By Dr. Claudia Zlotea, Institut de Chimie et des Matériaux Paris Est, CNRS-UPEC, France
Multi-Principal-Element Alloys (MPEAs) belong to a new metallurgical paradigm based ont he alloying of four or more elements with equal concentrations. Most of reports concerning these alloys describe their structure, microstructure and mechanical properties, whereas functional properties such as, hydrogen sorption, are only scarcely investigated. We present here the study of hydrogen absorption properties of MPEAs based on refractory metals. The quaternary TiVZrNb alloy  and quinary TiVZrNbX (X = Mg, Al and Ta) alloys have been synthesized by classical high temperature methods or mechanosynthesis under inert atmosphere. To directly produce hydrides we have employed the reactive ball milling under hydrogen gas starting from the pure metal powders. The properties of materials have been studied by several experimental techniques: X-ray diffraction, electron microscopy, neutron diffraction, pressure-composition-isotherm, thermal desorption spectroscopy. All the alloys are bcc single-phased and undergo one-step reaction with hydrogen forming a dihydride phase. We suggest that the lattice distortion, δ, might play an important role:
larger δ would favor a single-step reaction, whereas small δ would favor a two-steps phase, as encountered for conventional bcc alloys. The hydrogen absorption/desorption is completely reversible and the capacities varies between 2 and 3 wt%. Despite a fading of the capacity for the first cycles, the reversible capacity of the TiVZrNb material stabilizes around 2 wt%. To complement the experimental approach, a theoretical investigation combining a random distribution technique and first principle calculation was done to estimate the stability of the hydride phase for the TiVZrNb alloy.
In summary, this is an original research topic in the field of solid-state hydrogen storage that might open new routes for the design of multifunctional materials.
Claudia Zlotea and Jorge Montero
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 M. C. Gao, D. B. Miracle, D. Maurice, X. Yan, Y. Zhang, and J. A. Hawk, “High-entropy functional materials,” Journal of Materials Research, pp. 1–18, 2018.
 J. Montero, C. Zlotea, G. Ek, J.-C. Crivello, L. Laversenne, and M. Sahlberg, “TiVZrNb Multi-Principal-Element Alloy: Synthesis Optimization, Structural, and Hydrogen Sorption Properties,” Molecules, vol. 24, no. 15, p. 2799, Jan. 2019.
CZ is a permanent researcher at ICMPE CNRS and her scientific interests focus on the synthesis and characterization of materials for applications in the clean energy field. She received her PhD in Materials Science from Joseph Fourier University in Grenoble (France) in 2002. Recently, her research emphasis on nanosizing/nanoconfinement effects on the physicochemical properties of nanoscaled materials and their interaction with hydrogen. The considered materials are foreseen in different applications such as, hydrogen storage, electrochemical conversion and heterogenous catalysis.