Cyclic Voltammetry of ZrO2 Powder in the Metallic Cavity Electrode in Molten CaCl2

The electrochemical reduction of the insulative ZrO2 powder in molten CaCl2 was investigated using the metallic cavity electrode (MCE) in molten CaCl2 at 850 degrees C. Cyclic voltammograms (CVs) revealed two consecutive reduction peaks corresponding to (i) ZrO2 to ZrxO (x >= 1) and (ii) ZrxO to Zr. The intermediate, ZrxO2 was metastable and underwent disproportionation to ZrO2 and Zr, which was responsible for the detection of Zr metal in the potentiostatic reduction at less negative potentials. In the anodic scan, four main oxidation processes were observed. The relevant reactions were rationalized as the reoxidation of (iii) ZrxO to ZrO2, (iv) Zr to ZrO2, (v) Zr to ZrCl2, and (vi) Zr to ZrCl4. The metastable intermediate also contributed to the unique current variations in the anodic potential scans under different conditions. Potentiostatic electrolysis of the ZrO2 powder in the MCE at the feature potentials of the CVs and analyses of the electrolysis products by scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed the electroreduction mechanism and revealed the localized conversion of the dense aggregates of the submicrometer particles of ZrO2 to cauliflower-like aggregates of the nanoparticulates of Zr in the early stage of the electroreduction process. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3244568] All rights reserved.