Recent progress in material science might soon allow the replacement of the consumable carbon anode by an inert material. This is likely to induce changes in the overall process, and particularly in the gas evolution. Video recordings of oxygen-evolving anodes (SnO 2 , Cu, Cu-Ni) and carbon anodes were performed in laboratory electrolysis cells, using direct observation from above, a see-through cell, and radiography techniques. The gas behavior was very different between the two kinds of anodes, and probably linked to the wettability of the material by the electrolyte.

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Metal oxides are potential materials for thermochemical heat storage via reversible endothermal/exothermal redox reactions, and among them, cobalt oxide and manganese oxide are attracting attention. The synthesis of mixed oxides is considered as a way to answer the drawbacks of pure metal oxides, such as slow reaction kinetics, loss-incapacity over cycles or sintering issues, and the materials potential for thermochemical heat storage application needs to be assessed. This work proposes a study combining thermodynamic calculations and experimental measurements by simultaneous thermogravimetric analysis and calorimetry, in order to identify the impact of iron oxide addition to Co and Mn-based oxides. Fe addition decreased the redox activity and energy storage capacity of Co 3 O 4 /CoO, whereas the reaction rate, reversibility and cycling stability of Mn 2 O 3 /Mn 3 O 4 was significantly enhanced with added Fe amounts above~15 mol%, and the energy storage capacity was slightly improved. The formation of a reactive cubic spinel explained the improved re-oxidation yield of Mn-based oxides that could be cycled between bixbyite and cubic spinel phases, whereas a low reactive tetragonal spinel phase showing poor re-oxidation was formed below 15 mol% Fe. Thermodynamic equilibrium calculations predict accurately the behavior of both systems. The possibility to identify other suitable mixed oxides becomes conceivable, by enabling the selection of transition metal additives for tuning the redox properties of mixed metal oxides destined for thermochemical energy storage applications.

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The traditional electrolyte for aluminum electrolysis is composed of molten cryolite (Na 3 AlF 6 ) and alumina (Al 2 O 3 ). One of the objectives of the industry is to lower the operating temperature of the electrolytic process, which is currently around 960 °C. The benefits commonly evoked of a temperature decrease in the aluminum plotlines are multiple: reduction of the energetic consumption and thus of the global environmental footprint, increase of the cell life due to limited corrosion, reduction of production costs, etc. In this work, an overview of some properties of molten fluoride systems (Na-cryolite-based electrolytes (NaF-AlF 3 ) and K-cryolitebased electrolytes (KF-AlF 3 )) is presented. To a lesser extent, the case of all-chloride and mixed chlorofluoride salts is also discussed. Many physicochemical properties of salt mixtures are of major importance to evaluate the potential of a given electrolyte. When available, the following properties are reported and compared: the liquidus temperature, the electrical conductivity, the density, the vapor pressure, the solubility of alumina, and the solubility of liquid aluminum.

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In this work, a detailed electrochemical study of the molten LiF-CaF 2-ZrF 4 system is provided in the 810-920 • C temperature range, allowing the determination of the reduction potential, the diffusion coefficient and the reduction mechanism of dissolved Zr(IV) on an inert Ta electrode. Addition of CaO in the molten salt is shown to cause Zr(IV) precipitation into an equimolar mixture of solid compounds, most likely ZrO 2 and ZrO 1.3 F 1.4. Underpotential deposition of Zr on Cu and Ni electrodes is also evidenced and Gibbs energy of formation of Cu-Zr compounds calculated by open circuit chronopotentiometry.