Electrochemical sensor with dry ionomer membrane

Abstract

A miniaturized gas sensor comprised of film type electrodes, on a non-conductive supportive substrate, and in contact with a dry ionomer electrolyte, for detection of toxic gases, i.e., carbon monoxide, and other oxidizable or reducible gases and vapors and method of making same is described. The all-solid planar sensor cell has two or more film type electrodes arranged on a non-conductive planar surface of a supportive substrate. Manufacturing the electrochemical sensor with dry ionomer prevents electrode flooding and allows for improved response time upon assembly. The sensor cell contains no liquid electrolyte and is operated in a constant-voltage, potentiostatic or potentiodynamic mode. A high sensitivity to a select gas or vapor is achieved by a three-phase contact area design for a sensing electrode, which provides contact with the solid ionomer electrolyte, as well as the gas sample via diffusion openings or holes that penetrate through the supportive substrate.

1 . A sensor cell for detecting gas comprising:
 a substrate;   a sensing electrode in close proximity with said substrate for detecting gas;   a dry ionomer membrane in contact with said substrate and said sensing electrode wherein said dry ionomer membrane acts as an electrolyte;   at least one opening in said substrate for keeping gas in contact with both said dry ionomer membrane and said sensing electrode   
   
   
       2 . The apparatus of  claim 1  wherein said dry ionomer membrane is composed of dry sheet Nafion®. 
   
   
       3 . The apparatus of  claim 1  wherein said dry ionomer membrane contains at least one opening. 
   
   
       4 . The apparatus of  claim 3  wherein the at least one opening is a hole. 
   
   
       5 . The apparatus of  claim 1  wherein the said substrate, sensing electrode, and ionomer membrane are in alignment with one another. 
   
   
       6 . The apparatus of  claim 5  wherein said ionomer membrane is dry during alignment of said substrate, sensing electrode, and ionomer membrane. 
   
   
       7 . The apparatus of  claim 1  wherein the sensor is assembled prior to wetting said dry ionomer membrane. 
   
   
       8 . The apparatus of  claim 1  wherein said at least one opening in the substrate is aligned with the electrode for defining a gas passage. 
   
   
       9 . The apparatus of  claim 1  further including a polymer layer positioned upon said sensing electrode for slowing inputs of gas moving through said at least one opening in said substrate onto a surface of said sensing electrode. 
   
   
       10 . The apparatus of  claim 1  further comprising a counter electrode in contact with the dry ionomer membrane such that upon wetting the dry ionomer membrane the counter electrode provides an electrical connection. 
   
   
       11 . The apparatus of  claim 1  further comprising a reference electrode in contact with the dry ionomer membrane such that upon wetting the dry ionomer membrane a reference point is created against which the potential of other electrodes can be measured. 
   
   
       12 . The apparatus of  claim 1  wherein the dry ionomer membrane is a perfluorosulfonic acid membrane. 
   
   
       13 . The apparatus of  claim 1  further comprising a reservoir in contact with the dry ionomer membrane. 
   
   
       14 . The apparatus of  claim 13  wherein said reservoir does not initially contain liquid. 
   
   
       15 . The apparatus of  claim 14  wherein said reservoir can be filled with liquid for hydrating the ionomer membrane. 
   
   
       16 . The apparatus of  claim 1  wherein said reservoir can be filled with liquid for hydrating the ionomer membrane. 
   
   
       17 . The apparatus of  claim 1  further including a counter electrode in contact with said dry ionomer membrane such that upon wetting said dry ionomer membrane said counter electrode provides an electrical connection to said ionomer membrane so current may be applied to said sensing electrode. 
   
   
       18 . The apparatus of  claim 1  further including a reference electrode in contact with said dry ionomer membrane such that upon wetting said dry ionomer membrane a reference point is created against which the potential of other electrodes can be measured. 
   
   
       19 . The apparatus of  claim 1  wherein said dry ionomer membrane is a perfluorosulfonic acid membrane. 
   
   
       20 . The apparatus of  claim 1  wherein said sensing electrode is in contact with said substrate for detecting gas. 
   
   
       21 . The apparatus of  claim 1  further comprising two or more sensing electrodes. 
   
   
       22 . A method of making an electrochemical sensor for the detection of an analyte in a gas sample comprising:
 providing a dry ionomer membrane;   providing a substrate that has holes through its surface and an electrode layer adjacent to said holes;   punching holes in said dry ionomer membrane; and   mating said dry ionomer membrane to said substrate such that the holes in said dry ionomer membrane align with the holes in said substrate forming a gas inlet and wherein said dry ionomer membrane has on its surface an electrode layer in operative connection with said ionomer membrane which reacts with a gas to produce mobile electrons.   
   
   
       23 . The method of  claim 22  wherein the step of providing a dry ionomer membrane further includes selecting dry sheet Nafion®. 
   
   
       24 . The method of  claim 22  further including making said sensor cell prior to wetting said dry ionomer membrane. 
   
   
       25 . The method of  claim 22  further including positioning a polymer layer upon said sensing electrode for slowing inputs of gas moving through said inlet onto a surface of said sensing electrode. 
   
   
       26 . The method of  claim 22  where the step of providing a substrate further includes positioning a counter electrode in contact with said dry ionomer membrane such that upon wetting said dry ionomer membrane said counter electrode provides an electrical connection to said ionomer membrane so current may be applied to said sensing electrode. 
   
   
       27 . The method of  claim 22  where the step of providing a substrate further includes positioning a reference electrode in contact with said dry ionomer membrane such that upon wetting said dry ionomer membrane a reference point is created against which the potential of other electrodes can be measured. 
   
   
       28 . The method of  claim 22  where the step of obtaining a dry ionomer membrane further includes obtaining a perfluorosulfonic acid membrane. 
   
   
       29 . A method of making an electrochemical sensor for the detection of an analyte in a gas sample comprising: 
     a) providing a dry ionomer membrane free from liquid droplets; 
     b) providing a substrate with at least one opening through its surface and a first electrode layer adjacent to said opening; 
     c) connecting said dry ionomer membrane to said substrate; 
     d) aligning said at least one opening in said substrate with the first electrode for defining a gas passage; and 
     e) depositing a second electrode on said substrate for operatively connecting said ionomer membrane, said first electrode, and said second electrode.