Materials for hydrogen storage: ab-initio Molecular Dynamics study in the ENEA-GRID environment

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Romano Galli
6 anni fa
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1 Materials for hydrogen storage: ab-initio Molecular Dynamics study in the ENEA-GRID environment M. Celino and S. Giusepponi ENEA Italian Agency for New Technologies, Energy and Environment Physical Technologies and New Materials Department Casaccia Research Centre Rome, Italy

2 Introduction: MgH 2 It can store significant quantities of hydrogen (7.7 wt% of hydrogen) Low cost of production High abundance BUT Too high temperature of decomposition Slow decomposition kinetics

3 Introduction: MgH 2 Improvements comes from: High energy ball milling Adding small amounts of catalytic metals High density of crystal defects Fine dispersion of second phase particles

4 Experimental results Now the problem is to control at the atomic level the phase transformation of the milled samples

Fe particles induces a nucleation process diffused in the material giving raise to a strongly

5 Experimental results It is possible to perform SEM observation at high spatial resolution of the phases distribution in partially decomposed Mg-MgH 2 containing heavier catalyzing particles The addition of Fe particles induces a nucleation process diffused in the material giving raise to a strongly interconnected microstructure Mg/MgH 2 10h milled MgH 2 Mg/MgH 2 Fe (10%)10h milled Fe Mg Thanks to A. Montone, ENEA

among all the atoms New atomic positions Compute

6 Molecular Dynamics Simulations input N atoms 3N degrees of freedom t=1,t max Distances among the atoms Forces among all the atoms New atomic positions Compute physical quantities m dx dt 2 i 2 = i V ({ x }) i Data storage output

7 CPMD: code performance Time Speedup 120 IBM SP CRESCO Mesh: 72x576x Processing Elements Processing Elements

8 CPMD: code performance Speedup Rotate system: mesh 576 on x axis IBM SP5: ~ 8 sec - 64 PE CRESCO: ~ 8 sec 150 PE ~ 3 sec 576 PE Processing elements

9 Hydrogen desorption: the MgH 2 -Mg interface Starting configuration Idrogeno Magnesio Mg: 72 atoms Mg surface MgH 2 : 60 Mg atoms H atoms MgH 2 surface L x = 6.21 Å L y = Å Interface L z = Å

10 Molecular dynamics at T= 700 K Starting configuration T= 700 K

11 Molecular dynamics (NVT ensemble) T= 700 K Starting configuration T= 800 K T= 900 K

12 Mg-MgH 2 interface : Fe Starting configuration with a Fe atom near the interface: Increase of Hydrogen mobility Lower desorption temperature Fe in POS 1 Fe T= 500 K

13 Mg-MgH 2 interface : Fe Fe in POS 2 Fe in POS 3

14 Mg-MgH 2 interface : Fe Fe in POS 1 Fe in POS 2 T= 500 K Fe in POS 3

15 Mg-MgH 2 interface : Fe Fe in POS 1 T= 400 K Fe in POS 2 Fe in POS 3

16 T= 400 K POS 2 Mg-MgH 2 interface : Fe Fe atom: first and second shell of Mg coordination

17 Mg-MgH 2 interface : Fe T= 400 K POS 3

18 Conclusions It is possible to characterize experimentally and numerically the hydrogen desorption from MgH 2 The addition of catalyzing particles induces a nucleation process diffused in the material giving raise to a strongly interconnected microstructure The interplay of interfaces and catalyzing particles lowers Hydrogen desorption temperature: Fe atoms induce a depression region able to lower the bonding between H and Mg

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