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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
2
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.
3
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
4
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
5
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
6
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
8
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
15
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
16
• 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
17
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)
19
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.
20
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
21
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
22
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
23
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
24
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
26
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.
27
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
28
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
30
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)
31
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
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