Effect of conditioning protocol, redox species and material thickness on the pH sensitivity and hysteresis of sputtered RuO2 electrodes

In this paper, the effects of conditioning-pH, RuO2 material thickness and oxidizing/reducing agents on the E0 value and hysteresis of RuO2 pH-sensitive working electrodes is investigated. Experimental results show that, in order to obtain a pH sensor that Exhibits 0.01 units of precision, it is necessary to use an electrode with at least 500 nm thickness of RuO2; whilst thinner RuO2 electrodes (> 50 nm) can be used to achieve a precision of 0.05 pH units. In addition, investigation of the redox interference and pH sensing performance of RuO2 electrodes at high/low pH suggests that hysteresis and redox interference are due to shifts in the E0 value due to a change in the electrode's composition, i.e. the ratio of RuIII to RuIV present in the electrode material.