Na3Zr2Si2PO12-based CO2 gas sensor with heat-treated mixture of Li2CO3 and Nd2O3 as an auxiliary electrode

Carbon dioxide sensing performance of gas sensors using a NASICON (Na3Zr2Si2PO12) solid electrolyte and a Li2CO3-based auxiliary phase was examined. Gradual changes (drifts) in the EMF level with time were observed for the sensor using only Li2CO3 as an auxiliary electrode. A new auxiliary electrode material based on Li2CO3 and Nd2O3 was developed to improve the sensing stability. The mixture of Li2CO3 and Nd2O2+2x(CO3)1−xLi2x was stable to humidity. The Nd2O2+2x(CO3)1−xLi2x phase between an auxiliary electrode and NASICON acted as a stable diffusion boundary layer. For the mixture of Na2CO3 and Nd2O3, a similar treatment induced formation of only Nd2O2CO3. A higher reactivity of the Li+ ions with Nd2O2CO3 and a lower reactivity of the Na+ ions effectively stabilized the diffusion boundary layer.