Electrochemical method for separating O2 from a gas; generating electricity; measuring O2 partial pressure; and fuel cell

Abstract

.Iadd.A fuel cell and method of operation of same is detailed for measuring oxygen pressure, separating oxygen from a gas, or generating electrical energy. The fuel cell has first and second electrodes of selected materials with a solid partition of a solid electrolyte between the electrodes. The solid electrolyte consists of a solid solution of selected oxides having a high degree of oxygen ion conductivity. .Iaddend.

What is claimed is: 
     
       1. A fuel cell comprising: a solid partition of a solid electrolyte consisting essentially of a solid solution of oxides having a high degree of oxygen ion conductivity compared with either electronic conductivity or cation conductivity, said solid electrolyte having the formula   (MO.sub.2).sub.1-x (R.sub.y O.sub.z).sub.x     where M represents at least one tetravalent element forming an oxide highly stable at temperatures of about 500°C to about 1200°C selected from the group consisting of zirconium, thorium and hafnium, R represents at least one element from the group consisting of elements of Groups II-A and III-B of the Periodic Table which form cations with stable +2 and +3 valences in the oxide, x represents a number having a value from about 0.05 to about 0.3 and y and z represent numbers having values necessary to make (R y  O z ) electrically neutral; a first porous electrode consisting of lanthanum nickel oxide applied to a first face of said partition; a second porous electrode consisting of a mixture of nickel and platinum applied to the opposite face of said partition; said electrodes being stable at temperatures of about 500° C to about 1200° C; .[.mean.]. .Iadd.means .Iaddend.for supplying gas containing oxygen to said first electrode; means for supplying a fuel capable of reacting with oxygen on the opposite side of said partition near to said second electrode; means for heating said electrodes to an elevated temperature of about 500° C to 1200° C whereby oxygen forms ions at said first electrode which migrate through said partition upon placing it in a closed circuit and react with said fuel at the second electrode, said electrodes thereby developing a potential difference; and means for withdrawing the reaction products from near said second electrode.   
     
     
       2. A fuel cell as in claim 1 wherein: R represents at least one element from the group consisting of calcium, barium, strontium, yttrium and lanthanum. 
     
     
       3. A fuel cell as in claim 1 wherein: said solid electrolyte has the formula (ZrO 2 ) 1-x  (CaO) x  where x represents a number having a value from about 0.1 to about 0.3. 
     
     
       4. A method for separating oxygen from a gas containing oxygen or for producing substantially pure oxygen comprising: supplying a gas containing oxygen to a first electrically conductive porous electrode of an electrochemical cell comprising a solid electrolyte consisting essentially of a solid solution of oxides having a high degree of oxygen ion conductivity compared with either electronic conductivity or cation conductivity, said solid electrolyte having the formula (MO 2 ) 1-x  (R y  O z ) x  where M represents at least one tetravalent element from the group consisting of zirconium, thorium, valent element from the group consisting of zirconium, thorium, and hafnium, R represents at least one element from the group consisting of elements of Groups II-A and III-B of the Periodic Table which form cations with stable +2 and +3 valences in the oxide, x represents a number having a value of from about .[.0.05.]. .Iadd.0.1 .Iaddend.to about 0.3 and y and z represent numbers having values sufficient to make R y  O z  electrically neutral; said first electrically conductive porous electrode and a second electrically conductive porous electrode being disposed on opposite surfaces of said solid electrolyte; heating said electrolyte and electrodes, while supplying said gas, to a temperature within the range of from about 500°C to 1200°C; applying, while supplying said gas and heating said electrolyte and electrodes, a DC potential difference across said electrodes of a polarity such that said first electrode is negative with respect to said second electrode so that substantially pure oxygen is produced at said second electrode. 
     
     
       5. A method as in claim 4 wherein: said gas containing oxygen contains said oxygen in molecular form.  .[.6. A method as in claim 4 wherein: x 
     
     
        represents a number having a value from about 0.1 to about 0.3..]. 7. A method as in claim .[.6.]. .Iadd.4 .Iaddend.wherein R represents at least one element from the group consisting of calcium, barium, strontium, yttrium and lanthanum; and said gas containing oxygen contains said oxygen 
     
     
        in molecular form. 8. A method for generating electrical energy comprising: establishing unequal oxygen partial pressures at first and second electrically conductive porous electrodes of an electrochemical cell comprising said electrodes on opposite surfaces of a solid electrolyte consisting essentially of a solid solution of oxides having a high degree of oxygen ion conductivity compared with either electronic conductivity or cation conductivity; said solid electrolyte having the formula (MO 2 ) 1-x  (R y  O z ) x  where M represents at least one tetravalent element from the group consisting of zirconium, thorium and hafnium, R represents at least one element from the group consisting of elements of Groups II-A and III-B of the Periodic Table which form cations with stable +2 and +3 valences in the oxide, x represents a number having a value of from about .[.0.05.].  .Iadd. 0.1 .Iaddend.to about 0.3 and y and z represent numbers having values sufficient to make R y  O z  electrically neutral; said electrodes being electrically connected across a load in an external circuit; excluding oxidizable fuel from said electrodes to develop electrical power across said load by reason of said unequal oxygen partial pressures at said electrodes.  .[.9. A method as in claim 8 wherein: x represents a 
     
     
        number having a value of from about 0.1 to about 0.3..]. 10. A method as in claim .[.9.]. .Iadd.8 .Iaddend.wherein: R represents at least one element from the group consisting of calcium, barium, strontium, yttrium 
     
     
        and lanthanum. 11. A method as in claim .[.9.]. .Iadd.8 .Iaddend.wherein: the establishing of unequal oxygen partial pressures and the excluding of oxidizable fuel are effected by providing an enclosure completely enclosing said electrolyte and said electrodes with said enclosure containing oxygen gas and a compressor means disposed therein to maintain said partial pressures unequal.  .[.12. A method for the measurement of oxygen pressure comprising: establishing and maintaining an oxygen partial pressure of known value at a first electrically conductive porous electrode of an electrochemical cell including a solid electrolyte consisting essentially of a solid solution of oxides having a high degree of oxygen ion conductivity compared with either electronic conductivity or cation conductivity, said solid electrolyte has the formula (MO 2 ) 1-x  (R y  O z ) x  where M represents at least one tetravalent element from the group consisting of zirconium, thorium, and hafnium, R represents at least one element from the group consisting of elements of Groups II-A and III-B of the Periodic Table which form cations with stable +2 and +3 valences in the oxide, x represents a number having a value of from about 0.05 to about 0.3 and y and z represent numbers having values sufficient to make R y  O z  electricallly neutral, said first electrically conductive porous electrode and a second electrically conductive porous electrode being disposed on opposite surfaces of said solid electrolyte; supplying a gas containing an unknown oxygen partial pressure to said second electrode; measuring an electrical output across said electrodes as a measure of said unknown oxygen partial 
     
     
        pressure..]. 13. A method .[.as in claim 12 wherein:.]. .Iadd.for the measurement of oxygen pressure comprising: establishing and maintaining an oxygen partial pressure of known value at a first electrically conductive porous electrode of an electrochemical cell including a solid electrolyte consisting essentially of a solid solution of oxides having a high degree of oxygen ion conductivity compared with either electronic conductivity or cation conductivity, said solid electrolyte has the formula (MO 2 ) 1-x  (R y  O z ) x  where M represents at least one tetravalent element from the group consisting of zirconium, thorium and hafnium, R represents at least one element from the group consisting of elements of Groups II-A and III-B of the Periodic Table which form cations with +2 and +3 valences in the oxide, .Iaddend.x represents a number having a value of from about 0.1 to about 0.3 .Iadd.and y and z represent numbers having values sufficient to make R y  O.sub. z electrically neutral, said first electrically conductive porous electrode and a second electrically porous electrode being disposed on opposite surfaces of said solid electrolyte; supplying a gas containing an unknown oxygen partial pressure to said second electrode; measuring an electrical output across said electrodes as a measure of said unknown oxygen partial pressure. 
     
     
        .Iaddend. 14. A method as in claim 13 wherein: R represents at least one element of the group consisting of calcium, barium, strontium, yttrium and lanthanum; and further comprising measuring the cell temperature, while measuring said electrical output, so that electrical output variations due to temperature varitions can be accounted for.