A Stable Aqueous Silver/Silver Chloride Reference Electrode with an Operational Temperature Window from 233 to 353 K for Extreme Environments and Space Applications

Reliable reference electrodes (REs) are essential for accurate electrochemical measurements in extreme environments, including space missions, polar regions, and cryogenic systems. The electrolyte in conventional aqueous reference electrodes typically freeze under these conditions, rendering them unusable. To address this gap, we report on the development and validation of a custom Ag/AgCl | 5.49 M LiCl reference electrode designed to operate between -40 °C (233 K) and +80 °C (353 K). This reference electrode demonstrated stable and reproducible performance during cyclic voltammetry of the ferrocyanide/ferricyanide [Fe (CN)₆ ]^3-/4- redox couple across the full temperature range. The reference potential of this RE was established through Nernstian calculations and measurements against the reversible hydrogen electrode (RHE), including liquid junction potential correction, and showed remarkable agreement between theoretical (0.155 V vs standard hydrogen electrode, SHE) and experimental (0.152 V vs SHE) values. The pH-dependent open circuit potential (OCP) measurements showed an ideal Nernstian response of ∼60 mV/pH. This work introduces the Ag/AgCl | 5.49 M LiCl system as a new reference electrode standard for electrochemical applications in space missions to water worlds - including the Moon, Mars, Europa, Enceladus, and other ocean worlds, as well as in cryogenic systems and harsh terrestrial environments where conventional systems fail.