Electrochemical properties of Gd(III) ions in LiCl-KCl-GdCl₃ at 723–1023 K

Electrochemical behavior of Gd(III) ions in molten LiCl-KCl-GdCl₃ was investigated at 723–1023 K via cyclic voltammetry using tungsten as a working electrode, Gd-Bi (mole fraction, x_Gd = 0.16) as a reference electrode, and Gd-Bi (x_Gd = 0.02) as a counter electrode. A single reduction–oxidation wave was observed, confirming a single-step, 3-electron transfer Gd(III)/Gd transition. The cathodic peak potential exhibited minimal change (<13 mV) over a wide range of scan rates (0.05–0.30 V s⁻¹), indicating facile charge transfer kinetics (i.e., a reversible electrode process). A nucleation overpotential associated with solid Gd deposition was observable at low temperatures (T < 823 K). The mass transport properties of Gd(III) ions were estimated using the Berzins and Delahay relation based on diffusion-limiting peak current. The diffusivity values were determined to be D_Gd(III) = 0.5–2.7 × 10⁻⁵ cm² s⁻¹ at 723–1023 K with an associated activation energy of E_a = 33.9 (±1.0) kJ mol⁻¹. The two-phase [liquid + GdBi] Gd-Bi alloy reference electrode experienced less than 0.5 mV of drift over 5 days of repeated electrochemical measurements, indicating high stability.