CO-sensing Properties of Potentiometric Gas Sensors Using an Anion-conducting Polymer Electrolyte and Au-loaded Metal Oxide Electrodes

Abstract 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( n Au/MO( T m)), respectively, MO: metal oxide (In 2 O 3 , ZnO or Co 3 O 4 ), n : the loading amount of Au, 0.5∼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 °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 In 2 O 3 and ZnO drastically improved the magnitude of CO response of the EC(In 2 O 3 ) and EC(ZnO) sensors, respectively. The EC( 2.0 Au/In 2 O 3 ( 400 air)) 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( 2.0 Au/ZnO( 400 air)) sensor. The influence of moisture on the CO response of the EC( 2.0 Au/In 2 O 3 ( 400 air)) sensor was almost negligible in the humidity range of 40∼100%RH. The magnitude of CO response of the EC( 2.0 Au/In 2 O 3 ( 400 air)) 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( 2.0 Au/In 2 O 3 ( 400 air)) 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 In 2 O 3 powder largely affected the CO-sensing properties of the EC( 2.0 Au/In 2 O 3 ( T m)) sensors. Among these sensors heat-treated in various conditions, the as-fabricated EC( 2.0 Au/In 2 O 3 ( 250 H 2 )) sensor showed the most excellent CO selectivity against H 2 in their concentration range of 10∼3000 ppm.