Nanometer-scale analysis of hydrogen storage in complex hydrides using small angle neutron scattering and simulations
Date:
Topic: Analysis of hydrogen diffusion in nanoscale and its imapact of storage performance in the engineering length scale.
Authors
Arnab Majumdar, Martin Müller, and Sebastian Busch
Abstract
The current practice of using fossil fuels to satisfy the ever-growing energy demand is expected to cause an irreversible increase in temperature. Alternative fuels like hydrogen can be part of a solution to this problem due to its high gravimetric energy density. However, the low volumetric density of hydrogen in gas and liquid phases incurs problems related to storage [1]. To circumvent this problem, the chemical storage of hydrogen using a complex hydride system can be opted for. Amongst several options within complex hydrides, a mixture of Mg(NH2)2, LiBH4, and LiH was chosen in this work to investigate using Small Angle Neutron Scattering (SANS) experiments and simulations [2].
SANS is commonly used for the investigation of nanoscale structures. In this work, in situ SANS measurements were performed to reveal information about the absorption and desorption of hydrogen on the nanometer length scale. However, the measurements do not allow a direct deduction of the process or structure in real space. Therefore, several models were proposed based on different hypotheses and the in situ SANS data was calculated from the simulation for comparison with experiments, accounting for all relevant instrument details [3–5].
As the simplest possible model, diffusion of hydrogen into and out of an isotropic grain of hydrogen storage material was hypothesized. The disparity between the simulation data and the experiment shows that a more complicated model is required to describe the experimental observation. Therefore, micro-structures of absorbed and desorbed states were generated probabilistically. The calculated data from the simulation is compatible with the experiments after the addition of micro-structural details.
Using the appropriate computational model and in situ SANS experiment, it was found that hydrogen gas must be partially entrapped on the nanometer length scale during desorption. Using the findings in the nanometer length scale, the volumetry performance related to the engineering length scale was predicted and a good match with the measurement was found.
References:
[1] Pistidda et al., doi:10.3390/hydrogen2040024
[2] Aslan et al., doi:10.3233/JNR-190116
[3] Mühlbauer et al., doi:10.1016/j.nima.2016.06.105
[4] Karge et al., doi:10.1107/S1600576717011463
[5] Majumdar et al., doi:10.3390/ijms25031547