Abstract

The response of potentiometric anion selective electrodes employing undoped GaN or In 0.2 Ga 0.8 N films as sensing element to detect various anions was investigated in solutions of KF, KNO 3 , KCl, HOC 6 H 4 COONa, KSCN, CH 3 COOK, KClO 4 and KBr salts. The calibration plots for the GaN and In 0.2 Ga 0.8 N semiconductor electrodes contained linear regions extending over four decades of activity change in most solutions. The structure of the GaN and In 0.2 Ga 0.8 N semiconductor electrode/ electrolyte interface was studied through electrochemical impedance spectroscopy. Analogous equivalent circuits modeling the GaN or In 0.2 Ga 0.8 N electrode/electrolyte interface were proposed and their parameters were calculated. The space charge layer of the GaN and In 0.2 Ga 0.8 N semiconductors dominated the impedance of the electrochemical system at high frequencies (> 10 kHz), whereas at low frequencies (< 10 kHz), the impedance was controlled by the diffusion of electroactive species across the layer of adsorbed ions at the surface of the electrode. Results imply a strong dependence of the electrodes performance on the adsorption capacity of tested anions.