Electrode coating and method of use in a reverse polarity electrolytic cell

Abstract

An electrode having an electrocatalytic surface or coating composed of a mixture with iridium oxide is used in a reversible polarity electrolytic cell to selectively produce an alkali metal hypohalite, preferably sodium hypochlorite, from brine made from hard water. The mixture also may have a platinum group metal oxide and a valve metal oxide, preferably, ruthenium oxide and titanium oxide respectively.

What is claimed is:  
     
         1 . A reversible polarity electrolytic cell comprising: 
 an electrolyte in a cell compartment;    electrodes immersed in the electrolyte;    a power source for applying a current to the electrodes at a first polarity; and    means for reversing the polarity of the current, 
 wherein the electrodes are coated with a mixture comprising iridium oxide.  
   
     
     
         2 . The electrolytic cell as in  claim 1 , wherein the mixture further comprises a binder.  
     
     
         3 . The electrolytic cell as in  claim 2 , wherein the binder is titanium oxide.  
     
     
         4 . The electrolytic cell as in  claim 3 , wherein the mixture further comprises an electrocatalyst.  
     
     
         5 . The electrolytic cell as in  claim 4 , wherein the electrocatalyst is ruthenium oxide.  
     
     
         6 . The electrolytic cell as in  claim 5 , wherein the mixture is about 0.5 to about 10 mole percent iridium oxide.  
     
     
         7 . The electrolytic cell as in  claim 6 , wherein the mixture is about 10 to about 30 mole percent ruthenium oxide.  
     
     
         8 . The electrolytic cell as in  claim 7 , wherein the mixture is about 2 mole percent iridium oxide.  
     
     
         9 . The electrolytic cell as in  claim 8 , wherein the electrodes are coated with a total coating load of at least 10 g/m 2 .  
     
     
         10 . The electrolytic cell as in  claim 9 , wherein the total coating load is at least 20 g/m 2 .  
     
     
         11 . The electrolytic apparatus as in  claim 10 , wherein the electrolyte comprises a sodium chloride solution.  
     
     
         12 . The electrolytic apparatus as in  claim 11 , wherein the hypohalite is hypochlorite.  
     
     
         13 . The electrolytic apparatus as in  claim 11 , wherein the hypohalite is hypobromite.  
     
     
         14 . A method of producing a hypohalite comprising: 
 immersing electrodes in an electrolyte;    supplying a current to the electrodes at a first polarity; and    reversing the polarity of the current, 
 wherein the electrodes are coated with a mixture comprising iridium oxide.  
   
     
     
         15 . The method as in  claim 14 , wherein the mixture further comprises ruthenium oxide.  
     
     
         16 . The method as in  claim 15 , wherein the mixture further comprises titanium oxide.  
     
     
         17 . The method as in  claim 16 , wherein the mixture is about 0.5 to about 10 mole percent iridium oxide.  
     
     
         18 . The method as in  claim 17 , wherein the mixture is about 10 to about 30 mole percent ruthenium oxide.  
     
     
         19 . The method as in  claim 18 , wherein the mixture is about 2 mole percent iridium oxide.  
     
     
         20 . The method as in  claim 19 , wherein the electrodes are coated with a total coating load of at least 10 g/m 2 .  
     
     
         21 . The method as in  claim 20 , wherein the total coating load is at least 20 g/m 2 .  
     
     
         22 . The method as in  claim 20 , further comprising measuring at least one operating parameter in the electrolytic cell.  
     
     
         23 . The method as in  claim 22 , wherein reversing the polarity of the current depends upon at least one measured operating parameter.  
     
     
         24 . The method as in  claim 20 , wherein the hypohalite is hypochlorite.  
     
     
         25 . The method as in  claim 20 , wherein the hypohalite is hypobromite.  
     
     
         26 . A method of producing an electrolytic product comprising: 
 immersing a first electrode and a second electrode in an electrolyte;    applying a current at a first polarity to the first electrode and the second electrode to populate the first electrode with electron donors and populate the second electrode with electron acceptors;    changing the first polarity to populate the first electrode with electron acceptors and populate the second electrode with electron donors, 
 wherein the first and second electrodes are coated with a mixture comprising iridium oxide.  
   
     
     
         27 . The method as in  claim 26 , wherein the mixture further comprises a binder.  
     
     
         28 . The method as in  claim 27 , wherein the mixture further comprises ruthenium oxide.  
     
     
         29 . The method as in  claim 28 , wherein the binder is titanium oxide.  
     
     
         30 . The method as in  claim 29 , wherein the mixture is about 0.5 to about 10 mole percent iridium oxide.  
     
     
         31 . The method as in  claim 30 , wherein the mixture is about 10 to about 30 mole percent ruthenium oxide.  
     
     
         32 . The method as in  claim 31 , wherein the mixture is about 2 mole percent iridium oxide.  
     
     
         33 . The method as in  claim 32 , wherein the electrodes are coated with a total coating load of at least 10 g/m 2 .  
     
     
         34 . The method as in  claim 33 , wherein the total coating load is at least 20 g/m 2 .  
     
     
         35 . The method as in  claim 34 , wherein the electrolytic product is an alkali metal hypohalite.  
     
     
         36 . The method as in  claim 35 , wherein the electrolyte is a brine solution.  
     
     
         37 . The method as in  claim 36 , wherein the alkali metal hypohalite is sodium hypochlorite.  
     
     
         38 . The method as in  claim 36 , wherein the alkali metal hypohalite is sodium hypobromite.