Reference half-cell and electrochemical sensor with the reference half-cell

Abstract

A reference half-cell for application in an electrochemical sensor, comprising a housing, in which a chamber containing a reference electrolyte is formed, wherein the reference electrolyte is in contact with a medium surrounding the housing via a liquid junction arranged in a wall of the housing, wherein the liquid junction comprises a porous diaphragm, and wherein the diaphragm has, at least partially, a coating, which comprises at least one metal.

What is claimed is: 
     
         1 . A liquid junction for use in a reference half-cell, comprising:
 a liquid-permeable solid body comprising an electrically non-conductive first material and an electrically conductive second material,   wherein the body is formed primarily of the first material, and   wherein the second material is distributed sufficiently uniformly on and within the body, whereby the liquid-permeability of the body is reduced and an electrical resistance of the body is reduced by the distributed second material.   
     
     
         2 . The liquid junction of  claim 1 , wherein the first material is selected from the group consisting of zirconium dioxide, ceramic, glass, and PTFE. 
     
     
         3 . The liquid junction of  claim 1 , wherein the second material is selected from the group consisting of copper, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold. 
     
     
         4 . The liquid junction of  claim 1 , the solid body further comprising an electrically conductive third material,
 wherein the third material is distributed sufficiently uniformly on and within the body, whereby the liquid-permeability of the body is reduced and the electrical resistance of the body is reduced by the distributed third material, and   wherein the third material is selected from the group consisting of copper, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.   
     
     
         5 . The liquid junction of  claim 1 , wherein the solid body further comprises an adherence-promoting material composed of molecules having functional thiol groups, the adherence promoting material distributed uniformly on and within the body. 
     
     
         6 . The liquid junction of  claim 1 , wherein the second material has a biocidal effect. 
     
     
         7 . A reference half-cell for an electrochemical sensor, comprising:
 a housing defining a chamber containing a reference electrolyte; and   a liquid junction disposed in a wall of the housing, the liquid junction comprising a diaphragm made of porous media, the diaphragm having an outer surface defining a volume, the volume including a plurality of pores within the media, each of the plurality of pores having an inner surface,   wherein the diaphragm includes a conductive material distributed on the outer surface and on the inner surfaces of the plurality of pores, such that the conductive material at least partially covers the outer surface and the inner surfaces,   wherein the conductive material includes at least one metal, and   wherein the reference electrolyte is in contact via the liquid junction with a medium surrounding the housing.   
     
     
         8 . The reference half-cell of  claim 7 , wherein the porous media is selected from the group consisting of zirconium dioxide, ceramic, glass, and PTFE. 
     
     
         9 . The reference half-cell of  claim 7 , wherein the at least one metal is selected from the group consisting of copper, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold. 
     
     
         10 . The reference half-cell of  claim 7 , wherein the conductive material forms a coating at least partially covering the outer surface and the inner surfaces. 
     
     
         11 . The reference half-cell of  claim 10 , wherein the coating has a biocidal effect. 
     
     
         12 . The reference half-cell of  claim 10 , wherein the coating has a first layer composed of a first metal and a second layer composed of a second metal. 
     
     
         13 . The reference half-cell of  claim 7 , further comprising:
 an electrode of a second type contained in the chamber and configured to act as a potential forming system.   
     
     
         14 . The reference half-cell of  claim 13  wherein the electrode is a silver/silver halide electrode. 
     
     
         15 . An electrochemical sensor for measuring at least one measured variable of a measured medium, comprising:
 at least one reference half-cell, the reference half-cell comprising:
 a housing defining a chamber containing a reference electrolyte; and 
 a liquid junction disposed in a wall of the housing, the liquid junction comprising a diaphragm made of porous media, the diaphragm having an outer surface defining a volume, the volume including a plurality of pores within the media, each of the plurality of pores having an inner surface, 
 wherein the diaphragm includes a conductive material distributed on the outer surface and on the inner surfaces of the plurality of pores, such that the conductive material at least partially covers the outer surface and the inner surfaces, 
 wherein the conductive material includes at least one metal, and 
 wherein the reference electrolyte is in contact via the liquid junction with a medium surrounding the housing. 
   
     
     
         16 . The electrochemical sensor of  claim 15 , wherein the material forms a coating at least partially covering the outer surface and the inner surfaces. 
     
     
         17 . The electrochemical sensor of  claim 15 , further comprising:
 at least one sensorially active component in contact with the measured medium during measuring having a property changing as a function of a measured variable to be determined; and   a measuring circuit interacting with the reference half-cell and the at least one sensorially active component and embodied to produce a measurement signal dependent on the property of the sensorially active component representing the measured variable.   
     
     
         18 . The electrochemical sensor of  claim 17 , wherein the sensorially active component comprises one of: a metal redox electrode, a non-metallic redox electrode, a surface of a metal-metal oxide electrode, an ion-selective field effect transistor, or an ion-selective glass membrane. 
     
     
         19 . The electrochemical sensor of  claim 15 , further comprising:
 a working electrode and a counter electrode, which, with the reference half-cell, form a three-electrode arrangement; and   a control circuit that is embodied to set a predetermined voltage between the counter electrode and the reference half-cell and to register the electrical current flowing through the measured medium between the counter electrode and the working electrode.