A Resistor-type Sensor for the Detection of CO in Reformed Gases

Resistor-type sensor devices using a samaria-doped ceria electrolyte with different working electrodes were fabricated for detecting carbon monoxide (CO) in reformed gases between 250 and 425°C. The electrochemical oxidation of H2 over a Pd working electrode was the most sensitive to a reversible poisoning by 50-4000 ppm CO in the presence of 50% hydrogen, 10% carbon dioxide, and 6% water vapor, which provided an increase in the electrode-reaction resistance at the electrode-electrolyte interface. The resulting sensor signal was strongly dependent on the CO concentration, where linear relationships between the signal and the logarithm of the CO concentration were obtained, especially below 1000 ppm with 90% response and 90% recovery times of about 20 seconds. An improvement in the CO-sensing properties of the present sensor device above 300°C was also carried out by the addition of Au to the Pd working electrode.