A potentiometric CO2 gas sensor was fabricated using the compound Li3PO4-Li2SiO3 thin film as electrolyte, and its sensing performances were compared with the conventional Li3PO4-based sensor. The Li3PO4-Li2SiO3 electrolyte was prepared by RF magnetron sputtering while the Li3PO4 electrolyte by thermal evaporation. The microstructures and phase composition of both sensors were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The sensors were examined in CO2 atmosphere at a large temperature range from 350 degrees C to 500 degrees C. As the testing results revealed, both sensors' electromotive force (emf) have a good linear relationship with logarithmic gas concentrations, and the Li3PO4-Li2SiO3-based sensor showed higher sensitivity, shorter response and recovery times, and more stable output emf. The novel sensor exhibited sensitivity as high as 90.80 mV/dec, response and recovery times as short as 6.5 s and 17 s at 500 degrees C. After comparison, it is quite clear that the characteristics of the electrolyte have great influence on the sensor's properties. The improvement is considered to be caused by the electrochemical properties of the Li3PO4-Li2SiO3 thin film, whose micro morphologies and higher ionic conductivity help to enhance lithium-ion transmission in the chemical reactions. (C) 2018 The Electrochemical Society.