Electrochemical DO sensor based on sub-micron ZnO-doped RuO2 sensing electrode: Influence of sintering temperature on sensing performance

Electrochemical dissolved oxygen (DO) sensors based on thick-film sub-micron 20 mol% ZnO-doped RuO2 sensing electrode (SE) were fabricated on the alumina sensor substrates and were annealed at different sintering temperatures (STs) during the preparation. Their structural and electrochemical properties were closely studied and analysed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and cyclic voltammetry (CV). STs for this research were designated to be 750 °C, 800 °C, 850 °C and 900 °C, in order to examine the influence STs on SE characteristics. SEM images demonstrated contrasting surface morphology for different STs. Furthermore, both FTIR spectra and CV plots obtained also signify the variations of ST on SEs. The relationship between the DO and the sensor's response at STs of 800 °C and between pH and SE's response was found to be relatively linear with high DO sensitivity for sub-micron 20 mol% ZnO-doped RuO2-SE. It has been experimentally established that the optimum results have been obtained when the SEs were sintered at 800 °C. Moreover, morphology of the “thick” SE revealed both the presence of “inner” active surfaces within SE and the developed open porosity of SE. Lastly, the pH dependence was quantified and verified in order to determine the effect of various sintering temperatures on the characteristics on the SEs.