CO and CO_2 sensing properties of electrochemical gas sensors using an anion-conducting polymer as an electrolyte

摘要

CO_2 and CO sensing properties of an electrochemical gas sensor employing an anion-conducting polymer (ACP) membrane as an electrolyte and Pt only, Pt mixed with ACP or 10wt% Pt-loaded carbon black (Pt/CB) mixed with ACP as an electrode material, which were denoted as an EC(Pt), EC(Pt-ACP) or EC(Pt/CB-ACP) sensor, respectively, have been investigated in this study. All sensors showed positive Nernstian response to 400-20,000 ppm CO_2 in humid air at 30℃, and the EC(Pt-ACP) sensor showed large CO_2 response in comparison with those of EC(Pt) and EC(Pt-CB/ACP) sensors. These CO_2-sensing properties were largely dependent on humidity in sample and reference gases and CO_2 concentration in the reference gas. In addition, the electromotive force (EMF) of the sensors also varied with a change in O_2 concentration in a CO_2-free sample gas, when CO_2-free air was used also as a reference gas. However, the EMF was little dependent on the O_2 concentration in the sample gas containing CO_2. From these results, a 2-electron O_2-free redox reaction of CO_2 may determine the potential of the sensing electrode under atmosphere containing CO_2. On the other hand, EC(Pt-ACP) and EC(Pt/CB-ACP) sensors showed slow and negative response to CO in humid air at 21℃, and the magnitude of CO response of these sensors was almost proportional to the logarithm of CO concentration. In addition, the EMF was largely dependent on the O_2 concentration in the sample gas containing CO. The O_2 response behavior and current-voltage characteristics in N_2 containing 1000 ppm CO or 20% O_2 confirmed that the mixed potential consisting of CO oxidation and O_2 reduction is the most important factor to determine the magnitude of CO response.