and the membrane 130 contains electrospun nanofibers. Embodiments of the nanofiber membrane and the nanofiber electrodes and their fabrications are respectively disclosed in co-pending U.S. patent application Ser. Nos. 13/567,857 and 13/823,968, which are incorporated herein in their entireties by reference. Please refer to the disclosures of co-pending U.S. patent application Ser. Nos. 13/567,857 and 13/823,968 for the details. The following description summarizes only the key features of the nanofiber membrane and the nanofiber electrodes and their fabrications.

(21) The membrane 130 is ionically conductive, or proton conductive. In one embodiment, the membrane includes nanofibers of an uncharged (or minimally charged) polymer surrounded by a matrix of a proton conducting polymer. In another embodiment, the membrane includes nanofibers of a proton conducting polymer surrounded by a matrix of an uncharged (or minimally charged) polymer. In one embodiment, the uncharged (or minimally charged) polymer is polyphenylsulfone, and the proton conducting polymer is a perfluorosulfonic acid polymer. In one embodiment, the perfluorosulfonic acid polymer is Nafion.

(22) In one embodiment, the membrane includes a fiber network, formed from a dual or multi fiber mat of one or more first-type polymer fibers and one or more second-type polymer fibers; and a polymer matrix encompassing the fiber network, where the polymer matrix is formed by softening and flowing at least one of the one or more of the first-type polymer fibers of the dual or multi fiber mat to fill in the void space between the one or more second-type polymer fibers of the dual or multi fiber mat, or by softening and flowing at least one of the one or more of the second-type polymer fibers of the dual or multi fiber mat to fill in the void space between the one or more first-type polymer fibers of the dual or multi fiber mat. The one or more first-type polymer fibers include charged polymer fibers or charged polymer precursor fibers, and the one or more second-type polymer fibers include uncharged polymer fibers.

(23) In one embodiment, the one or more first-type polymer fibers include proton conducting polymer fibers, and the one or more second-type polymer fibers includes uncharged (or minimally charged) polymer fibers. In one embodiment, the uncharged (or minimally charged) polymer is polyphenylsulfone, and the proton conducting polymer is a perfluorosulfonic acid polymer.

(24) In one embodiment, the membrane is fabricated by the following steps: At first, one or more first-type polymer solutions are formed from one or more first-type polymers and one or more second-type polymer solutions from one or more second-type polymers, respectively. Each of the one or more first-type polymers includes a charged polymer, while each of the one or more second-type polymers includes an uncharged (or minimally charged) polymer. Next, the one or more first-type polymer solutions and the one or more second-type polymer solutions are electrospun, separately and simultaneously, to form a dual or multi fiber mat of one or more first-type polymer fibers and one or more second-type polymer fibers. Then, the dual or multi fiber mat is processed by softening and flowing at least one of the one or more first-type polymer fibers to fill in the void space between the one or more second-types polymer fibers, or by softening and flowing at least one of the one or more second-type polymer fibers to fill in the void space between the one or more first-types polymer fibers, so as to form the membrane.

(25) In one embodiment, the processing step includes the steps of compressing the dual or multi fiber mat; and thermal annealing the dual or multi fiber mat to soften and flow at least one of the one or more first-type polymer fibers to fill in the void space between the one or more second-type polymer fibers.

(26) In another embodiment, the processing step includes the steps of compressing the dual or multi fiber mat; and exposing the dual or multi fiber mat to solvent vapor to soften and flow at least one of the one or more second-type polymer fibers to fill in the void space between the one or more first-type polymer fibers. In one embodiment, the processing step further includes the steps of thermal annealing the dual or multi fiber mat.

(27) In one embodiment, each of the anode and cathode electrodes includes a catalyst. In one embodiment, the catalyst includes platinum-supported carbon (Pt/C).

(28) In one embodiment, at least one of the anode electrode and the cathode electrode is formed of nanofibers by electrospinning of a polymer solution containing the catalyst and an ionomer or an uncharged (or minimally charged) polymer. In one embodiment, the ionomer or uncharged (or minimally charged) polymer includes Nafion.

(29) In one embodiment, each of the anode electrode and the cathode electrode is fabricated by forming a polymer solution containing the catalyst and the ionomer or an uncharged (or minimally charged) polymer; electrospinning the polymer solution to generate electrospun fibers so as to form a nanofiber mat; and pressing the nanofiber mat to fabricate the electrode.

(30) In one embodiment, each of the anode and cathode electrodes may be coated on one side with a thin catalyst layer, and the anode and cathode electrodes are separated by a PEM. The MEA is disposed between two flow-field plates, and in operation, hydrogen and air or some other fuel and oxidant are provided to the electrodes of the MEA via channels that are formed in the flow field plates. More particularly, one flow-field plate directs hydrogen to the anode and another flow-field plate directs oxygen in the air to the cathode. At the anode, a catalyst layer facilitates separation of the hydrogen into protons and electrons. Free electrons produced at the anode are conducted as a usable electric current through an external circuit. At the cathode, hydrogen protons that have passed through the PEM come together with oxygen in air and electrons that return from the external circuit, to form water and heat.

(31) The fuel cell MEA may also have a first gas diffusion layer disposed between the anode electrode and the membrane; and a second gas diffusion layer disposed between the cathode electrode and the membrane. In one embodiment, the first and second gas diffusion layers are formed of electrospun nanofibers.

(32) In one embodiment, a first entirely electrospun fuel cell MEA has been fabricated (e.g., a fuel cell MEA containing an electrospun anode, an electrospun cathode and an electrospun membrane). The electrospun membrane has been shown to provide enhanced fuel cell durability relative to commercial Nafion films, while the electrospun electrodes have been shown to provide enhanced fuel cell power output and durability, as compared to conventional/benchmark decal electrodes [4, 5]. Thus, the combination of these two materials into a single MEA has considerable advantages over current fuel cell MEA technologies (i.e., decal electrodes on a commercial Nafion membrane or catalyst coated gas diffusion layers that are hot pressed onto a proton conducting membrane).

(33) In the following example, the electrospun MEA (E-MEA) was constructed by separately preparing an electrospun membrane and electrospun electrodes (anode and cathode) and then hot-pressing the components into a single MEA construct. However, according to the invention, the fuel cell MEA can also be fabricated by forming a first electrospun nanofiber electrode; sequentially forming a electrospun nanofiber membrane on the first electrospun nanofiber electrode; and sequentially forming a second electrospun nanofiber electrode on the electrospun nanofiber membrane to construct the fuel cell MEA, where one of the first and second electrospun nanofiber electrodes is an anode electrode, and the other of the first and second electrospun nanofiber electrodes is a cathode electrode.

(34) Without intent to limit the scope of the invention, descriptions and processing for the membrane and electrodes are described as follows. In the exemplary embodiment, the membrane is formed such that a proton conducting polymer is reinforced by an electrospun nanofiber mat of an uncharged polymer. Variants of this construct, for example, a membrane is formed such that the uncharged polymer surrounds an electrospun mat of proton conducting nanofibers, or one electrode (e.g., the anode) contains no nanofiber in structure, can also be utilized to the practice the invention.

(35) Preparation of Nanofiber Membrane

(36) Separate Nafion and polyethylene oxide (PEO) solutions were prepared by dissolving Nafion powder (prepared by evaporating the solvent from LIQUION 1115, Ion Power, Inc.) and PEO powder (Sigma-Aldrich, 400 kDa MW) into a 2:1 weight ratio n-propanol:water mixture. These two solutions were then combined to form a Nafion/PEO electrospinning solution where the PEO constituted about 1 wt % of the total polymer content.

(37) A polyphenylsulfone (Radel R 5500NT, 63 kDa MW, from Solvay Advanced Polymers, LLC) solution was prepared by dissolving polymer powder in an 80:20 wt. ratio of n-methyl-2-pyrrolidone:acetone. The polyphenylsulfone (PPSU) solution and the Nafion/PEO solution were each drawn into separate syringes and electrospun using a 22 gauge needle (Hamilton Company). PPSU fibers and Nafion/PEO fibers were simultaneously collected on a rotating aluminum drum that also oscillated laterally to ensure a random distribution and orientation of fibers with a uniform fiber density. The flow rates and concentrations of the Nafion/PEO and the PPSU were varied to produce fiber mats of varying compositions (i.e., different Nafion volume fractions). The Nafion/PEO solution was electrospun at a flow rate of about 0.20 mL/hr and a concentration of about 20 wt %. The PPSU solution was electrospun at a flow rate of about 0.038 mL/hr, at a constant concentration of about 25 wt %. For the Nafion/PEO electrospinning, a spinneret-to-collector distance (SCD) was fixed at about 6.5 cm and the voltage was set at about 4.15 kV. The PPSU solution was electrospun at about 8.5 kV with an SCD of about 8.5 cm. All electrospinning experiments were performed at room temperature, where the relative humidity was about 35%.

(38) The electrospun dual nanofiber mat was compressed at about 15,000 psi and about 127 C. for about 10 seconds. The sample was rotated 90 three times and successively compressed to ensure even compression. The dual nanofiber mat was then annealed in vacuum at about 150 C. for about 2 hours so as to produce the membrane. The resulting membrane, where PPSU nanofibers are embedded in a Nafion polymer matrix, was boiled in about 1 M sulfuric acid and deionized water for about one hour each to remove residual PEO and to protonate all ion-exchange sites.

(39) Preparation of Nanofiber Electrode:

(40) An electrospinning cathode dispersion (ink) was prepared by mixing Pt/C particles (about 40% Pt on carbon black, from Alfa Aesar), Nafion powders (made by drying a LIQUION 1115 solution from Ion Power, Inc.) and poly(acrylic acid) (MW=450,000 g/mol, from Aldrich) in a 2:1 wt ratio isopropanol:water solvent. The total polymer plus powder content of the ink was about 13.4 wt %, where the Pt/C:Nafion:PAA weight ratio was about 72:13:15.

(41) The ink was pumped out of a needle spinneret (a 22 gauge needle) and deformed into a Taylor cone by the strong applied potential at the needle tip, +7.0 kV relative to a grounded stainless steel rotating drum nanofiber collector. The spinneret-to-collector distance was fixed at about 9 cm, and the flow rate of ink was about 1.5 mL-h.sup.1. Nanofibers were collected on an aluminum foil that was fixed to the collector drum (rotating at about 100 rpm). The drum oscillated horizontally to improve the uniformity of deposited nanofibers. Prior to hot-pressing, the electrospun nanofiber mat was pre-compressed between two PTFE sheets under mild pressure (about 217 Pa) and annealed for about 2 hours at about 150 C. under vacuum. The Pt-loading of the nanofiber mat was calculated from its total weight and the weight-fraction of Pt/C catalyst used for its preparation.

(42) MEA Performance in a Fuel Cell

(43) In this exemplary embodiment, the anode and cathode electrodes and the membrane were prepared separately. However, it should be appreciated that E-MEAs could also be fabricated by successively (sequentially) electrospinning nanofibers for the anode, the membrane, and the cathode and then processing the entire E-MEA simultaneously. In the exemplary embodiment, the membrane and electrodes were prepared separately, and the electrospun electrodes were hot-pressed onto the electrospun membrane at about 283 F. and about 100 psi for about 10 minutes. The E-MEA was then loaded into a fuel cell test fixture and pre-conditioned for about 3 hours at about 80 C. by successively running the fuel cell for about 2 minutes at low current density (about 150 mA/cm.sup.2) and about 2 minutes at low voltage (about 0.2V). Fuel cell performance at about 80 C. and about 100% relative humidity was then measured with a Scribner Fuel Cell Test Station. For comparison, similar MEA preparation/conditioning steps were performed using a commercial Nafion membrane and decal electrodes. The Nafion/decal MEA had the same loading of Pt catalyst in the electrodes (about 0.15 mg/cm.sup.2 each for the anode and cathode) and the electrospun MEA. The fuel cell performance for both MEAs is shown in FIG. 2. As can be seen, the E-MEA produced more power than the standard Nafion/decal MEA at all operating voltages (the measured current density was higher at all cell voltages). At a typical fuel cell operating voltage of about 0.6V, the E-MEA has a power output of about 480 mW/cm.sup.2, as compared to about 377 mW/cm.sup.2 for a Nafion/decal MEA, which is a 27% improvement. The maximum power for the E-MEA is about 516 mW/cm.sup.2, as compared to about 460 mW/cm.sup.2 for the Nafion/decal MEA.

(44) In sum, the present invention, among other things, recites an entirely electrospun fuel cell MEA containing an electrospun anode, an electrospun cathode and an electrospun membrane, for the first time, which has considerable advantages over a conventional Nafion/decal MEA.

(45) The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching.

(46) The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.

LISTING OF REFERENCES

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