Electrochemical sensing of trace level NH3: active electrode and electrolyte optimizations

Amperometric mode of electrochemical gas sensor requires several systematic approaches to optimize compositions of electrodes and electrolyte materials when both the electrodes are exposed to same gas environment. Using Gd-doped ceria electrolyte, Ni2+ doped CuO active electrode and fixed inactive electrode La0.5Sr0.5CoO3 electrochemical sensors were investigated for 3–40 ppm ammonia in base gas (5%O2 + N2). Highest sensitivity of 225 μA/decade at 550 °C was obtained for sensor with 15 mol% of Gd-doped ceria (GDC 15) and 2 mol% of Ni2+ doped CuO as electrolyte and active electrode, respectively, when studied in the range 300–650 °C. Among all the electrolyte compositions, GDC 15 showed highest electrical conductivity (0.84 × 10–2 S/cm at 550 °C), and thus, highest sensitivity was correlated at a particular temperature. The vacancy trap mechanism was found to influence electrical conductivity of electrolyte. The same sensor configuration showed highest potentiometric sensitivity of 116 mV/decade at 550 °C. High sensitivity to ppm level NH3, selectivity, short-term and long-term stability are some of the promising results of the developed sensor for exhaust gas applications.