High-temperature molten electrolytes

On the negative side, the MCFC suffers from sealing and cathode corrosion problems induced by its high-temperature molten electrolyte. Thermal cycling is also limited because once the electrolyte solidifies it is prone to develop cracks during reheat-... 

From the various methods for the preparation of Ti film, such as CVD, PVD and electrochemical processes, the electrochemical deposition in ionic melts appears to be one of the most effective, as it makes it possible to deposit Ti films, depending on the composition of the electrolyte and the operating parameters of electrolysis, that is temperature, current density, current forms and so on. The high-temperature molten electrolytes (generally above 650 C) employed in the electrodeposition of Ti film can essentially be divided... 

Reviews of batch calorimeters for a variety of applications are published in the volume on Solution Calorimetry [8] cryogenic conditions by Zollweg [22], high temperature molten metals and alloys by Colinet andPasturel [19], enthalpies of reaction of inorganic substances by Cordfunke and Ouweltjes [16], electrolyte... 

It has been shown that the electrodeposition of molybdenum chalcogenides from high-temperature molten salts can give large, well-defined crystals of these compounds. The preparation of M0S2 as well as WS2 by electrolytic reduction of fused salts was first reported by Weiss [145], who produced small hexagonal blue-gray platelets under drastic conditions of electrolysis. Schneemeyer and Cohen... 

High-temperature molten-carbonate fuel cells (MCFCs). The electrolyte is a molten mixture of carbonates of sodium, potassium, and lithium the working temperature is about 650°C. Experimental plants with a power of up to... 

Lithium Iron Sulfide (High Temperature). High-temperature molten salt Li—Al/LiCl— KCl/FeS - cells are known for their high energy density and superior safety. At one point they were being actively pursued for electric vehicle and pulse-power applications. Historically, boron nitride (BN) cloth or felt has been used as the separator in flooded-electrolyte cells, while MgO pressed-powder plaques have been used in starved-electrolyte cells. 

Comprehensive reviews describing the preparation, purification, and physical and electrochemical properties of these melts have been published [17-20]. The most popular systems are mixtures of A1C13 with either l-(l-butyl)pyridinium chloride (BupyCl) or 1 -methyl-3-ethylimidazolium chloride (MeEtimCl). These systems are very versatile solvents for electrochemistry because they are stable over a wide temperature range. In many ways they can be considered to be a link between conventional nonaqueous solvent/supporting electrolyte systems and conventional high-temperature molten salts. 

In general, although surface protonation of perovskite oxides in contact with aqueous electrolytes and consequent build up of a potential barrier at the oxide surface under cathodic polarization represents a serious drawback, perovskite oxide electrodes are good candidate electrocatalyst materials in molten carbonate [390] and high-temperature solid electrolytes [391],... 

Room-temperature ionic liquids are the promising electrolytes for the electrodeposition of various metals because they have the merits of both organic electrolytes and high-temperature molten salts. Ionic liquids can be used in a wide temperature range, so temperatures can be elevated to accelerate such phenomena as nucleation, surface diffusion and crystallization associated with the electrodeposition of metals. In addition the process can be safely constracted because ionic liquids are neither flammable nor volatile if they are kept below the thermal decomposition temperature of the organic cations. 

Metals are important resources and have a wide range of applications. Metals are often extracted from ores. Once the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometalluigy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants. Most metals are obtained by hydrometallurgical processes such as aqueous acids or alkalis are predominantly used to dissolve the metal oxides, sulfides, or silicates. Electrowinning and solvent extraction are frequently used to recover and concentrate the metals. A limited number of high-temperature molten salts have also been used for the recovery of refractory metals, such as titanium and aluminum, from their ores... 

Applications of the ILs in the electrochemistry of polyvalent metals are based on their ability to dissolve the compounds of these metals and to be stable in a wide range of applied voltages. Thus, the requirements are similar for both ILs and classical high-temperature molten salt electrolytes. 

Finally, high-temperature molten salt electrolyte batteries (NaS, Zebra) require completely inorganic separators capable of withstanding liquid metal temperature and chemical attack, effectively acidic conditions at temperatures >200 °C. Beta-AlaOs has been significantly engineered to serve this role [10]. 

The electrodeposition of AlSb cannot be achieved from aqueous solution because the reduction potential is far beyond the aqueous electrolyte potential limit. Furthermore, the high volatility of Sb complicates the electrodeposition of AlSb from high-temperature molten salt electrolytes. Consequently, the electrodeposition of AlSb is limited to be in the room-temperature molten salts which are also termed ionic liquids. Freyland and coworkers [164,165] first explored the nanoscale electrodeposition of AlSb on Au(l 11) using in situ scanning probe techniques such as STM and STS from AlCls-l-butyl-S-methylimidzolium chloride (1 1) ionic liquid containing SbCs. At a potential positive to 0.0 V (vs. an A1/A1(III) quasireference electrode), only Sb was deposited. The codeposition of AlSb occurred at more negative potentials. The deposition obtained at —0.9 V was Sb-rich whereas that at —1.5 V was Al-rich. Homogeneous distributed stoichiometric AlSb with a band gap of 2.0 0.2 eV was obtained at —1.1 V. 

HT-PEFC High temperature polymer electrolyte fuel cell. MCFC Molten carbonate fuel ceU. 

Corrosion and heat consumption by high-temperature molten salt electrolytes, caused by high operating temperature, are avoided. 

Aqueous ionic liquid microemulsions as electrolytes for electrochemical deposition are special and different from traditional aqueous solution and ionic liquids. Electrochemical approaches have been among the first to be used for the fabrication of inorganic nanopartides and nanostructured films in ionic Hquids. The properties of ionic liquids opened the door to the electrodeposition of metals and semiconductors at room temperature, which was ptreviously only possible from high-temperature molten salts. For example, Al, Mg, Ti, Si, Ge and rare-earth-elements related materials can be obtained from ionic hquids. 

Molten lithium fluoride is used in salt mixtures for an electrolyte in high temperature batteries (qv) (FLINAK) (20), and as a carrier in breeder reactors (FLIBE) (21) (see Nuclear reactors). 

---