Nickel-based electrochemical sensor with a wide detection range for measuring hydroxyl ions and pH sensing

The importance of hydroxyl ions concentration measurement in solution necessitates the development of suitable and simple sensing methods for online detection. To address this need, an electrochemical sensor was developed using nickel as the working electrode that enabled specificity towards hydroxyl ions and their successfully quantification. The electrochemical reaction between nickel and hydroxyl ions in solution generates a current which is proportional to the concentration of hydroxyl ions and consequently is also correlated to the pH of the solution. Cyclic voltammetry and chronoamperometry techniques were used to prepare and activate the nickel electrode for detection. The analysis of chronoamperometric experiments in different solutions exhibited three calibration curves between the current and hydroxyl ion concentrations for three regions in the range of 0.3 µM to 4.8 M with a short response time of 14 s. Up to now, no other hydroxyl ion sensor has been reported that can reach this detection limit. This sensor also holds promise to work perfectly in highly alkaline environments where only costly commercial electrodes are available to quantify pH. The results show three linear calibration curves between the current and pH of the solution over the pH range of 7.4 to 14.6. In addition to the wide detection range, the sensor exhibits a relative standard deviation percentage lower than 7% over 9 months of experiments, confirming repeatability of measurements and stability of the electrode. The potential of the proposed method to measure pH in real applications was demonstrated by testing the sensor in solutions containing urea, nitrates, phosphates, and sulfates.