Process For Making A Catalytic Electrode And Electrochemical Cell Using The Electrode

Abstract

A process for making a catalytic electrode, a process for making an electrochemical cell with a catalytic electrode, and an electrochemical cell made according to the process. The catalytic electrode has an active layer comprising a catalytic material, an electrically conductive material and a binder, and a gas diffusion layer including a material that is permeable to gas entering or escaping from the cell but essentially impermeable to electrolyte. The gas diffusion layer is adhered to the active layer by a patterned pressure bonding process to provide the catalytic electrode in which the entire gas diffusion area is adhered to the active layer, with areas of relatively high and relatively low adhesion. The electrode has a high overall bond strength, and the permeability of the gas diffusion layer remains high it has been adhered to the active layer to provide excellent high power capability.

1 . An electrochemical cell comprising a catalytic electrode, a counter electrode, a separator between the catalytic and counter electrodes, and an electrolyte, all disposed within a housing having at least one opening for allowing a gas to enter into or escape from the housing; wherein:
 the catalytic electrode has a multilayer structure comprising an active layer and a gas diffusion layer;   the active layer comprises a catalytic material for oxidizing or reducing an active material, an electrically conductive material, and a binder;   the gas diffusion layer comprises a material that is permeable to the gas entering or escaping the housing and is essentially impermeable to the electrolyte to seal the electrolyte within the housing; and   the gas diffusion layer has a surface with a gas diffusion area for diffusion of the gas therethrough, the entire gas diffusion area is adhered to the active layer, and adhesion of the gas diffusion area to the active layer has areas of relatively high adhesion and areas of relatively low adhesion.   
     
     
         2 . The cell according to  claim 1 , wherein the adhesion of the gas diffusion area to the active layer is characterized by an overall bond strength of from 65 to 250 grams per 25.4 mm and the catalytic electrode has sufficient permeability to be capable of providing 220 mW/cm 2  to 700 mW/cm 2  maximum power on a Half Cell AC Impedance/Potential Dynamic Scan test. 
     
     
         3 . The cell according to  claim 2 , wherein the bond strength is at least 75 grams per 25.4 mm and the maximum power the catalytic electrode is capable of providing on the Half Cell AC Impedance/Potential Dynamic Scan test is at least 250 mW/cm 2 . 
     
     
         4 . The cell according to  claim 1 , wherein the gas diffusion layer is pressure bonded to the active layer. 
     
     
         5 . The cell according to  claim 1 , wherein the gas diffusion layer material is a fluorinated polymer. 
     
     
         6 . The cell according to  claim 5 , wherein the gas diffusion layer sheet comprises a polytetrafluoroethylene sheet. 
     
     
         7 . The cell according to  claim 6 , wherein the polytetrafluoroethylene sheet, prior to bonding the gas diffusion layer sheet to the active layer sheet, has an air permeability value of from 1 to 300 seconds and an apparent density of 1.5 to 1.7 g/cm 2 . 
     
     
         8 . The cell according to  claim 1 , wherein the electrolyte is an aqueous alkaline electrolyte and the gas diffusion layer material is a hydrophobic material. 
     
     
         9 . The cell according to  claim 8 , wherein the counter electrode comprises zinc as an active material. 
     
     
         10 . The cell according to  claim 9 , wherein the cell contains no added mercury. 
     
     
         11 . The cell according to  claim 1 , wherein the catalytic electrode is an oxygen reduction material capable of reducing oxygen entering the housing through the one or more openings therein. 
     
     
         12 . The cell according to  claim 1 , wherein the catalytic material comprises a manganese oxide represented by an overall formula MnO x , where x is from 0.5 to 2.0. 
     
     
         13 . The cell according to  claim 1 , wherein the catalytic material comprises a composite material comprising nano-metal particles adhered to activated carbon particles. 
     
     
         14 . The cell according to  claim 13 , wherein the nano-metal particles comprise nano-manganese. 
     
     
         15 . An electrochemical cell comprising a catalytic electrode, a counter electrode, a separator between the catalytic and counter electrodes, and an aqueous alkaline electrolyte, all disposed within a housing having at least one opening for allowing oxygen to enter the housing; wherein:
 the catalytic electrode has a multilayer structure comprising an active layer, a gas diffusion layer and a current collector;   the active layer comprises a catalytic material, an electrically conductive carbon and a binder;   the gas diffusion layer comprises a polytetrafluoroethylene material that is permeable to the oxygen entering the housing and is essentially impermeable to the electrolyte to seal the electrolyte within the housing;   the gas diffusion layer has a surface with a gas diffusion area for diffusion of the oxygen therethrough to the active layer, the entire gas diffusion area is adhered to the active layer, and adhesion of the gas diffusion area to the active layer has areas of relatively high adhesion and areas of relatively low adhesion;   
       bond strength of from 65 grams per 25.4 mm to 250 grams per 25.4 mm;
 the catalytic electrode has sufficient permeability to be capable of providing 220 mW/cm 2  to 700 mW/cm 2  maximum power on a Half Cell AC Impedance/Potential Dynamic Scan test; 
 the current collector comprises an expanded metal comprising nickel, coated with graphite; and 
 the cell contains no added mercury. 
 
     
     
         16 . A process for making a catalytic electrode for an electrochemical cell, comprising the steps:
 (a) mixing a catalytic material for oxidizing or reducing an active material with an electrically conductive material and a binder;   (b) forming the mixture from step (a) into an active layer sheet;   (c) disposing a first surface of a gas diffusion layer sheet against a first surface of the active layer sheet;   (d) applying pressure to a second surface of the active layer sheet and a second surface of the gas diffusion layer sheet to bond the gas diffusion layer sheet to the active layer sheet to produce a gas diffusion area for diffusion of a gas therethrough to the active area such that the entire gas diffusion area is bonded to the active layer with areas of relatively high adhesion and relatively low adhesion between the gas diffusion layer and active layer; and   (e) forming the bonded layers into an electrode having adhesion between essentially the entire adjacent second surfaces of the bonded layers.   
     
     
         17 . The process according to  claim 16 , wherein a first surface of a textured interleaf sheet is disposed against the second surface of the gas diffusion layer sheet, and the pressure is applied to the second surfaces of the interleaf sheet and the gas diffusion layer sheet. 
     
     
         18 . The process according to  claim 17 , wherein the textured interleaf sheet comprises woven threads, fibers, filaments, hairs, or wires. 
     
     
         19 . The process according to  claim 18 , wherein the interleaf sheet comprises a woven silk fabric. 
     
     
         20 . The process according to  claim 17 , wherein the pressure is applied by a combination of two plates, platens or rollers. 
     
     
         21 . The process according to  claim 16 , wherein the adhesion of the gas diffusion area to the active layer is characterized by an overall bond strength of from 65 grams per 25.4 mm to 250 grams per 25.4 mm and the catalytic. 
     
     
         22 . The process according to  claim 16 , wherein the pressure is applied by a combination of two plates, platens or rollers, at least one of which has a textured surface to produce the areas of relatively high adhesion and relatively low adhesion. 
     
     
         23 . The process according to  claim 16 , wherein the gas diffusion layer sheet comprises a hydrophobic material. 
     
     
         24 . The process according to  claim 23 , wherein the hydrophobic material comprises a fluorinated polymer. 
     
     
         25 . The process according to  claim 24 , wherein the gas diffusion layer sheet comprises a polytetrafluoroethylene sheet. 
     
     
         26 . The process according to  claim 25 , wherein the polytetrafluoroethylene sheet, prior to bonding the gas diffusion layer sheet to the active layer sheet, has an air permeability value of from 1 to 300 seconds and an apparent density of 1.5 to 1.7 g/cm 2 . 
     
     
         27 . The process according to  claim 16 , wherein the process further comprises the step of incorporating an electrically conductive current collector. 
     
     
         28 . The process according to  claim 27 , wherein the current collector is made from an expanded metal comprising nickel and has a coating comprising graphite. 
     
     
         29 . The process according to  claim 27 , wherein the current collector is embedded into the second surface of the active layer sheet.