Improvement of hydrogen sorption properties of compounds based on Vanadium “bcc” alloys by mean of intergranular phase development

Abstract

Body centered cubic structure (bcc) type alloys based on Vanadium [1] reveal promising characteristics for mobile applications. These disordered solid solutions have particular metal/hydride equilibrium and some regulation aspects have leaded us to pay special attention to this type of material [2]. Compounds based on Vanadium-rich solid solution have been elaborated in order to destabilize γ hydride phase (corresponding to the face centered cubic (fcc) structure of VH2). Addition of Ni and Zr-rich Laves phase as a secondary phase results in the development of a particular microstructure composed of a principal bcc matrix rounded by intergranular activating phase. This results in a facilitated and faster activation of these compounds. The present study shows that some constituting species of the secondary phase have diffused in the main matrix and therefore have modified the thermodynamic of hydride. In fact, chromium diffusion into the bcc matrix destabilizes hydride. It is correlated to the lower stability of chromium hydride compared to Vanadium hydride. The enthalpic terms of each sample have been measured (assuming standard entropy of 130 J mol−1 K−1). The equilibrium metal/hydride can be easily switched in order to adapt it to a mobile hydride tank and obtain low working temperature in regard to the potential use.