Amorphous TiCu-Based Additives for Improving Hydrogen Storage Properties of Magnesium Hydride

Abstract

Magnesium hydride has long been regarded as a promising candidate material for hydrogen and heat storage due to its high hydrogen capacity, reversibility, and low cost. Catalytic doping has been demonstrated as one of the most effective methods to improve hydrogen storage properties of MgH2. In this study, amorphous Ti45Cu41Ni9Zr5 and Ti40Cu47Zr10Sn3 alloys are used as additives for MgH2. Nanostructured MgH2 doped with amorphous or crystalline TiCu-based alloys are prepared by using a high-energy mechanochemical synthesis method. Results show that the amorphous TiCu additives provide enhanced catalytic effects compared to crystalline alloys of the same composition. Doping MgH2 using an amorphous Ti45Cu41Ni9Zr5 alloy yielded improved dehydrogenation kinetics compared to using crystalline Ti40Cu47Zr10Sn3 alloy. The analysis using transmission electron microscopy reveals that there are nanostructured catalytic particles uniformly distributed in the amorphous TiCu-catalyzed MgH2. The MgH2 system catalyzed by amorphous TiCu-based alloy shows little degradation during hydrogenation and dehydrogenation cycling at 300 °C. The amorphous TiCu-based catalysts are thermally stable at temperatures up to 360 °C. Heating the amorphous Ti45Cu41Ni9Zr5-catalyzed MgH2 to temperatures above 360 °C led to disproportionation of the catalyst alloy and the formation of MgCu2 and Ti2Cu. In addition, PCI analysis of the amorphous Ti45Cu41Ni9Zr5-catalyzed MgH2 shows a slight increase in hydrogen equilibrium pressure, resulting in a reaction enthalpy of −78.7 kJ/mol·H2 and an entropy of 145.0 J/K·mol·H2. The entropy calculated from this study is approximately 10 J/K·mol·H2 higher than values previously reported for undoped and catalyzed Mg–H systems.

Transformation of Metallic Ti to TiH2 Phase in the Ti/MgH2 Composite and Its Influence on the Hydrogen Storage Behavior of MgH2

“…Therefore it is reasonable to consider that for systems where thermodynamic changes are noticed through error free experimental data, other possible factors unrelated with the chemical identity of the additive should not be ignored. As for example, a recent study performed by Zhou et al . suggests that the crystallinity of additive makes an observable influence on the thermodynamics of MgH 2 .…”

“…However, high working temperature (typically >350 °C), poor H‐sorption performance due to high desorption enthalpy (74 kJ/mol H 2 ) and high activation energy (153 kJ/mol H 2 ), are potential obstacles to the practical use of MgH 2 . In this respect, researchers have demonstrated that it is possible to substantially improve the H 2 storage performance of MgH 2 by incorporating additives, notably, oxides, chlorides, fluorides, metals, intermetallics and carbon nanostructures . Particularly, a wide variety of Ti based additives, as for example, Ti, TiH 2 , Ti−Fe, TiO 2 , TiCl 3 , TiF 3 , TiN and Ti(OBu) 4 have been proposed by various researchers .…”

Enhancing Hydrogen Storage Properties of MgH2 by Transition Metals and Carbon Materials: A Brief Review

“…More importantly, MgH 2 has a high gravimetric capacity of 7.6 wt% (volumetric capacity of 110 g/L) and excellent reversibility. However, the practical application of MgH 2 has been hindered by the high desorption temperature and poor hydrogen absorption/desorption kinetics caused by high thermal stability (ΔH = 76 kJ/mol) and kinetic barrier (Ea =160 kJ/mol) (Webb, 2015 ; Peng et al, 2017 ; Zhou et al, 2019a ; Jain et al, 2020 ).…”

Excellent catalysis of Mn3O4 nanoparticles on the hydrogen storage properties of MgH2: an experimental and theoretical study

“…7 Among numerous materials, magnesium hydride (MgH 2 ) with high mass hydrogen storage capacity (7.76 wt%), good reversibility, low cost and other outstanding performances (LIB anode) has attracted intense attention worldwide. [8][9][10][11] Nevertheless, two challenges (stable thermodynamics and poor kinetics) still need to be conquered before the large scale application of MgH 2 . [12][13][14] In the past few decades, extensive research has been conducted to overcome these challenges through diverse methods, such as catalyst doping, [15][16][17][18][19][20] alloying [21][22][23][24] and nanotechnology.…”