Methods of making an electrochemical gas sensor
This disclosure relates to an improved electrochemical sensor that has a simplified electrode assembly. The electrode assembly incorporates electrodes into or onto a single polymeric substrate. The working electrode can be porous, to enable an analyte, such as a toxic gas, to access an electrode-electrolyte interface. Ionic connection between electrodes can be made by an electrolyte on a back side of the electrode assembly, and external electronic circuitry can be connected directly to the electrode assembly. This construction dramatically simplifies the sensor, resulting in reduced costs and potentially improved performance. The construction is compatible with batch fabrication methods.
1. A method of making an electrochemical gas sensor, the method comprising:
selecting a self-supporting pre-form comprising a solid agglomerated continuous conductive material, the pre-form comprising a working electrode device region and a counter electrode device region and a reference electrode device region, wherein each device region comprises two pre-electrode regions in electrical communication spaced apart in a first direction and extending across the pre-form in a second direction; and
forming a plurality of apertures in the self-supporting pre-form to provide a porous working electrode device region; and
connecting the device regions by an electrolyte on the back side of the pre-form; and
forming an insulating material comprising a polymeric material about each device region in a manner that the insulating material fills spacings defined in the first direction between the three electrode device regions; and
forming one or more apertures in the insulating material at the working electrode in a manner to allow a gas to pass through to the working electrode; and
severing electrical connection of the pre-form into discrete spaced apart working, counter, and reference electrodes carried by the insulating material to provide an electrode assembly; and
enclosing the electrode assembly in a molded plastic enclosure in a manner that external electronic circuitry can be connected directly outside the enclosure, and
protecting the front side of the enclosure by a gas permeable membrane to allow gases to pass into the enclosure for easy detection, while keeping out liquids, such as water, that could damage the electrode assembly, and
protecting the backside of the enclosure that includes the electrolyte in chemical communication with each electrode with a gas impermeable cover.
2. The method of claim 1 , wherein the forming of the insulating material about each device region is performed using injection molding.
3. The method of claim 1 , wherein the pre-form is made by chemically etching or stamping a sheet of metal.
4. A method comprising: manufacturing an electrochemical gas sensor by the method of claim 1 ; and connecting external electronic circuitry directly to the electrode assembly to measure electrical output from the electrodes when a detectable species is present, as current proportional to the species concentration is produced in the external circuit.
5. A method comprising: manufacturing an electrochemical gas sensor by the method of claim 1 ; and connecting a third reference external electronic circuitry directly to the electrode assembly to improve stability of the electrical output, by maintaining a fixed potential.