In a pO2 sensor, what are the correct materials for the cathode and anode?

• A. Cathode: Platinum; Anode: Silver chloride
• B. Cathode: Carbon; Anode: Copper
• C. Cathode: Gold; Anode: Silver
• D. Cathode: Silver; Anode: Gold

Answer: (A)

In this sensor, the working electrode (cathode) must efficiently catalyze the reduction of oxygen, while the other electrode provides a stable reference potential. Platinum is the best choice for the cathode because it is an excellent catalyst for the four-electron reduction of O2 to water and it remains chemically stable in the electrolyte, giving a clean, reproducible signal.

The reference/second electrode is typically a silver/silver chloride electrode in a potassium chloride solution. This combination sets a well-defined, stable potential that does not depend on the oxygen level, which is essential for accurately relating the measured voltage to pO2.

Other materials aren’t as suitable: carbon doesn’t catalyze O2 reduction as effectively and can behave unpredictably under polarization, copper tends to oxidize, and gold is not used here as the stable reference electrode. So the correct pairing is a platinum cathode with a silver chloride reference electrode.