borohydride

The influence of small amounts of the Fe, Co, and Ni impurities on the spontaneous hydrolytic process of borohydride was studied within a temperature range of 60–100°C. The object under study was a simulated solution containing 9.53 M of OH⁻ ions and 0.14 M of BH₄⁻ ions, used as a fuel for borohydride fuel cells. The rate constant k of borohydride hydrolysis for a small amount of impurities at different temperature was estimated. The lowest non-accelerating concentrations of the impurities were established ( ∼ 10 ppm for iron;  ∼ 1 ppm for cobalt).

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.

The study of the anodic oxidation of borohydride-ion BH₄^– on catalytically active nickel electrode by methods of potentiostatic inclusion, galvanostatically inclusion, cyclic voltammetry and infrared spectroscopy with Fourier transformation. The composition of some intermediates of the process of electrochemical oxidation of BH₄^– and the mechanism of decomposition of borohydride, which includes the following basic stages: BH₄^– → BH₃(OH)^– → BH₂(OH)₂^– → BH(OH)₃^– → B(OH)₄^–, is determined. The regularities of the kinetics of the electrochemical oxidation of BH₄^– – ion Ni-electrode is determined. The diffusion coefficient BH₄^– ion in aqueous solution at a temperature of 25°C, measured by electrochemical methods, ranges from 5.3·10^–5 to 1.6·10^–5, the average value of 2·10^–5 cm²/s.