Membrane-Supported Nanorod PEC H 2 Production SUNLIGHT-DRIVEN MEMBRANE-SUPPORTED PHOTOELECTROCHEMICAL WATER SPLITTING Nathan S. Lewis, Harry A. Atwater Harry B. Gray, Bruce S. Brunschwig Jim Maiolo, Kate Plass, Josh Spurgeon, Brendan Kayes, Mike Filler, Mike Kelzenberg, Morgan Putnam California Institute of Technology Pasadena, CA 91125
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Membrane-Supported Nanorod PEC H2 Production
SUNLIGHT-DRIVEN MEMBRANE-SUPPORTED PHOTOELECTROCHEMICAL WATER
SPLITTING
Nathan S. Lewis, Harry A. AtwaterHarry B. Gray, Bruce S. Brunschwig
Jim Maiolo, Kate Plass, Josh Spurgeon, Brendan Kayes, Mike Filler, Mike Kelzenberg, Morgan Putnam
California Institute of TechnologyPasadena, CA 91125
LightFuel
Electricity
Photosynthesis
Fuels Electricity
Photovoltaics
sc
e
SC
CO
Sugar
H O
O
2
2
2
Energy Conversion Strategies
Semiconductor/LiquidJunctions
H2
O
O H22
SC
Fuel from Sunlight
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Photoelectrochemical
Cell
metal
e-
e-
O2
H2
O
H2
H2
O
e -
h+
Light is Converted to Electrical+Chemical Energy
LiquidSolid
SrTiO3
Membrane-Supported Nanorod PEC H2 Production
FTO slide printed with binary combinations of eight metals, pyrolyzed
to form mixed metal oxides.
Typical photocurrent map of a slide of metal oxides. The X-
and Z-coordinates give each spot’s identity, which is correlated with photo-catalytic activity. Here, combinations of Zn and Co in row #9 show photoanodic
current
Combinatorial Discovery of Nanorod MaterialsCombinatorial Discovery of Nanorod Materials
Membrane-Supported Nanorod PEC H2 Production
Lessons from PhotosynthesisLessons from Photosynthesis
Membrane-Supported Nanorod PEC H2 Production
Turner CellTurner Cell
Membrane-Supported Nanorod PEC H2 Production
2H2
O2
catalystanode
H2
catalystcathodeSolar PV & membrane
H2
O
O24H+
System ConceptSystem Concept
Membrane-Supported Nanorod PEC H2 Production
Why Radial Junction Solar Cells?Why Radial Junction Solar Cells?
•
Traditional device design requires long minority carrier diffusion lengths, and therefore expensive materials
p-type
n-type
hν
Traditional
single junction solar cell
Idealized radial junction
nanorod solar cell
~Ln
1/α
•
Radial geometry allows for high quantum efficiency despite short
minority carrier diffusion lengths
~Ln
Membrane-Supported Nanorod PEC H2 Production
Device ModelingDevice Modeling
Comparison of photovoltaic efficiency for (a) planar and (b) nanowire Si devices as afunction of absorber thickness and minority carrier diffusion length
B.M. Kayes, H. A. Atwater, and N. S. Lewis, J. Appl. Phys. 97
114302 (2005)
Relatively high efficiencies possible despite low diffusion lengths if depletion region recombination can be minimized
Membrane-Supported Nanorod PEC H2 Production
Structural Organization in NatureStructural Organization in Nature
RootForest
Stomata Leaf
Membrane-Supported Nanorod PEC H2 Production
Enables New MaterialsEnables New Materials•
High efficiencies possible despite low diffusion lengths=> Inexpensive materials
quantities (10-20 TW by 2050) of clean energy, CO2
levels will continue to rise
•
The only sufficient supply-side cards we have are “clean”
coal, nuclear fission (with a closed fuel cycle), and/or cheap solar fuel
•
We need to pursue globally scalable systems that can efficiently
and cost-
effectively capture, convert, and store sunlight in the form of chemical fuels
–
He that can not store, will not have power after four
•
Semiconductor/liquid junctions offer the only proven method for achieving this goal, but we have a great deal of fundamental science to learn to enable the underpinnings of a cost-effective, deployable technology
–
Nanorods, randomly ordered junctions to generate the needed potential
–
Catalysts to convert the incipient electrons into fuels by rearranging the chemical bonds of water (and CO2