Yttria-Stabilized Zirconia Aided Electrochemical Investigation on Ferric Ions in Mixed Molten Calcium and Sodium Chlorides

Abstract

Electrolytic reduction of dissolved iron oxide to metal iron in molten salts with an inert anode is an alternative short route for steelmaking without CO2 emissions. A novel and simple integrated yttria-stabilized zirconia (YSZ) cell was constructed from a YSZ tube with a closed end. The YSZ tube played multiple functions, including the container for the molten salts, the solid electrolyte membrane in the O 2-| YSZ | Pt | O2 (air) reference electrode (RE), and the solid electrolyte membrane between the working and counter electrodes (WE and CE). Electrochemical behavior of ferric ions (Fe 3+) that were formed by dissolution of 0.5 wt pct Fe2O3 in the molten CaCl2-NaCl eutectic mixture was investigated on a Pt WE at 1273 K by various electrochemical techniques including cyclic voltammetry, linear scan voltammetry, square wave voltammetry, chronopotentiometry, chronoamperometry, and potentiostatic electrolysis. Analysis of the mechanism of electrode reactions was further assisted by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Some electrochemical parameters were obtained, including the number of exchanged electrons and the diffusion coefficient of ferric ions in the mixed molten salts. The results from various electrochemical techniques are in good agreement with each other, and show that the electrochemical reduction of Fe 3+ to Fe in the molten salt mixture could be a single three-electron transfer step and diffusion controlled reaction that was also possibly reversible. This work may form the foundation for extraction of iron and alloys from molten salts and also provid a stable O 2-| YSZ | Pt | O2 (air) RE with wide applicability for investigation on electrochemical properties of other electroactive metal oxides in molten salts.

Preparation of Zinc Oxide and Zinc Ferrite from Zinc Hypoxide by Wet Process and Electrochemistry

“…The leaching solution of zinc suboxide was tested with square wave voltammetry at different frequencies (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) in the potential range of −1.2 V to 0 V. The results are shown in Figure 4a. It can be seen from the Figure that there are two peaks (B′, C′) in the potential range of −1 V to −0.6 V, and peak B′ corresponds to the reduction process of cadmium.…”

“…It can be observed that the measured Iτ 1/2 has nothing to do with I and closely matches the horizontal straight line within the required accuracy. Therefore, it can be determined that the reduction in this step is a diffusion control process in solution [17].…”

The Electrochemical Reduction Mechanism of ZnFe2O4 in NaCl-CaCl2 Melts

“…In order to reduce the error, the origin and experimental data points were put together to fit a straight line. Some researchers had also adopted this method [24][25][26].…”

Yttria-Stabilized Zirconia Assisted Green Electrochemical Preparation of Silicon from Solid Silica in Calcium Chloride Melt

“…After the YSZ tube was ultrasonically cleaned with alcohol, the porous annular Pt CE (area about 6.28 cm 2 ) and RE (area about 1.88 cm 2 ) were prepared according to the method provided in literature. [26,28] The Pt leads (diameter 0.5 mm and length 800 mm) for the RE and the CE were each protected in a thin double-bore alumina tube.…”

“…After holding the temperature, a Ni wire (purity 99.99%, diameter 0.5 mm) was used as cathode to pre-electrolyze for 90 min at -1.8 V. After the Ni wire was removed, the Mo-SiO2 WE was slowly lowered from the furnace top to the above of the melt level, and then the melt level was determined by the open circuit potential method to ensure that the whole SiO2 cylinder was immersed in the melt. [28] Electrochemical behavior of the Mo-SiO2 WE was investigated by cyclic voltammetry (CV) method. Based on this test, the electroreduction of solid SiO2 was studied at a lower overpotential by chronoamperometry (potentiostatic electrolysis) method.…”