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.