Mechanochemical Synthesis and Hydrogen Sorption Properties of a V-Ni Alloy

Oriele Palumbo,Francesco Trequattrini,Nicholas Carboni,Annalisa Paolone,Sergio Brutti

doi:10.3390/hydrogen3010009

Oriele Palumbo, Francesco Trequattrini + Show 3 more

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https://doi.org/10.3390/hydrogen3010009

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Abstract

Vanadium can store large quantities of hydrogen (about 4 mass%). However, only half of it can be reversibly absorbed. To avoid this issue, various partial substitutions were previously proposed, such as Ni. In this work, we explore the synthesis of a V85Ni15 alloy by means of ball milling, a simpler and more scalable method compared to arc or induction melting usually applied for metal alloys. After ball milling the powders of the pure metals for 15 h in argon, SEM–EDX measurements confirmed the stoichiometry of the synthesized material, which has a typical particle dimension of the order of a few microns and is composed from the coalescence of nanometric primary particles. XRD indicated a BCC crystalline structure with a typical grain size of ≈3 nm. Hydrogen can be absorbed without activation procedures at high temperatures. Up to H/M ≈ 0.08, one can observe the occurrence of a solid solution of hydrogen in the alloy, while at a higher hydrogen content, the formation of a hydride is likely to occur. The maximum hydrogen content is H/M ≈ 0.4 at the maximum investigated pressure in this study of p ≈ 45 bar. Both the hydrogenation enthalpy and entropy decrease as the hydrogen content increases, and the shape of the sorption isotherms is different from that of V85Ni15 produced by induction melting, possibly because of the nanometric dimensions of the particles produced by ball milling.

Highlights

Pure vanadium can store large quantities of hydrogen, as it can reach the composition of the dihydride, VH2
One way to partially mitigate the irreversible storage of hydrogen in vanadium is the partial substitution of V with other metals, such as Ti, Cr, Ni, Fe, etc., which generally leads to a higher equilibrium pressure and a sloping plateau [3,5–7] in the pressure composition isotherms
An SEM analysis at high magnification highlights the presence of secondary particles of typical dimensions of a few microns, each of them composed of primary particles in the nanometer size scale

Summary

Introduction

Pure vanadium can store large quantities of hydrogen, as it can reach the composition of the dihydride, VH2. Due to the relatively low mass of vanadium, VH2 has a high storage capacity of about 4 mass%, which can be reached at room temperature [1]. When measuring the pressure composition isotherms, one can observe various pressure plateaus; the one corresponding to the transition from the solid solution (α phase) to VH0.5 has an extremely low pressure, on the order of 1 mbar [3,4]; it is extremely difficult to remove hydrogen at low hydrogen concentrations. One way to partially mitigate the irreversible storage of hydrogen in vanadium is the partial substitution of V with other metals, such as Ti, Cr, Ni, Fe, etc., which generally leads to a higher equilibrium pressure and a sloping plateau [3,5–7] in the pressure composition isotherms

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