Improved kinetic behaviour of Mg(NH2)2-2LiH doped with nanostructured K-modified-LixTiyOz for hydrogen storage

Gökhan Gizer,Julián Puszkiel,Martin Dornheim,José Martín Ramallo-López,Jo-Chi Tseng,Maria Victoria Castro Riglos,Martin Mizrahi,Claudio Pistidda,Thomas Gemming,Thomas Klassen,Antonio Santoru

doi:10.1038/s41598-019-55770-y

Abstract

The system Mg(NH2)2 + 2LiH is considered as an interesting solid-state hydrogen storage material owing to its low thermodynamic stability of ca. 40 kJ/mol H2 and high gravimetric hydrogen capacity of 5.6 wt.%. However, high kinetic barriers lead to slow absorption/desorption rates even at relatively high temperatures (>180 °C). In this work, we investigate the effects of the addition of K-modified LixTiyOz on the absorption/desorption behaviour of the Mg(NH2)2 + 2LiH system. In comparison with the pristine Mg(NH2)2 + 2LiH, the system containing a tiny amount of nanostructured K-modified LixTiyOz shows enhanced absorption/desorption behaviour. The doped material presents a sensibly reduced (∼30 °C) desorption onset temperature, notably shorter hydrogen absorption/desorption times and reversible hydrogen capacity of about 3 wt.% H2 upon cycling. Studies on the absorption/desorption processes and micro/nanostructural characterizations of the Mg(NH2)2 + 2LiH + K-modified LixTiyOz system hint to the fact that the presence of in situ formed nanostructure K2TiO3 is the main responsible for the observed improved kinetic behaviour.

Highlights

The system Mg(NH2)2 + 2LiH is considered as an interesting solid-state hydrogen storage material owing to its low thermodynamic stability of ca. 40 kJ/mol H2 and high gravimetric hydrogen capacity of 5.6 wt.%
Results obtained from the thermal behaviour, mass spectroscopy, desorption activation energy, volumetric measurements, ex situ powder X-ray diffraction method (PXD), in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and infrared spectroscopy for all the compositions are presented
The presence of reflections belonging to Li2Mg(NH)[2] at around 170 °C indicates that the desorption reaction has already started, which is in good agreement with DTA analysis (Fig. 1A)

Summary

Introduction

The system Mg(NH2)2 + 2LiH is considered as an interesting solid-state hydrogen storage material owing to its low thermodynamic stability of ca. 40 kJ/mol H2 and high gravimetric hydrogen capacity of 5.6 wt.%. We investigate the effects of the addition of K-modified LixTiyOz on the absorption/ desorption behaviour of the Mg(NH2)2 + 2LiH system. Studies on the absorption/desorption processes and micro/nanostructural characterizations of the Mg(NH2)2 + 2LiH + K-modified LixTiyOz system hint to the fact that the presence of in situ formed nanostructure K2TiO3 is the main responsible for the observed improved kinetic behaviour. TiO2 is one of the low-cost additives which enhance the hydrogen storage properties of the 2LiBH4 + MgH2 reactive hydride composite (RHC) system[44,45,46]. Puszkiel et al showed that 2LiH + MgB2/2LiBH4 + MgH2 RHC system doped with core-shell LixTiO2 nanoparticles shows improved the kinetic and cycling behaviour[44]. We investigate the effect of LixTiyOz and potassium-modified LixTiyOz additives on the microstructural and hydrogen storage properties of Mg(NH2)2 + 2LiH system.

Results

Discussion

Conclusion