By Dr. Sarika Phadke-Kelkar National Chemical Laboratory 24-March-2011

ByDr. Sarika Phadke-Kelkar

National Chemical Laboratory24-March-2011

Solar Powered Hydrogen Generation: Systems, Materials and Performance

Outline

• Energy Crisis• Alternative Fuels• Hydrogen as fuel• Hydrogen production from water using solar energy

– Photo-chemical decomposition of water– Photo-electro-chemical water splitting

• Materials: Selection criteria, important candidates• Current Status & Future Trend

Historical and Projected Variations in Earth’s Surface Temperature

Years

IPCC Reports

Energy Demand in present and near future

* Present : 12.8 TW 2050 년 : 28-35 TW

* Needs at least 16 TW Bio : 2 TW Wind : 2 TW Atomic : 8 TW (8000 power plant) Fossil : 2 TW

* Solar: 160,000 TW

2010 2020

Hydrogen• Hydrogen, a gas, will play an important role in developing sustainable transportation in the United States, because in the future it may be produced in virtually

unlimited quantities using renewable resources. • Hydrogen and oxygen from air fed into a proton exchange membrane fuel

cell produce enough electricity to power an electric automobile, without producing harmful emissions. The only byproduct of a hydrogen fuel cell is water.

• Currently there are no original equipment manufacturer vehicles available for sale to the general public. Experts estimate that in approximately 10-20 years hydrogen vehicles, and the infrastructure to support them, will start to make an impact.

Applications of Hydrogen Fuel

What is a Fuel Cell?• A Fuel Cell is an electrochemical device that

combines hydrogen and oxygen to produce electricity, with water and heat as its by-product.

How can Fuel Cell technology be used?

• Transportation– All major automakers are working

to commercialize a fuel cell car– Automakers and experts speculate

that a fuel cell vehicle will be commercialized by 2010

– 50 fuel cell buses are currently in use in North and South America, Europe, Asia and Australia

– Trains, planes, boats, scooters, forklifts and even bicycles are utilizing fuel cell technology as well

How can Fuel Cell technology be used?

• Stationary Power Stations– Over 2,500 fuel cell systems have been installed

all over the world in hospitals, nursing homes, hotels, office buildings, schools and utility power plants

– Most of these systems are either connected to the electric grid to provide supplemental power and backup assurance or as a grid-independent generator for locations that are inaccessible by power lines

How can Fuel Cell technology be used?

• Telecommunications– Due to computers, the Internet and sophisticated

communication networks there is a need for an incredibly reliable power source

– Fuel Cells have been proven to be 99.999% reliable

How can Fuel Cell technology be used?

• Micro Power– Consumer electronics could

gain drastically longer battery power with Fuel Cell technology

– Cell phones can be powered for 30 days without recharging

– Laptops can be powered for 20 hours without recharging

Hydrogen Production

• The biggest challenge regarding hydrogen production is the cost

• Reducing the cost of hydrogen production so as to compete in the transportation sector with conventional fuels on a per-mile basis is a significant hurdle to Fuel Cell’s success in the commercial marketplace

Hydrogen Production

• There are three general categories of Hydrogen production– Thermal Processes– Electrolyte Processes– PhotocatalyticProcesses

Hydrogen Production

• PhotocatalyticProcesses– Uses light energy to split water into hydrogen and

oxygen– These processes are in the very early stages of

research but offer the possibility of hydrogen production which is cost effective and has a low environmental impact

– Two types: a) Photochemical b) Photo-electro-chemical

Photo-catalytic water splitting1. Direct Water Splitting: 2. Water Splitting using photo-

electrochemical cell (PEC):

p n

H+/H2

e-

e-

h+ h1

h+

h2O2

H2O/O2

h

H2 TCO with ohmic contact

Experimental setupDirect Water Splitting:

PEC water splitting:

Potentiostat

Metal

P-type semiconductor

P-type semiconductor

N-type semiconductor

N-type semiconductor

Metal

Phto-electrochemistry of water decomposition

• Basic principle

Reaction Mechanism2hν→ 2e + 2h′ + (1)2h+ + H2O(liquid) → 1/2O2(gas) + 2H+ (2)

2H+ + 2e → H′ 2(gas) (3)

Overall Reaction2hν + H2O(liquid) → 1/2O2(gas) + H2(gas)

= 1.23 eV

Electrochemical decomposition of water is possible when EMF of cell ≥ 1.23 V

Band model representation

A

B

C

D

Materials Aspects of PEC

• Two main functions of photoelectrodes– Optical function: maximum absorption of solar energy– Catalytic function: water decomposition

• Desired properties of photoelectrodes– Bandgap– Flatband potential– Schottky barrier– Electrical resistance– Helmholtz potential– Corrosion resistance– Microstructure

Band structure of photoelectrode material

Metals

No band gap

Only reduction or oxidation

Depends on the band position

Insulators

High band gap

High energy requirement

Metals

VB

CB

VB

CB

VB

CBH+/H2

H2O/O2

Insulators

SC

E

WHY SEMICONDUCTOR ?

26

For conventional redox reactions, one is interested in either reduction or oxidation of a substrate.

For example consider that one were interested in the oxidation of Fe2+ ions to Fe 3+ ions then the oxidizing agent that can carry out this oxidation is chosen from the relative potentials of the oxidizing agent with respect to the redox potential of Fe2+/Fe3+ redox couple.

The oxidizing agent chosen should have more positive potential with respect to Fe3+/Fe2+ couple so as to affect the oxidation, while the oxidizing agent undergoes reduction spontaneously. This situation throws open a number of possible oxidizing agents from which one of them can be easily chosen.

Concepts –Why semiconductors are chosen as photo-catalysts?

27

Bandgap

Flatband potential

Other important parameters

• Electrical Conductivity

• Helmholtz Potential Barrier

• Corrosion Resistance:– Electrochemical corrosion resistance– Photocorrosion resistance– Dissolution

Criterion for PE corrosion stability

Free enthalpy of oxidation reactionPhoto anode

Free enthalpy of reduction reactionPhoto cathode

What modifications?

• various conceptual principles have been incorporated into typical TiO2 system so as to make this system responsive to longer wavelength radiations. These efforts can be classified as follows:

• Dye sensitization• Surface modification of the semiconductor to

improve the stability • Multi layer systems (coupled semiconductors)• Doping of wide band gap semiconductors like TiO2

by nitrogen, carbon and Sulphur • New semiconductors with metal 3d valence band

instead of Oxide 2p contribution • Sensitization by doping.• All these attempts can be understood in terms of

some kind sensitization and hence the route of charge transfer has been extended and hence the efficiency could not be increased considerably. In spite of these options being elucidated, success appears to beeluding the researchers.

33

Conditions to be satisfied?

• The band edges of the electrode must overlap with the acceptor and donor states of water decomposition reaction, thus necessitating that the electrodes should at least have a band gap of 1.23 V, the reversible thermodynamic decomposition potential of water. This situation necessarily means that appropriate semiconductors alone are acceptable as electrode materials for water

• The charge transfer from the surface of the semiconductor must be fast enough to prevent photo corrosion and shift of the band edges resulting in loss of photon energy.

34

without deterioration of the stability

should increase charge transfer processes at the interface

should improvements in the efficiency

ENGINEERING THE SEMICONDUCTOR ELECTRONIC STRUCTURES

35

Positions of bands of semiconductors relative to the standard potentials of several redox couples

36

Identifying and designing new semiconductor materials with considerable conversion efficiency and stability

Constructing multilayer systems or using sensitizing dyes - increase absorption of solar radiation

Formulating multi-junction systems or coupled systems - optimize and utilize the possible regions of solar radiation

Developing nanosize systems - efficiently dissociate water

THE AVAILABLE OPPORTUNITIES

37

high surface area

morphology

presence of surface states

wide band gap

position of the VB & CB edge

CdS – appropriate choice for the hydrogen production

eV

ADVANTAGES OF SEMICONDUCTOR NANOPARTICLES

38

The opportunities

• The opportunities that are obviously available as such now include the following:

– Identifying and designing new semiconductor materials with considerable conversion efficiency and stability

– Constructing multilayer systems or using sensitizing dyes so as to increase absorption of solar radiation.

– Formulating multi-junction systems or coupled systems so as to optimize and utilize the possible regions of solar radiation.

– Developing catalytic systems which can efficiently dissociate water.

39

Opportunities evolved

• Deposition techniques have been considerably perfected and hence can be exploited in various other applications like in thin film technology especially for various devices and sensory applications.

• The knowledge of the defect chemistry has been considerably improved and developed.

• Optical collectors, mirrors and all optical analysis capability have increased which can be exploited in many other future optical devices.

• The understanding of the electronic structure of materials has been advanced and this has helped to our background in materials chemistry.

• Many electrodes have been developed, which can be a useful for all other kinds of electrochemical devices.

40

Limited success – Why?The main reasons for this limited success in all these

directions are due to:• The electronic structure of the semiconductor controls the

reaction and engineering these electronic structures without deterioration of the stability of the resulting system appears to be a difficult proposition.

• The most obvious thermodynamic barriers to the reaction and the thermodynamic balances that can be achieved in these processes give little scope for remarkable improvements in the efficiency of the systems as they have been conceived and operated. Totally new formulations which can still satisfy the existing thermodynamic barriers have to be devised.

• The charge transfer processes at the interface, even though a well studied subject in electrochemistry has to be understood more explicitly, in terms of interfacial energetics as well as kinetics. Till such an explicit knowledge is available, designing systems will have to be based on trial and error rather than based on sound logical scientific reasoning.

41

• Nanocrystalline (mainly oxides like TiO2, ZnO, SnO and Nb2O5 or chalcogenides like CdSe) mesoscopic semiconductor materials with high internal surface area If a dye were to be adsorbed as a monolayer, enough can be retained on a given area of the electrode so as to absorb the entire incident light.

• Since the particle sizes involved are small, there is no significant local electric field and hence the photo-response is mainly contributed by the charge transfer with the redox couple.

• Two factors essentially contribute to the photo-voltage observed, namely, the contact between the nano crystalline oxide and the back contact of these materials as well as the Fermi level shift of the semiconductor as a result of electron injection from the semiconductor.

42

Another aspect of thee nano crystalline state is the alteration of the band gap to larger values as compared to the bulk material which may facilitate both the oxidation/reduction reactions that cannot normally proceed on bulk semiconductors.

The response of a single crystal anatase can be compared with that of the meso-porous TiO2 film sensitized by ruthenium complex (cis RuL2 (SCN)2, where L is 2-2’bipyridyl-4-4’dicarboxlate).

The incident photon to current conversion efficiency (IPCE) is only 0.13% at 530 nm ( the absorption maximum for the sensitizer) for the single crystal electrode while in the nano crystalline state the value is 88% showing nearly 600-700 times higher value.

43

This increase is due to better light harvesting capacity of the dye sensitized nano crystalline material but also due to mesoscpic film texture favouring photo-generation and collection of charge carriers .

It is clear therefore that the nano crystalline state in combination with suitable sensitization is one another alternative which is worth investigating.

44

• The second option is to promote water splitting in the visible range using Tandem ells. In this a thin film of a nanocrystalline WO3 or Fe2O3 may serve as top electrode absorbing blue part of the solar spectrum. The positive holes generated oxidize water to oxygen

• 4h+ + 2H2O --- O2 + 4 H+

• The electrons in the conduction band are fed to the second photo system consisting of the dye sensitized nano crystalline TiO2 and since this is placed below the top layer it absorbs the green or red part of the solar spectrum that is transmitted through the top electrode. The photo voltage generated in the second photo system favours hydrogen generation by the reaction

• 4H+ + 4e- --- 2H2

• The overall reaction is the splitting of water utilizing visible light. The situation is similar to what is obtained in photosynthesis

45

• Dye sensitized solid hetero-junctions and extremely thin absorber solar cells have also been designed with light absorber and charge transport material being selected independently so as to optimize solar energy harvesting and high photovoltaic output. However, the conversion efficiencies of these configurations have not been remarkably high.

• Soft junctions, especially organic solar cells, based on interpenetrating polymer networks, polymer/fullerene blends, halogen doped organic crystals and a variety of conducting polymers have been examined. Though the conversion efficiency of incident photons is high, the performance of the cell declined rapidly. Long term stability will be a stumbling block for large scale application of polymer solar cells.

46

New Opportunities

1. New semi-conducting materials with conversion efficiencies and stability have been identified. These are not only simple oxides, sulphides but also multi-component oxides based on perovskites and spinels.

2. Multilayer configurations have been proposed for absorption of different wavelength regions. In these systems the control of the thickness of each layer has been mainly focused on.

47

New Opportunities

3. Sensitization by dyes and other anchored molecular species has been suggested as an alternative to extend the wavelength region of absorption.

4. The coupled systems, thus giving rise to multi-junctions is another approach which is being pursued in recent times with some success

5. Activation of semiconductors by suitable catalysts for water decomposition has always fascinated scientists and this has resulted in various metal or metal oxide (catalysts) loaded semi conductors being used as photo-anodes

48

New opportunities (Contd)• Recently a combinatorial electrochemical synthesis

and characterization route has been considered for developing tungsten based mixed metal oxides and this has thrown open yet another opportunity to quickly screen and evaluate the performances of a variety of systems and to evolve suitable composition-function relationships which can be used to predict appropriate compositions for the desired manifestations of the functions.

• It has been shown that each of these concepts, though has its own merits and innovations, has not yielded the desired levels of efficiency. The main reason for this failure appears to be that it is still not yet possible to modulate the electronic structure of the semiconductor in the required directions as well as control the electron transfer process in the desired direction.

49

PREPARATION OF CdS NANOPARTICLES

1 g of Zeolite (HY, H, HZSM-5)

1 M Cd(NO3)2 , stirred for 24 h, washed with water

Cd / Zeolite

1 M Na2S solution, stirred for 12 h, washed with water

CdS / Zeolite

48 % HF, washed with water

CdS Nanoparticles

50

XRD PATTERN OF CdS

20 30 40 50 60 70 80

CdS-Z

CdS-

CdS-Y

CdS (bulk)

Inte

nsit

y (a

.u.)

2 theta

M. Sathish, B. Viswanathan, R. P. Viswanath Int. J. Hydrogen Energy (In press)51

Debye Scherrer Equation

dSPACING AND CRYSTALLITE SIZE

0.89

cosT

q = diffraction angle T = Crystallite size = wave length = FWHM

d-spacing (Å)Catalyst (0 0 2) (1 0 1) (1 1 2)

CrystalliteSize(nm)

CdS (bulk) 1.52 1.79 2.97 21.7

CdS (bulk)(HF treated)

1.52 1.79 2.93 21.7

CdS-Y 1.53 1.79 2.96 8.8

CdS- 1.52 1.78 2.93 8.6

CdS-Z 1.52 1.79 2.97 7.2

52

UV –VISIBLE SPECTRA OF CdS SAMPLES

Samples Band Gap (eV)

CdS – Z

CdS – Y

CdS -

Bulk CdS

2.38

2.27

2.21

2.13

500 600 700

Ab

so

rb

an

ce (a.u

.)

CdS (bulk) CdS - CdS - Z CdS - Y

Wavelength (nm)

M. Sathish, B. Viswanathan, R. P. Viswanath Int. J. Hydrogen Energy (In press)53

PHOTOCATALYTIC PRODUCTION OF HYDROGEN

35ml of 0.24 M Na2S and 0.35 M Na2SO3 in Quartz cell

0.1 g CdS400 W Hg lamp

N2 gas purged before the reaction and constant stirring

Hydrogen gas was collected overwater in the gas burette

54

AMOUNT OF HYDROGEN EVOLVED BY CdS PHOTOCATALYST

0 1 2 3 4 5 60

100

200

300

400

500

600

700

Am

ou

nt

of

Hyd

rog

en (

mic

ro m

ole

s / 0

.1g

)

Time (h)

CdS - Y CdS - Z CdS - CdS - with HY CdS (bulk)

55

TEM IMAGE OF CdS NANOPARTICLES

Catalyst Particle Size (nm)

Surfacearea (m2/g)

Rate of hydrogenproduction ( moles /h)

CdS - Y 8.8 36 102

CdS - Z 6 46 68

CdS - 11 26 67

CdS - Bulk 23 14 45

CdS-Z

CdS-

100 nm100 nm

CdS-Z

56

SCANNING ELECTRON MICROGRAPHS

57

CdS-Z CdS-Y

CdS- CdS- bulk

PHOTOCATALYSIS ON Pt/TiO2 INTERFACE

Electrons are transferred to metal surface

Reduction of H+ ions takes place at the metal surface

The holes move into the other side of semiconductor

The oxidation takes place at the semiconductor surface

TiO2Pt

Vacuum level

Aq. Sol Aq. Sol

pH=0

pH = 7H+/H2

C.B

V.B

EF

T.Sakata, et al Chem. Phys.Lett. 88 (1982) 5058

MECHANISM OF RECOMBINATION REDUCTION BY METAL DOPING

Conduction Bande- e- e- e- e- e- e- e- e- e- e- e-

Valence Bandh+ h+ h+ h+ h+ h+ h+ h+ h+ h+

Electron/hole pairrecombination

Electron/hole pair generation

e-(M) <-- M+e-

Eg

Metallic promoter attracts electrons from TiO2 conduction band and slows recombination reaction

52

0 1 2 3 4 5 60

500

1000

1500

2000

2500

3000

3500

4000H-ZSM-5

Am

ou

nt

of

Hyd

rog

en (

mic

ro m

ole

s / 0

.1g

)

Time (h)

Pt / CdS Pd / CdS Rh / CdS CdS (Bulk) Ru / CdS

0 1 2 3 4 5 60

500

1000

1500

2000

2500

3000

HY

Am

ou

nt

of

Hyd

rog

en

(m

icro

mo

les / 0

.1g

)

Time (h)

Pt / CdS Pd / CdS CdS (Bulk) Rh / CdS Ru / CdS

Activity of the catalyst is directly proportional to work function of the metal and M-H bond strength.

PHOTOCATALYTIC HYDROGEN EVOLUTION OVER METAL LOADED CdS NANOPARTICLES

0 1 2 3 4 5 60

500

1000

1500

2000

2500

3000

3500H beta

(A

mo

un

t o

f h

ydro

gen

(m

icro

mo

les/

0.1

g))

Time (h)

Pt / CdS Pd / CdS Rh / CdS CdS (Bulk) Ru / CdS

60

MetalRedox

potential(E0)

Metal- hydrogen bond energy (K cal mol-1)

Work function

(eV)

Hydrogen evolution rate*(µmol h-1 0.1g-1)

PtPdRhRu

1.1880.9510.7580.455

62.864.565.166.6

5.655.124.984.71

60014411454

HYDROGEN PRODUCTION ACTIVITY OF METAL LOADED CdS PREPARED FROM H-ZSM-5

*1 wt% metal loaded on CdS-Z sample. The reaction data is presented after 6 h under reaction condition.

M. Sathish, B. Viswanathan, R. P. Viswanath Int. J. Hydrogen Energy (In press)61

Pt, Pd & Rh show higher activity

High reduction potential.

Hydrogen over voltage is less for Pt, Pd & Rh

EFFECT OF METALS ON HYDROGEN EVOLUTION RATE

Ru

Ni

Pt

Pd

Ag

Fe

Cu

Rh

Au

10

100

1000

3 %

62

0 2 4 6 8 10 12 14 16 18 20 2240

45

50

55

60

65

70

75

80

Bulk CdS

CdS (ZSM-5)

CdS (ZSM-5)/MgO

CdS (ZSM-5)/Al2O

3

Bulk CdS/MgO

Bulk CdS/Al2O

3

Rat

e o

f h

ydro

gen

pro

du

ctio

n

(µm

ol h

-1 0

.1g

-1)

CdS (Wt %)

EFFECT OF SUPPORT ON THE CdS PHOTOCATLYTIC ACTIVITY

2, 5,10 and 20 wt % CdS on support - by dry impregnation method

MgO support has higher photocatalytic activity - favourable band position

Alumina & Magnesia supports enhance photocatalytic activity

63

Pb2+/ ZnS

Absorption at 530nm (calcinations at 623-673K)

Formation of extra energy levels between the band gap by Pb 6s orbital

Low activity at 873K is due to PbS formation on the surface (Zinc blende to wurtzite)

(a) 573 K, (b) 623 K, (c) 673 K, (d) 773 K, and (e) 873K Band structure of ZnS doped with Pb.

Eg

I. Tsuji, et al J. Photochem. Photobiol. A. Chem 622 (2003) 1 64

250 ml of 5 mM Na2S solution

250 ml of 1 mM Cd(NO3)2

Rate of addition 20 ml / h

Ultrasonic waves

= 20 kHz

The resulting precipitate was washed with distilled water until the filtrate was free from S2- ions

PREPARATION OF MESOPOROUS CdS NANOPARTICLE BY ULTRASONIC MEDIATED PRECIPITATION

65

0.0 0.2 0.4 0.6 0.8 1.00

20

40

60

80

100

120

140

0 20 40 60 80 1000

2

4

6

8

Relative volum

e (%

)

Pore range (A)

Vo

lu

me (cm

3 /g

)

P/Po

The specific surface area and pore volume are 94 m2/g and 0.157 cm3/g respectively

The adsorption - desorption isotherm – Type IV (mesoporous nature)

Mesopores are in the range of 30 to 80 Å size

The maximum pore volume is contributed by 45 Å size pores

N2 ADSORPTION - DESORPTION ISOTHERM

66

20 30 40 50 60 70

(311)(220)

(111)

In

ten

sity (a.u

.)

2 theta

XRD pattern of as-prepared CdS -U shows the presence of cubic phase

The observed “d” values are 1.75, 2.04 and 3.32 Å corresponding to the (3 1 1) (2 2 0) and (1 1 1) planes respectively - cubic

The peak broadening shows the formation of nanoparticles

The particle size is calculated using Debye Scherrer Equation

The average particle size of as- prepared CdS is 3.5 nm

X- RAY DIFFRACTION PATTERN

M. Sathish and R. P. Viswanath Mater. Res. Bull(Communicated)67

The growth of fine spongy particles of CdS-U is observed on the surface of the CdS-U

The CdS-bulk surface is found with large outgrowth of CdS particles

The fine mesoporous CdS particles are in the nanosize range

The dispersed and agglomerated forms are clearly observed for the as-prepared CdS-U

CdS-U CdS - Bulk

TEM SEM

ELECTRON MICROGRAPHS

68

CdS-U

100 nm

Metal CdS-U CdS-Z CdSbulk

-

Rh

Pd

Pt

73

320

726

1415

68

114

144

600

45

102

109

275

1 wt % Metal loaded CdS – U is 2-3 times more active than the CdS-

Z

PHOTOCATALYTIC HYDROGEN PRODUCTION

Na2S and Na2SO3 mixture used as sacrificial agent

Amount of hydrogen (µM/0.1 g)

0 1 2 3 4 5 60

2000

4000

6000

8000

10000

Time (h)

Am

ou

nt o

f h

yd

ro

gen

/M

0.1g

-1

Pt / CdS-U Pd / CdS-U Rh / CdS-U CdS-U

69

Difficulties on controlling the semiconductor electronic structure without deterioration of the stability

Little scope on the thermodynamic barriers and the thermodynamic balances for remarkable improvements in the efficiency

Incomplete understanding in the interfacial energetic as well as in the kinetics

LIMITED SUCCESS – WHY?

70

Deposition techniques -thin film technology, for various devices and sensory applications.

Knowledge of the defect chemistry has been considerably improved and developed.

Optical collectors, mirrors and all optical analysis capability have increased

Understanding of the electronic structure of materials

Many electrodes have been developed- useful for all other kinds of electrochemical devices.

THE OTHER OPPORTUNITIES EVOLVED

71

Thank you all foryour kind attention

Metal

P-type semiconductor

P-type semiconductor

N-type semiconductor

N-type semiconductor

Metal

Photo-electrochemical H2 Generation

• Basic principle

Reaction Mechanism

• 2hν→ 2e + 2h+ ′ (1)• 2h+ + H2O(liquid) → 1/2O2(gas) + 2H+ (2)

• 2H+ + 2e → H′ 2(gas) (3)• Overall Reaction• 2hν + H2O(liquid) → 1/2O2(gas) + H2(gas)

= 1.23 eV

Electrochemical decomposition of water is possible when EMF of cell ≥ 1.23 V

Metal Oxide Requirements

• Two main functions of photoelectrodes– Optical function: maximum absorption of solar energy– Catalytic function: water decomposition

• Desired properties of photoelectrodes– Bandgap– Flatband potential– Schottky barrier– Electrical resistance– Helmholtz potential– Corrosion resistance– Microstructure

Bandgap

Flatband Potential

Other important parameters

• Electrical Conductivity

• Helmholtz Potential Barrier

• Corrosion Resistance:– Electrochemical corrosion resistance– Photocorrosion resistance– Dissolution

Criterion for PE corrosion stability

Free enthalpy of oxidation reactionPhoto anode

Free enthalpy of reduction reactionPhoto cathode

Dye-Sensitized TiO2

J. AM. CHEM. SOC. 2009, 131, 926–927

Mesoporous Fe2O3

J. AM. CHEM. SOC. 9 VOL. 132, NO. 21, 2010

WO3 Nanowires

Double-Sided CdS and CdSe Quantum Dot Co-Sensitized ZnONanowire Arrays for PEC Hydrogen Generation

NanoLett. 2010, 10, 1088–1092

Summary

• Metal oxide nanomaterials offer great versatility in properties

• Optoelectronic properties can be tuned by choosing/controlling the synthesis protocol

• Hybridization with organic/molecular materials provide unique combinations of properties

• Low temperature and solution based processing is the key for future metal oxide based energy devices

Thank You!

What is Nanoscale

1.27 × 107 m

ww

.mat

hwor

ks.c

om

0.22 m 0.7 × 10-9 m

Fullerenes C60

12,756 Km 22 cm 0.7 nm

10 millions times smaller

1 billion times smaller

ww

w.p

hysi

cs.u

cr.e

du

How Small is Nano Really ?

Gold nanoparticles of different sizes

InP nanoparticles

Passivated Carbon NanodotsSun et al. JACS 128, 7756 (2006)

Quantum Phenomena

Large Surface to Volume Ratio