Characteristics and performance of binary carbonate auxiliary phase CO2 sensor based on Li3PO4 solid electrolyte

Abstract Bulk type solid state potentiometric CO 2 sensors were fabricated based on Li 2 CO 3 –BaCO 3 binary auxiliary phase as a sensing electrode, Li 3 PO 4 mixed with 5 mol% SiO 2 as a solid electrolyte and Li 2 TiO 3 mixed with 10 mol% TiO 2 two phase system as a reference electrode. The concentration of BaCO 3 was varied in the auxiliary phase (mol%). The electromotive force (emf) of the investigated cells was linearly dependent upon the logarithm of CO 2 partial pressure over a wide range of 500–5000 ppm. The sensors have shown good CO 2 sensing properties at low concentrations of Barium carbonate additive. 10 mol% BaCO 3 loaded Li 2 CO 3 sensor has shown the highest absolute emf and a very close theoretical Δemf/dec value at 500 °C than the other counterparts. The slopes of emf as a function of log P CO2 were in good accordance with the Nernstian slopes based on a two electron electrode reaction between the temperatures 450–500 °C. During the heat treatment, the interface formed between the sensing electrode and electrolyte and revealed by SEM, EDAX and X-ray diffraction studies indicates a new glassy phase consisting of Barium silicate (Ba 4 Si 6 O 16 ) and Barium phosphate (Ba 3 P 4 O 13 ). The penetration or diffusion of the Barium components deep inside the interfacial layer along with rich Li 2 O content was proposed to be responsible for the improved sensing characteristics of the sensor.