Pure and Ce-Doped MnO₂–ZnO Nanocomposites for Colossal Dielectric Energy Storage and Gas Sensing Applications

ZnO-based nanocomposites have attracted a great attention for energy storage systems and detection of volatile organic compounds. In this study, pure and Ce-doped MnO₂–ZnO composites were fabricated through a co-precipitation method. The results of X-ray diffraction verified the formation of tetragonal MnO₂ and hexagonal ZnO phases. Scanning electron microscope images of pure and Ce-doped MnO₂–ZnO composites displayed the formation of rods and semi-spherical particles. The pure and Ce-doped MnO₂–ZnO composites exhibited semi-stable colossal dielectric constant values of 2.12 × 10⁵ and 1.36 × 10⁵, respectively, at a frequency of 45 Hz, which are proper for capacitive energy storage applications. Gas sensing measurements demonstrated that Ce-doped MnO₂–ZnO composite has a high sensitivity toward 100 ppm acetone gas at operating temperature of 240 °C, while for 100 ppm ethanol this sensor has a high sensitivity at 180 °C. As a result, through adjusting the operating temperature, the selectivity of Ce-doped MnO₂–ZnO sensor can be controlled for acetone and ethanol gases. Furthermore, this sensor possesses good selectivity and stability as well as proper linear relations between the sensitivity and concentrations of acetone and ethanol gases.