Manganese oxide based catalyst and electrode for alkaline electrochemical system and method of its production

Abstract

A catalyst, active layer, and cathode for metal air and other air-assisted cells and methods of producing these are disclosed. The cathode produced comprises a substantially unoxidized carbon support with a manganese or other oxide catalyst. The support maintains its inherent water repellency, conductivity and active sites. The cathode is therefore capable of sustaining significantly high currents for prolonged duration, at higher operating voltages, enabling the extension of metal air technology for higher power devices.

We claim:  
     
         1 . A carbon support comprising at least one of conductive carbon black and activated carbon and having an oxide catalyst loaded thereupon, the carbon support being substantially unoxidized.  
     
     
         2 . A carbon support as claimed in  claim 1 , the conductive carbon black having a surface area of at least 1200 m 2 /g.  
     
     
         3 . A carbon support as claimed in  claim 1 , the activated carbon having a surface area of at least 700 m 2 /g.  
     
     
         4 . A carbon support as claimed in  claim 1 , the oxide catalyst comprising manganese.  
     
     
         5 . A carbon support as claimed in  claim 1 , the oxide catalyst comprising manganese dioxide.  
     
     
         6 . A carbon support as claimed in  claim 1 , the oxide catalyst comprising primary particles of submicron size.  
     
     
         7 . A carbon support as claimed in  claim 1 , the oxide catalyst comprising secondary particles of between about 100 nanometers and 30 microns in size.  
     
     
         8 . An active layer for an air cathode, the active layer comprising a hydrophobic binder and a carbon support comprising at least one of conductive carbon black and activated carbon and having an oxide catalyst loaded thereupon, the carbon support being substantially unoxidized.  
     
     
         9 . A cathode active layer as claimed in  claim 8  comprising, by weight, 70-80% carbon and 2-20% oxide catalyst.  
     
     
         10 . An air cathode for an electrochemical cell, the air cathode comprising a metallic substrate, an active layer on a first side of the substrate, a hydrophobic diffusion layer on a second side of the substrate, the active layer comprising a hydrophobic binder and a carbon support comprising at least one of conductive carbon black and activated carbon and having an oxide catalyst loaded thereupon, the carbon support being substantially unoxidized.  
     
     
         11 . An air cathode as claimed in  claim 10  wherein the diffusion layer comprises PTFE.  
     
     
         12 . An air cathode as claimed in  claim 10  comprising, by weight, 70-80% carbon and 2-20% oxide catalyst.  
     
     
         13 . An electrochemical cell comprising: 
 an anode;    an air cathode comprising a metallic substrate, an active layer on a first side of the substrate, a hydrophobic diffusion layer on a second side of the substrate, the active layer comprising a hydrophobic binder and a carbon support comprising at least one of conductive carbon black and activated carbon and having an oxide catalyst loaded thereupon, the carbon support being substantially unoxidized;    a separator between the anode and the cathode; and    an electrolyte in contact with the anode and the cathode.    
     
     
         14 . A method for making an air cathode for an electrochemical cell, the method comprising the steps of: 
 combining a carbon slurry comprising at least one of conductive carbon black and activated carbon, with a suspension of oxide catalyst particles having particles ranging in size from about 100 nanometers to about 30 microns and a waterproofing agent to form a mixture, the carbon in the mixture being substantially unoxidized;    forming the mixture into an active layer for an air cathode, the carbon in the cathode being substantially unoxidized; and    incorporating the active layer into an air cathode.    
     
     
         15 . A method for making an air cathode as claimed in  claim 14  wherein the suspension of oxide catalyst particles is formed by a method comprising the step of mixing an oxidizing agent that comprises manganese with a reducing agent to yield a suspension of oxide catalyst particles.  
     
     
         16 . A method for making an air cathode as claimed in  claim 14  wherein the oxidizing agent comprises a soluble manganese compound having a valence state higher than +4.  
     
     
         17 . A method for making an air cathode as claimed in  claim 14  wherein the oxidizing agent comprises a permanganate salt selected from the group consisting of a lithium salt, a sodium salt, a potassium salt, a silver salt, an ammonium salt, a cobalt salt, and a mixture thereof.  
     
     
         18 . A method for making an air cathode as claimed in  claim 14  wherein the reducing agent is selected from the group consisting of an organic reducing agent and an inorganic reducing agent.  
     
     
         19 . A method for making an air cathode as claimed in  claim 14  wherein the reducing agent is selected from the group consisting of a nitrate, a chloride, a sulfate, and a perchlorate of a manganese compound having a valence of +2 and hydrogen peroxide.  
     
     
         20 . A method for making an air cathode as claimed in  claim 14  wherein the reducing agent is selected from the group consisting of fumaric acid, citric acid, formic acid, a salt of any of the foregoing acids, an alcohol that can be readily oxidized, and an aldehyde that can be readily oxidized.  
     
     
         21 . A method for making an air cathode for an electrochemical cell, the method comprising the steps of: 
 mixing an oxidizing agent comprising manganese with a reducing agent and with a carbon support under conditions that favor a redox reaction between the oxidizing agent and the reducing agent over a reaction between the oxidizing agent and the carbon to form oxide catalyst particles and to load the particles in situ onto the carbon support;    mixing a waterproofing agent with the oxide-catalyst-loaded carbon support to form a mixture;    forming the mixture into an active layer for an air cathode, the carbon in the cathode being substantially unoxidized; and    incorporating the active layer into an air cathode.    
     
     
         22 . A method for making an air cathode as claimed in  claim 21  wherein the oxidizing agent comprises a soluble manganese compound having a valence state higher than +4.  
     
     
         23 . A method for making an air cathode as claimed in  claim 21  wherein the oxidizing agent comprises a permanganate salt selected from the group consisting of a lithium salt, a sodium salt, a potassium salt, a silver salt , an ammonium salt, a cobalt salt, and a mixture thereof.  
     
     
         24 . A method for making an air cathode as claimed in  claim 21  wherein the reducing agent is selected from an organic reducing agent and an inorganic reducing agent.  
     
     
         25 . A method for making an air cathode as claimed in  claim 21  wherein the reducing agent is selected from the group consisting of a nitrate, a chloride, a sulfate, a perchlorate and hydrogen peroxide.  
     
     
         26 . A method for making an air cathode as claimed in  claim 21  wherein the reducing agent is selected from the group consisting of fumaric acid, citric acid, formic acid, a salt of any of the foregoing acids, an alcohol that can be readily oxidized, and an aldehyde that can be readily oxidized.