Electrochemically functional membranes

Abstract

A system includes an electrochemically functional membrane, and a support structure constructed and arranged so as to support the membrane while leaving within the membrane a chemically active area having an area utilization of at least about 50%. In some embodiments, the support structure may include a plurality of grids that are sized and shaped so that the contact area between the grids and the membrane is reduced to less than about 40%. In some embodiments, the support structure may include aerogels, for example PVA-reinforced CNT aerogels having a conductivity that is increased by pyrolysis. The system may be a gas separation system; a gas production system; a gas purification system; or an energy generation system such as an SOFC.

What is claimed is: 
     
         1 . A system comprising:
 an electrochemically functional membrane; and   a support structure constructed and arranged so as to support the membrane while leaving within the membrane a chemically active area having an area utilization of at least about 50%;   wherein the support structure comprises at least one of:   a plurality of grids that are sized and shaped so as to reduce the contact area between the grids and the membrane to less than about 40%; and   one or more aerogels.   
     
     
         2 . The system of  claim 1 , wherein the system is one of:
 a gas separation system; a gas production system; a gas purification system; and   an energy generation system.   
     
     
         3 . The system of  claim 2 , further comprising a substrate, and an electrode layer deposited on each side of the membrane. 
     
     
         4 . The system of  claim 1 , wherein the grids comprise plated metallic grids, and wherein the energy generation system comprises an SOFC. 
     
     
         5 . The system of  claim 4 , wherein the grids are constructed by:
 depositing the membrane and a cathode layer on a substrate;   etching metallic grids by DC-sputtering on the surface of the cathode layer; and   forming a back-side pattern by reactive ion etching and wet etching of the substrate.   
     
     
         6 . The system of  claim 5 , wherein the grids comprise nickel and have a line width of about 5-10 μm and a pitch of 25-50 μm; and wherein the membrane is a LSCF/yttrium-stabilized zirconium/platinum membrane having a thickness of about 200 μm. 
     
     
         7 . The system of  claim 4 , wherein shapes of the grids comprise one of: a hexagon; and a circle. 
     
     
         8 . The system of  claim 4 , wherein the grids comprise Pt or Ag, and have a thickness of about 1 micrometers. 
     
     
         9 . The system of  claim 8 , wherein the membrane is a 8 mol % yttrium doped zirconium membrane having a thickness of about 50 to about 150 nm, and wherein the area utilization of the membrane is more than 85%. 
     
     
         10 . The system of  claim 1 , wherein the aerogels comprise a silica aerogel reinforced with carbon fibers. 
     
     
         11 . The system of  claim 10 , wherein the silica aerogel is created in flow channels etched into the underside of a silicon chip bonded to the top of the membrane. 
     
     
         12 . The system of  claim 1 , wherein the aerogels comprise a PVA (polyvinyl alcohol)-reinforced CNT (carbon nanotube) aerogel having a conductivity that is increased by pyrolysis. 
     
     
         13 . The system of  claim 12 , wherein the PVA-reinforced CNT aerogel is fabricated by:
 suspending CNTs in water to form a gel;   performing PVA infiltration by covering the gel with a water/PVA solution;   replacing the water with alcohol and then with CO 2 ;   super critically removing the CO 2 ; and   pyrolyzing the gel by heating it to a temperature between about 400 and 1000° C.   
     
     
         14 . A system comprising:
 a substrate;   an electrochemically functional membrane deposited on the substrate;   a cathode layer deposited on the membrane; and   a plurality of supporting grids etched on the surface of the cathode layer according to a grid pattern;   wherein the grids are shaped and sized so as to support the membrane while reducing the contact area between the grids and the membrane to less than about 15%, thereby leaving within the membrane a chemically active area having an area utilization of at least about 60%.   
     
     
         15 . The system of  claim 14 , wherein the grid pattern ends outside the active area of the membrane so that current collected in the grid can flow down to the substrate. 
     
     
         16 . The system of  claim 14 , wherein the substrate is a Si substrate coated with an insulating layer; and wherein the insulating layer is patterned with the grid pattern. 
     
     
         17 . The system of  claim 16 , wherein the plurality of grids comprise a current collector grid etched on the patterned insulating layer. 
     
     
         18 . The system of  claim 14 , wherein the membrane is a nanostructured electrolyte membrane comprising yttrium doped zirconia; and wherein the cathode layer comprises LSCF. 
     
     
         19 . The system of  claim 14 , wherein the substrate has a back-side pattern etched thereon by reactive ion etching and wet etching. 
     
     
         20 . The system of  claim 14 , wherein the grids comprise one of: a metal, and a semiconductor material; and wherein the shapes of the grids comprise one of: a hexagon; and a circle. 
     
     
         21 . A method of fabricating grids for supporting an electrochemically functional membrane in a device, the method comprising:
 depositing a layer of the electrochemically functional membrane on a silicon wafer that is coated both sides with silicon nitride;   sputtering a layer of metal onto the surface of the wafer, and patterning the layer of matter into a grid pattern using photolithography;   patterning the nitride from the back side, and etching the wafer through; and   removing the silicon nitride from the back side of the wafer,   wherein the grid pattern shapes a plurality of grids so as to decrease the contact area between each grid and the membrane to less than about 40% of the total area of the membrane.   
     
     
         22 . The method of  claim 21 , wherein the grid comprises a current collector grid for the device. 
     
     
         23 . A method of increasing the active area of an electrochemically functional membrane, the method comprising:
 depositing the membrane on a substrate;   covering the membrane with a high porosity material; and   removing the substrate.   
     
     
         24 . The method of  claim 23 , wherein the high porosity material comprises silica aerogel reinforced with carbon fibers. 
     
     
         25 . The method of  claim 24 , wherein the aerogel is created in flow channels etched into the underside of a silicon chip bonded to the top of the membrane. 
     
     
         26 . A method of fabricating a PVA (polyvinyl alcohol) reinforced CNT (carbon nanotube) aerogel for supporting an electrochemically functional membrane in a system, the method comprising:
 suspending CNTs in water to form a gel;   performing PVA infiltration by covering the gel with a water/PVA solution;   replacing the water with alcohol and then with CO 2 ;   super critically removing the CO 2 ; and   pyrolyzing the gel by heating it to a temperature between about 400 and 1000° C.