Wet process-preparation of Re-doped WO3 for wide range of NO2 detection

In order to reduce the electric resistance of the WO₃ sensing film fabricated from the ion-exchange method, lamellar-structured and Re-doped WO₃ was prepared through the acidification method. The mixed solution of Na₂WO₄ and Re₂O₇ was dropped into the mixed solution of H₂SO₄ and HCHO. Then the obtained gel was deposited on alumina substrate with Au electrode for thick film devices and calcined at 300°C. The size of the Re-doped WO₃ particles was smaller in one order in magnitude than that of the WO₃ by the ion-exchange method. The electric resistance of Re-doped WO₃ device in air showed minimum value at the 4 at% Re doping due to the increase in the donor density in the WO₃ crystal. As a result, the Re-doped WO₃ device exhibited low electric resistance less than 10⁸ Ω even in the 800 ppb NO₂. Such a low electric resistance device is suitable for the detection of the wide range of NO₂.