RECENT ACHIEVEMENTS ON NANOCRYSTALLINE MATERIALS FOR SOLID STATE HYDROGEN STORAGE

(1)

RECENT ACHIEVEMENTS ON

NANOCRYSTALLINE MATERIALS FOR

SOLID STATE HYDROGEN STORAGE

VII CONVEGNO NAZIONALE INSTM SULLA SCIENZA E TECNOLOGIA DEI MATERIALI, Tirrenia (PI) 9-12 Giugno 2009 G. Principi, F. Agresti, A. Khandelwal, A. Maddalena, S. Lo Russo

(2)

Diapositiva 1

Hilfe2 Diese Folie enthält zwei Mastergruppen (Master und Titelmaster), welche den Corporate-Design-konformen Auftritt definieren. Der jetzt

zugewiesene Empa-Master 1 sieht für die Titelfolie das Empa-Logo vor. Den weiteren Folien ist kein Logo zugewiesen. Für längere Vorträge mit Zwischentiteln empfehlen wir, den Folien mit Zwischentiteln den Empa-Master 2 (mit Logo unten rechts) zuzuweisen. Dazu öffnen Sie via Ansicht > Aufgabenbereich > Foliendesign-Entwurfsvorlage rechts die Masterauswahl. Nun markieren Sie im linken Ansichtsfenster die Folien, denen Empa-Master 2 zugewiesen werden soll (mindestens zwei, ansonsten für den ganzen Satz Empa-Master 1 verwendet wird). Weitere Hilfe erhalten Sie bei Monika Ernst, 4995 (Empa, Dübendorf)

(3)

The problem of hydrogen storage

Maggiore capacità volumetrica di idrogeno:

Max 30 Kg/m3 in high pressure cylinders 70 Kg/m3 in liquid hydrogen

Up to 150 Kg/m3 in metal hydrides

More safety with respect to high pressure cylinders and cryostats

(4)

Outline

Hydrogen storage studies in MgH₂ pellets

Mechano-chemical synthesis of LiBH₄ starting from LiH and B

(5)

0 5000 10000 15000 20000 0 1 2 3 4 5 6 0 5000 10000 15000 0 1 2 3 4 5 6 H y d ro g e n , w t. % Time, s A Storage degradation Kinetics degradation Time, s cycle 8 cycle 14 cycle 20 B

Compaction of the powder in various regions

of the tank , implying different thermal conductivity in various regions that leads to kinetic and storage degradation*

*M. Verga et. al, “Scaling up effects of Mg hydride in a temperature and pressure controlled hydrogen storage device”, Int. J. Hydrogen Energy 34 (2009) 4602

(6)

Pellets of catalyzed MgH₂

0.7 cm 0.7 cm

• MgH₂ with 0.5 mol % Nb₂O₅ and 1 wt% Graphite, ball milled for 20 hrs

• Pellets prepared by compacting the milled powder at the pressure of 230 MPa

0 200 400 600 800 1000 0 1 2 3 4 5 6 t (s) w t% H 2 320 °C 1,2 atm MgH₂ + 0,5 mol% Nb₂O₅ BM 20 h 1 2 3 4 5 6 7 8 9 10

(7)

Pellets of catalyzed MgH₂ + Al 0 400 800 1200 0 1 2 3 4 5 6 320 °C 1,2 atm

Pellet with 5wt% Al preheated at 450OC

H y d ro g e n ( w t % ) t (sec) 1 5 10 15 20 25 30 35 40 45 50

The desorption behaviour becomes almost stable just after 10 cycles and the pellet remains mechanically very consistent and hard even after 50 cycles

(8)

Pellets of catalyzed MgH₂ + Al 20 30 40 50 60 70 80 90 Data Rietveld fit in te n s it y ( a .u .) 2θ χ ∀ ∗ ∀ ∗ _∗ ∗ ∗ χ ♥ ♥ ♥ ♦ ♦ ♣ ♣ ♣ ♣ ♣ ♣ ♣ ♣ ♣ ♣ ♣ ♣ ♣ _{♣ β}_MgH 2 ♦ MgO ♥ Al χ Al 3Mg2 ∗ Al 12Mg17 ∀ Al 3Nb

(9)

Pellets of catalyzed MgH₂ + Al – SEM micrographs

(10)

Conclusions #1

• Problem of degradation of kinetic and storage proprieties during scaling up studies can be avoided by using pellets in place of powder

(11)

Outline

(12)

• Most used compound in organic chemistry as reducing agent for aldehydes, ketones, acid chlorides, esters etc.

• One of the most studied complex metal hydride for hydrogen storage • Theoretical gravimetric hydrogen storage capacity = 18.4 wt %

• Decomposition reaction:

LiBH₄ → LiH +B + 3/2 H₂ (>400 °C)

• Practical maximum hydrogen storage capacity = 13.4 wt% due to high stability of LiH up to 730O_C

(13)

Milling

• Milling LiH powder and B pieces with stoichiometric ratio of 1:1 • SPEX 8000M mill

• Stainless steel vial

• Stainless steel and WC balls • Ball to powder ratio = 30:1

• H₂Pressure inside vial = 3, 4.5 and 10 atm • Milling time: 12, 30, 120 and 138 hrs

Separation and re-crystallization

• Dissolved in methyl tert-butyl ether and filtered • Re-crystallised using vacuum evaporation

Mechano-chemical synthesis of LiBH

₄

starting from LiH and B

F. Agresti and A. Khandelwal, “Evidence of formation of LiBH₄by high energy ball-milling of LiH and B in a hydrogen atmosphere”, Scripta Mater. 60 (2009) 753

(14)

Sample A: SS balls - 3 atm H₂ - 12 hrs

Sample B: SS balls - 3 atm H₂ - 30 hrs

Sample C: SS balls - 4.5 atm H₂ - 120 hrs

Sample D: SS balls - 10 atm H2 - 138 hrs

Mechano-chemical synthesis of LiBH

₄

starting from LiH and B

0 100 200 300 400 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 0 50 100 150 200 250 300 350 400 450 500 550 Sample A Sample B Sample C Sample D Sample E D e s o rb e d H 2 ( w t% ) T ( °C ) time (min) 20 30 40 50 60 70 80 ♠ ♠ ♦ ♦ ♦ ♦ ♦ ♦ ♦♣ ♣ ♣ ♣ ♣ LiH ♦ WC ♠ Sample holder decomposed I n te n s it y ( a .u .) 2θ (deg) as milled

(15)

All the identified peaks in re-crystallized specimen belong to orthorhombic LiBH₄

Mechano-chemical synthesis of LiBH

₄

starting from LiH and B

50 75 100 125 150 175 200 225 250 275 300 D S C ( a .u .) T (°C) Exo. Endo. as milled pure LiBH₄ orthorhombic to hexagonal LiBH₄phase transition

LiBH 4 melting 10 20 30 40 50 60 70 80 90 ∗ ∗ 0 50 100 150 200 250 300 0 100 200 300 400 500 0 2 4 6 8 10 12 D e s o rb e d H 2 ( w t% ) T ( °C ) time (min) ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ 2θ (deg) In te n s it y ( a .u .) recrystallized sample holder ∗ LiBH₄ (orthorhombic)

(16)

• Synthesis of LiBH₄starting from LiH and B has been presented for the first time

• The amorphous-like state of LiBH4 and the chemical surrounding in the as-milled samples seem to considerably reduce the decomposition temperature • A yield of formation of LiBH₄is calculated to be about 27 % by weight

(17)

Outline

(18)

100 200 300 400 500 -12 -10 -8 -6 -4 -2 0 h y d ro g e n ( w t % ) T (oC) LiBH₄ LiBH₄:CNT 0.11g:0.2g LiBH₄:CNT 0.11g:0.1g LiBH₄:CNT 0.11g:0.05g 0 50 100 150 200 250 300 350 200 210 220 230 240 250 260 B E T S u rf a c e A re a ( m 2 /g )

Ball Milling Time (min)

Liquid dispersion of LiBH

₄

in modified MWCNT

• Commercial MWCNT modified by high energy ball milling

(19)

Conclusions #3

• LiBH₄ solved in MTBE and dispersed on MWCNT show a reduced decomposition temperature with respect to the pure material

(20)