New NASICON-based all-solid-state reference electrode towards a pH sensor for the electrochemical measurement of harsh environments

We developed a new, all-solid-state reference electrode using high-densified NASICON ceramics. In order to understand the influence of hydrothermal vent conditions, some NASICON ceramic specimens were treated under 400 °C 40 MPa supercritical conditions. The characteristics and stability of the as-prepared reference electrode before and after supercritical treatment were investigated in aqueous buffer solutions with varying pH. The impedance and I–V curves were also tested and compared. Finally, the NASICON reference electrode was combined with an Ir/IrO₂ working electrode to produce an all-solid-state pH sensor, which was used to measure the pH of simulated seawater and track variations in pH by potential during the addition of acid or alkaline solutions. The developed, simple reference electrode is stable under harsh conditions; thus, when combined with different sensing electrodes, it can be used for the electrochemical measurement of harsh environments, such as deep-sea and high-temperature/pressure environments.