Teledyne OT-3 operating instructions Electrochemical Reactions

Installation OT-3

electrical circuitry, to one of the external contacts in the connector receptacle, which is on the top 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:

O2 +2H2O + 4e- —> 4OH- (cathode)

In this reaction, 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- —> Pb+2 + H2O + 2e- (anode)

In this reaction, 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 + O2 —> 2PbO

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.

The output of the fuel cell is limited by:

(1)the amount of oxygen in the cell at the time and

(2)the amount of stored anode material.

In the absence of oxygen (or any gases capable of oxidizing lead), no current is generated.

Teledyne Analytical Instruments 8