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.