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

摘要

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 degrees C. Among all the EC(MO) sensors, the EC(CeO2) sensor showed the largest CO response and excellent CO selectivity against H-2 and the EC(Bi2O3) sensor showed relatively large CO and H-2 responses (no CO selectivity against H-2). Other EC(MO) sensors hardly showed both CO and H-2 responses. However, the Au loading just onto In2O3 and SnO2 was effective in improving the magnitude of CO and H-2 responses of the EC(In2O3) and EC(SnO2) sensors, respectively, which resulted in relatively poor CO selectivity against H-2. 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 H-2, among all the sensors in this study. The heat treatment of N/MO powders in H-2 at 250 degrees C reduced only the H-2 response of the EC(Au/SnO2) sensor, leading to an improvement of the CO selectivity of only the EC(Au/SnO2) sensor against H-2. On the other hand, the heat treatment drastically enhanced both CO and H-2 responses of the EC(Pt/SnO2) sensor, resulting in a decrease in its CO selectivity against H-2. The CO and H-2 responses of other EC(N/SnO2) sensors before and after the heat treatment in H-2 at 250 degrees 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.