Versatile, low-cost, non-toxic potentiometric pH-sensors based on niobium

Abstract

A low-cost potentiometric pH electrode based on niobium/niobium oxide was developed with excellent stability over several months under various storage conditions. Three fast and simple preparation routes including thermal growth as well as chemical and electrochemical deposition were tested. Our data demonstrates that the electrochemical manufacturing method produces pH electrodes with high reproducibility and a sensitivity of −41 mV/pH. OCP (Open Circuit Potential) measurements showed that the pH electrode can be used over a wide pH range from pH 2 to 12. Furthermore, the oxide layer of all produced electrodes was characterized and compared via SEM (Scanning Electron Microscopy), EDX (Energy-Dispersive X-Ray Spectroscopy) and EIS (Electrochemical Impedance Spectroscopy). It was shown that the electrochemical fabrication route leads to the highest porosity, which is in turn linked to the highest sensitivity. The hysteresis of this pH sensor was determined to be 2 mV in a pH region between 4 and 10. In long-term experiments a drift of 1.1 mV/h was obtained. Negligible interference was observed with NaCl and KCl ions, whereas sensitivity and linearity were affected by Li-ions.