Materials for hydrogen storage: ab-initio Molecular ... · Catania, 11.2.09 Massimo Celino ENEA,...

Progetto CRESCOCatania, 11.2.09

Massimo Celino ENEA, Dipartimento Tecnologie Fisiche e Nuovi MaterialiC. R. Casaccia, Rome, [email protected]

M. Celino and S. Giusepponi

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

ENEAItalian Agency for New Technologies, Energy and EnvironmentPhysical Technologies and New Materials DepartmentCasaccia Research CentreRome, Italy



• It can store significant quantities of hydrogen (7.7 wt% of hydrogen)

• Low cost of production• High abundance

Introduction: MgH2

• Too high temperature of decomposition • Slow decomposition kinetics

BUT



Improvements comes from:

Introduction: MgH2

Adding small amounts of catalytic metals

High energy ball milling• High density of crystal

defects• Fine dispersion of

second phase particles



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

Experimental results



It is possible to perform SEM observation at high spatial resolution of the phasesdistribution in partially decomposed Mg-MgH2 containing heavier catalyzing particles

Mg/MgH2 Fe (10%)10h milledMg/MgH2 10h milled

Mg

MgH2

Fe

Experimental results

The addition of Fe particles induces a nucleation process diffused in the material giving raise to a strongly interconnected microstructure

Thanks to A. Montone, ENEA



Molecular Dynamics Simulations

{ }( )iii xV

dtdxm −∇=2

2

N atoms3N degrees of freedom

New atomic positions

output

input

Distances among the atoms

t=1,Tmax

Forces among all the atoms

Compute physical quantities

Data storage



0

100

200

300

400

0 10 20 30 40 50 60 70

0

20

40

60

80

100

120

0 50 100 150 200 250 300

IBM SP5

CRESCO

Mesh: 72x576x180

Time Speedup

Processing Elements

Processing Elements

CPMD: code performance



CPMD: code performance

0

100

200

300

400

500

0 200 400 600 800 1000

Rotate system:

mesh 576 on x axisSpeedup

Processing elements

IBM SP5: ~ 8 sec - 64 PE

CRESCO: ~ 8 sec – 150 PE ~ 3 sec – 576 PE



Hydrogen desorption: the MgH2-Mg interface

Starting configuration

Mg surface

MgH2surface

InterfaceLx= 6.21 Å

Ly= 50.30 Å

Lz= 15.10 Å

MgH2:60 Mg atoms + 120 H atoms

IdrogenoMagnesio

Mg: 72 atoms



Molecular dynamics at T= 700 K


T= 700 K



Molecular dynamics (NVT ensemble)


T= 700 K

T= 800 K

T= 900 K



Starting configuration with a Fe atom near the interface:

• Increase of Hydrogen mobility • Lower desorption temperature

Fe

Mg-MgH2 interface : Fe

T= 500 K

Fe in POS 1



Fe in POS 2

Fe in POS 3




T= 500 K

Fe in POS 1

Fe in POS 2

Fe in POS 3




T= 400 KFe in POS 1

Fe in POS 2

Fe in POS 3




T= 400 K POS 2


Fe atom: first and second shellof Mg coordination



T= 400 K

POS 3




Conclusions

• It is possible to characterize experimentally and numerically the hydrogen desorption from MgH2

• 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

Materials for hydrogen storage: ab-initio Molecular ... · Catania, 11.2.09 Massimo Celino ENEA,...

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