| Abstract Scope |
The absence of a stable reference electrode remains a key barrier to investigating fluoride salt electrochemistry. A thermodynamic reference electrode housed in an ion-conducting capsule is the most promising solution, however, existing materials exbibit limitations: oxide ceramics undergo dissolution in fluoride salts, boron nitride requires wetting times of hours to weeks, porous graphite forms uranium carbides in uranium-bearing salts, and a Ni-membrane Ni capsule drifts ~10 mV per day. To address these deficiencies, we developed a Ni/NiF₂ reference electrode encapsulated in a 3D-printed Inconel 718 container. Its wall porosity enables rapid ionic conduction while resisting fluoride attack, and the Ni/NiF₂ couple establishes a stable, well-characterized half-cell potential. Performance was evaluated in molten FLiNaK at 700 °C using cyclic voltammetry, open-circuit potential, and chronopotentiometry. Over 1,000 hours, the electrode exhibited low impedance (~3 Ω), potential drift below 20 mV, and negligible wetting time, demonstrating reliable long-term performance for precise potential control. |