Electrochemical cells for direct oxide reduction, and related methods

Abstract

A method of direct oxide reduction includes forming a molten salt electrolyte in an electrochemical cell, disposing at least one metal oxide in the electrochemical cell, disposing a counter electrode comprising a material selected from the group consisting of osmium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, lithium iridate, lithium ruthenate, a lithium rhodate, a lithium tin oxygen compound, a lithium manganese compound, strontium ruthenium ternary compounds, calcium iridate, strontium iridate, calcium platinate, strontium platinate, magnesium ruthenate, magnesium iridate, sodium ruthenate, sodium iridate, potassium iridate, and potassium ruthenate in the electrochemical cell, and applying a current between the counter electrode and the at least one metal oxide to reduce the at least one metal oxide. Related methods of direct oxide reduction and related electrochemical cells are also disclosed.

What is claimed is: 
     
         1 . An electrochemical cell, comprising:
 at least one anode comprising monolithic iridium or monolithic ruthenium;   at least one cathode comprising at least one metal oxide; and   at least one molten salt electrolyte.   
     
     
         2 . The electrochemical cell of  claim 1 , wherein the at least one cathode comprises a spent nuclear fuel comprising the at least one metal oxide. 
     
     
         3 . The electrochemical cell of  claim 2 , wherein the spent nuclear fuel comprises fission byproducts comprising at least one of selenium, tellurium, or iodine. 
     
     
         4 . The electrochemical cell of  claim 2 , wherein the at least one metal oxide comprises uranium oxide. 
     
     
         5 . The electrochemical cell of  claim 1 , wherein the at least one metal oxide comprises a transition metal oxide, a non-metal oxide, a lanthanide oxide, an actinide oxide, or combinations thereof. 
     
     
         6 . The electrochemical cell of  claim 1 , wherein the at least one molten salt electrolyte comprises an alkali halide salt, an alkaline earth metal halide salt, an alkali oxide, an alkaline earth metal oxide, or combinations thereof. 
     
     
         7 . The electrochemical cell of  claim 1 , wherein the at least one molten salt electrolyte comprises at least one of:
 lithium chloride and lithium oxide,   calcium chloride and calcium oxide,   a eutectic mixture of sodium chloride and potassium chloride, or   a eutectic mixture of sodium chloride and calcium chloride.   
     
     
         8 . An electrochemical cell, comprising:
 at least one counter electrode comprising a monolithic body comprising a substantially uniform composition of ruthenium or iridium;   at least one working electrode comprising, or in electrical communication with, at least one metal oxide in the electrochemical cell; and   at least one molten salt electrolyte.   
     
     
         9 . The electrochemical cell of  claim 8 , further comprising a basket carrying the at least one metal oxide, the at least one working electrode being in electrical communication with the basket and the at least one metal oxide. 
     
     
         10 . The electrochemical cell of  claim 9 , wherein the basket comprises at least one of nickel, cobalt, iron, molybdenum, or stainless steel. 
     
     
         11 . The electrochemical cell of  claim 10 , wherein the basket comprises an alloy of:
 nickel and copper,   nickel, iron, and molybdenum, or   nickel, chromium, iron, and molybdenum.   
     
     
         12 . The electrochemical cell of  claim 8 , wherein the at least one working electrode consists essentially of the at least one metal oxide. 
     
     
         13 . The electrochemical cell of  claim 8 , further comprising a reference electrode in electrical communication with the at least one counter electrode and with the at least one working electrode. 
     
     
         14 . The electrochemical cell of  claim 13 , wherein the reference electrode comprises:
 glassy carbon,   nickel, nickel oxide, or a combination thereof, or   silver/silver chloride.   
     
     
         15 . The electrochemical cell of  claim 8 , further comprising, for each of the at least one counter electrode and the at least one working electrode, a sheath disposed around at least a portion thereof. 
     
     
         16 . The electrochemical cell of  claim 15 , wherein the sheath comprises at least one of alumina or magnesia. 
     
     
         17 . A method of direct oxide reduction, the method comprising:
 disposing a molten salt electrolyte in an electrochemical cell;   at least partially immersing an anode in the molten salt electrolyte, the anode comprising monolithic iridium or monolithic ruthenium;   disposing a cathode in the electrochemical cell, comprising disposing at least one metal oxide in contact with the molten salt electrolyte;   applying an electric potential between the anode and the cathode.   
     
     
         18 . The method of  claim 17 , wherein disposing the cathode in the electrochemical cell further comprises disposing, in the electrochemical cell, an electrode consisting essentially of the at least one metal oxide. 
     
     
         19 . The method of  claim 17 , wherein:
 disposing a molten salt electrolyte in the electrochemical cell comprises disposing, in the electrochemical cell, a lithium chloride/lithium oxide (LiCl—Li 2 O) molten salt electrolyte; and   further comprising, at least while the at least one metal oxide is disposed in contact with the molten salt electrolyte, maintaining a temperature of the electrochemical cell at or above a melting temperature of the molten salt electrolyte but below 650° C.   
     
     
         20 . The method of  claim 17 , wherein:
 disposing a molten salt electrolyte in the electrochemical cell comprises disposing, in the electrochemical cell, a calcium chloride-calcium oxide (CaCl 2 —CaO) molten salt electrolyte or a sodium chloride-calcium chloride (NaCl—CaCl 2 )) molten salt electrolyte; and   further comprising, at least while the at least one metal oxide is disposed in contact with the molten salt electrolyte, operating the electrochemical cell at a pressure below about 1.0 GPa.