Electrochemical pH sensor based on a hydrogen-storage palladium electrode with Teflon covering to increase stability

Abstract

A pH sensor was fabricated using a modified hydrogen-storage palladium electrode. The Pd electrode stores H₂ generated electrochemically at suitable potentials. After the Pd electrode had become coated with palladium hydride (PdHₓ), the resting potential of the modified Pd electrode responded to changes in the pH with a near-Nernstian response of −56.2 ± 0.2 mV pH⁻¹ in the range from pH 1 to pH 13. Although such Pd electrodes are usually unstable due to the release of H₂, their stability could be dramatically increased by covering with a Teflon tube. The Pd electrode can be easily regenerated by electrolysis. As H₂ gas is spontaneously released from the modified Pd electrode, the partial pressure of H₂ gas on the surface of the Pd electrode is almost constant (H₂ gas is almost saturated in the vicinity of the electrode). Accordingly, the potential is assumed to be determined by the pH value of the aqueous solution based on the redox potential of the H₂|H⁺ couple. When the pH value of the solution is almost constant, the modified Pd electrode can act as a reference electrode without any leakage of the inner electrolyte that occurs with Ag|AgCl|sat. KCl electrodes.