Temperature-Induced Transformation of the Phase Diagrams of Ternary Systems NaBO₂+ NaOH + H₂O and KBO₂+ KOH + H₂O

Abstract

Concentrated water-alkaline solutions of sodium and potassium borohydrides are used as a fuel and hydrogen source in hydrogen power engineering, including low-temperature fuel cells; borohydrides convert into metaborates. The performance of fuel mixtures is determined by their solubility in water. The solubility in the ternary systems NaBOwas studied by means of isothermal saturation within the range (-10 to 50) °C. The composition of equilibrium solid phases and those of mixtures corresponding to nonvariant equilibrium points were determined; the solubility diagrams of these systems were constructed. The systems with sodium and potassium ions are considerably different in relation to the temperature influence on the solubility of the solid components. The presence of a range of homogeneous solutions and fields of crystallization of hydrated and anhydrous forms of the metaborates and hydroxides is characteristic for both systems at all investigated temperatures. The composition of crystalline hydrates depends on the component ratio in the mixture and the cation nature.

Polythermal diagrams of aqueous boundary ternary systems involving sodium borohydride hydrolysis for hydrogen generation

“…A polythermal diagram of each ternary system was proposed according to experimental solubility data of these systems and their subsystems. Ternary system solubility data consider previous work from the author [11] and other authors [12][13][14].…”

“…In a previous work, the solubility limit of the hydrolysis's by-products, NaBO2.yH2O, has been investigated and the experimental results for the solubility limit in the ternary system NaBO2-NaOH-H2O under ambient pressure at 10, 25 and 50 °C have been presented [11]. In this present work, polythermal diagrams of the two aqueous boundary ternaries NaBH4-NaOH-H2O (corresponding to 0 % of hydrolysis reaction conversion) and NaBO2-NaOH-H2O (100 % of conversion) will be proposed from critical analysis of the description of several isotherm sections of each system [11][12][13][14] and will be completed by DSC analysis with the intent to give more precision about invariant transformations of the system. The third aqueous boundary ternary system NaBH4-NaBO2-H2O cannot be experimentally evaluated because of the spontaneous decomposition of NaBH4 in water, i.e.…”

Phase Equilibria and Phase Diagrams for the Ternary Aqueous System Containing Lithium, Sodium, and Pentaborate Ions at 298.15 and 323.15 K and 101.325 kPa

“…e solid-liquid-phase equilibrium of the ternary system LiB 5 O 8 + NaB 5 O 8 + H 2 O at 298.15 and 323.15 K was studied by the isothermal dissolution equilibrium method as described previously [16]. On the basis of the binary solubility, a series of artificial synthetic complexes were prepared by mixing lithium pentaborate and sodium pentaborate with DDW.…”

Separate Determination of Borohydride, Borate, Hydroxide, and Carbonate in the Borohydride Fuel Cell by Acid-Base and Iodometric Potentiometric Titration

“…where the current equilibrium values of molar concentrations are determined by (14) and (15). Equation 17is very convenient for computer simulations.…”

“…In these systems, electrical energy is generated by means of hydrolysis and electrochemical oxidation of borohydrides into borates. In alkaline media, these are LiBO 2 , NaBO 2 , and KBO 2 [10][11][12] whose solubility essentially influences the power characteristics of FC [13][14][15]. The difficulty of the design of effective and sustainable anode electrocatalysts for the anodic oxidation of borohydride limits the efficiency and power density attainable in these devices [16][17][18].…”