ECOLOGICALLY SAFE DISSOLVED OXYGEN SENSOR WITH AN ADDITIONAL ZINC ELECTRODE TO RESTORE THE FUNCTIONALIT OF THE COPPER ANODE

Abstract

This work considers the need for oxygen sensors for monitoring the aquatic environment, which, while relatively cheap, require minimal operating costs, and are also environmentally friendly and highly reliable. These requirements are best met by amperometric sensors of a two-electrode system, which are distinguished by a current signal that is convenient to register with its linear dependence on the concentration of the component being determined, as well as high reliability and resistance to overloads. However, the most common electrochemical system of such sensors for determining oxygen is the Clark element with a lead anode. Given modern trends in the environmental friendliness of technology, the use of lead in consumable components is considered unacceptable. There are works on replacing lead anodes with copper ones, but their reliability over time turned out to be lower than that of lead ones. The work solves the problem of developing an amperometric oxygen sensor of a two-electrode system that generates an analytical current signal without supplying additional electricity from the outside, that is, it is essentially a chemical source of current of nanowatt power. Oxygen is measured according to the amperometric principle on a silver working electrode, the potential of which is set by a copper auxiliary electrode shorted to it. That is, the sensor does not contain highly toxic lead, which is replaced by copper. The experimental electrochemical cell of the sensor is impregnated with a weak, practically neutral 0.05M solution of sodium bicarbonate in order to complicate the operating conditions of the copper auxiliary electrode, which began to passivate after approximately two days of continuous measurement of oxygen in water. The restoration of the operability of the copper auxiliary electrode in the event of its passivation was carried out by shorting it to the second auxiliary electrode of the sensor – zinc, which is operated only to remove or prevent passivation. An operating mode of such a two-electrode sensor with an additional zinc auxiliary electrode is proposed, which allows to avoid passivation of the copper electrode and deterioration of the technical characteristics of the sensor, and also does not require either additional electrical power or the complication of the necessary secondary electronic devices.