electrochemical reversible formation of alane · 2010. 6. 24. · 1 electrochemical reversible...

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Electrochemical Reversible Formation of AlaneRagaiy Zidan, Brenda García-Díaz,

Michael Martínez-Rodríguez, Joseph Teprovich

June 9, 2010

Energy Security DirectorateSavannah River National Laboratory

Project ID #: ST063

This presentation does not contain any proprietary, confidential, or otherwise restricted information

2010 DOE Hydrogen Program Review

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Overview

• Brookhaven National Laboratory

• University of Hawaii

• University of New Brunswick

• Argonne National Laboratory

Start: 10/1/06

End: In Progress

Percent complete: 90 %

• Store hydrogen required for conventional driving range (greater than 300 mi)

• Technical Targets

• System gravimetric capacity > 6%

• Storage cost < 30% of hydrogen cost

• Funding received in FY09

• $500K

• Funding for FY10

• $375K

Timeline

Budget

Barriers

Partners

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Objectives

• Develop a low-cost rechargeable hydrogen storage material with cyclic stability and favorable thermodynamics and kinetics fulfilling the DOE onboard hydrogen transportation goals.

Specific Objectives

• Avoid the impractical high pressure needed to form AlH3.

• Avoid chemical reaction route of AlH3 that leads to the formation of alkali halide salts such as LiCl or NaCl.

• Utilize electrolytic potential to translate chemical potential into electrochemical potential and drive chemical reactions to form AlH3.

Aluminum hydride (Alane - AlH3), having a gravimetric capacity of 10 wt%and volumetric capacity of 149 g/L H2 and a desorption temperature of~60°C to 175°C (depending on particle size and the addition of catalysts)has potential to meet the 2010 DOE onboard system desorption targets.

Relevance

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Known Methods to Produce Alane

A) Formation of alane from the elements:

Al + 3/2 H2 → AlH3 at 105 bar of H2 pressure

B) Traditional chemical method to produce alane:

3 LiAlH4 + AlCl3 → 4 AlH3 + 3 LiCl

3 Li+ / 3 AlH4− + Al3+ / 3 Cl−

4 AlH3

3 LiCl

Ether or THF

Thermodynamicsink

Develop a methodto avoid the

formation of halides.

LiCl

Relevance

innovative methods are needed to avoid both the high hydriding pressure of aluminum or the formation of stable by-products such as LiCl

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Electrochemical Synthesis of Alane

The electrolysis is carried out in an electrochemically stable, aprotic,and polar solvent such as THF or ether. MAlH4 (M = Li, Na) is dissolvedin this solvent, forming the ionic solution as shown below which is usedas an electrolyte.

MAlH4 / THF ↔ M+ / AlH4- / THF

Though not directed at the regeneration of alane, extensive studies onthe electrochemical properties of this type of electrolyte have beenreported.3,4

3. H. Senoh, T. Kiyobayashi, N. Kuriyama, K. Tatsumi and K. Yasuda, J. Power Sources, 2007, 164, 94–99.4. H. Senoh, T. Kiyobayashi and N. Kuriyama, Int. J. Hydrogen Energy, 2008, 33, 3178–3181.

Electrolyte

Technical Approach

Concern: Al and AlH3 will be oxidized in aqueous environment. This requires using non-aqueous approaches.

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Previous Attempts

Although many attempts in the past were made to makealane electrochemically1,2 none of these attempts haveisolated or characterized alane. These attempts werenot directed at hydrogen storage. Our group is the firstto show a reversible cycle utilizing electrochemistry anddirect hydrogenation, where gram quantities of alaneare produced, isolated and characterized.

1. N. M. Alpatova, T. N. Dymova, Y. M. Kessler and O. R. Osipov, Russ. Chem. Rev., 1968, 37, 99–114.2. H. Clasen, Ger. Pat., 1141 623, 1962.

Relevance

Our regeneration method is based on a complete cycle that uses electrolysis and catalytic hydrogenation of spent Al(s)

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Electrochemical Synthesis of Alane

Anode:

Electrode is expected to dissolve

Hydrogen bubbles at the anode

PtReaction 1: M+ + ½ H2 + e− → MH

Possible Reactions When AlH3 is Generated in a Closed Material Cycle

Reaction 1: AlH4¯ → AlH3 nTHF + ½ H2↑ + e−

Reaction 2: 3AlH4¯ + Al (Anode) → 4AlH3 nTHF + 3e−

Reaction 2: M+ + PdH (Cathode) + e− → MH + Pd

Regeneration: 2 MH + 2 Al + 3H2 → 2 MAlH4

Cathode:

Technical Approach

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Electrochemically Generated AlH3

-3 -2-2.5 -1.5V vs. SHE

I0

2 42 2.28Al H Na e NaAlH E V+ −+ + + ↔ = −

0 2.71Na e Na E V+ −+ ↔ = −

03 2 4

1 1.732

AlH H Na e NaAlH E V+ −+ + + ↔ = −

03 44 3 3 3 1.57AlH Na e NaAlH Al E V+ −+ + ↔ + = −

-3 -2-2.5 -1.5V vs. SHE

I0

2 42 2.28Al H Na e NaAlH E V+ −+ + + ↔ = −

0 2.71Na e Na E V+ −+ ↔ = −

03 2 4

1 1.732

AlH H Na e NaAlH E V+ −+ + + ↔ = −

03 44 3 3 3 1.57AlH Na e NaAlH Al E V+ −+ + ↔ + = −

Experimental and hypothetical cyclic voltammograms for the electrochemical formation ofalane. (a) A hypothetical cyclic voltammogram was formulated from the equilibrium potentialdata for possible reactions and the anticipated state of each species generated. (b) Bulkelectrolysis experiment at an aluminum wire electrode for a cell containing a 1.0 M solution ofNaAlH4 in THF at 25°C.5

5. Zidan et. al, “Aluminum Hydride: A Reversible Material for Hydrogen Storage” Chem. Commun., 2009, 3717–3719

Cyclic Voltammograms (CV)

-15

-10

-5

0

5

10

15

-3.2 -3 -2.8 -2.6 -2.4 -2.2 -2 -1.8 -1.6 -1.4 -1.2

Voltage vs SHE (V)C

urre

nt (m

A)

Limiting current ~ 9.7 mA

(a) (b)

Technical Accomplishments and Progress

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Methods have been developed to extract alane from THF. Thesemethods involve the heating and vacuum distillation of THF adductedalane solutions with subsequent crystallization of alane in toluene orother non coordinating solvents.

Aluminum electrode dissolved after an electrochemical run as expected when AlH3 is formed.5

Two grams of AlH3electrochemically generated.

5. Zidan et. al, “Aluminum Hydride: A Reversible Material for Hydrogen Storage” Chem. Commun., 2009, 3717–3719

Electrochemically generatedAlH3-TEDA


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10 20 30 40 50 60 70 800

10

20

30

40

50

60 _

XRD shows pure α-Alane

Two-Theta (deg)

Inte

nsity

(Cou

nts)

10 20 30 40 50 60 70 800

10

20

30

40

50

60 _


Two-Theta (deg)

Inte

nsity

(Cou

nts)

40

60

20

0 6020 40 802θ (deg)

Inte

nsity

(Cou

nts)

10 20 30 40 50 60 70 800

10

20

30

40

50

60 _


Two-Theta (deg)

Inte

nsity

(Cou

nts)

10 20 30 40 50 60 70 800

10

20

30

40

50

60 _


Two-Theta (deg)

Inte

nsity

(Cou

nts)

40

60

20

0 6020 40 802θ (deg)

Inte

nsity

(Cou

nts)


92

100

96

98

94

Temperature (°C)250 300100 15050 200

TG (%

)

0.0

-1.2

-0.4

-1.6

-0.8Mass Change: -9.69%

Onset: 159.4°C

DTA

(mW

/mg)

92

100

96

98

94

Temperature (°C)250 300100 15050 200

TG (%

)

0.0

-1.2

-0.4

-1.6

-0.8Mass Change: -9.69%

Onset: 159.4°C

DTA

(mW

/mg)

TGA decomposition of electrochemically generated alane releases almost full H2capacity expected in AlH3.

XRD

Raman

TGA

TGA, XRD, Ramanconfirm the product is high

purity AlH3, alane.


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H2 Release from Electrochemically Formed AlH3-TEDA Catalyzed with Ti

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120 140 160 180

Temperature (°C)

Vol

ume

(mL

)

C11H24

C11H24 + TEDA

C11H24 + AlH3-TEDA

C11H24 + AlH3-TEDA w/TiCl3

H2 release ended

H2 release started

(Undecane as solvent)


AlH3-TEDA release H2easily when catalyzed

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Storage Energy as a Percent of LHV (1 kg basis)

( )

3

23

3

3

3 2

:

61.2 kJ 33.3 mol AlH 10 kg AlH 1 kWhmol AlH kg AlH

kJ61.2mol AlH

kWh 5.66kg Hkg H 3,600 kJ

= =

= =

ocellEnergy InpIdeal

Ideal Cost

ut nF E

Ideal 10033.3 kW5.66 1

hkWh 7%= =x

2 2

kWh 5. 1 = kWh: 6 8.32kg 6

6H8%kg H

Actu Energy Ia nputl =

10033.3 8

k.3

Wh2 kWhActual 25%= =x

Feasibility of Electrochemical Synthesis of Alane

68% is based on overpotential value

Energy Consumption Relative to Energy Stored Efficiency

Actual % 75=

Ideal 83%=


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Ideal 10033.3 kW5.66 1

hkWh 7%= =x

10033.3 8

k.3

Wh2 kWhActual 25%= =x

Efficiency and Energy lossesEnergy Consumption

Relative to Energy StoredEfficiency

Actual % 75=

Ideal 83%=

The above relative energy consumption is only the energy consumed by the electrochemical cell (dos not include AlH3 separation via heating and vacuuming)

Goal is for energy consumption relative to energy stored not to exceed 30% (narrow margin)

Higher efficiency is sought for all possible steps of the process (electrochemical cell, yield and AlH3 separation)


Achieving higher efficiencies in every step of the regeneration is ongoing effort

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Electro-Catalytic Additive (ECA)to Increase Yield

Electrochemical cells producing AlH3 with and without ECA. Also very small amount of dendrites.

With ECA

Before

Before

After

After

Without ECA

The use of the ECA increased the amount of AlH3 produced in the cell.

Visual Observation of Higher Yield


Increase Yield

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The bulk electrolysis to produce alane show that cell 2 has almost two times of thetotal charge and the amount of AlH3-TEDA as compared to cell 1. An 80% increase incurrent was observed after the current is steady.

Effect of ECA on the Production of Alane

ECA increased current and alane yield


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The open circuit voltage (OCV) for cell 2 is shifted to -1.5 V from the original cell 1 (OCV = -1.9). This means that the overpotential required for cell 2 is less when performing theelectrolysis at 2.1 V. Consequently, lower energy is required for cell 2 to produce AlH3, whichimplies that cell 2 is more efficient because it has more current with less voltage input.

CVs Showing Effect of ECA

ECA improves cell efficiency.


Without ECA 75%With ECA 78%

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Electrochemical impedance spectroscopy(EIS) was performed on the cells with andwithout the ECA. The resistance for bothcells is ~112 Ωcm2. This shows that theECA does not have a significant effect inthe resistance (or conductivity) of thesolution. That is, the ECA is not acting asan electrolyte. Consequently, the increasein current and efficiency shown previouslyare an electro-catalytic effect of the addedspecies.

0

10

20

30

40

100 110 120 130 140

Re (Z) / Ω cm2

-Im

(Z) /

Ω c

m2

LiAlH4 + ECA in THFLiAlH4 in THF

f = 105 Hz

f = 103 Hz

Impedance Showing Effect of ECA

Results indicate that the ECA does not act

as an electrolyte but rather as a catalyst


ECA Function:

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H2 Pressurized Electrochemical Cell


Higher Efficiency AlH3 Separation

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Higher Efficiency AlH3 Separation CellTechnical Accomplishments and Progress

New Modified System

Digital pressure transducer

Analog pressure transducer

K-type thermocouple

Electrodes

Valve to vent

Valve bubbler

1

Alane Generation Reversible Cycle

Proposed reversible cycle for alane. All components of the electrochemicalprocess can be recycled to continually afford a viable solid-state storagematerial.


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Summary

Continued to produce gram quantities of alane with high purity.

LiAlH4 was also used to produce alane and shows higher efficiency

An electro-catalytic additive was discovered and found to greatly enhance the process.

Started Improving efficiencies in every step of the regeneration method and achieved success

Yield was increased and higher electrochemical cell efficiency was achieved

A pressurized ECC is being constructed for close material regeneration cycle and the use of more efficient separation.

Very small amount of dendrites.

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Proposed Future Work

Examine catalysts in accelerating formation and regeneration- Started

Advanced Analytical Methods

Use other techniques (e.g. NMR, Prompt Gamma Activation Analysis (PGAA, In Situ neutron and Raman) to quantify and characterize AlH3-On going

Optimization and Scale-Up Electrolytic Cell

Develop closed and efficient AlH3 extracting system based on new solvents-Started

Optimize all parameters needed for producing several grams of AlH3efficiently-On going

Explore, reversibly, forming other high capacity complex hydrides such as Mg and Ca based complex hydrides using electrochemical methods

Design and construct a lager electrochemical cell capable of producing larger quantities of AlH3

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Acknowledgements and Collaboration

• Doug Knight

• Long Dinh

• Christopher Fewox

• Jennifer Pittman

• Ashley C. Stowe

• Andrew G. Harter

• Joshua Gray

• Rob Lascola

• Don Anton

• Ted Motyka

• Joe Wheeler

• Jason Graetz, James Wegrzyn and Jim Reilly (BNL)• Craig Jensen (University of Hawaii)• Sean McGrady (University of New Brunswick)• Rana Mohtadi and Sivasubramanian PremKumar (Toyota)• Rosario Cantelli (Università di Roma)

• Ned Stetson (US-DOE)

SRNL:

Collaboration:

electrochemical reversible formation of alane · 2010. 6. 24. · 1 electrochemical reversible...

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