Mechanochemical synthesis and first-principles simulations of Mg-based hydrogen storage materials

Abstract

A systematic investigation of the structural stability, evolution and hydrogen-storage properties of Mg-based hydrides and nanostructures was carried out, involving experimental mechanical milling and chemical alloying, and electronic structural simulations of hydrogen-metal interactions. The effects of milling on particle size, lattice parameters, microstructure, and phase composition of the powder mixtures were characterized using SEM, X-Ray diffraction analyses. Mechanical milling was shown to be an effective method of refining the particle size, particularly when MgH2 is involved. The influences of the selected chemical elements, including transition metals, on hydrogen desorption of various milled mixtures were clearly identified using coupled Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC). The asreceived MgH2 shows an onset desorption temperature of 420°C. Mechanical milling reduces the onset temperature to 330°C. Chemical alloying, via surface catalysis and/or solid-solutioning, further increases the desorption kinetics and reduces the desorption temperature down to 250°C. The degree of such effect decreases from Ni, Al, Fe, Nb, Ti, to Cu. A multi-component mixture of (MgH2+Al+Ni+Y+Ce) exhibits relatively fast desorption kinetics and the lowest desorption temperature at about 200°C. Electronic structural simulations further clarify the effects of alloying elements on the stability and bonding of modified hydride systems. The coupled experimental and theoretical approach has laid a valuable foundation for continued development of new and cost-effective hydrogen storage systems with a high capacity, a low desorption temperature and rapid kinetics.