Electrochemical Characterization

Electrolyte pellets were pressed using a pressing mold with an inner diameter of 12 mm. The material was weighed and loaded into the mold and pressed using a knuckle joint press inside the glovebox. The thickness of the resulting pellet was determined with a caliper (between 0.5 and 0.8 mm). Electrochemical measurements were performed in 2-electrode stainless steel cells, which were assembled inside an argon filled glovebox. A spring was used to maintain mechanical contact between electrodes and electrolyte.

Electrochemical impedance spectroscopy (EIS) was measured using a Zahner IM6ex electrochemical workstation in the frequency range 3 × 10⁶ − 0.1 Hz. Polished molybdenum blocks were used as Mg blocking electrodes. Impedance spectra were obtained at 30, 40, 50, 60 and 70 °C, after thermal equilibration for 2 h at each temperature.

Cyclic voltammetry (CV) measurements were performed at 60 °C after thermal equilibration for 4 h with a Biologic VMP3 electrochemical workstation. An asymmetric cell was prepared with Mg foil (99.95% Mg, 11 mm diameter, 0.05 mm thickness, GalliumSource) as counter electrode and Pt as working electrode. The OCV stabilized at 0.66 V and cyclic voltammetry was carried out between −0.5 and 1.7 V with a scan rate of 10 mVs⁻¹. A similar cell, but with a Cu working electrode was built. Mg was plated at a current of 3 nA for ca. 200 h at overpotentials below −0.1 V at 60 °C. SEM images were taken with a FEI NanoSEM 230 at 25 kV. EDX analysis was performed with an Oxford X-Max SDD EDX system.