Background: The transition to a hydrogen fuel economy is hindered by the lack of a practical storage method and concerns associated with its safe handling. Chemical hydrides have the potential to address these concerns. Sodium borohydride (sodium tetrahydroborate, ), is the most attractive chemical hydride for generation and storage in automotive fuel cell applications, but recycling from sodium metaborate , is difficult and costly. An electrochemical regeneration process could represent an economically feasible and environmentally friendly solution. Method of Approach: We report a study of the properties of concentrated alkaline aqueous solutions that are necessary to the development of electrochemical recycling methods. The solubility, pH, density, conductivity, and viscosity of aqueous solutions containing varying weight percentages (1, 2, 3, 5, 7.5, and ) of alkali hydroxides (NaOH, KOH, and LiOH) were evaluated at . The precipitates formed in supersaturated solutions were characterized by x-ray diffraction and scanning electron microscopy. Results: All physicochemical properties investigated, except solubility, increased with increased hydroxide ion concentration. The solubility of was enhanced by the addition of KOH to the saturated solution, but decreased when LiOH and NaOH were used. The highest ionic conductivity was obtained from the filtrate of saturated aqueous solutions containing more than and NaOH prior to filtration. At hydroxide, the viscosity of the solution was the highest in the case of LiOH (11.38 cP) and lowest for those containing NaOH (6.37 cP). The precipitate was hydrated, for all hydroxides, but its hydration level was unclear. Conclusions: The use of KOH as the electrolyte was found to be more advantageous for the storage and generation system based on solubility and solution half-life. However, the addition of NaOH led to the highest ionic conductivity, and its use seems more suitable for the electroreduction of . Further investigations on the impact of KOH and NaOH on the electroreduction of in aqueous media have the potential to enhance the commercial viability of .
Physicochemical Properties of Alkaline Aqueous Sodium Metaborate Solutions
Cloutier, C. R., Alfantazi, A., and Gyenge, E. (April 17, 2006). "Physicochemical Properties of Alkaline Aqueous Sodium Metaborate Solutions." ASME. J. Fuel Cell Sci. Technol. February 2007; 4(1): 88–98. https://doi.org/10.1115/1.2393310
Download citation file: