Evaluation of quasi- and true reference electrodes in high-temperature Li₂O/LiCl molten salts

Abstract

Reference electrodes (REs) are critical for accurate electrochemical measurements and understanding the redox chemistry of high-temperature molten salts. This study evaluates the electrochemical behaviors of three quasi-reference electrodes (QREs) including glassy carbon (GC), tungsten (W), and molybdenum (Mo), in comparison to a true reference electrode, Ni/NiO, in molten Li2O/LiCl salts at 650 °C. The electrode potentials versus the Li/Li+ reference were determined in Li2O/LiCl salt mixtures with Li2O concentrations increasing from 0 to 4.00 wt.%. The Ni/NiO reference electrode exhibited stable potential across the entire Li2O concentration range, confirming its suitability as a true reference electrode under these conditions. In contrast, QREs’ potentials increased with Li2O content up to 0.75 wt.% then plateaued, suggesting a change in surface oxidation kinetics at low Li2O content, likely followed by a limitation imposed by the available electrode surface area. The stable Ni/NiO reference electrode enabled redox reaction kinetics studies on platinum working electrode across the full concentration range using anodic cyclic voltammetry.