On the Catalytic Mechanism of 3d and 4d Transition-Metal-Based Materials on the Hydrogen Sorption Properties of Mg/MgH2

The slow hydrogenation/dehydrogenation kinetics and high thermodynamic stability of the Mg–H bond are the two major limitations for the large-scale utilization of MgH2. In this review, we introduce the catalytic mechanism of 3d and 4d transition metal (TM) on the hydrogen sorption properties of Mg/MgH2. The relative contribution of interatomic interactions to the thermodynamic stability of the TM-substituted MgH2 system is discussed. A synergy effect between the electronegativity and the radius of the TM element is proposed to explain the charge transfer process between TM and H in the TM-substituted MgH2 system. The catalytic mechanism of TM nearby the surface of Mg is more complicated than that in the volume of Mg, as the surface-doped TM can experience more options for doping sites, leading to the hindrance effect and causing various contributions of the d band center to the dissociation of hydrogen molecules and the diffusion of hydrogen atoms nearby the surface of Mg. In terms of the catalytic mechanism of TM for hydrogen sorption kinetics of Mg/MgH2, we particularly focused on the “hydrogen pump” effect existing in the Mg–TM–H system. Other mechanisms, such as a possible catalytic mechanism of TM for the hydrogen sorption properties of nano-sized freestanding Mg/MgH2, were also presented.

Superfunctional Materials by Ultra-Severe Plastic Deformation

Superfunctional materials are defined as materials with specific properties being superior to the functions of engineering materials. Numerous studies introduced severe plastic deformation (SPD) as an effective process to improve the functional and mechanical properties of various metallic and non-metallic materials. Moreover, the concept of ultra-SPD-introducing shear strains over 1000 to reduce the thickness of sheared phases to levels comparable to atomic distances-was recently utilized to synthesize novel superfunctional materials. In this article, the application of ultra-SPD for controlling atomic diffusion and phase transformation and synthesizing new materials with superfunctional properties is discussed. The main properties achieved by ultra-SPD include: (i) high-temperature thermal stability in new immiscible age-hardenable aluminum alloys; (ii) room-temperature superplasticity for the first time in magnesium and aluminum alloys; (iii) high strength and high plasticity in nanograined intermetallics; (iv) low elastic modulus and high hardness in biocompatible binary and high-entropy alloys; (v) superconductivity and high strength in the Nb-Ti alloys; (vi) room-temperature hydrogen storage for the first time in magnesium alloys; and (vii) superior photocatalytic hydrogen production, oxygen production, and carbon dioxide conversion on high-entropy oxides and oxynitrides as a new family of photocatalysts.

Mechanochemistry of Metal Hydrides: Recent Advances

This paper is a collection of selected contributions of the 1st International Workshop on Mechanochemistry of Metal Hydrides that was held in Oslo in May 2018. In this paper, the recent developments in the use of mechanochemistry to synthesize and modify metal hydrides are reviewed. A special emphasis is made on new techniques beside the traditional way of ball milling. High energy milling, ball milling under hydrogen reactive gas, cryomilling and severe plastic deformation techniques such as High-Pressure Torsion (HPT), Surface Mechanical Attrition Treatment (SMAT) and cold rolling are discussed. The new characterization method of in-situ X-ray diffraction during milling is described.

Catalytic effect of (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 on hydrogen storage properties of ultrafine magnesium particles

The Mg–(Ti_0.85Zr_0.15)_1.05Mn_1.2Cr_0.6V_0.1Cu_0.1 composites synthesized by milling TiMn₂ alloy with ultrafine Mg particles display significantly enhanced hydrogen storage properties.