Fractional Factorial Experimental Design Applied to the Development of an Impedancemetric NO_x Sensor

摘要

Four single cell impedancemetric NO_x sensors were fabricated in the context of a two level, half fractional factorial experimental design (~2m~(3-1)) to determine the effect of design features on sensitivity to NO or NO_2. Three design factors were varied: number of working electrode sensing wires, electrolyte thickness, and the distance between sensing wires. Sensing ability was measured by performing electrochemical impedance spectroscopy and calculating the phase angle difference at 10 Hz for 50 ppm NO or NO_2 in 10% oxygen. As determined by ANOVA, the most significant effect was electrolyte thickness for NO sensing. One sensor investigated in depth showed a linear relationship between phase angle difference and NO at low concentration, insensitivity to total flow rate, and the larger sensitivity to NO_x species than O_2 by several orders of magnitude. A larger response for NO_2 compared to NO was found. At 10~5 Hz, phase angles were linearly related to temperature, independent of gas species.