Potentiometric solid-state sensor for DO measurement in water using sub-micron Cu0.4Ru3.4O7 + RuO2 sensing electrode

The dissolved oxygen (DO) sensing electrode (SE) concept utilizing sub-micron-sized ruthenium oxide (RuO2), doped with other nanostructured oxides, has been extended to investigate the possibility of employing copper (II) oxide (Cu2O) as a dopant in order to improve sensor's characteristics and meet long term antifouling needs for SEs. In this work, a thin-film SE made of RuO2 was constructed on the alumina sensor substrate, and a range of dopants and their concentrations was added to it in order to optimize SE properties. The Cu2O-doped RuO2 SE had shown a linear response to DO between 0.5 and 8.0 ppm at various temperatures, with two sensitivity maxima of 47.4 and 46.0 mV per decade for Cu2O concentrations of 10 and 20 mol%, respectively. The maximum sensitivity for Cu0.4Ru3.4O7 + RuO2-SE was obtained at a dopant concentration of 10%. Selectivity measurements revealed that the presence of Ca2+, Mg2+, Li+, Na+, NO3−, PO43−, SO42−, F−, K+ and Cl− in the solution had no significant effect on the sensor's emf. The sensor allows overcoming the problem of an insufficient selectivity of semiconductor-based water sensors. It was also found that the doping of RuO2-SE by Cu2O allowed it to function at full capacity in a natural outdoor water body with no obvious effects of biofouling.