Will ChuehMaterials Science & Engineering ∙ Precourt Institute of Energy
Stanford UniversitySIMES, SLAC National Accelerator Laboratory
chuehlab.stanford.edu
Pushing the Efficiency Limits of Energy Conversion and Storage
Through Rational Materials Design
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D. Diliff
R. Laddish
C.‐Y. Yu
London
Toyko
Chicago
W.C. Chueh
Solar conversion
H2O
H2Capture
Storage
Delivery
Utilization
HydrogenStorage
Carbon‐free Source
HydrocarbonBatteries
e‐
Fuel cell
e‐
, CO2
H2O , CO2
Vision: Energy when & where it’s needed
3Courtesy S. Haile
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Theme: Material optimization & discovery guided by fundamental insights
Model Systems High Performance Devices
200 µm1 µm
4
5 nm
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ALSSSRL SNC
Sensitivity Spatial ResolutionTimescale
Theme: Material optimization & discovery guided by fundamental insights
ppb ps ‐ fs Å
As Electrochemistry Takes Place
W.C. Chueh
Solar conversion
H2O
H2Capture
Storage
Delivery
Utilization
HydrogenStorage
Carbon‐free Source
HydrocarbonBatteries
e‐
Fuel cell
e‐
, CO2
H2O , CO2
Vision: Energy when & where it’s needed
6
W.C. Chueh 7
Understanding battery charging & dischargingYiyang Li, Johanna Nelson
W.C. Chueh
Understanding battery charging & discharging
A123
DelithiatedLithiated
8
500 nm
W.C. Chueh
Can we see lithium move inside a battery?
705 710 715
Abso
rban
ce /
arb
Photon Energy / eV
LiFePO4
FePO4
500 nm
Lithium MapX‐ray Absorption
Photon Energy = 708 eV
J. Vila‐Comamala et al. Optics Express 22 (2011) 21333‐21344.
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W.C. Chueh 10
Snapshots of battery charging
Chueh et al. Nano Lett. (2013). Accepted.
0 20 40 60 80 1000
20
40
60
80
100
169
nm
171
nm
151
nm
165
nm
106
nm
Frac
tion
/ %
Percentile in Particle Size
Li-rich Li-poor
133
nm
214
nm
248
nm
321
nm
191
nm
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Snapshots of battery charging
Chueh et al. Nano Lett. (2013). Accepted.
W.C. Chueh 12
What’s next?
Live imaging of battery charging in 3D
Improving rate capabilities of LiFePO4
Propagation Limited Initiation Limited
Polyester Film
Polymer Separator
Cathode
Current collector
Anode
X-rays
W.C. Chueh
Solar conversion
H2O
H2Capture
Storage
Delivery
Utilization
HydrogenStorage
Carbon‐free Source
HydrocarbonBatteries
e‐
Fuel cell
e‐
, CO2
H2O , CO2
Vision: Energy when & where it’s needed
13
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ChuehLab.stanford.edu
1 gram of platinum for every kiloton of sand
93% of platinum is imported, 80% of world reserves in South Africa
Just enough platinum in the world to convert all American cars to fuel cells
Reduce the use of precious materials
U.S. Geological Survey, Fact Sheet 087‐02 14
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Electrolyte
Air E
lectrode
Fuel Electrode
Fuel cells
GM Bloom Energy
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Operating Temperature~ 400 to 600 °C
• Inexpensive system components (steel)
• Reliability
• Fast start‐up time
• Fast reaction rates
• No precious catalysts required
“Best of Both Worlds”
< 100 °C > 800 °C
Fast Oxygen Ion Conducting
Oxides
Not too cold, not too hot
Low Temp
High Temp
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Ceria
YSZ
Ceria
YSZ
Ceria
YSZ
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200 µm
1 µm
W. C. Chueh et al. Nature Mater. 11, 155‐161 (2012)
Eliminating metal altogether
Pt
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Rxn. Coord
Energy
25 to 400 °C 109 increase in rate
1 eVSolid Electrolyte
e‐
Gas
O2‐
O2‐ O2‐ O2‐ O2‐e‐ e‐ e‐ e‐
SurfaceSub‐Surface
Bulk
?
Visualizing electrochemical reactions in fuel cells
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Albert Feng, Mike Machala, David Mueller, Yezhou Shi
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ChuehLab.stanford.edu
Bulk properties;Surface properties measured ex‐situ
Surface properties measured in‐situ
Electro‐catalytic
Activ
ity
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Electro‐catalytic
Activ
ity
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Ambient PressureX‐ray Spectroscopy
Surface X‐ray Scattering
X‐ray O
M
z
Environmental Transmission Electron Microscopy
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Electrostatic Lenses
X‐ray Source
Sample~ 10 Torr
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Going to a simpler, model system
500 µm
Bloom Energy
50 cm500 μm
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How is charge transferred in a fuel cell electrode?
Ce CeO
CeO
CeO
H2 H2OH+
Ce Ce-O
Ce-O
CeO
H+
H2(g) + O2‐ H2O(g) + 2e‐
Solid Electrolyte
e‐
O2‐
O2‐ O2‐ O2‐ O2‐e‐ e‐ e‐ e‐
H2OH2
CeO2
Absence of surface oxygen
Surface electrons
W.C. Chueh
Solar conversion
H2O
H2Capture
Storage
Delivery
Utilization
HydrogenStorage
Carbon‐free Source
HydrocarbonBatteries
e‐
Fuel cell
e‐
, CO2
H2O , CO2
Vision: Energy when & where it’s needed
23
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Re‐thinking the optimal temperature for water splitting
System cost
Reaction rates
Free energy for H2O dissociation
Temperature25°C > 1,000°C
Temperature
Dark Current
Traditional PEC
Ligh
t Abs
orbe
r
Water
sunlight
H2O(l) H2(g) + O2(g)
Is room temperature the best temperature?
Xiaofei Ye, Madhur Boloor
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Ligh
t Abs
orbe
r
WaterSolid
Electrolyte “Shell”
Ligh
t Abs
orbe
r
A new class of elevated‐temperature photo‐electrochemical cell
• All solid, no liquid
• Reduced corrosion
• Potentially more efficient
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ChuehLab.stanford.edu
H2O
H2
O2‐
O2
e‐
h+
hν
O2‐ ½O2(g) + 2e‐
H2O(g) + 2e‐ H2(g) + O2‐
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A new class of elevated‐temperature photo‐electrochemical cell
Solid Electrolyte
“Shell”
Ligh
t Abs
orbe
r
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A new class of elevated‐temperature photo‐electrochemical cell
10%
Efficiency
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A new class of elevated‐temperature photo‐electrochemical cell
2.0 eV light absorber bandgap
Van
Mac
kele
nber
gh
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• Finding materials with the right properties
• Stability at high temperatures
• Proof‐of‐concept device underway
What’s next?
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Take home message
Fundamental insights enabled by new experimental techniques are challenging the current materials design and
optimization paradigms in energy conversion
These insights are leading to unexpected ways to improve performance and efficiency of batteries, fuel cells, and solar
fuels membranes
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ChuehLab.stanford.edu
Johanna Nelson, Yezhou Shi (not shown)
Nick Melosh, ZX Shen, Mike Toney, Hirohito Ogasawara, Anders Nilsson
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David Mueller
Yiyang Li
Xiaofei Ye
Michael Machala
Albert FengMe