Structures and fabrication techniques for solid state electrochemical devices

Abstract

Porous substrates and associated structures for solid-state electrochemical devices, such as solid-oxide fuel cells (SOFCs), are low-cost, mechanically strong and highly electronically conductive. Some preferred structures have a thin layer of an electrocatalytically active material (e.g., Ni-YSZ) coating a porous high-strength alloy support (e.g., SS-430) to form a porous SOFC fuel electrode. Electrode/electrolyte structures can be formed by co-firing or constrained sintering processes.

1 . A method of separating oxygen from air, comprising:
 providing an electrochemical device having a membrane, the membrane comprising a sintered substrate consisting essentially of a material selected from the group consisting of a porous non-noble transition metal, a porous non-noble transition metal alloy, and a porous cermet incorporating one or more of a non-noble, non-nickel transition metal and a non-noble transition metal alloy; and a sintered coating of a ceramic material on the substrate wherein said coating is a mixed ionic electronic conductor;   providing air on one side of the membrane, whereby oxygen ions migrate through the membrane to produce pure oxygen at the other side of the membrane.   
     
     
         2 . The method of  claim 1 , wherein said mixed ionic electronic conductor is selected from the group consisting of SrCo 1−x Fe x O 3−δ  (0.30≧X≧0.20), La 0.6 Sr 0.4 Co 0.6 Fe 0.4 O 3−δ , La 0.8 Sr 0.2 MnO 3 , La 0.65 Sr 0.30 MnO 3 , La 0.45 Sr 0.55 MnO 3 , Sr 0.7 Ce 0.3 MnO 3−δ , LaNi 0.6 Fe 0.4 O 3 , Sm 0.5 Sr 0.5 CoO 3  and La 1−x Sr x CoO 3−δ . 
     
     
         3 . The method of  claim 2 , wherein said MIEC is La 0.6 Sr 0.4 Co 0.6 Fe 0.4 O 3−δ . 
     
     
         4 . The method of  claim 1 , wherein the membrane film is 1 to 50 microns thick. 
     
     
         5 . The method of  claim 4 , wherein the membrane film is 5 to 20 microns thick. 
     
     
         6 . The method of  claim 1 , wherein the device is tubular. 
     
     
         7 . The method of  claim 1 , wherein the device is planar. 
     
     
         8 . The method of  claim 1 , wherein in the providing of the electrochemical device the sintered coating is made by co-firing of the substrate and coating. 
     
     
         9 . The method of  claim 1 , wherein in the providing of the electrochemical device the sintered coating is made by constrained sintering of the substrate and coating. 
     
     
         10 . The method of  claim 1 , wherein the electrochemical device comprises: 
       the sintered substrate consisting essentially of a material selected from the group consisting of a porous non-noble transition metal, a porous non-noble transition metal alloy, and a porous cermet incorporating one or more of a non-noble, non-nickel transition metal and a non-noble transition metal alloy; 
       a first porous electrode material having high electrocatalytic activity on the substrate; 
       the sintered coating of mixed ionic electronic conductor ceramic material on the electrode wherein said coating is dense; and 
       a second porous electrode on the coating.