Potentiometric CO sensors using anion-conducting polymer electrolyte: Effects of the kinds of noble metal-loaded metal oxides as sensing-electrode materials on CO-sensing properties

•CO sensors using an anion-conducting polymer electrolyte and oxide-based electrodes were developed in this study.•The Pt or Au loading onto the SnO2 electrode and the Au loading onto the In2O3 electrode improved their CO responses.•Only the Pt loading onto the SnO2 electrode of the sensor drastically improved the CO selectivity against H2.•The heat treatment of the Pt-loaded SnO2 in hydrogen at 250 °C enhanced both the CO and H2 responses of the sensor. Potentiometric CO-sensing properties of electrochemical gas sensors using an anion-conducting polymer as an electrolyte and a metal oxide (MO; Bi2O3, CeO2, In2O3, SnO2, or V2O5) loaded with or without 2.0 wt% noble metal (N; Ag, Au, Ir, Ru, Rh, Pd, or Pt) as an electrode material (EC(N/MO) or (EC(MO) sensor; N/MO: N-loaded MO) were investigated in wet synthetic air (57%RH) at 30 °C. Among all the EC(MO) sensors, the EC(CeO2) sensor showed the largest CO response and excellent CO selectivity against H2 and the EC(Bi2O3) sensor showed relatively large CO and H2 responses (no CO selectivity against H2). Other EC(MO) sensors hardly showed both CO and H2 responses. However, the Au loading just onto In2O3 and SnO2 was effective in improving the magnitude of CO and H2 responses of the EC(In2O3) and EC(SnO2) sensors, respectively, which resulted in relatively poor CO selectivity against H2. On the other hand, the Pt loading only onto SnO2 extremely enhanced only the magnitude of CO response of the EC(SnO2) sensor, and thus the EC(Pt/SnO2) sensor showed the most excellent CO selectivity against H2, among all the sensors in this study. The heat treatment of N/MO powders in H2 at 250 °C reduced only the H2 response of the EC(Au/SnO2) sensor, leading to an improvement of the CO selectivity of only the EC(Au/SnO2) sensor against H2. On the other hand, the heat treatment drastically enhanced both CO and H2 responses of the EC(Pt/SnO2) sensor, resulting in a decrease in its CO selectivity against H2. The CO and H2 responses of other EC(N/SnO2) sensors before and after the heat treatment in H2 at 250 °C were also examined, and the effectiveness of the noble metal loading and the heat treatment on the CO-sensing properties was discussed in this study. In addition, gas-sensing mechanism was also proposed on the basis of chemical surface states of representative N/MO.