Energy-Efficient and Environmentally Friendly Solid Oxide Membrane Electrolysis Process for Magnesium Oxide Reduction: Experiment and Modeling

This paper reports a solid oxide membrane (SOM) electrolysis experiment using an LSM(La0.8Sr0.2MnO3-delta)-Inconel inert anode current collector for production of magnesium and oxygen directly from magnesium oxide at 1423 K (1150 degrees C). The electrochemical performance of the SOM cell was evaluated by means of various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scan, and electrolysis. Electronic transference numbers of the flux were measured to assess the magnesium dissolution in the flux during SOM electrolysis. The effects of magnesium solubility in the flux on the current efficiency and the SOM stability during electrolysis are discussed. An inverse correlation between the electronic transference number of the flux and the current efficiency of the SOM electrolysis was observed. Based on the experimental results, a new equivalent circuit of the SOM electrolysis process is presented. A general electrochemical polarization model of SOM process for magnesium and oxygen gas production is developed, and the maximum allowable applied potential to avoid zirconia dissociation is calculated as well. The modeling results suggest that a high electronic resistance of the flux and a relatively low electronic resistance of SOM are required to achieve membrane stability, high current efficiency, and high production rates of magnesium and oxygen. (C) The Minerals, Metals & Materials Society and ASM International 2014