Minimising carbon transfer in an electrolytic cell

Abstract

An electrolytic cell for reducing a metal oxide, such as titania, in a solid state is disclosed. The electrolytic cell includes an anode formed from carbon and a cathode formed at least in part from the metal oxide. The electrolytic cell also includes a membrane that is permeable to oxygen anions and is impermeable to carbon in ionic and non-ionic forms positioned between the cathode and the anode to thereby prevent migration of carbon to the cathode.

1 . An electrolytic cell for reducing a metal oxide in a solid state, which electrolytic cell includes an anode formed from carbon, a cathode formed at least in part from the metal oxide, and a membrane that is permeable to oxygen anions and is impermeable to carbon in ionic and non-ionic forms positioned between the cathode and the anode to thereby prevent migration of carbon to the cathode.  
     
     
         2 . The cell defined in  claim 1  wherein the anode is formed from graphite.  
     
     
         3 . The cell defined in  claim 1  wherein the membrane is formed from a solid electrolyte.  
     
     
         4 . The cell defined in  claim 3  wherein the solid electrolyte is yttria stabilised zirconia.  
     
     
         5 . The cell defined in  claim 1  wherein the cathode also includes an electrical conductor.  
     
     
         6 . A method of reducing a metal oxide in a solid state using an electrolytic cell that includes an anode formed from carbon, a cathode formed at least in part from the metal oxide, and a membrane that is permeable to oxygen anions and is impermeable to carbon in ionic and non-ionic forms positioned between the cathode and the anode to thereby prevent migration of carbon to the cathode, which method includes operating the cell at a potential that electrolytically reduces the metal oxide.  
     
     
         7 . The method defined in  claim 6  includes operating the cell at a potential that is above a decomposition potential of at least one of the constituents of the electrolyte so that there are cations of a metal other than that of the metal oxide in the electrolyte.  
     
     
         8 . The method defined in  claim 6  wherein the metal oxide is a titanium oxide, such as titania and the electrolyte is a CaCl 2 -based electrolyte that includes CaO as one of constituents.  
     
     
         9 . The method defined in  claim 8  includes operating the cell at a potential that is above the decomposition potential for CaO.  
     
     
         10 . The method defined in  claim 8  includes operating the cell at a potential that is below the decomposition potential for CaCl 2 .  
     
     
         11 . The method defined in  claim 6  wherein the cell potential is less than or equal to 3.0 V.  
     
     
         12 . The method defined in  claim 11  wherein the cell potential is below 2.5 V.  
     
     
         13 . The method defined in  claim 12  wherein the cell potential is below 2.0 V.  
     
     
         14 . The method defined in  claim 6  wherein the cell potential is above 1.5 V.