Conventional physical sensor for $CO_2$ such as NDIR absorption sensor is precise but expensive, large and difficult to repair. Therefore, the electrochemical sensor has gained a great interest since it has a lot of advantages such as simple detection principle, small volume and low price.
In this work, the electrochemical cell for $CO_2$ sensing consisted of working eletrode to detect $CO_2$ partial pressure by acid-base reaction, reference electrode to fix the activity of Na ion on one side and solid electrolyte to transport Na ion.
EMF test showed the linear relationship between logarithm of $CO_2$ concentration (ppm) and EMF signals (volts) which explains the Nernstian behavior of the cell.
