High Hydroxide Conductivity

For high-performance HEMFC applications, HEMs and HEIs are required to have high hydroxide conductivity, excellent chemical stability, sufficient physical stability, controlled solubility, and other important properties. 

The metallic salts of trifluoromethanesulfonic acid can be prepared by reaction of the acid with the corresponding hydroxide or carbonate or by reaction of sulfonyl fluoride with the corresponding hydroxide. The salts are hydroscopic but can be dehydrated at 100°C under vacuum. The sodium salt has a melting point of 248°C and decomposes at 425°C. The lithium salt of trifluoromethanesulfonic acid [33454-82-9] CF SO Li, commonly called lithium triflate, is used as a battery electrolyte in primary lithium batteries because solutions of it exhibit high electrical conductivity, and because of the compound s low toxicity and excellent chemical stabiUty. It melts at 423°C and decomposes at 430°C. It is quite soluble in polar organic solvents and water. Table 2 shows the electrical conductivities of lithium triflate in comparison with other lithium electrolytes which are much more toxic (24). 

A second class of fuel cells employs hydroxide-conducting (alkaline) electrolytes, again either in form of a solid membrane (alkaline membrane fuel cells) or a liquid electrolyte (alkaline fuel cells). While the modem era of fuel cells began with the latter type, the former type is under intense research today because a stable, highly conducting alkaline membrane with good C02 tolerance has remained elusive to date. 

There are several important hydrated forms of alumina corresponding to the stoichiometries A1(0)0H and Al(OH)3. Addition of ammonia to a boiling solution of an aluminum salt produces a form of A1(0)0H known as boehmite, which may be prepared in other ways also. A second form of A1(0)0H occurs in Nature as the mineral diaspore. The true hydroxide Al(OH)3 is obtained as a crystalline white precipitate when carbon dioxide is passed into alkaline aluminate solutions. It occurs in Nature as the mineral gibbsite. Materials sometimes referred to as /1-aluminas have other ions such as Na+ and Mg2+ present. They possess the idealized composition Na2011Al203. They can act as ion exchangers, have high electrical conductivity, and are potential solid state electrolytes for batteries. 

The typical electrolyte of the Ni-Cd battery is the concentrated potassium hydroxide (KOH) aqueous solution ( 30% by weight). This electrolyte solution provides high ionic conductivity and a wide temperature window of a liquid phase. In addition, both the cathodic and the anodic active materials have low solubility in this electrolyte. These properties make a substantial contribution to the performance of the Ni-Cd, especially the high rate, wide operational temperature range, long cycle life, and long shelf life. 

Hence, the major general criterion for eluent selection is a different equivalent conductance compared to the sample ions and a high enough affinity for the resin to promote effective elution of the sample ions. So far we have emphasized that the eluent should have a low equivalent conductance. But an eluent such as sodium hydroxide, with a high equivalent conductance, can be used in non-suppressed 1C. This eluent is discussed in Section 6.3.3.5. 

The theory of negative peaks for sample anions is easy to understand. Suppose wc use 1.0 X 10 M sodium hydroxide as the eluent. The background conductance will be the sum of the sodium and hydroxide conductances and will be relatively high. Injection of a sample will result in the uptake of the anions by the resin column with an equivalent amount of resin hydroxide ion passing into solution. Once the matrix peak is through, the anion concentration of the column effluent will be constant, as fixed by the 1.0 x 10 M eluent concentration. When a sample anion, A , is eluted from the column and passed through the detector, the eluent hydroxide ion will be decreased because a constant anion concentration must be maintained... 

Because hydronium- and hydroxide ions can move without actually moving and thus without having to plow their way through the solution by shoving aside water molecules as do other ions, solutions which are acidic or alkaline have extraordinarily high electrical conductivities. 

Ionomer membranes fabricated from these polymers show high hydroxide ion conductivities, up to 144 mS cm at 80 °C. The membrane retained its high conductivity in hot water at 80 °C for 5000 h [118]. 

Lai, M. and Howe, A. T. 1980. High proton conductivity in pressed pellets of zinc-chromium hydroxide. J. Chem. Soc. Chem. Commun. 15 737. 

When analysing a large amount of sample at a slow scanning rate, a silver sample vessel is recommended owing to its high thermal conductivity. A reaction between the solvent and the inner surfaces of a sample vessel can cause unexpected features to be observed on the DSC curve. For example, water in a sample can react with aluminium and an exothermic peak is observed in the region of 400 K. The peak is due to the formation of aluminium hydroxide [AI(OH)3 ] on the inner surface of... 

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