This paper reviews a clean metals, production technology that utilizes an oxygen-ion-conducting solid oxide membrane (SOM) to directly electrolyze metal oxides dissolved in a non-consumable molten salts. During the SOM electrolysis process, the desired metal such as magnesium, aluminum, silicon, or a rare earth is produced at the cathode while pure oxygen gas evolves at the anode. Compared with current state-of-the-art metal production processes, such as a chloride-based electrolysis process for magnesium production and the Hall–Héroult process for smelting aluminum, the SOM process brings various advantages such as simplified design, lower cost, lower energy use, and zero emissions. It provides a general route for producing various metals and has great potential to replace current metals, production processes. This paper examines the past and present progress of the SOM process, the challenges faced in commercialization, and the directions for future work.

Anode-supported planar solid oxide fuel cells (SOFC) were fabricated by a single step co-firing process. The cells were composed of a Ni <mml:math display="inline"><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:math>+ yittria-stabilized zirconia (YSZ) anode, a YSZ electrolyte, an industrial Ca-doped <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>LaMnO</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>LaMnO3 (LCM) (or lab-made LCM) <mml:math display="inline"><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:math>+ YSZ cathode active layer, and an industrial LCM (or lab-made LCM) cathode current collector layer. The fabrication processes involved tape casting of the anode, screen printing of the electrolyte and the cathode, and one step co-firing of the green-state cells at <mml:math display="inline"><mml:mrow><mml:mn>1300</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>1300°C for <mml:math display="inline"><mml:mrow><mml:mn>2</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">h</mml:mi></mml:mrow></mml:math>2h . The performance of the cells was greatly improved by optimization of these materials and fabrication processes. The electrochemical performance tests of these cells showed that they could provide a stable power density of 0.2– <mml:math display="inline"><mml:mrow><mml:mn>1.0</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">W</mml:mi><mml:mo>∕</mml:mo><mml:msup><mml:mi>cm</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>1.0W∕cm2 with hydrogen as fuel and air as oxidant while operating in the temperature range 700– <mml:math display="inline"><mml:mrow><mml:mn>900</mml:mn><mml:mo>°</mml:mo><mml:mi mathvariant="normal">C</mml:mi></mml:mrow></mml:math>900°C . The effects of various polarization losses including ohmic polarization, activation polarization, and concentration polarization were studied by impedance spectroscopy measurements and curve-fitting experimentally measured voltage vs current density traces into an appropriate model. Based on these measurements and curve fitting results, the relationships between cell performance and various polarization losses and their dependence on temperature and microstructure, were rationalized.