Electrochemical setup and procedure

A three electrode cell assembly was used for all the electrochemical measurements. Two different working electrodes have been used: (1) a metallic cavity electrode (MCE) and (2) a liquid Sn electrode. The MCE was fabricated from Mo foil (2.0 mm width and 1.0 mm thickness, with 1.0 mm diameter circular through-hole cavities), and it was used as a working electrode to record cyclic voltammograms (CVs) [11]. The Dy2O3 (99.99%, Chempur) powder was pressed at 15 MPa and sintered at 1173 K (900 °C) for 12 h to obtain a dense pellet which was used as electroactive specie. The sintered material was ground into powder and the MCE cavities were filled by repeatedly pressing this Dy2O3 powder on both sides of the foil around the through-holes. Any powder left on the surface of the foil was wiped off carefully. The liquid Sn electrode was prepared by placing Sn shot in a closed-end alumina crucible (0 6 mm x 6 mm), which was immersed in a CaCl2 melt. A molybdenum wire of 1.5 mm diameter sheathed in a B4C tube of 5 mm outer diameter was immersed in the Sn phase and used as a lead wire. The surface area of the liquid Sn electrode is approximately 2 10 3 m2. A 6 mm diameter graphite rod served as the counter electrode. A platinum wire (99.99%, 1.0 mm diameter and 30 mm length) was used as pseudo-reference electrode. All the potentials reported in this paper are with respect to this pseudo-reference electrode. Cyclic voltammetry was carried out using a Solartron 1287 potentiostat/galvanostat and the scan rate is 50 mVs-1.

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