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.

1 . 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; and   applying an electric potential between the anode and the cathode.   
     
     
         2 . The method of  claim 1 , 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. 
     
     
         3 . The method of  claim 1 , 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.   
     
     
         4 . The method of  claim 1 , 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.   
     
     
         5 . A method of reducing nuclear fuels comprising uranium oxide, the method comprising:
 providing an electrochemical cell comprising a working electrode, and a counter electrode comprising one or more materials selected from the group consisting of osmium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, lithium iridate, lithium ruthenate, lithium rhodates, 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;   disposing a uranium oxide material on or proximate the working electrode;   exposing the uranium oxide to a molten salt electrolyte comprising at least one of lithium chloride, lithium oxide; calcium chloride, calcium oxide, and sodium chloride; and   passing an electric current between the counter electrode and the working electrode to reduce the uranium oxide material.   
     
     
         6 . The method of  claim 5 , further comprising selecting the counter electrode to comprise a platinum group metal. 
     
     
         7 . The method of  claim 5 , further comprising selecting the counter electrode to comprise a substrate material selected from the group consisting of high density graphite, molybdenum, tantalum, titanium, nickel, chromium, tungsten, and combinations thereof, wherein the substrate material is coated with the one or more materials selected from the group consisting of osmium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, lithium iridate, lithium ruthenate, lithium rhodates, 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. 
     
     
         8 . The method of  claim 5 , further comprising selecting the counter electrode to comprise a substrate material coated with a coating material comprising the one or more materials selected from the group consisting of osmium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, lithium iridate, lithium ruthenate, lithium rhodates, 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 and having a thickness between about 3.0 mm and about 5.0 mm. 
     
     
         9 . The method of  claim 5 , further comprising selecting the counter electrode to comprise ruthenium. 
     
     
         10 . The method of  claim 5 , further comprising selecting the molten salt electrolyte to comprise lithium chloride and lithium oxide. 
     
     
         11 . The method of  claim 5 , further comprising selecting the counter electrode to comprise lithium iridate, lithium ruthenate, or a lithium rhodate. 
     
     
         12 . The method of  claim 5 , further comprising selecting the molten salt electrolyte to comprise calcium chloride and calcium oxide. 
     
     
         13 . The method of  claim 5 , further comprising selecting the uranium oxide to comprise unirradiated uranium oxide. 
     
     
         14 . A method of direct oxide reduction, the method comprising:
 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, 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.   
     
     
         15 . The method of  claim 14 , wherein forming a molten salt electrolyte in the electrochemical cell comprises forming the molten salt electrolyte from one or more of at least one chloride salt and at least one bromide salt. 
     
     
         16 . The method of  claim 14 , wherein disposing at least one metal oxide in the electrochemical cell comprises forming a working electrode of the electrochemical cell from at least one of uranium oxide, tantalum pentoxide, titanium monoxide; titanium dioxide, zirconium oxide, hafnium oxide, tungsten oxide, chromium oxide, molybdenum oxide, iron oxide, nickel oxide, neodymium oxide, samarium oxide, and silicon oxide. 
     
     
         17 . The method of  claim 14 , wherein disposing at least one metal oxide in the electrochemical cell comprises forming a working electrode of the electrochemical cell from at least one of at least one lanthanide oxide and at least one actinide oxide. 
     
     
         18 . The method of  claim 14 , wherein disposing a counter electrode in the electrochemical cell comprises disposing a counter electrode comprising a ternary compound of a platinum group metal. 
     
     
         19 . The method of  claim 18 , further comprising selecting the ternary compound to further comprise at least one of an alkali metal and an alkaline earth metal. 
     
     
         20 . The method of  claim 14 , wherein:
 disposing at least one metal oxide in the electrochemical cell comprises disposing more than one metal oxide 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 comprises reducing the more than one metal oxide to form a metal alloy.   
     
     
         21 . The method of  claim 14 , wherein applying a current between the counter electrode and the at least one metal oxide comprises applying the current between the counter electrode and the at least one metal oxide comprising iridium oxide and ruthenium oxide to reduce the iridium oxide and ruthenium oxide to iridium and ruthenium.