водородная энергетика

Concentrated water-alkaline mixtures of sodium and potassium borohydrides and borates are used as fuel and a hydrogen source in hydrogen power engineering, including low-temperature fuel cells. The performance of such mixtures is determined by their physicochemical properties. An algorithm to calculate the density, viscosity, and specific electric conductivity of mixed solutions of the five-component water + salt system (Na,K)BH₄ + (Na,K)BO₂ + (Na,K)OH + H₂O based on the quasiadditivity of these properties is proposed. The concentration-temperature dependences of the density, viscosity, and specific conductivity of aqueous KOH, NaOH, KBO₂, NaBO₂, NaBH₄, and KBH₄ solutions of any composition in a temperature range of (0 to 60)°C and the whole concentration range are described mathematically. The technique and algorithm of calculation have been verified by comparison with measured properties.

A study of the solubility in the ternary systems NaBH₄–NaOH–H₂O, KBH₄–KOH–H₂O, NaOH–NaBO₂–H₂O и KOH–KBO₂–H₂O is of special fundamental and practical interest. The first two systems are used as a fuel and as a hydrogen source in hydrogen power engineering that includes the low-temperature fuel cells; borohydrides are converted into metaborates. Hence, the last two systems represent the discharged by-product. The performance of such mixtures is determined by the solubility of their components, negative temperatures being especially critical. Therefore, in the present work the solubility in the ternary systems was studied by means of isothermal saturation at – 10°C. The compositions of the equilibrium liquid and solid phases and compositions of the eutonic and peritonic equilibria, and the coordinates of the homogeneous solution ranges have been determined. The best solubility of the solid components is characteristic of systems NaBH₄–NaOH–H₂O and KBO₂–KOH–H₂O.

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 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.