Membrane electrode assembly for organic/air fuel cells

Abstract

A membrane electrode assembly for an organic/air fuel cell is provided comprising a proton exchange membrane, an anode electrode, and a cathode electrode. The proton exchange membrane is made of a highly fluorinated ion-exchange polymer. The anode electrode is comprised of an anode electrocatalyst of platinum and ruthenium supported on particulate carbon and a highly fluorinated ion-exchange polymer binder, and the metal loading in the anode electrode is less than 3 mg/cm 2 . The cathode electrode is comprised of a cathode electrocatalyst of platinum supported on particulate carbon and a highly fluorinated ion-exchange polymer binder, and the metal loading in the cathode electrode is less than 3 mg/cm 2 . Organic/air fuel cells comprised of such membrane electrode assemblies are also provided. A process for operating such membrane electrode assemblies of an organic/air fuel cell is also provided.

1 . A membrane electrode assembly for an organic/air fuel cell comprising:
 a proton exchange membrane made of a highly fluorinated ion-exchange polymer, said membrane having opposite first and second sides;   an anode electrode adjacent said first side of the membrane, said anode electrode comprised of 50 to 90 wt % of an anode electrocatalyst and 10 to 50 wt % of a highly fluorinated ion-exchange polymer binder, said anode electrocatalyst being comprised of an anode metal supported on carbon, wherein the anode metal is comprised of platinum and ruthenium and the carbon is particulate carbon, said anode electrocatalyst being comprised of at least 40 wt % platinum, at least 15 wt % ruthenium, and 15 to 50 wt % particulate carbon wherein the total loading of the anode metal in the anode electrode is less than 3 mg/cm 2 ;   a cathode electrode adjacent said second side of the membrane, said cathode electrode comprised of 50 to 90 wt % of a cathode electrocatalyst and 10 to 50 wt % of a highly fluorinated ion-exchange polymer binder, said cathode electrocatalyst being comprised of a cathode metal supported on carbon, wherein the cathode metal is comprised of platinum and the carbon is particulate carbon, said cathode electrocatalyst being comprised of at least 50 wt % platinum and 15 to 50 wt % particulate carbon wherein the total loading of the cathode metal in the cathode electrode is less than 3 mg/cm 2 .   
     
     
         2 . The membrane electrode assembly of  claim 1 , wherein the anode electrocatalyst consists essentially of platinum, ruthenium and particulate carbon. 
     
     
         3 . The membrane electrode assembly of  claim 2 , wherein the anode electrocatalyst includes 40 to 60 wt % platinum, 20 to 40 wt % ruthenium and 20 to 30 wt % particulate carbon. 
     
     
         4 . The membrane electrode assembly of  claim 1 , wherein the cathode electrocatalyst consists essentially of platinum and particulate carbon. 
     
     
         5 . The membrane electrode assembly of  claim 4 , wherein the cathode electrocatalyst includes 60 to 80 wt % platinum and 20 to 40 wt % particulate carbon. 
     
     
         6 . The membrane electrode assembly of  claim 1  wherein the total loading of the anode metal in the anode electrode is less than 2.5 mg/cm 2 , and wherein the total loading of the cathode metal in the cathode electrode is less than 2.5 mg/cm 2 . 
     
     
         7 . The membrane electrode assembly of  claim 1  wherein the total loading of the anode metal in the anode electrode is less than 2 mg/cm 2 , and wherein the total loading of the cathode metal in the cathode electrode is less than 2 mg/cm 2 . 
     
     
         8 . The membrane electrode assembly of  claim 1  wherein the sum of the total loading of anode metal in the anode electrode and cathode metal in the cathode electrode is less than 5 mg/cm 2 . 
     
     
         9 . The membrane electrode assembly of  claim 8  wherein the sum of the total loading of anode metal in the anode electrode and cathode metal in the cathode electrode is less than 3.5 mg/cm 2 . 
     
     
         10 . The membrane electrode assembly of  claim 1  wherein the proton exchange membrane consists essentially of a perfluorinated sulfonic acid membrane in acid form. 
     
     
         11 . The membrane electrode assembly of  claim 10  wherein the highly fluorinated ion-exchange polymer binder in both the anode electrode and the cathode electrodes consist essentially of a perfluorinated sulfonic acid membrane in proton form. 
     
     
         12 . The membrane electrode assembly of  claim 11  wherein the proton exchange membrane consists essentially of a perfluorinated sulfonic acid membrane in acid form, and wherein the highly fluorinated ion-exchange polymer binder in both the anode electrode and the cathode electrodes consist essentially of a perfluorinated sulfonic acid membrane in acid form. 
     
     
         13 . The membrane electrode assembly of  claim 1  wherein the anode and cathode electrodes are adhered directly to the opposite first and second sides of the polymer exchange membrane. 
     
     
         14 . The membrane electrode assembly of  claim 1  wherein the anode and cathode electrodes are coated on the opposite first and second sides of the polymer exchange membrane. 
     
     
         15 . The membrane electrode assembly of  claim 1  further comprising
 a first electrically conductive gas diffusion substrate disposed on the first side of the proton exchange membrane, said anode electrode being disposed between said first conductive gas diffusion substrate and the first side of the proton exchange membrane, wherein said anode electrode is adhered to the first conductive gas diffusion substrate and is in direct contact with the first side of the proton exchange membrane, and   a second electrically conductive gas diffusion substrate disposed on the second side of the proton exchange membrane, said cathode electrode being disposed between said second conductive gas diffusion substrate and the second side of the proton exchange membrane, wherein said cathode electrode is adhered to the second conductive gas diffusion substrate and is in direct contact with the second side of the proton exchange membrane.   
     
     
         16 . The membrane electrode assembly of  claim 15 , wherein the electrically conductive gas diffusion substrate is a carbon-fiber based paper or cloth. 
     
     
         17 . The membrane electrode assembly of  claim 1 , wherein the particulate carbon is from the group of turbostratic or graphitic carbons. 
     
     
         18 . The membrane electrode assembly of  claim 1  wherein said anode electrocatalyst is in the form of anode electrocatalyst particles and said cathode electrocatalyst is in the form of cathode electrocatalyst particles, and wherein at least 98% of the anode and cathode electrocatalyst particles have a particle diameter of less than 10 microns. 
     
     
         19 . An organic/air fuel cell comprising the membrane electrode assembly of  claim 1 . 
     
     
         20 . A process for producing a membrane electrode assembly for an organic/air fuel cell, comprising
 (a) providing a proton exchange membrane made of a highly fluorinated ion-exchange polymer, said membrane having opposite first and second sides;   b) forming an anode electrode adjacent said first side of the membrane, said anode electrode comprised of 50 to 90 wt % of an anode electrocatalyst and 10 to 50 wt % of a highly fluorinated ion-exchange polymer binder, said anode electrocatalyst being comprised of an anode metal supported on carbon, wherein the anode metal is comprised of platinum and ruthenium and the carbon is particulate carbon, said anode electrocatalyst being comprised of at least 40 wt % platinum, at least 15 wt % ruthenium, and 15 to 50 wt % particulate carbon wherein the total loading of the anode metal in the anode electrode is less than 3 mg/cm 2 ; and   (c) forming a cathode electrode adjacent said second side of the membrane, said cathode electrode comprised of 50 to 90 wt % of a cathode electrocatalyst and 10 to 50 wt % of a highly fluorinated ion-exchange polymer binder, said cathode electrocatalyst being comprised of a cathode metal supported on carbon, wherein the cathode metal is comprised of platinum and the carbon is particulate carbon, said cathode electrocatalyst being comprised of at least 50 wt % platinum and 15 to 50 wt % particulate carbon wherein the total loading of the cathode metal in the cathode electrode is less than 3 mg/cm 2 .   
     
     
         21 . The process of  claim 20 , wherein forming the membrane electrode assembly for an organic/air fuel cell includes the steps of
 making an anode electrocatalyst ink comprised of highly fluorinated ion-exchange polymer, anode electrocatalyst particles of the platinum and ruthenium supported on particulate carbon, and a solvent, wherein at least 98% of such anode electrocatalyst particles have a diameter of less than 10 microns,   forming the anode electrode by forming a coating of the anode electrocatalyst ink and removing the solvent from the anode electrocatalyst ink,   making a cathode electrocatalyst ink comprised of highly fluorinated ion-exchange polymer, cathode electrocatalyst particles of the platinum supported on particulate carbon, and a solvent, wherein at least 98% of such cathode electrocatalyst particles have a diameter of less than 10 microns, and   forming the cathode electrode by forming a coating of the cathode electrocatalyst ink and removing the solvent from the cathode electrocatalyst ink.   
     
     
         22 . The process of  claim 20 , wherein forming the membrane electrode assembly for an organic/air fuel cell includes the steps of
 making an anode electrocatalyst ink comprised of highly fluorinated ion-exchange polymer, platinum and ruthenium supported on particulate carbon, and a fluorinated solvent, the highly fluorinated ion-exchange polymer being a perfluorinated polymer having sulfonyl fluoride end groups,   forming the anode electrode by forming a coating of the anode electrocatalyst ink and removing the solvent from the anode electrocatalyst ink,   making a cathode electrocatalyst ink comprised of highly fluorinated ion-exchange polymer, the platinum supported on particulate carbon, and a fluorinated solvent, the highly fluorinated ion-exchange polymer being a perfluorinated polymer having sulfonyl fluoride end groups,   forming the cathode electrode by forming a coating of the cathode electrocatalyst ink and removing the solvent from the cathode electrocatalyst ink,   applying the anode and cathode electrodes to opposite side of the proton exchange membrane, and   converting the sulfonyl fluoride end groups in the ion-exchange polymer of the anode electrode and cathode electrode to acid end groups by a hydrolysis treatment followed by an acid exchange step.   
     
     
         23 . The process of  claim 20 , wherein forming the membrane electrode assembly for an organic/air fuel cell includes the steps of
 making an anode electrocatalyst ink comprised of highly fluorinated ion-exchange polymer, platinum and ruthenium supported on particulate carbon, and a solvent, the highly fluorinated ion-exchange polymer being a perfluorinated polymer having sulfonic acid end groups,   forming the anode electrode by forming a coating of the anode electrocatalyst ink and removing the solvent from the anode electrocatalyst ink,   making a cathode electrocatalyst ink comprised of highly fluorinated ion-exchange polymer, the platinum supported on particulate carbon, and a solvent, the highly fluorinated ion-exchange polymer being a perfluorinated polymer having sulfonic acid end groups,   forming the cathode electrode by forming a coating of the cathode electrocatalyst ink and removing the solvent from the cathode electrocatalyst ink,   applying the anode and cathode electrodes to opposite side of the proton exchange membrane, said proton exchange membrane being comprised of a highly fluorinated ion-exchange polymer in proton form.   
     
     
         24 . A process for operating a membrane electrode assembly of an organic/air fuel cell, comprising
 (a) providing a proton exchange membrane made of a highly fluorinated ion-exchange polymer, said membrane having opposite first and second sides;   (b) forming an anode electrode adjacent said first side of the membrane, said anode electrode comprised of 50 to 90 wt % of an anode electrocatalyst and 20 to 50 wt % of a highly fluorinated ion-exchange polymer binder, said anode electrocatalyst being comprised of an anode metal supported on carbon, wherein the anode metal is comprised of platinum and ruthenium and the carbon is particulate carbon, said anode electrocatalyst being comprised of at least 40 wt % platinum, at least 15 wt % ruthenium, and 15 to 50 wt % particulate carbon wherein the total loading of the anode metal in the anode electrode is less than 3 mg/cm 2 ;   (c) forming a cathode electrode adjacent said second side of the membrane, said cathode electrode comprised of 50 to 90 wt % of a cathode electrocatalyst and 15 to 50 wt % of a highly fluorinated ion-exchange polymer binder, said cathode electrocatalyst being comprised of a cathode metal supported on carbon, wherein the cathode metal is comprised of platinum and the carbon is particulate carbon, said cathode electrocatalyst being comprised of at least 50 wt % platinum and 15 to 50 wt % particulate carbon wherein the total loading of the cathode metal in the cathode electrode is less than 3 mg/cm 2 ,   (d) forming an electric circuit between the anode and cathode electrodes, and   (e) feeding a liquid organic fuel to the anode electrode and oxygen to the cathode electrode so as to generate an electric current in said electric circuit.   
     
     
         25 . The process of  claim 24  wherein the liquid organic fuel is selected from the group of methanol, ethanol, formaldehyde, formic acid, and combinations thereof. 
     
     
         26 . The process of  claim 25  wherein the liquid organic fuel is methanol.