Principle of Operation
Electrochemical sensors operate by reacting with
the gas of interest and producing an electrical
signal proportional to the gas concentration.
A typical electrochemical sensor consists
of a sensing electrode (or working electrode),
and a counter electrode separated by a
thin layer of electrolyte, Figure 3.
Gas that comes in contact with the sensor
first passes through a small capillary-type opening and
then diffuses through a hydrophobic barrier, and eventually
reaches the electrode surface. This approach is
adopted to allow the proper amount of gas to react at
the sensing electrode to produce a sufficient electrical
signal while preventing the electrolyte from leaking
out of the sensor, Figure 4.
The gas that diffuses through the barrier reacts at
the surface of the sensing electrode involving either an
oxidation or reduction mechanism. These reactions are
catalyzed by the electrode materials specifically developed
for the gas of interest.
With a resistor connected across the electrodes, a
current proportional to the gas concentration flows between
the anode and the cathode. The current can be
measured to determine the gas concentration. Because
a current is generated in the process, the electrochemical
sensor is often described as an amperometric gas sensor
or a micro fuel cell.