Aqueous ionomeric gels and products and methods related thereto

Abstract

An aqueous ionomer gel having a high viscosity, particularly a proton conducting ionomer, as well as to related products incorporating such gels. Such aqueous ionomer gels are suitable for suspending catalysts for formation of catalyst inks, which in turn are suitable for screen printing on a variety of surfaces. Representative surfaces are the electrode or membrane surfaces in an electrochemical fuel cell. Methods for making aqueous ionomer gels are also disclosed.

1 . A method for making an aqueous ionomer gel having an ionomer solids content ranging from about 4% to about 18% by weight of the gel and a viscosity in excess of 5,000 centipoise at a shear rate of 10 seconds −1 , comprising the steps of: 
 providing a solution comprising an ionomer, water and a nonaqueous solvent having a boiling point less than 100° C., wherein the nonaqueous solvent is miscible with water; and    evaporating the nonaqueous solvent at less than ambient pressure to produce the aqueous ionomer gel.    
     
     
         2 . The method of  claim 1  wherein the nonaqueous solvent is evaporated in the absence of applied heat.  
     
     
         3 . The method of  claim 1  further comprising the step of cooling the aqueous ionomer gel following the evaporating step.  
     
     
         4 . The method of  claim 1  further comprising the step of adding a catalyst to the aqueous ionomer gel following the evaporating step.  
     
     
         5 . The method of  claim 1  wherein the solution comprising the ionomer, water and the nonaqueous solvent further comprises a catalyst prior to the evaporation step.  
     
     
         6 . The method of  claim 1  wherein the nonaqueous solvent has a boiling point ranging from about 50 to less than 100° C.  
     
     
         7 . The method of  claim 1  wherein the nonaqueous solvent is an alcohol or a ketone.  
     
     
         8 . The method of  claim 7  wherein the alcohol is methanol.  
     
     
         9 . The method of  claim 7  wherein the ketone is acetone.  
     
     
         10 . The method of  claim 1  wherein the solution comprising the ionomer, water and the nonaqueous solvent is provided by addition of the nonaqueous solvent to an aqueous solution of ionomer.  
     
     
         11 . The method of  claim 1  wherein, prior to the step of evaporating, the solution comprising the ionomer, water and the nonaqueous solvent is heated to facilitate solvation of the ionomer.  
     
     
         12 . The method of  claim 11  wherein heating to facilitate solvation is at a temperature up to about 40° C.  
     
     
         13 . The method of  claim 1  wherein the solution comprising the ionomer, water and the nonaqueous solvent is provided by addition of water to a nonaqueous solution of ionomer.  
     
     
         14 . A method for making an aqueous ionomer gel having an ionomer solids content ranging from about 4% to about 18% by weight of the gel and a viscosity in excess of 5,000 centipoise at a shear rate of 10 seconds −1 , comprising the steps of: 
 rapidly cooling an aqueous ionomer solution to a temperature below −5° C. to form a substantially frozen form of the aqueous ionomer solution; and    thawing the substantially frozen form of the aqueous ionomer solution to produce the aqueous ionomer gel.    
     
     
         15 . The method of  claim 14  wherein the aqueous ionomer solution is cooled at a rate greater than 6° C./minute.  
     
     
         16 . The method of  claim 15  wherein the aqueous ionomer solution is cooled at a rate greater than 110° C./minute.  
     
     
         17 . The method of  claim 14  wherein the aqueous ionomer solution is cooled to temperature below −25° C.  
     
     
         18 . The method of  claim 17  wherein the aqueous ionomer solution is cooled to temperature below about −70° C.  
     
     
         19 . The method of  claim 14  further comprising the step of diluting the aqueous ionomer gel to achieve a desired viscosity.  
     
     
         20 . The method of  claim 14  wherein the aqueous ionomer solution further comprises a catalyst.  
     
     
         21 . The method of  claim 17  further comprising the step of adding a catalyst to the aqueous gel.  
     
     
         22 . The method of  claim 1  or  14  further comprising the step of suspending a catalyst ink in the aqueous ionomer gel after or simultaneously with formation of the aqueous ionomer gel to yield a catalyst ink.  
     
     
         23 . The method of  claim 22  further comprising the step of applying the catalyst ink to at least one surface of a substrate.  
     
     
         24 . The method of  claim 23  further comprising the step of annealing the catalyst ink.  
     
     
         25 . A substrate made by the method of  claim 23 .  
     
     
         26 . An annealed substrate made by the method of  claim 24.