- -- -

Energy Energy ConversionConversion

Cha

rge

Tran

sfer

Pro

cess

es

Organized Hybrid Assemblies

Quantum DotSolar Cells

TiO2

Au

Nanostructure Architectures for Solar Energy Conversion

TiO2

Pt

h

e

2H+

H2

4OH

2H2O + O2 hTiO2

Pt

h

e

2H+

H2

4OH

2H2O + O2 h

CdSe

TiO2

OTE

h

e

e h

h

hCdSe

TiO2

OTE

h

e

e h

h

h

SAu SS

S

S

S

S

S

SS

SS

SSSS

Prashant V. Kamathttp://www.nd.edu/~pkamat

http://politicalhumor.about.com

Light Crude Oil (CL, NYMEX)Monthly Price Chart

Increasing demand is driving oil prices higher

MOTIVATION FOR SOLAR ENERGY RESEARCH

Possible Options for meeting the 10 TW- Clean Energy Challenge by 2050

Carbon Neutral Energy (fossil fuel in conjunction with carbon sequestration) -Need to find secure storage for 25 billion metric tons of CO2 produced annually (equal to the volume of 12500 km3 or volume of lake superior!)

Nuclear Power -Requires construction of a new one-gigawatt-electric (1-GW) nuclear fission plant everyday for the next 50 years

Renewable Energy Sources- hydroelectric resource 0.5 TW- from all tides & ocean currents 2 TW- geothermal integrated over all the land area 12 TW- globally extractable wind power 2-4 TW- solar energy striking the earth 120,000 TW !!!

PtAcceptor TiO 2

e

Our Research Focus

Molecular linker

Donor

Photoinduced electron transfer in light harvesting systemsDonor- AcceptorSemiconductor-SensitizerSemiconductor-SemiconductorSemiconductor-Metal

CdSeTiO2

h

e

ethanol products

he e

e

h hh

Ag

TiO2

ethanol products

he e

e

h hh

Ag

TiO2

ethanol products

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e

h hh

ethanol products

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ee

hh hhhh

Ag

TiO2

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eeh

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eeh

C60C60

C60

Researchers who make it possible in our group

Graduate students Post-Docs/Visiting ScientistsBrian Seger (Chem. Eng.) Yochiro MatsunagaMatt Baker (Physics) K. VinodgopalDavid Becker (Chem. Eng.) Julie PellerKevin Tvrdy (Chemistry) Clifton Harris (Chemistry)

Undergraduate studentsPat BrownMeghan JebbSahib HashimiChris Beesley

Recent GraduatesDr. Julie Peller –CHEM ‘03

(Faculty at IUN)Dr. Roxana Nicolaescu – CHEM ‘04

(Scientist at Serim)Dr. V Subramanian – CHEM ‘04

(Faculty, U. Nevada)Dr. Istvan Robel – Physics ’07

(Argonne National Lab.)Summer 2007

Applications

Design & Synthesis

PropertiesElectron storage,

transport and interfacial processesMolecular assemblies,

composites & hybrid systems

Catalysis, Photovoltaics, Fuel Cells, Sensors

SS

S

S

S

S

S

S

SS

SS

SS

SS

SS

S

S

S

S

S

S

SS

SS

SS

SS

SS

S

S

S

S

S

S

SS

SS

SS

SS

SS

S

S

S

S

S

S

SS

SS

SS

SS

SS

S

S

S

S

S

S

SS

SS

SS

SS

e-

Pt

e-

OTEI-/ I3-

OTE: Optically Transparent Electrode

e-

h

Porphyrin C60 Gold Nanoparticle

e- ZnO

Emission probe

R-COOH

TiO2

CO2

ZnO

Emission probe

R-COOH

TiO2

CO2

OO

OO

SS

SS

SS

S

S SS

SSO

OO

O

O

O

O

O

reactant products

h

hAg

TiO2

hh

eee

h

et ht

VB

–

+

+

–CB

2H2O+ O

4OH

2H2H

H2

Pt

1. Semiconductor Assisted Catalysis

Hydrogen Evolution rates for various Photocatalysts (l/hr)

Pt/TiO2 7.7Pd/TiO2 6.7Rh/TiO2 2.8Ru/TiO2 0.2Sn/TiO2 0.2Ni/TiO2 0.1TiO2 <0.1Toshima, J. Phys. Chem. 1985, 89, 1902

What about gold and other noble metals? - Explore size dependent properties of nanometals and alloys

How to extend the response into the visible? - Design new photocatalysts and composites

How to improve the photocatalytic efficiency?-Understand the charge transfer processes at the interface

Issues:

No Au8 nm Au

5 nm Au

3 nm Au

Effect of Gold Particle Size on the Catalytic Reduction Efficiency of TiO2

particles

10 nm

(b)

10 nm10 nm

(a)

ab

5 nm5 nm

(c)

5 nm5 nm

(c)

Vaidyanathan, Wolf, Kamat J. Am. Chem. Soc., 2004, 126, 4943-4950

2. Quantum Dot Solar Cells

Tunable band edge Offers the possibility to harvest light energy over a wide range of visible-ir light with selectivity

Hot carrier injection from higher excited state (minimizing energy loss during thermalization of excited state)

Multiple carrier generation solar cells.Utilization of high energy photon to multiple electron-hole pairs

2.3nm2.6nm

3.0nm3.7nm

450 500 550 600 650 7000.0

0.3

0.6

0.9

bcd

a

CdSe Particle Diametera. 3.7 nmb. 3.0 nmc. 2.6 nmd. 2.3 nm

Abs

orba

nce

Wavelength, nm

350 400 450 500 550 600 650 700

0

10

20

30

40

50 (A) 3.7 nm 3.0 nm 2.6 nm 2.3 nm

Wavelength (nm)

IPC

E (%

)

Tuning the Photoresponse of Quantum Dot Solar Cells

CdSeTiO2

VB

CB

ee

e

hh h

RO

Advantages High surface area Good electronic conductivity, excellent chemical and

electrochemical stability Good mechanical strength

3. Carbon nanostructures as conduits to transport 3. Carbon nanostructures as conduits to transport

charge carrierscharge carriers

c

GoalEffective utilization of carbon nanostructures for improving the performance of energy conversion devices

- To develop electrode assembly with CNT supports- Improve the performance of light harvesting assemblies- Facilitate charge collection and transport in nanostructured

assemblies

Pt

…..towards achieving ordered assemblies on electrode surface

0 20 40 60

0

20

40

60

b

a

a) SWCNT/TiO2

b) TiO2

Time, secP

hoto

curr

ent, A

/cm

2

Photocurrent GenerationCFE/TiO2 versus CFE/SWCNT –TiO2

CFE/TiO2 and CFE/SWCNT/TiO2 films were tested for their photoelectrochemical response with UV irradiation (>300 nm)

UV light

1 m

Charge Equilibration in SWCNT-Semiconductor Composite

EF

e

hEF

h eEF O/R

O/R

E*f (TiO2)= Efb = E0O/R + 0.059 log ([O]/[R])

Stepwise charging of semiconductor nanoparticle followed by equilibration with SWCNT and redox couple facilitates determination of apparent Fermi level of the composite system

Kongkanand, A.; Kamat, P.V., Electron Storage in Single Wall Carbon Nanotubes. Fermi Level Equilibration in Semiconductor–SWCNT Suspensions. ACS Nano, 2007. 1, 13-21

……The third technique, being developed by Prashant Kamat of theUniversity of Notre Dame, Indiana, and his colleagues, uses thatfashionable scientific tool, the carbon nanotube. This is a cylindercomposed solely of carbon atoms, and one of its properties is goodelectrical conductivity. In effect, nanotubes act as wires a few billionthsof a metre in diameter. …

September 16, 2006

Carbon Nanotubes could boost efficiency of solar cells -- Researchers at the University of Notre Dame in Indiana say they have found a new and promising way to boost the efficiency of solar cells. In preliminary studies, carbon nanotubes that were engineered into the architecture of semiconductor solar cells. In some cases, the efficiency of solar cells jumped from 5 percent to 10 percent in the presence of carbon nanotubes, according to Prashant Kamat, Ph.D., a professor of chemistry at the University.

Where do we go from here?

200nm 500nm

Ti/TiO2 nanotubesOTE/TiO2 nanoparticles

CdSe

TiO

2Ti

O2

TiO2

TiO

2

CdSe

Rainbow Solar Cells

Current & Future Research

h

eeh

Charge separation

Eg1

VB

CB

VB

CB

e

hEg2

e

Charge collection

Organized light harvesting assembly using carbon nanostructures

hh

eeh

eeh

eeh

eeh

eeh

eeh

A

B

50 nm

200 nm

Stacked-Cup Carbon Nanotubes for Photoelectrochemical Solar Cells, Angew Chem. Int. Ed. 2005, 45, 755-759

What will the future hold?

Over the last twenty years, the per-kWh price

of photovoltaics has dropped from about $500 to nearly $5; think of what the next twenty years will

bring.

DOMER RUN 2006