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Percent Oxygen Analyzer
The entire space between the diffusion membrane, above the
cathode, and the flexible rear membrane, beneath the anode, is filled
with electrolyte. Cathode and anode are submerged in this common
pool. They each have a conductor connecting them to one of the external
contact rings on the contact plate, which is on the bottom of the cell.
2.2.3 Electrochemical Reactions
The sample gas diffuses through the Teflon membrane. Any
oxygen in the sample gas is reduced on the surface of the cathode by the
following HALF REACTION:
O
+ 2H
2
(Four electrons combine with one oxygen molecule—in the
presence of water from the electrolyte—to produce four hydroxyl ions.)
When the oxygen is reduced at the cathode, lead is simultaneously
oxidized at the anode by the following HALF REACTION:
Pb + 2OH
(Two electrons are transferred for each atom of lead that is
oxidized. Therefore, it takes two of the above anode reactions to balance
one cathode reaction and transfer four electrons.)
The electrons released at the surface of the anode flow to the cathode
surface when an external electrical path is provided. The current is
proportional to the amount of oxygen reaching the cathode. It is measured
and used to determine the oxygen concentration in the gas mixture.
The overall reaction for the fuel cell is the SUM of the half
reactions above, or:
2Pb + O
(These reactions will hold as long as no gaseous components
capable of oxidizing lead—such as iodine, bromine, chlorine and
fluorine—are present in the sample.)
Teledyne Analytical Instruments
–
–
→ 4OH
O + 4e
2
–
→ Pb
+2
+ H
O + 2e
2
→2PbO
2
Operational Theory
(cathode)
–
(anode)
11
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