Response characteristics of CO2 gas sensors using KSmSi2O6 as electrolyte and Li2CO3/K2CO3 as sensing electrode

Two types of solid-state electrochemical cells were designed and their CO2 gas-sensing characteristics were compared. One was a heterojunction-type sensor, whereas the other was a conventional homojunction-type sensor. A potassium ionic conductor was used as the solid electrolyte and lithium carbonate (Li2CO3) or potassium carbonate (K2CO3) were used as the sensing electrodes. The electromotive force (EMF) of the cell, having Li2CO3 as the electrode (heterojunction-type sensor), increased linearly with an increase in the partial pressure of CO2 gas. Similar behavior was observed in the cell using the K2CO3 electrode (homojunction-type sensor). The slopes of Nernst’s equation suggest that the two-electron reduction associated with the carbon dioxide molecules occurs on the sensing electrode. The EMF of the heterojunction-type sensor showed excellent performance, and the 90% EMF response time of this sensor at 450 °C was only a few minutes on changing the carbon dioxide partial pressure.