Potentiometric sensor based on NASICON and In2O3 for detection of CO2 at room temperature — modification with foreign substances

In an attempt to improve the CO2 sensing properties of NASICON (Na+ conductor)-based potentiometric device attached with In2O3 at room temperature, Na3PO4, NaHCO3 and Na2CO3 were introduced as single-components or combinations in the CO2 sensing layer of the device. Although, the original device suffered disturbance by humidity seriously, the disturbance could be reduced effectively, in some case almost completely, in the resulting modified devices, while the sensitivity to CO2 could be even promoted. The best device obtained, for which both of Na3PO4 and NaHCO3 were introduced, showed fairly excellent sensing characteristics, i.e. high sensitivity to CO2 and high resistance to disturbance by humidity at 30°C. The emf of the device was linear to the logarithm of CO2 concentration in the range 300–3000 ppm following well the Nernst equation for a 1.2 electron-reduction of CO2.