CO-sensing properties of potentiometric gas sensors using an anion-conducting polymer (ACP) as an electrolyte and metal oxides loaded with and without Au as electrodes (EC(MO) or EC(nAu/MO(Tm)), respectively, MO: metal oxide (In2O3, ZnO or Co3O4), n: the loading amount of Au, 0.5 similar to 2.0 wt%, T: heat-treatment temperature, m: heat-treatment atmosphere, air or H-2) have been investigated in wet synthetic air (57% RH) at 30 degrees C. In addition, H-2-sensing properties of these sensors have also been investigated in the same gaseous conditions, to evaluate their CO selectivity against H-2. All of the EC(MO) sensors showed relatively small changes in electromotive force (EMF), i.e. responses, to both CO and H-2, but the Au loading to In2O3 and ZnO drastically improved the magnitude of CO response of the EC(In2O3) and EC(ZnO) sensors, respectively. The EC(2.0Au/In2O3(400air)) sensor showed larger CO response, faster CO response speed, excellent CO selectivity against H-2 and better long-term stability than those of the EC (2.0Au/ZnO(400air)) sensor. The influence of moisture on the CO response of the EC(2.0Au/In2O3(400air)) sensor was almost negligible in the humidity range of 40 similar to 100% RH. The magnitude of CO response of the EC(2.0Au/In2O3(400air)) sensor in wet synthetic air showed a good linear relationship with CO concentration, but the CO response was largely affected by the concentration of O-2. These results indicate that the EMF of the EC(2.0Au/In2O3(400air)) sensor is probably determined by the mixed potential resulting from CO oxidation and O-2 reduction. The heat-treatment conditions of the 2.0 wt% Au-loaded In2O3 powder largely affected the CO-sensing properties of the EC(2.0Au/In2O3(Tm)) sensors. Among these sensors heat-treated in various conditions, the as-fabricated EC(2.0Au/In2O3(250H(2))) sensor showed the most excellent CO selectivity against H-2 in their concentration range of 10 similar to 3000 ppm. (C) 2015 Elsevier Ltd. All rights reserved.