Ruthenium dioxide occurs in two morphologically varied structures: anhydrous and hydrous form; both of them were studied in the scope of this work and applied as mediation layers in ion-selective electrodes. The differences between the electrochemical properties of those two materials underlie their diverse structure and hydration properties, which was demonstrated in the paper. One of the main differences is the occurrence of structural water in RuO2•xH2O, which creates a large inner surface available for ion transport and was shown to be a favorable feature in the context of designing potentiometric sensors. Both materials were examined with SEM microscope, X-ray diffractometer, and contact angle microscope, and the results revealed that the hydrous form can be characterized as a porous structure with a smaller crystallite size and more hydrophobic properties contrary to the anhydrous form. Potentiometric and electrochemical tests carried out on designed GCD/RuO2/K+-ISM and GCD/RuO2•xH2O/K+-ISM electrodes proved that the loose porous microstructure with chemically bounded water, which is characteristic for the hydrous form, ensures the high electrical capacitance of electrodes (up to 1.2 mF) with consequently more stable potential (with the potential drift of 0.0015 mV/h) and a faster response (of a few seconds).

This article presents the fast and easy method of designing K + -selective electrodes with the use of ceramic nanoparticles. Ruthenium dioxide implemented into electrode's construction as a mediation layer turned out to exhibit remarkable electrical parametersevaluated with chronopotentiometry, electrochemical impedance spectroscopy and cyclic voltammetry methods -what resulted in noticeably high electrical capacitance of designed electrodes (1070 μF). This property of the material layer can be attributed to both redox reactions, in which ruthenium dioxide exchanges ions and electrons, and large surface area associated with nanometric size of RuO 2 particles. The potentiometric response of RuO 2 -contacted electrodes toward potassium ions was studied in the presence of coated-disc electrode without solid-contact layer. Since electrical parameters of electrodes determine their analytical performance, for electrodes of GCD/RuO 2 /K + -ISM type the linear range was wider (10 −6 to 10 −1 M), the potential response was more stable (with 0.085 mV potential value change per hour) and reversible in comparison with GCD/K + -ISM type. Developed potassium selective sensors were successfully applied for environmental samples analysis and the results obtained using potentiometry method were in good agreement with the reference method.

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A new approach is presented for the design of ion selective electrodes. Ruthenium dioxide nanoparticles were incorporated into solid-contact electrodes, and their properties were studied for the case of pH-selective electrodes. The use of the RuO2 is shown to significantly improve the potentiometric response, while no redox response is observed. The use of RuO2 results in a Nernstian slope (59 mV/decade) towards hydrogen ions over a wide linear range (pH 2 to 12). The results obtained by chronopotentiometry reveal small resistance, and the capacitance is as high as 1.12 mF. This results in a good stability of the response and in a low potential drift (0.89 μV∙s−1). The electrodes exhibit properties nearly as excellent as those of a glass electrode, but they are much smaller, less fragile, and easy to use. Graphical abstractSchematic representation of the construction of the new kind of electrodes along with calibration and chronopotentiometric plots compared to non-modified GCD/H+-ISM and modified GCD/RuO2/H+-ISM electrodes, respectively. The use of ruthenium dioxide results in a wide analytical pH range (2–12) and in high electrical capacitance (1.12 mF).

This work presents the first-time application of the ruthenium dioxide–poly(3,4-ethylenedioxythiophene) polystyrene sulfonate high-capacity composite material as a mediation layer in potassium selective electrodes, which turned out to significantly enhance the electrical and analytical parameters of the electrodes. The idea was to combine the properties of two different types of materials: a conducting polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, and a metal oxide, ruthenium dioxide, in order to obtain the material for a solid-contact layer of great electrical and physicochemical parameters. The preparation method for composite material proposed in this work is fast and easy. The mediation layer material was examined using a scanning electron microscope and chronopotentiometry in order to confirm that all requirements for mediation layers materials were fulfilled. Ruthenium dioxide–poly(3,4-ethylenedioxythiophene) polystyrene sulfonate nancomposite material turned out to exhibit remarkably high electrical capacitance (of approximately 17.5 mF), which ensured great performance of designed K+-selective sensors. Electrodes of electrical capacity equal to 7.2 mF turned out to exhibit fast and stable (with only 0.077 mV potential change per hour) potentiometric responses in the wide range of potassium ion concentrations (10−6 M to 10−1 M). The electrical capacity of ruthenium dioxide–poly(3,4-ethylenedioxythiophene) polystyrene sulfonate-contacted electrodes characterized by electrical capacitance parameters was the highest reported so far for this type of sensor.