# Presentation: 197981

## Darlene Slattery, Ph.D.
Florida Solar Energy Center
1679 Clearlake Road
Cocoa, FL 32922
Phone: (321) 638-1449 Fax: (321) 638-1010

**Florida Solar Energy Center**
**1679 Clearlake Road**
**Cocoa, FL 32922**
**Phone: (321) 638-1449 Fax: (321) 638-1010**

**Alanates as Hydrogen Storage Compounds**

## Complex Hydrides containing AlH4-

	NaAlH4		LiAlH4	Mg(AlH4)2
	Ca(AlH4)2 	KAlH4	Ti(AlH4)4

- 	NaAlH4		LiAlH4	Mg(AlH4)2
- 	Ca(AlH4)2 	KAlH4	Ti(AlH4)4

**What are Alanates?**

## Hydrogen atoms arranged tetrahedrally around Al
Hydrogens retain significant hydride or electron-rich character
18 previously reported alanates

see hydpark.ca.sandia.gov

- Hydrogens retain significant hydride or electron-rich character
- 18 previously reported alanates
- see hydpark.ca.sandia.gov

## A.E. Finholt, A.C. Bond Jr., H.I. Schlesinger J. Am. Chem. Soc. 69, 1199-1203 (1947).

4 LiH  +  AlCl3   ether   LiAlH4  +  3 LiCl

Also noted evidence for NaAlH4 and Ca(AlH4)
   Wiberg (Angew.Chem., 65, 16 (1953)) reports Mg(AlH4)2

**4 LiH  +  AlCl****3**   **ether****   LiAlH****4****  +  3 LiCl**
- Also noted evidence for NaAlH4 and Ca(AlH4)
-    Wiberg (*Angew.Chem*., **65**, 16 (1953)) reports Mg(AlH4)2

** **

## E. Ashby, G. Brendel, H. Redman, Inorg. Chem., 2, 499  (1963). Quant. Yield in THF, 140°C, 5000 psi H2 
NaH  +  Al  +  3/2 H2          NaAlH4
Na  +  Al  +  2 H2           NaAlH4

T. Dymova, N. Eliseeva, S. Bakum, Yu. M. Dergachev, Dokl. Akad. Nauk SSSR, 215, 256 (1974). melt, 270-280°C, 2539 psi
Na  +  Al  +  2 H2            NaAlH4

**NaH  +  Al  +  3/2 H****2****          NaAlH****4**
**Na  +  Al  +  2 H****2****           NaAlH****4**
- T. Dymova, N. Eliseeva, S. Bakum, Yu. M. Dergachev, *Dokl. Akad. Nauk SSSR, ***215**, 256 (1974). melt, 270-280°C, 2539 psi
**Na  +  Al  +  2 H****2****            NaAlH****4**

**Improved Synthesis**

## T.N. Dymova, et al. Russ. J. Coord. Chem., 19(1993) 607.

MH + AlH3             MAlH4

Ball to powder ratio, 20:1
Vibration time of 3 hours

**MH + AlH****3****             MAlH****4**
- Ball to powder ratio, 20:1
- Vibration time of 3 hours

**Mechanical Alloying**

## 
Reducing agent in synthetic chemistry
		    O	                 

CH3C     OH                   CH3CH2OH

FeCl3 + 3 LiAlH4      3 LiCl + Fe.3Al + 6 H2

- Reducing agent in synthetic chemistry
**	****	****    ****O****	****    ****             **
**CH****3****C     OH                   CH****3****CH****2****OH**
**FeCl****3**** + 3 LiAlH****4****      3 LiCl + Fe****.****3Al + 6 H****2**

**Complex Hydride Uses**

##   Hydride               H2 Content
LiAlH4 			10.5
NaAlH4 		  	  7.5
KAlH4  			  5.7
Be(AlH4)2 		11.3 
Mg(AlH4)2 		  9.3
Ca(AlH4)2 		   7.7
Ti(AlH4)4 		  9.3

- LiAlH4 			10.5
- NaAlH4 		  	  7.5
- KAlH4  			  5.7
- Be(AlH4)2 		11.3
- Mg(AlH4)2 		  9.3
- Ca(AlH4)2 		   7.7
- Ti(AlH4)4 		  9.3

**Hydrogen Storage?**

## NaAlH4             1/3 Na3AlH6 +  2/3 Al  + H2 

Na3AlH6                    3 NaH  +  Al  +  3/2  H2

Dymova, et al. described multi-step decomp. but practical reversibility not demonstrated prior to 1995

**Na****3****AlH****6   ****      ****           ****3 NaH  +  Al  +  3/2  H****2**
- Dymova, et al. described multi-step decomp. but practical reversibility not demonstrated prior to 1995

**Decomposition Reaction**

## B. Bogdanovic, M. Schwickardi, U.S. Patent 6,106,801, 2000.

NaAlH4 + Ti(OBu)4             Ti-NaAlH4

NaAlH4  + TiCl4                  Ti-NaAlH4

**NaAlH****4**** + Ti(OBu)****4****             Ti-NaAlH****4**
**NaAlH****4****  + TiCl****4****                  Ti-NaAlH****4**

**Reversibility**

## NaAlH4             1/3 Na3AlH6 +  2/3 Al  + H2 

Na3AlH6                    3 NaH  +  Al  +  3/2  H2

**Na****3****AlH****6   ****      ****           ****3 NaH  +  Al  +  3/2  H****2**

## Slide 12

## Reversibility
Reversible content of doped = 3.1 - 4.2 wt% undoped = 0.5 – 0.8 wt%
Improved H2 desorption rate
Higher cycle stability
Reduction in dehydriding T by 50 OC

- Reversible content of doped = 3.1 - 4.2 wt% undoped = 0.5 – 0.8 wt%
- Improved H2 desorption rate
- Higher cycle stability
- Reduction in dehydriding T by 50 OC

**Advantages of Ti Doping**

## C.M. Jensen et al., Int. J. Hydrogen Energy, 24 (1999) 461-465.  Dry doped with Ti(OBu)4

- C.M. Jensen et al., *Int. J. Hydrogen Energy*, **24 **(1999) 461-465.  Dry doped with Ti(OBu)4

## J. Alloys and Compounds, 285 (1999) 119-122.

**H/M wt.%**

**temperature, ****o****C**

*J. Alloys and Compounds*, **285** (1999) 119-122.

## Zr inferior to Ti for NaAlH4 to Na3AlH6
Zr superior for Na3AlH6 to NaH and Al
Doping with both Zr and Ti improves overall dehydriding reaction

- Zr superior for Na3AlH6 to NaH and Al
- Doping with both Zr and Ti improves overall dehydriding reaction

**Zr as a Dopant****	**

## Use of alkoxides contaminates desorbed H2 
Weight penalty
Oxygen from decomp. of alkoxide contaminates active material

K.J. Gross, G.J. Thomas, C.M. Jensen, J. Alloys and Compounds, 330-332 (2002) 683-690.

- Weight penalty
- Oxygen from decomp. of alkoxide contaminates active material
- K.J. Gross, G.J. Thomas, C.M. Jensen, *J. Alloys and Compounds*, **330-332** (2002) 683-690.

**Difficulties Resulting from Doping Procedures**

## TiCl4  +  4 NaAlH4                Ti  +  4 NaCl + 4 Al  + 8 H2

For every mole of TiCl4 added, 4 moles of NaAlH4 consumed
4 mole of NaCl contributing to weight

- For every mole of TiCl4 added, 4 moles of NaAlH4 consumed
- 4 mole of NaCl contributing to weight

**Doping with TiCl****4**

## Ball milling of elemental Ti and NaAlH4
Kinetics of initial release better than ball milling alone
Reduction in decomp. T < for TiCl4
Rehydrides at 120 oC and 800 psi 
Subsequent dehydriding maintains content but kinetics poor 

- Kinetics of initial release better than ball milling alone
- Reduction in decomp. T < for TiCl4
- Rehydrides at 120 oC and 800 psi
- Subsequent dehydriding maintains content but kinetics poor

**Doping with Ti**

## A. Zaluska et al., J. Alloys and Compounds, 298 (2000) 125-134.
NaAlH4 ball milled with 10 wt% C
Kinetics improved over other dopants 
 Rate increases with subsequent cycles
Second step of decomp also affected but slower than first step
Rehydrog occurs under practical conditions

- NaAlH4 ball milled with 10 wt% C
- Kinetics improved over other dopants
-  Rate increases with subsequent cycles
- Second step of decomp also affected but slower than first step
- Rehydrog occurs under practical conditions

**Doping with Carbon**

## K.J. Gross, et al., J. Alloys and Compounds, 297 (2000) 270-281.
Surface localized species

V.P. Balema et al., J. Alloys and Compounds, 329 (2001), 108-114
Ti  + 4 Al      Al3Ti  + Al

- Surface localized species
- V.P. Balema et al., *J. Alloys and Compounds,* **329** (2001), 108-114
**Ti  + 4 Al      Al****3****Ti  + Al**

**Nature of Catalyst**

## D. Sun et al., J. Alloys and Compounds, 337 (2002) L8-L11.
Lattice Expansion = Substitution

- Lattice Expansion = Substitution

## Chen, et al., J. Phys. Chem. B, 105 (2001) 11214-11220.
Showed that vibrating-mill technique produces Ti-doped LiAlH4 and Li3AlH6 powders with nanocrystallites
1st decomp step at ~100 oC releases 5.3 wt%
2nd decomp step at ~135 oC releases 2.6 wt%

- Showed that vibrating-mill technique produces Ti-doped LiAlH4 and Li3AlH6 powders with nanocrystallites
- 1st decomp step at ~100 oC releases 5.3 wt%
- 2nd decomp step at ~135 oC releases 2.6 wt%

**Other Alanates – LiAlH****4**

## T.N. Dymova, et al., Russian Journal of Coordination Chem. 21(3) (1995)165-172.
Melting during decomp allows rearrangement from tetrahedral to octahedral
AlLi intermetallic compound forms

- Melting during decomp allows rearrangement from tetrahedral to octahedral
- AlLi intermetallic compound forms

**LiAlH****4**** - continued**

## Huot, et al., J. Alloys and Compounds, 383 (1999) 304-306.
NaH + LiH + NaAlH4  MA    Na2LiAlH6

B. Bogdanovic, M. Schwickardi J. Alloys and Compounds, 253-254 (1997) 1-9.
LiAlH4 + NaH    toluene/H2    Na2LiAlH6

**NaH + LiH + NaAlH****4  ****MA****    Na****2****LiAlH****6**
- B. Bogdanovic, M. Schwickardi *J. Alloys and Compounds*, **253-254** (1997) 1-9.
**LiAlH****4**** + NaH    ****toluene/H****2****    ****Na****2****LiAlH****6**

**Other Alanates– Na****2****LiAlH****6**

## Slide 26

## Morioka, et al., J. Alloy and Compounds, 353 (2003) 310-314.

KAlH4     300      1/3 K3AlH6 +  2/3 Al  + H2 

K3AlH6       340          3 KH  +  Al  +  3/2  H2

Reversible without a catalyst

**KAlH****4****     ****300**** ****     ****1/3 K****3****AlH****6**** +  2/3 Al  + H****2**** **
**K****3****AlH****6   ****    ****340****  ****        ****3 KH  +  Al  +  3/2  H****2**
- Reversible without a catalyst

**Other Alanates -  ****KAlH****4**

## M. Fichtner, O. Fuhr J. Alloys and Compounds, 345 (2002) 286-296.
2 LiAlH4 + MgX2    THF   Mg(AlH4)2 + 2 LiX
where X = Br or Cl
Forms as solvent adduct
M. Fichtner, et al., In press
Decomp. at 163 oC, rehydriding not studied

**2 LiAlH****4**** + MgX****2****    ****THF****   Mg(AlH****4****)****2**** + 2 LiX**
**where X = Br or Cl**
- Forms as solvent adduct
- M. Fichtner, et al., In press
- Decomp. at 163 oC, rehydriding not studied

**Other Alanates – Mg(AlH****4****)****2**

## Dymova et al., Russian J. of Coordination Chem. 25(5), (1999) 312-315
Does not form intermediate complex hydrides 
Mg(AlH4)2  135-155 C   MgH2* + 2 Al* + 3 H2

MgH2* + 2 Al*     300 C      0.43 Al0.93 Mg0.07 + 2.58 Al0.62Mg0.38 + H2

- Does not form intermediate complex hydrides
**Mg(AlH****4****)****2****  ****135-155 C****   MgH****2********* + 2 Al********* + 3 H****2**
**MgH****2********* + 2 Al*****     ****300 C****      ****0.43 Al****0.93 ****Mg****0.07 ****+ 2.58 Al****0.62****Mg****0.38**** + H****2**

**Mg(AlH****4****)****2**** – Cont.**

## G. Sandrock, et al., J. Alloys and Compounds, 330-332 (2002) 696-701
Contamination of resulting H2
Weight penalty from dopants
Self-heating exceeds m.p. 
Volume changes lower than conventional
Desorption kinetics (down to r.t.)

- Contamination of resulting H2
- Weight penalty from dopants
- Self-heating exceeds m.p.
- Volume changes lower than conventional
- Desorption kinetics (down to r.t.)

**Engineering Considerations**

## Future Work Needed

B. Bogdanovic, G. Sandrock, MRS Bulletin, Sept. 2002, 712-716.

- B. Bogdanovic, G. Sandrock, *MRS Bulletin, *Sept. 2002, 712-716.

## XRD and microscopic analyses have failed 
amorphous
too fine
part of alanate lattice

- amorphous
- too fine
- part of alanate lattice

- ID and Mechanism of Ti Catalyst

## Concentration on Ti, Zr, Fe, C
Is there something better
Can decomp of Na3AlH6 be improved

- Is there something better
- Can decomp of Na3AlH6 be improved

**Optimization of Catalyst**

## 
Achieving full cyclic potential
H2 content to fixed amount of Al 
More cyclic data needed
Additional techniques

- Achieving full cyclic potential
- H2 content to fixed amount of Al
- More cyclic data needed
- Additional techniques

**H****2**** Capacity and Cyclic Retention**

## What configuration should be used for alanate beds
Thermal conductivities
Expansion behavior
Potential reactions with container materials
Need to quantify safety aspects

- Thermal conductivities
- Expansion behavior
- Potential reactions with container materials
- Need to quantify safety aspects

**Engineering Data**

## Substitution in intermetallics
Li substituted for Na
Response to catalysis
Increasing plateau pressure w/o losing hydrogen capacity

- Li substituted for Na
- Response to catalysis
- Increasing plateau pressure w/o losing hydrogen capacity

**Thermodynamic Tailoring**

## Only LiAlH4 available in industrial quantities
NaAlH4 expensive
Other alanates not commercially available
Best method for catalyzing

- NaAlH4 expensive
- Other alanates not commercially available
- Best method for catalyzing

**Improved Synthesis**

## Borohydrides, BH4-
Beryllium hydrides, BeH3-
Transition metal complex hydrides
FeH64-
PdH22-
PtH42-

- Beryllium hydrides, BeH3-
- Transition metal complex hydrides
- FeH64-
- PdH22-
- PtH42-

**Other Complex Hydrides**

## Prior to Bogdanovic’s discovery, complex hydrides thought to be irreversible
NaAlH4 has been studied extensively
Data for other complex hydrides still limited
Much work remains before DOE goals are achieved

- NaAlH4 has been studied extensively
- Data for other complex hydrides still limited
- Much work remains before DOE goals are achieved

**Conclusions**