Gasless and gas bubble-free electrodes

Abstract

Gas bubble-free electrodes are necessary for stable long-term operation of millimeter-scale electrokinetic (EK) pumps when currents exceed 10-50 μA. An accompanying Technical Advance describes EK pumps that draw 1-3 mA. We have developed gasless and gas bubble-free electrodes that can run millimeter-scale (and smaller) EK pumps continuously at high current densities. Two types of gasless electrodes based on porous carbon and ruthenium/tantalum-on-titanium oxides have been developed that are supercapacitors which store ions from a fluid electrolyte. The gas bubble-free electrodes isolate gas generated by water electrolysis of the pump fluid from the fluid channels by means of an electrically-conductive polymer. Nafion® tubing is a cationic-selective polymer that is used to pass currents and water for electrolysis at titanium and platinum surfaces. The gas bubble-free electrodes are easy to fabricate and can operate well even with typical, low-conductivity electrolytes. The gas bubble-free cathode seals to 1500 psi for high-pressure microhydraulic actuation

1 . An electrode assembly, comprising: 
 an electronically conducting body, said conducting body having one or more exterior surfaces;    a conductor attached to and making electrical contact with said conducting body; and    a cation-selectable polymer jacket covering some portion of said one or more exterior surfaces, wherein an interface between said covered portion is open to an ambient exterior atmosphere    
   
   
       2 . The electrode assembly of  claim 1 , wherein the conducting body comprises a metal foil or a metal wire.  
   
   
       3 . The electrode assembly of  claim 2 , wherein the metal foil or a metal wire is titanium or tantalum.  
   
   
       4 . The electrode assembly of  claim 1 , wherein the conducting body comprises a metal frit,  
   
   
       5 . The electrode assembly of  claim 4 , wherein the metal frit comprises titanium or tantalum.  
   
   
       6 . An electrode assembly, comprising: 
 an electronically conducting collector substrate;    an ionically conducting porous layer disposed on one or more surfaces of said collector substrate; and    an electronic conductor making electrical contact with said collector substrate.    
   
   
       7 . The electrode assembly of  claim 6 , wherein said ionically conductive porous layer is an oxide layer.  
   
   
       8 . The electrode assembly of  claim 7 , wherein the oxide layer is a co-precipitated binary oxide.  
   
   
       9 . The electrode assembly of  claim 8 , wherein the co-precipitated binary oxide are oxides of ruthenium and tantalum.  
   
   
       10 . The electrode assembly of  claim 6 , wherein the metal collector substrate is an expanded metal screen or a metal foil.  
   
   
       11 . The electrode assembly of  claim 10 , wherein the expanded metal screen or metal foil is titanium.  
   
   
       12 . The electrode assembly of  claim 6 , wherein said ionically conductive porous layer is a porous carbon layer.  
   
   
       13 . The electrode assembly of  claim 12 , wherein the porous carbon layer is a carbon xerogel or a carbon paste suspension.  
   
   
       14 . The electrode assembly of  claim 13 , wherein the collector substrate is an expanded aluminum screen.  
   
   
       15 . A flow-through electrode assembly, comprising: 
 a metal body, comprising generally parallel first and second surfaces and a central opening therethrough, said first and second surfaces and said central opening covered by a cation-selective polymer jacket surrounding and isolating said surfaces and said central opening, wherein an interface between said surfaces and said central opening is open to an ambient exterior atmosphere; and    a conductor attached to said metal body.