1 Department of Chemistry, Science and Technology, Aarhus University2 Department of Chemistry - Centre for Energy Materials (CEM), Department of Chemistry, Science and Technology, Aarhus University3 Interdisciplinary Nanoscience Center, Science and Technology, Aarhus University4 Suranaree University of Technology5 Helmholtz Zentrum Geesthacht, Centre for Materials & Coastal Research HZG, Helmholtz Association, Inst Mat Res6 Department of Chemistry, Science and Technology, Aarhus University
To improve nanoconfinement of LiBH4 and MgH2 in carbon aerogel scaffold (CAS), particle size reduction of MgH2 by premilling technique before melt infiltration is proposed. MgH2 is premilled for 5 h prior to milling with LiBH4 and nanoconfinement in CAS to obtained nanoconfined 2LiBH(4)-premilled MgH2. Significant confinement of both LiBH4 and MgH2 in CAS, confirmed by SEM-EDS mapping results, is achieved due to MgH2 premilling. Due to effective nanoconfinement, enhancement of CAS:hydride composite weight ratio to 1:1, resulting in increase of hydrogen storage capacity, is possible. Nanoconfined 2LiBH(4)-premilled MgH2 reveals a single-step dehydrogenation at 345 degrees C with no B2H6 release, while dehydrogenation of nanoconfined sample without MgH2 premilling performs in multiple steps at elevated temperatures (up to 430 degrees C) together with considerable amount of B2H6 release. Activation energy (E-A) for the main dehydrogenation of nanoconfined 2LiBH(4)-premilled MgH2 is considerably lower than those of LiBH4 and MgH2 of bulk 2LiBH(4)-MgH2 (Delta E-A = 31.9 and 55.8 kJ/mol with respect to LiBH4 and MgH2, respectively). Approximately twice faster dehydrogenation rate are accomplished after MgH2 premilling. Three hydrogen release (T = 320 degrees C, P(H-2) = 3-4 bar) and uptake (T = 320-325 degrees C, P(H-2) = 84 bar) cycles of nanoconfined 2LiBH(4)-premilled MgH2 reveal up to 4.96 wt. % H-2 (10 Wt. % H-2 with respect to hydride composite content), while the 1st desorption of nanoconfined sample without MgH2 premilling gives 4.30 wt. % of combined B2H6 and H-2 gases. It should be remarked that not only kinetic improvement and B2H6 suppression are obtained by MgH2 premilling, but also the lowest dehydrogenation temperature (T = 320 degrees C) among other modified 2LiBH(4)-MgH2 systems is acquired. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
International Journal of Hydrogen Energy, 2014, Vol 39, Issue 28, p. 15614-15626