Hydrogen energy

A study of the solubility in the ternary systems NaOH-NaBO₂-H₂O and KOH-KBO₂-H₂O is of special interest from a fundamental and practical point of view. These systems represent the discharged products of the borohydrides fuel cells. The performance of such mixtures is determined by the solubility of their components. Therefore, in the present work the solubility in the ternary systems was studied by means of isothermal saturation within 1 (H-50°C. The compositions of the equilibrium liquid and solid phases and compositions of the eulonic and perilonic equilibria, the coordinates of the homogeneous solution ranges have been determined. The systems with sodium and potassium ions considerably differ by the temperature influence on solubility of solid components.

A model connecting the weight, volume, and chemical changes of heterogeneous borohydride fuel occurring at discharge of the direct borohydride fuel cell is presented. The experimental data measured with a fuel on the basis of water-alkaline solution of potassium borohydride KBH4 at temperature 25°C arc compared with theoretically calculated curves. Good conformity is acknowledgement of the 8-electron mechanism of borohydride ion oxidation.

The paper studies the influence of temperature (50–100°C) and alkalinity (C OH – = 2.33–9.53 M) of aqueous solutions on the hydrolysis (self-destruction) kinetics of borohydride ions BH4 – . Characteristic peculiarities of the kinetic curve have been established and formulae to approximate the temperature-concentration dependence of the hydrolysis rate are proposed. An increase in temperature leads to an increase in the rate constant k of borohydride hydrolysis, and the temperature dependence of k satisfactorily obeys Arrhenius' equation. The influence of solution alkalinity on the borohydride hydrolysis rate was explored. Within the temperature range studied, the k = f(C OH -) curve consists of two fragments, each with the prevalence of one of two different mechanisms (paths) of borohydride hydrolysis. In highly-alkaline aqueous solutions, non-catalytic hydrolysis mainly occurs, whose rate is determined by temperature, being p�-independent. At lower alkalinity, the hydrolysis rate sharply increases due to catalysis by � + ions. A power dependence of k on the � + concentration has been found; the point where the mechanisms are switched is determined by temperature.