Expanding Clean Energy Research and Education Program

at the University of South Carolina

Ralph E. WhiteUniversity of South Carolina

April 13, 2007

Project ID # STP20

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

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Overview of ProjectsProject I: Low Temperature Electrolytic Hydrogen Production (Dr. John Weidner). Purpose: to

lower the cost and improve the efficiency of methods for producing hydrogen from thermal and electrical energy.

Project II: Development of Complex Metal Hydride Hydrogen Storage Materials (Dr. James Ritter). Purpose: to carry out a systematic study on the preparation, characterization and testing of new metal doped complex hydrides for reversible hydrogen storage using conventional and proprietary physiochemical processing routes.

Project V: Using EIS and RDE to Study Pt Catalyst Aging (Dr. Ralph White). Purpose: to use the electrochemical impedance spectroscopy (EIS) and the rotating disk electrode (RDE) to characterize the aging of Pt catalyst for the oxygen reduction reaction (ORR) in a polymer electrolyte membrane (PEM) fuel cell.

Project III: Hydrogen Storage Using Chemical Hydrides (Dr. Michael Matthews). Purpose: to use fundamental kinetic, chemical and thermodynamic reaction data on the novel steam + chemical hydride reaction to evaluate this technology as a means to deliver hydrogen for automotive fuel cells.

Project VI: Molecular Simulation of Hydrogen Storage Materials (Dr. Jerome Delhommelle). Purpose: to use molecular modeling to characterize the properties of new hydrogen storage materials (metal-organic frameworks, clathrate hydrates and doped complex hydrides) and to provide leads to improve them.

Project IV: Understanding Internal Air Bleed Effect on CO Poisoning in a PEMFC (Dr. John Van Zee). Purpose: to characterize and quantify the effect of internal O2 on CO poisoning (internal air bleed, to examine the effect of MEA thickness on internal air bleed, and to develop a model to explain the effect of internal air bleed and predict the anode over-potential.

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2005-2007 Total Project BudgetTotal Funding (18 mo Period Beginning 11/05)

Personnel

$1,984,000

6 co-PIs (White, Weidner, Matthews, Ritter, Van Zee and Delhommelle)2 Research Professors (Ebner and Davis)

11 PhD Students

Equipment

Materials and Supplies

Travel

XPS System and 32 Node 64 Processor Cluster

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Hybrid Sulfur Cycle

O2SO2

H2O

H2

Electrolysis

H2SO4

850o C

Heat

H2SO4Decomposition

Anode: SO2(g) + 2H2O → H2SO4 + 2 H+(aq) + 2 e-

Cathode: 2H+(aq) + 2 e- → H2(g)Overall: SO2(g) + 2H2O → H2(g) + H2SO4 E°=0.18 V

Project I: Low Temperature Electrolytic Project I: Low Temperature Electrolytic Hydrogen ProductionHydrogen Production

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Hybrid Sulfur Electrolyzer Performance

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Current Density (A/cm2)

Cel

l Vol

tage

(V)

Nafion® 115

Nafion® 212

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Exiting H2SO4 Concentrations and Model Predictions

0

1

2

3

4

5

6

7

8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Current Density (A/cm2)

H2S

O4 C

once

ntra

tion

(M)

Nafion® 115

Nafion® 212

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Objectiveintroduce new class of reversible H2 storage materials with high capacity at relatively high but still engineering temperatures based on Physiochemical Pathway and Thermal Hydrogenation Approaches

Project II: Development of Complex Metal Hydride Hydrogen Storage Materials

Approachprepare samples of materials based on Al and B complex hydride chemistry.characterize prepared samples in terms of their dehydrogenation and hydrogenation kinetics, capacity and reversibility

9J. A. Ritter, T. Wang, A. D. Ebner, J. Wang and C. E. Holland, Provisional Patent Application, filed May (2006).

70 140 210 280 350 4201.60E-008

1.80E-008

2.00E-008

2.20E-008

2.40E-008

2.60E-008

e RGA corresponding to a

b

a

c

Temperature ( oC)

Hyd

roge

n Pr

essu

re(T

orr)

d

e

0

3

6

9

12

15 a multi-catalysts (hi. loading) b multi-catalysts (mi. loading) c multi-catalysts (lo. loading) d co-catalysts(hi. loading)

Hydrogen D

esoption (wt%

)

Completely reversible materials:Temp. < 150 CH2 pres. < 1500 psig

Physiochemical Pathway ApproachNew Reversible H2 Storage Materials with High Capacity based on

Li, Al and B Complex Hydride

10

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60 80 100 120Time (Min)

Des

orbe

d H

2 (w

t.%)

1st charge WO C1st charge W C2nd charge WO C2nd charge W C

T= 500 oC

Thermal Hydrogenation ApproachLiBH4 with Al Weight Ratio of 7:3 with 4 mol% Ti and 0 or 5 wt% MWNT

11

0

1

2

3

4

5

6

7

8

9

10

200 300 400 500

Temperature (oC)

Wei

ght L

oss

(wt%

)

0.0E+00

3.0E-09

6.0E-09

9.0E-09

1.2E-08

1.5E-08

Pres

sure

(Tor

r)

1st Charged sample

Decomp. Sample

Hydrogen

Diborane

Only hydrogen detected by RGA

Thermal Hydrogenation ApproachLiBH4 with Al wt Ratio 6:4 with 4 mol% Ti and 5 wt% MWNT

12

0

2

4

6

8

10

12

0 20 40 60 80 10050

150

250

350

450

550

500oC

450oC

400oC

500oC

450oC

400oC

CTD of 77%LiBH4:23%Al Sample at 400, 450, 500 oC

Time (min)

Tem

pera

ture

(o C)

Sam

ple

Wei

ght L

oss (

wt%

)

13

1.E-07

1.E-06

1.E-05

500 1000 1500 2000 2500 3000

H2 400C

H2 450C

H2 500C

Time (sec)

Pres

sure

(tor

r)RGA of Pressure vs. Time of CTD Effluent at 400, 450, and 500oC

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Project III: Hydrogen Storage Using Chemical HydridesObjectives and Approach

• Quantify/optimize steam + solid chemical hydride reaction kinetics as the basis for production of hydrogen

• Operate reactor at low temperatures (100 –150OC) and pressures (~ atmospheric)

• Conduct basic research to minimize water utilization and maximize H2 delivery rate

• Understand the mechanism of steam hydrolysis and how it differs from aqueous hydrolysis

• Understand the role of water adsorption in the hydrolysis reaction

• Develop hydrogen storage and delivery technology based on steam hydrolysis of chemical hydrides for automotive fuel cell applications

NaBH4 + (2+x)H2O → 4H2 (g)+ NaBO2 ·x H2O + ΔHrxn

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• Reaction only occurs at low temperatures and high humidities

• The reaction does not initiate above 118oC at 50% humidity

Steam HydrolysisResults of Experimental Conditions Tested

0

10

20

30

40

50

100 110 120 130 140 150

Reaction Temperature (deg C)

% H

umid

ity

ReactionNo Reaction

N2

PT

T

N2, H2,water vapor

T

GasDrier

FM

Sat.N2 ventSaturator Condenser

FM

Heated lines

Borescope camera

Conditions Required for Initiation of Steam Hydrolysis of NaBH4

Visualization Reactor Apparatus

Glass Wool Plugs

NaBH4

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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100 200 300 400 500 600 700

time [sec]

gene

ratio

n ra

te [s

lpm

]

0

0.5

1

1.5

2

2.5

3

inte

grat

ed v

olum

e [s

l]

Hydrogen Storage Prototype Performance Data

1 part dry NaBH4

4 parts H2O(g) 110 oC

4 parts H2

1 part of NaBO2·2H2O

• Trxr = 110 oC• Avg. H2 yield = 91 %• Initial H2 generation rate = 0.38 g/s/kg NaBH4• Much higher H2 generation rates than seen in screening reactor (0.03 g/s/kg NaBH4)

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Project IV: Project IV: Understanding Internal Air Bleed Understanding Internal Air Bleed Effect on CO Poisoning in a PEMFCEffect on CO Poisoning in a PEMFC

Objectives• Characterize and quantify the effect of internal O2 on CO poisoning (internal

air bleed)• Examine the effect of MEA thickness on internal air bleed• Develop a model to explain the effect internal air bleed and predict the

anode over-potential

Conclusions• Anode polarization is decreased when the cathode back pressure is increased or

a thinner MEA is used.• The diffused oxygen (internal air bleed) shows promise to combat CO poisoning

only when thin MEA are used.• A model with internal air bleed term is developed to explain the observed effect of

cathode back pressure and to help quantify the effects on isotherms.• The model predictions of anode overpotential agree very well with the

experimental data.• The air-bleed effect is limited by the adsorption of O2 on Pt.

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Internal Diffusion through MEA = f (Pair, PCO, thickness)

Anode flow channelH2 /N2/CO and H2O

Cathode flow channelAir and H2O

Gas diffusion layer

Gas diffusion layer

MEAH2 O2

Current collector

Current collector

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CO Poisoning & Air Bleed EffectReactions Used in Model

Adsorption and Desorption

Pt + H2 ⇔ Pt-H2 kfh, bfhPt + CO ⇔ Pt-CO kfc, bfc

Electrochemical Reaction

Pt-H2 → Pt + 2H+ + 2e- kecChemical Reactions

O2 + 2CO → 2CO2

O2 + 2H2 → 2H2O

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Internal Air Bleed EffectComparison Between Model Predictions and Experimental Data with 50 ppm CO/H2

5 mm MEA 25 mm MEA

101 102 1032 3 4 5 6 7 8 2 3 4 5 6 7 8

Current density (mA/cm2)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

E H2

- EC

O/H

2 (v

olt)

50 ppm CO/H2 ,P(A/C)=101/101 kPa

50 ppm CO/H2 ,P(A/C)=101/303 kPa

P(A/C)=101/101 kPa γ=0.026P(A/C)=101/303kPa γ=0.0095

101 102 1032 3 4 5 6 7 8 2 3 4 5 6 7 8

Current density (mA/cm2)

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

E H2

- EC

O/H

2 (v

olt)

50 ppm CO/H2 ,P(A/C)=101/101 kPa

50 ppm CO/H2 ,P(A/C)=101/303 kPa

P(A/C)=101/101 kPa γ=0.094P(A/C)=101/303kPa γ=0.042

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Internal Air Bleed Effect

Overall ReactionsO2 + 2H2 → 2H2O

½ O2 + CO → CO2

Surface Reactions(1) Pt + CO ⇔ Pt-CO r1 = kf1 θM Pco - kb1 θco

(2) Pt + ½ O2 ⇔ Pt-O r2 = kf2 θM (Po2)1/2 - kb2 θo

(3) Pt-CO + Pt-O → 2Pt + CO2 r3 = kf3 θco θo

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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

θM (fraction of free sites)

0.0

0.4

0.8

1.2

1.6

2.0

2.4γN

O2 (

*10-1

0 mol

cm

-2 s

-1)

K=2.52*10-10 mol cm-2 s-1

● 25 μm MEA P(A/C)=101/101 kPa,

○ 25 μ m MEA P(A/C)=101/303 kPa,

■ 5 μ m MEA P(A/C)=101/101 kPa,

□ 5 μ m MEA P(A/C)=101/303 kPa.

0.0 0.1 0.2 0.3

θCOθM

0.0

0.4

0.8

1.2

1.6

2.0

2.4

γNO

2 (*1

0-10 m

ol c

m-2

s-1

)

Oxygen adsorption is rate limiting

for CO oxidation during Internal Air Bleed

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Project V: Using EIS and RDE to Study Pt Project V: Using EIS and RDE to Study Pt Catalyst AgingCatalyst Aging

• This work focuses on the peroxide generation in the ORR system at an RRDE in an acidic environment, as peroxide is an unfavorable side product in the cathode of the PEM fuel cells, and it causes membrane degradation.

• The phenomena of the humps and the tails shown in the RRDE experimental polarization curves will be captured in terms of the reaction mechanisms.

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Peroxide generation on different catalyst materials (a) and (b), with simultaneous 4 e- transfer reaction

i0,1=1e-9A/cm2, αc1=1.0, no peroxide reduction and decomposition

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Disk Separator Ring Protector

i0,1=1e-9A/cm2, αc1=1.0, i0,2=1e-5A/cm2, αc2=1.0,i0,3=1e-17A/cm2,αc3=0.35, no peroxide decomposition , Eappl=0.5V

Peroxide concentration distribution near an RRDE surface: simulation results with a 2-D model

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Project VI: Investigation of the Formation and Stability of Hydrogen Clathrate

Objectives• to understand the mechanism of formation of hydrogen clathrates• to evaluate the role played by additives (e.g. THF) in the

stabilization of hydrogen clathrateMethods• molecular dynamics of rare events (umbrella sampling +

order parameter)

• Hydrogen can be stored in cavities of structure II clathrates.• Lee et al. Nature, 434, 743 (2005)

CAGE A CAGE B

R. Radakrishnan et al. J. Chem. Phys. 117, 1786 (2002)J. Delhommelle et al. J. Am. Chem. Soc. 126, 12286 (2004)

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Project Safety• The most significant hydrogen hazards

associated with this project are:• High reactivity of solid chemical hydrides

when exposed to humidified air• Toxicity: Avoid ingestion or contact with eyes

and mucous membranes

• The approach to deal with this hazard is:• Handle hydrides in an inert atmosphere

within a glove box• Use small quantities for laboratory

experiments• Blanket reactor with inert gas