Solid oxide fuel cell having a dense barrier layer

Abstract

A solid oxide fuel cell with a dense barrier layer formed at or near the outer surface of the top and/or bottom electrode layers in a fuel cell stack. The dense barrier layer (DBL) acts as a seal to prevent gas in the electrode layer (either air in a cathode layer or fuel gas in an anode layer) from leaking out of the stack though the outer surface of the outermost electrode layers. The use of a DBL with porous outer electrode layers reduces the amount of gas escaping the stack and minimizes the chances for leak-induced problems ranging from decreases in performance to catastrophic stack failure.

What is claimed is: 
     
         1 . A solid oxide fuel cell, comprising:
 a first porous electrode layer;   a dense interconnect layer over the first porous electrode layer;   a second porous electrode layer over the dense interconnect layer, the second porous electrode layer defining at least one gas passage; and   a dense barrier layer disposed at an outer surface of the second porous electrode layer opposite the dense interconnect layer,   wherein the dense barrier layer is compositionally different from the dense interconnect layer.   
     
     
         2 . The solid oxide fuel cell of  claim 1 , wherein the first porous electrode layer is an anode layer and the second porous electrode layer is a cathode layer. 
     
     
         3 . The solid oxide fuel cell of  claim 1 , wherein the dense barrier layer is configured to prevent more than 50% of a gas flowing through the second porous electrode layer from leaking out through the outer surface of the second porous electrode layer. 
     
     
         4 . The solid oxide fuel cell of  claim 1 , wherein the dense barrier layer comprises at least one material component common to the second porous electrode layer. 
     
     
         5 . The solid oxide fuel cell of  claim 4 , wherein the dense barrier layer further comprises a material component different from the second porous electrode layer. 
     
     
         6 . The solid oxide fuel cell of  claim 1 , wherein the dense barrier layer comprises a gas-tight ceramic layer. 
     
     
         7 . The solid oxide fuel cell of  claim 1 , wherein the dense barrier layer is electrically conductive. 
     
     
         8 . The solid oxide fuel cell of  claim 1 , wherein the dense barrier layer has a CTE that is within about +5 ppm/° C. of the second porous electrode layer. 
     
     
         9 . The solid oxide fuel cell of  claim 1 , further comprising a transition layer disposed adjacent the dense barrier layer. 
     
     
         10 . A multilayer porous ceramic device, comprising:
 the solid oxide fuel cell of  claim 1 ;   an electrolyte layer between the first porous electrode layer and a third porous electrode layer.   
     
     
         11 . The multilayer porous ceramic device of  claim 10 , wherein the dense barrier layer comprises a material component common to the electrolyte. 
     
     
         12 . A fuel cell assembly, comprising:
 a stack of alternating layers of a porous electrode of a first type and a porous electrode of a second type, wherein:
 a total number of the layer of the porous electrode of the first type=n, wherein n is at least 1; 
 a total number of the layer of the porous electrode of the second type=n+1; and 
   a barrier layer disposed at an outer surface of an outermost layer of the porous electrodes of the first type and the second type,   wherein no dense barrier layer is disposed between the layers of the porous electrodes of the first and second types.   
     
     
         13 . The fuel cell assembly of  claim 12 , wherein the outermost layer of the porous electrodes is a cathode layer. 
     
     
         14 . The fuel cell assembly of  claim 12 , wherein the outermost layer of the porous electrodes is an anode layer. 
     
     
         15 . The fuel cell assembly of  claim 12 , wherein the outermost layer comprises an uppermost layer and a lowermost layer, wherein both of uppermost and lowermost layers are cathode layers. 
     
     
         16 . The fuel cell assembly of  claim 12 , wherein the dense barrier layer comprises at least one material component common to the outermost layer of the porous electrodes of the first and second type. 
     
     
         17 . The fuel cell assembly of  claim 12 , wherein the dense barrier layer comprises a ceramic layer. 
     
     
         18 . The fuel cell assembly of  claim 12 , comprising:
 a plurality of subcells, wherein each subcell comprises a layer of the porous electrode of the first type, a layer of the porous electrode of the second type, and an electrolyte partitioning the layers of the porous electrodes of the first and second types; and   a dense interconnect layer between the layer of the porous electrode of the first type of one subcell and the layer of the porous electrode of the second type of another subcell.   
     
     
         19 . The fuel cell assembly of  claim 18 , wherein the dense barrier layer is compositionally different from the dense interconnect layer. 
     
     
         20 . The fuel cell assembly of  claim 18 , wherein the dense barrier layer comprises at least one material component common to the outermost layer of the porous electrodes of the first and second types and at least one material component common to the electrolyte.