A solid-contact potassium-selective electrode with MoO₂ microspheres as ion-to-electron transducer

A solid-contact ion-selective electrode (SC-ISE) for potassium with MoO₂ microspheres as ion-to-electron transducer is described. MoO₂ microsphers can be synthesized via the reduction of MoO₃ nanobelts in an isopropanol solvent with a mild process, and the obtained MoO₂ microspheres have been characterized by X-ray diffraction and field-emission scanning electron microscopy. With the application of MoO₂ microspheres, the newly fabricated SC-ISE for K⁺ exhibits a stable and rapid potential response. A near Nernstian slope of 55 mV/decade to potassium activities in the range of 10^-5 ‒ 10^-3 M is found and the detection limit is 10^-5.5 M. Impedance spectra and chronopotentiometry results show that a smaller resistance together with a larger double layer capacitance is guaranteed due to the introduction of the intermediate layer of MoO₂ microspheres. Additionally, light, O₂ and CO₂ do not induce significant influences to the present SC-ISE, and a reduced water layer between the ion selective membrane and the underlying conductor is formed. Thus, it is clear that MoO₂ microspheres, as metallic analogues, can be used as a good candidate for the new type of transducing layer in SC-ISEs.