Cu (II) Ion-Selective Electrode Based on Mixed Silver-Copper Sulfide: Phase Structure and Electrochemical Properties

Mixed silver-copper sulfide precipitates have been prepared at different mole ratio between metal ions (Ag+; Cu2+) toward sulfide and tested for their suitability as Cu2+ ion-selective membranes (ISE). Characterization of prepared precipitates by X-ray diffractometry (XRD) showed that all three powders consisted of ternary sulfides while in two powders metallic silver was founded. Origin of different electrical resistance of the prepared materials is discussed. Potentiometric study in KNO3 together with spectrophotometric measurements in ethylendiamine solution showed that differences in detection limits can be attributed to the membranes solubility. Also, electrochemical impedance spectroscopy (EIS) study revealed contribution of the hysterisis effect on the high detection limit due to the contamination of the electrode surface by primary ions. Changes of electrical resistance of the electrode (Rmemb), related to the variation of the charge transfer resistance (Rct) and perturbation in the diffusion layer, as possible explanation for sub-Nernstian response are also discussed. Some potentiometric characteristics as: standard potential, calibration curves, detection limits, pH ranges and time responses of the electrodes are resumed and discussed. These findings offer a novel approach for understanding of response mechanism of electrodes based on the mixed metal sulfide.