Hubert Gasteiger at BASF Science Symposium 2015
Transcript of Hubert Gasteiger at BASF Science Symposium 2015
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 1
Electromobility – Batteries or Fuel Cells?
battery electric vehicles (BEVs) BEV constraints Li-ion battery projections Li-O2 batteries
fuel cell electric vehicles (FCEVs) performance attributes catalyst performance / aging
BEVs vs. FCEVs
Technical Electrochemistry, Chemistry DepartmentTechnische Universität München
H.A. Gasteiger
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 2
Electromobility = car + … + … demand: lowered/zero fossil fuel consumption
significant reduction of CO2 emissions
life-cycle CO2 savings × market-penetration = societal benefit
generationdistribution& storage
electricityhydrogen
use
Electromobility
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 3
BEV Battery Weight & Cost
projected performance of today’s LiB technology: - 0.20 kWh/kgbattery-pack*)
- 95% discharge efficiency- 80% state-of-charge range- 250 €/kWhname-plate
**)
**) “Transitions to Alternative Transportation Technologies – Plug-In Hybrid Electric Vehicles”, National Research Council (2010); see: www.nap.edu/catalog/12826.html
*) F.T. Wagner, B. Lakshmanan, M.F. Mathias; J. Phys. Chem. Lett. 1 (2010) 2204
energy required for small 4-passenger car: - 0.10 kWh/km*)
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 4
BEV Battery Weight & Cost
projected performance of today’s LiB technology: - 0.20 kWh/kgbattery-pack*)
- 95% discharge efficiency- 80% state-of-charge range- 250 €/kWhname-plate
**)
**) “Transitions to Alternative Transportation Technologies – Plug-In Hybrid Electric Vehicles”, National Research Council (2010); see: www.nap.edu/catalog/12826.html
*) F.T. Wagner, B. Lakshmanan, M.F. Mathias; J. Phys. Chem. Lett. 1 (2010) 2204
energy required for small 4-passenger car: - 0.10 kWh/km*)
150 km range 500 km range
required net energy: 15 kWhnet 50 kWhnet
required name-plate energy: 20 kWhname-plate 66 kWhname-plate
battery weight: 100 kg 330 kgbattery cost: 5000 € 16500 €
currently: ≈250-300 €/kWhname-plate & 0.15 kWh/kgbattery-pack
→ market penetration limited by “range anxiety” ?
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 5
Range Extension – Approaches
multiple potential pathways within different disciplines
multi-variate problem with many inter-dependencies !
Vehicle Components & Design
Energy Conversion& Storage
post-LiBs
light-weight matls. adv. cooling/heating electric drive effic.
Wh ↑Management & MobilityConcepts
integrated mobilityconcepts
Energy Management
rapid charging
Wh/km ↓range ↓
“range” ↑
Vehicle Components & Design
Energy Conversion& Storage
post-LiBs
light-weight matls. adv. cooling/heating electric drive effic.
Wh ↑Management & MobilityConcepts
integrated mobilityconcepts
Energy Management
rapid charging
Wh/km ↓range ↓
“range” ↑
H2-fuel cells
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Commercial Approach premium cars → ≈150 km range & 150 km/h (150 PS; 0 → 100 km/h in 7s)
→ technical data: - carbon-composite chassis (enables 0.13 kWh/km)- 19 kWh lithium-ion battery- charging: - possible in 0.5 hours (40 kW))
- ≈6-8 hours (3 kW)
limited range also for premium cars
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 7
Range Extension – Approaches
Vehicle Components & Design
Energy Conversion& Storage
post-LiBs
light-weight matls. adv. cooling/heating electric drive effic.
Wh ↑Management & MobilityConcepts
integrated mobilityconcepts
Energy Management
rapid charging
Wh/km ↓range ↓
“range” ↑
Vehicle Components & Design
Energy Conversion& Storage
post-LiBs
light-weight matls. adv. cooling/heating electric drive effic.
Wh ↑Management & MobilityConcepts
integrated mobilityconcepts
Energy Management
rapid charging
Wh/km ↓range ↓
“range” ↑
H2-fuel cells
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 8
Rapid Charging
charging time:
from:E.ON presentationat the IAS Openingby J. Eckstein (Oct., 2010)
rapid charging: - reduced charging efficiency (iR-drop, etc.) & durability issue- questionable business case for electric utilities→ 5 min. re-charge not feasible
tcharging = kWhbattery / kWsupply → ≈66 kWh in 5 mins. ≡ 0.8 MW !
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 9
Range Extension – Approaches
Vehicle Components & Design
Energy Conversion& Storage
post-LiBs
light-weight matls. adv. cooling/heating electric drive effic.
Wh ↑Management & MobilityConcepts
integrated mobilityconcepts
Energy Management
rapid charging
Wh/km ↓range ↓
“range” ↑
Vehicle Components & Design
Energy Conversion& Storage
post-LiBs
light-weight matls. adv. cooling/heating electric drive effic.
Wh ↑Management & MobilityConcepts
integrated mobilityconcepts
Energy Management
rapid charging
Wh/km ↓range ↓
“range” ↑
H2-fuel cells
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 10
battery electric vehicles (BEVs) BEV constraints Li-ion battery projections Li-O2 batteries
fuel cell electric vehicles (FCEVs) performance attributes catalyst performance / aging
BEVs vs. FCEVs
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Li-Ion Battery Limits
F.T. Wagner, B. Lakshmanan, M.F. Mathias; J. Phys. Chem. Lett. 1 (2010) 2204
specific energy [Wh/kg] of LiNi1/3Mn1/3Co1/3O2 / Graphite (+/-)→ active-materials: ≈0.45 kWh/kgactive-materials
NMC/Graphite limit of ≈0.20 kWh/kgbattery-system
through engineering design & product development
specific energy of the battery system→ battery managements, sensors, cooling, …
specific energy of cells→ includes weight of:
- separator (porous electrolyte-filled polymer)- electrolyte (organic solvents + Li-salt)- negative current collector (copper)- positive current collector (aluminum)
≈0.3 kWh/kgcell
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Advanced LiB Materials
from: K.G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu, V. Srinivasan; Energy Environ. Sci. 7 (2014) 1555
Si-anodes & HV/HE-cathodes:up to 0.25 kWh/kgbattery-pack projected
Li-anodes & HV/HE-cathodes:up to 0.30 kWh/kgbattery-pack projected
advanced LiBs: ≈1.5-fold gainover current 0.2 kWh/kg benchmark
→ cycle-life with Li & Si anodes ?→ stability of HV-electrodes ?
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4/21/2015
- EC-only electrolyte [1] → low signal background in mass spec- 13C labeled EC (E13C) → C and EC corrosion at different m/z
conductive carbon (“SuperC65”) stability study via on-line mass-spectrometry:
TO OEMS [2] →
CELL INLETCELL OUTLET
TWO-COMPARTMENT CELL
NORMAL ELECTROLYTE
CO2
ELECTRODE
CARBON
13C-LABELED ELECTROLYTE
H2O IN ELECTROLYTE
HIGH VOLTAGE
PHENOMENON
[1] M. Nie, B.L. Lucht; J. Electrochem. Soc. 161 (2014) A1001
E13C + H2O → 13CO2 + …ELECTROLYTE OXIDATION
12C + 2H2O → 12CO2 + 4H+ + 4e- [3]CARBON CORROSION
[3] L.M. Roen, C.H. Paik, T.D. Jarvi; Electrochem. & Solid-State Lett. 7 (2004) A19[2] N. Tsiouvaras, S. Meini, I. Buchberger, H.A. Gasteiger; J. Electrochem. Soc. 160 (2013) A471
CALIBRATED CAPILLARY LEAK (1 µl/min)
Carbon Stability in HV-Cathodes
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SuperC65 & EC Stability at 5.0 VLi
from: M. Metzger, C. Marino, J. Sicklinger, D. Haering, H.A. Gasteiger; J. Electrochem. Soc. (2015) in press.
oxidation rates of C ( ≡ 12CO2 + 12CO)& EC ( ≡ 13CO2 + 13CO)
→ anodic oxidation enhanced by H2O(via initial contamination or permeation)
at ≥40ºC: insufficient long-term stabilityof EC & conductive carbon
→ C-coatings less durable
→ improved electrolyte and/or additives
C & EC weight-loss over 100h at 5.0V:
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battery electric vehicles (BEVs) BEV constraints Li-ion battery projections Li-O2 batteries
fuel cell electric vehicles (FCEVs) performance attributes catalyst performance / aging
BEVs vs. FCEVs
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Energy Density Projections
from: K.G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu, V. Srinivasan; Energy Environ. Sci. 7 (2014) 1555
system-based energy densities:- closed system: O2 pressure vessel- open system: air clean-up
no gain in Wh/L if compared toSi/LMRNMC (Li-rich NMC, HE-NMC)& maximum 1.5x gain in Wh/kg (Li/O2 assumes stable Limetal-anode)
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Li-Air Cycle Life
from: M.M.O. Thotiyl, S.A. Freunberger, Z. Peng, Y. Chen, Z. Liu, P.G. Bruce; Nature Materials 12 (2013) 1050
100’s of cycles in several literature report → usually limited to partial discharge
long cycle-life & high capacities, but sometimes difficult to reproduce → need more fundamental insights
TiC cathode:in DMSO + 0.5M LiClO4
SuperP/C-Paper:LiCF3SO3 in TEGDME (1:4)from: H.-g. Jung, J. Hassoun, J.-B. Park, Y.-K. Sun, B. Scrosai; Nature Chemistry 4 (2012) 579
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Discharge (O2 reduction)
Li+
Li+
O2 + e− O2•−
e-
e-
electrolyte degradation products
Li2O2Li2O
Li2CO3
LiOH ?
O2
CO2, C
H2O
Li-O2 Discharge/Charge Reactions
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Discharge (O2 reduction)
Li+
Li+
O2 + e− O2•−
e-
e-
electrolyte degradation products
Li2O2Li2O
Li2CO3
LiOH ?
O2
CO2, C
H2O
Li-O2 Discharge/Charge Reactions
Charge (O2 evolution)
O2
ideally: O2, evolved ≡ O2, consumed
→ no parasitic reactions
Li2O2
Li2OLiOHLi2CO3
O2
see: S. Meini, N. Tsiouvaras, K.U. Schwenke,M. Piana, H. Beyer, L. Lange, H.A. Gasteiger;Phys. Chem. Chem. Phys. 15 (2013) 11478
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Li/O2 Charge/Discharge: O2 Recovery
from: N. Tsiouvaras, S. Meini, I. Buchberger,H.A. Gasteiger, J. Electrochem. Soc. 160 (2013) 471
2.0
2.5
3.0
3.5
4.0
0 1 2 3 4 5 cycle number
elec
tron
s/O
2
50
55
60
65
70
75
80
85
90
95
100
O2 r
ecov
ery
[%]
via on-line mass-spectrometry:
≈20-30% „missing“ O2 due toside reactions during charge/discharge→ reaction with electrolyte/carbon
from: B.D. McCloskey, D.S. Bethune, R.M. Shelby, T. Mori, R. Scheffler, A. Speidel, M. Sherwood, A.C. Luntz; J. Phys. Chem. Lett. 3 (2012) 3043
→ similarly high e-/O2 in most studies:- in NMP and DMSO
(C.J. Bondue, A.A. Abd-El-Latif, P. Hegemann, H. Baltruschat;J. Electrochem. Soc. 162 (2015) A479)
- with Pt, Au, or MnO2 cathodes (DME/LiTFSI)(B.D. McCloskey et al., JACS 133 (2011) 18038& C. Kavakli et al., ChemCatChem 5 (2013) 1)
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recently proposed new electrolyte:
Alternative Electrolytes: DMDMB
(B.D. Adams, R. Black, Z. Williams, R. Fernandes, M. Cuisinier, E.J. Berg, P. Novak, G.K. Murphy,L.F. Nazar; Adv. Energy Mater. (2014) 1400867)
→ CH3-groups prevent β-H abstraction
→ cycle-life & 1H-NMR suggest improved stability
→ OEMS (0.25 mA charge): ≈3.9 e-/O2
no O2 reversibility, despite high cycle-life→ stable electrolyte/cathode critical for Li-O2
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battery electric vehicles (BEVs) BEV constraints Li-ion battery projections Li-O2 batteries
fuel cell electric vehicles (FCEVs) performance attributes catalyst performance / aging
BEVs vs. FCEVs
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Fuel Cell Electric Vehicle Constraintssince ≈2008: 500 km range 70 MPa H2 (4-6 kgH2 at 5%wt) with refuelling <5 mins.
catalyst cost & supply (100kW car):current: ≈0.5 gPt/kW ≡ 50gPt/car
→ >10x vs. automotive emission catalysts
long-term: <0.1gPt/kW ≡ <10gPt/car → large-scale commercial viability
H2 generation & distribution infrastructure...
catalyst durability:≈4000 h vs. 5000 h target → advanced catalysts & controls
challenge: improved Pt catalysts or non-Pt catalystsfrom: Fuel Cell Technology Status AnalysisProject; Fact Sheet (Dec. 2014);http://www.nrel.gov/docs/fy15osti/62944.pdf
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H2/Air PEMFC – Processes / Electrodes
→ 60% void volume(dpore ≈50-100nm)
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H2/Air PEMFC Performance
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.0 0.3 0.6 0.9 1.2 1.5 [A/cm2]
Vol
tage
(V)
Ecell
ηHFR=90 mV (ηmem=30 mV)
ST19-S0559 (Nano-x coating) RC FCPM op-line
MEA: Gore 5720 (18 µm, 0.2/0.3 mgPt/cm2, I/C=1.2)DM/MPL: Pre-compressed SGL 25BC
ηtx,O2(dry)=26 mV
ηORR=410 mV
ηtx,H+ =18 mV
ηtx,O2(wet)=18 mV
H2/air (s=1.5/2), 150kPaabs, <50% RHinlet≈25µm membrane and ≈0.05/0.4mgPt/cm2
MEA
( 60 mV Rcontact)
from: W. Gu, D.R. Baker, Y. Liu, H.A. Gasteiger, in: Handbook of Fuel Cells, Wiley (2009): vol. 6, pp. 631.
( ηHOR < 5 mV*) )
undefined losses, ηtx,O2(wet), of only ≈20mV→ improvements require new materials
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H2/Air PEMFC Performance
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.0 0.3 0.6 0.9 1.2 1.5 [A/cm2]
Vol
tage
(V)
Ecell
ηHFR=90 mV (ηmem=30 mV)
ST19-S0559 (Nano-x coating) RC FCPM op-line
MEA: Gore 5720 (18 µm, 0.2/0.3 mgPt/cm2, I/C=1.2)DM/MPL: Pre-compressed SGL 25BC
ηtx,O2(dry)=26 mV
ηORR=410 mV
ηtx,H+ =18 mV
ηtx,O2(wet)=18 mV
kWg
cmW
cmmg
Pt
MEA
MEA
Pt
5.09.0
45.0
2
2
=
→ at 1.5 A/cm2:
H2/air (s=1.5/2), 150kPaabs, <50% RHinlet≈25µm membrane and ≈0.05/0.4mgPt/cm2
MEA
( 60 mV Rcontact)
from: W. Gu, D.R. Baker, Y. Liu, H.A. Gasteiger, in: Handbook of Fuel Cells, Wiley (2009): vol. 6, pp. 631.
( ηHOR < 5 mV*) )
undefined losses, ηtx,O2(wet), of only ≈20mV→ improvements require new materials
need 10x better ORR catalysts to reach 0.05/0.04 mgPt/cm2MEA → ≈0.1 gPt/kW
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Pt Savings through High-Power Density
Toyota Mirai (2015): increase of power density from ≈0.9 to ≈1.5 W/cm2
→ decrease gPt/kW by ≈1.5-fold
requires improved mass-transport concepts (cascaded bipolar plate)
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battery electric vehicles (BEVs) BEV constraints Li-ion battery projections Li-O2 batteries
fuel cell electric vehicles (FCEVs) performance attributes catalyst performance / aging
BEVs vs. FCEVs
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 29
Fuel Cell Cathode Catalyst Options
high mass activity [A/mgPt ] of Pt-based catalysts: → cost limited: need ultra-high TOF to meet gPt/kW
high volumetric activity [A/cm3electrode ] of non-Pt catalysts:
→ electrode thickness limited: need Pt-like turnover frequency (TOF)
TOF at 0.8V RHE 5)
(80°C, 100kPa O2)
4) H.A. Gasteiger & N.M. Marković, Science 324 (2009) 48
→ Fe/N/C based catalysts1)
→ nano-structured thin-films2)
& de-alloyed Pt-alloys3)
1) M. Lefèvre, E. Proietti, F. Jaouen, J.-P. Dodelet, Science 324 (2009) 71
→ shape-controlled Pt-alloys4)
3) K.C. Neyerlin, R. Srivasta, C. Yu, P.Strasser, J. Power S. 186 (2009) 261
2) M.K. Debe, A.K. Schmoeckel, G.D. Vernstrom, R. Atanasoski,
J. Power S. 161 (2006) 1002
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Pt-Based ORR Catalysts – Status de-alloyed Pt-alloys (e.g., Strasser group TUB)1)
1) M. Oezaslan, F. Hasché, P. Strasser; J. Phys. Chem. Lett. 4 (2013) 3273
→ ≈5-fold mass-activity enhancement for core/shell-type nanoparticles
shape-controlled Pt-alloys (e.g., Markovic/Stamenkovic group at ANL)2
2) C.Chen, Y. Kang, Z. Huo, Z. Zhu, W. Huang, H.L. Xin, et al., Science (2014), doi: 10.1126/science.1249061
Pt3Ni octahedra → Pt3Ni nanoframes
→ highest A/mgPt for C-supported catalysts so far
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Aging: Pt-Dissolution / Particle Growth
E/RHE [V]
Pt-foil, 196°C (H3PO4)
Pt/C, 80°C (H2SO4)
80°C Pourbaix (est.)
25°C Pourbaix
Pt dissolution during voltage cycling1)
1) P.J. Ferreira. G.J. la O’, Y. Shao-Horn, D. Morgan, R. Makharia, S.S. Kocha, H.A. Gasteiger, J. Electrochem. Soc. 152 (2005) A2256
→ Ostwald-ripening (nm) & diffusion (µm)
H2 + Pt2+
↓Pt + 2H+
membrane
carbonsupport
Pt Pt
Pt PtPt
Pt
Pt
Pt
PtPt
carbonsupport
Pt Pt
PtPt
PtPt
carbonsupport
PtPt
Pt2+
Pt Pt
H2
anod
e
Pt
Pt
≈10µm
timetime
cathode/DM interfacememb./cath. interf.
Diff
usio
n M
ediu
m (D
M)
cathode
Ptcarbonsupport
H2 + Pt2+
↓Pt + 2H+
membrane
H2 + Pt2+
↓Pt + 2H+
membrane
carbonsupport
PtPt PtPt
PtPt PtPtPtPt
PtPt
PtPt
PtPt
PtPtPtPt
carbonsupport
Pt Pt
PtPt
PtPt
carbonsupport
PtPt
PtPt PtPt
PtPtPtPt
PtPtPtPt
carbonsupport
PtPtPtPt
Pt2+
PtPt PtPt
H2
anod
e
PtPt
PtPt
≈10µm
timetimetimetime
cathode/DM interfacememb./cath. interf.
Diff
usio
n M
ediu
m (D
M)
cathode
PtPtcarbonsupportcarbonsupport
µm-scale Pt diffusion into ionomer
µm-scale Pt diffusion into ionomer
nm-scale Pt sintering on carbon
nm-scale Pt sintering on carbon
→ similar process for Pt-alloys ?
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processes: - Pt dissolution → re-deposition on particles or in membrane- Co dissolution → re-deposition thermodynamically not possible
from: S. Chen, H.A. Gasteiger, K. Hayakawa, T. Tada,Y. Shao-Horn; J. Electrochem. Soc. 157 (2010) A82
hybridization with high-power battery to minimize Pt-dissolution
Aging: Pt-Dissolution / Particle Growth
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Aging: Carbon Support Oxidation “start/stop” induced carbon-support oxidation: C + 2 H2O → CO2 + 4 H+ + 4 e-
air (O2)
air (O2)H2 start-upstart-up shutdownshutdown
≈1.4 - 1.6V≈1.4 - 1.6V≈1V≈1V air (O2)
anode
cathode
H2/air front at τ = 1.3s(80°C/66%RHin & 150kPaabs)
carbon-support instability largely addressed by system mitigation
e.g., T.A. Greszler, G.M. Robb, J.P. Salvador, B. Lakshmanan, H.A. Gasteiger; US 8,580,445 (2013)
200 nm
200 nm
new cathode: after start/stop:
→ 10-100x improvements:- short front times (≈0.1s)- partial stack-shorting at start/stop
→ 40,000 projected start/stops !
→ slow H2 bleed & recirculation→ <400 start/stops with H2/air-front
from: R.N. Carter, W. Gu, B. Brady, P.T. Yu, K. Subramanian, H.A. Gasteiger; Handbook of Fuel Cells; Wiley (2009) p. 829
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battery electric vehicles (BEVs) BEV constraints Li-ion battery projections Li-O2 batteries
fuel cell electric vehicles (FCEVs) performance attributes catalyst performance / aging
BEVs vs. FCEVs
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for >200 km range: BEVs with advanced batteries or FCEVs
Fuel Cells or Batteries ? comparison of the storage/conversion system mass
- battery: 0.20 kWh/kgbattery-system (80% battery utilization; 95% efficiency)- fuel cell: 70 MPa H2 and hybrid-battery
BEV
FCEV
BEV
FCEV
BEV
FCEV
150 km 500 km
from: F.T. Wagner, B. Lakshmanan, M.F. Mathias; J. Phys. Chem. Lett. 1 (2010) 2204
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Summary & Acknowledgements
• fuel cell electric vehicles offer large range → requires improved catalysts→ renewable H2 generation & distribution infrastructure…
• battery electric vehicles → ≈150-200 km range with today’s LiB technology, ≈300 km feasible long-term→ 5 minute charging likely not feasible
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Backup Slides
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 38
H2
H2O
O2H+
fast kinetics,1
≤ 0.05 mgPt/cm2slow kinetics
≈ 0.4 mgPt/cm2
H2-ox (HOR) @ anode
O2-red. (ORR) @ cathode
1) K.C. Neyerlin, W.B. Gu, J. Jorne, H.A. Gasteiger, J. Electrochem. Soc. 154 (2007) B631
Improved HOR catalyst for AMFCs!
mechanistic differences ?
2) W. Sheng, H.A. Gasteiger, and Y. Shao-Horn, J. Electrochem. Soc. 157 (2010) B1529
slow kinetics,inexpensive catalysts
slow kinetics,2
>> 0.05 mgPt/cm2
H2
H2O
OH− O2
Kinetics in PEMFCs and AMFCs
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H2 Oxidation/Evolution: Acid vs. Base
1) J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz, H.A. Gasteiger; Energy Environ. Sci. 7 (2014) 2255
HOR/HER on C-supported metals:→ ≈100-fold activity loss in base for all Pt-metals
→ analysis suggests increased M-H bond strength1)
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HOR Mechanism: Acid vs. Base
1) D. Strmcnik, M. Uchimura, C. Wang, R. Subbaraman, N. Danilovic, D. Van der Vliet, A.P. Paulikas, V. Stamenkovic, N. Markovic; Nat. Chem. 5 (2013) 300
acid: H2 ↔ 2H+ + 2e-
base: H2 + 2OH- ↔ 2H2O + 2e-
overall reaction:
e.g., Tafel-Volmer mechanism:
Tafel: H2 ↔ 2Had
Volmer-acid: Had ↔ H+ + e-
Volmer-base: Had + OH- ↔ H2O + e-
→ acid/base differences rationalized by additional OH-nucleation step in base→ more hydrophilic surfaces suggested to be more active (e.g., Ir > Pt)1)
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HOR Mechanism: Acid vs. Base
1) D. Strmcnik, M. Uchimura, C. Wang, R. Subbaraman, N. Danilovic, D. Van der Vliet, A.P. Paulikas, V. Stamenkovic, N. Markovic; Nat. Chem. 5 (2013) 300
acid: H2 ↔ 2H+ + 2e-
base: H2 + 2OH- ↔ 2H2O + 2e-
dissoc.: 2H+ + 2OH- ↔ 2H2O
overall reaction:
e.g., Tafel-Volmer mechanism:
Tafel: H2 ↔ 2Had
Volmer-acid: Had ↔ H+ + e-
dissoc.: H+ + OH- ↔ H2OVolmer-base: Had + OH- ↔ H2O + e-
→ acid/base differences rationalized by additional OH-nucleation step in base→ more hydrophilic surfaces suggested to be more active (e.g., Ir > Pt)1)
→ no obvious reason, why fundamental steps in acid and base should be different
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 42
→ carbon blacks (e.g., Super C65) as conductive additives
Example: LiCoPO4Spinel Oxides [2]Olivine Phosphates [1]
LiMPO4 (M = Fe, Co, Mn)High voltage spinel:
LiNi0.5Mn1.5O4 (LNMO)
[1] S. Wittingham, Chem. Rev. 104 (2004) 4271[2] D. Liu, RCS Adv. 4 (2014) 156
HV-Materials
stability of carbon-blacks & carbon-coatings at 5 VLi and effect of T and cH2O ?
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 43
(K. U. Schwenke et al., PCCP 15 (2013) 11830)C-electrode: 0.2 M LiTFSI in glymes
enhanced discharge capacity by contaminated/oxidized solvents and/or water
Effect of Contaminants
various contaminants avoid/delay surface passivation during discharge→ in pure electrolytes: passivating ≈2 ML thick films (≈500 µC/cm2
carbon )
0 500 1000 1500 2000 2500 30002.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
DME
PC/DME 2/1
1000 ppm H2O cont. DME
Cel
l Vol
tage
/ V
vs.
Li+ /L
i
Specific Capacity / mAhg-1carbon
H2O saturated O2 (2-3% vol. at RT)
0.1 M LiClO4 in DME, DME+H2O, and PC/DME( S. Meini et al., Electrochem. Solid-State Lett. 15 (2012) A45)
(S. Meini et al., J. Electrochem. Soc. 159 (2012) A2135)
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 44
(S. Meini et al., Electrochem. Solid-State Lett. 15 (2012) A45)
4000 3500 2000 1500 1000
0.2 M LiTFSI in diglyme
0.01 Abs
0.2 M LiTFSI in diglyme with water
0.001 Abs
Li2CO3 contamination LiOH
Abso
rban
ce
Wavenumber (cm-1)
Li2O2
10 11 12 13 14 15 16 17 18 19
LiOH*H2O
Li2O2
Al
Inte
nsity
/ a.
u.2θ / degree
0.2 M LiTFSI in diglymewith water
→ XRD & FTIR analysis of electrodes reveal Li2O2 and no/little LiOH
water effect in Li-O2 cells ?
initially assumed LiOH formation with H2O: 4Li+ + 4e– + H2O + O2 → 4LiOH
Li/O2 Discharge with 1% H2O
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 45
photometric titration using yellow [Ti(O2)]2+ complex
Li2O2 Discharge Yield with H2O
water substantially increases Li2O2 yield→ higher yield at faster rates ( ≡ shorter exposure time)
from: K.U. Schwenke et al., J. Electrochem. Soc. (2015) in press
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 46
previous observations: large Li2O2 crystals at low discharge rates
from: K.U. Schwenke et al., J. Electrochem. Soc. (2015) in press
Li/O2 Discharge: Li2O2 Morphology
(B.D. Adams et al., Energy Environ. Sci. 6 (2013) 1772)
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 47
previous observations: large Li2O2 crystals at low discharge rates
from: K.U. Schwenke et al., J. Electrochem. Soc. (2015) in press
Li/O2 Discharge: Li2O2 Morphology
(B.D. Adams et al., Energy Environ. Sci. 6 (2013) 1772)
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 48
previous observations: large Li2O2 crystals at low discharge rates
from: K.U. Schwenke et al., J. Electrochem. Soc. (2015) in press
Li/O2 Discharge: Li2O2 Morphology
Li2O2 crystal growth only with H2O or H+
(B.D. Adams et al., Energy Environ. Sci. 6 (2013) 1772)
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 49
Fuel Options for Low-T Fuel Cells
• liquid fuels- direct methanol oxidation: low power density & high gnoble-metal/kW - hydrocarbon/alcohol reforming: low efficiency, startup energy loss
• H2+tank storage capacitykWh/kg kWh/l
*) based on the density of liquefied gas(from: P. Piela and P. Zelenay, Fuel Cell Review 1 (2004) 17)
(A. Bouza et al., DOE Annual Hydrogen Program Review (2004))
→ for 500km range (≈5 kgH2): ≈100 kg/≈150 l tank
+ tank
- 1.9 kWh/kgH2+tank ≡ ≈5%wt. H2 → 20 kg/kgH2
- 1.3 kWh/lH2+tank → 30 l/kgH2
70 MPa H2 tank:
03/10/2015 Hubert Gasteiger — Chair of Technical Electrochemistry page 50
Formation of Core/Shell Particles voltage-cycled Pt0.5Co0.5 particles
→ rPt increases by ≈1.5 nm: ≈1.5 nm Pt-skin ?→ spot-resolved EDS (dsampling ≈ 2.5nm)
× × × ×× × × ×
10 nm 10 nm
a) near membrane interface b) in cathode center
× × × ×× × × ×
10 nm 10 nm
a) near membrane interface b) in cathode center
→ formation of Pt(-rich) skins
Pt-alloys become more Pt-like
→ loss of specific activity
from: S. Chen, H.A. Gasteiger, K. Hayakawa, T. Tada,Y. Shao-Horn; J. Electrochem. Soc. 157 (2010) A82