Solid state electrochemical cells for the dection of carbon dioxide gas

Abstract

As the importance of precise and continuous measurement and control of $CO_2$ concentration has been increasing, highly sensitive and reliable $CO_2$ sensor applicable everywhere has been of tremendous interest for a decade. In an effort to develop the low-cost, small-sized and reliable solid state electrochemical $CO_2$ sensor substituting for conventional bulky and expensive optical $CO_2$ analyzer, solid state galvanic cell, M, $O_2$, $CO_2$, $Me_2CO_3\mid S^+ \mid Me_2TixO_{2x+1}-TiO_2$, $O_2$, M where M, $S^+$ and $Me_2CO_3$ means noble metals such as Pt and Au, alkali ion conducting solid electrolytes such as Na-β-alumina and $Li_{1+X}Al_XTi_{2-X}(PO_4)_3$ and metal carbonates such as $Na_2CO_3$ and $Li_2CO_3$, respectively was constructed to measure the $CO_2$ concentration change in this study. Among them, the fabricated $CO_2$ sensor based on the cell of Pt, $Na_2CO_{3-1}$.$7BaCO_3/Na-β-alumina/Na_2Ti_6O_{13}-TiO_2-Pt$ showed reproducible and fast response with changing $CO_2$ concentration and its sensitivity was close to the theroretical value owing to the chemical stability of the electrolyte and thermodynamic clearness of the reference electrode system. Cross-sensitivity for NO and $SO_2$ was also investigated for this sensor as a preliminary experiment for the embodiment of $CO_2/NOx/SOx$ multi gas sensor. In the interfering gases concentration ranges of 50~150 ppm NO and 5~15 ppm $SO_2$, NO gas guaranteed a recovery of electromotive force (EMF) from the relatively small EMF deviation whereas $SO_2$ gas remarkably degraded the performance of the sensor. There has been no attempt to apply filter to the solid electrolyte type sensor although a catalytic filter has been used for surface adsorption type gas sensors. In this work, the effects of interfering NO and $SO_2$ gases on EMF behavior of $CO_2$ sensors with $Na_2CO_3-SnO_2-CuO$ based filters were investigated in terms of filter efficiency (F.E.) at 673K and 773K and it was found that all the fi...