Estimation of Diffusion-Kinetic and Thermodynamic Properties of Al‑Sm-H Alloys

Abstract

Metal hydride systems for hydrogen storage are now commercially manufactured and the demand for them is constantly growing. Metal hydrides have the following features: a unique combination of properties of metal-hydrogen systems; extremely high volumetric densities of hydrogen atoms in the metal matrix; a wide range of operating pressures and temperatures; the selectivity of the hydrogen absorption process; significant changes in the physical properties of the metal when it is saturated with hydrogen; their catalytic activity, etc. The purpose of our research was to study the effect of the temperature of cathodic polarisation on the diffusion-kinetic, thermodynamic, and physical properties of Al-Sm-H alloys. In our study we used electrodes of Al-Sm-H alloys obtained electrochemically using cathodic intercalation from a 0.5 M dimethylformamide solution of samarium salicylate at Еcp = –2.9 V (relative to the non-aqueous silver chloride electrode) and the temperature of 25 °С for 1 hour. We used the electromotive force method to determine the thermodynamic properties: Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH). The potentiostatic method was used to calculate the diffusionkinetic properties: intercalation constants, adsorption, switching current density, and the diffusion coefficient. The microstructural analysis allowed us to determine the effect of the temperature on the changes in the surface morphology. The study showed that an increase in the temperature results in an increase in ΔG, ΔS, and ΔH, which means that at higher temperatures the degree of the system disorder increases. Nevertheless, the calculated characteristics comply with the existing literature.

Keywords

• electromotive force method
• rare earth elements
• aluminum matrix
• hydrogen
• potentiostatic method
• microstructure
• diffusion-kinetic characteristics