Artificial Photosynthesis – Learning from material

development & Synchrotron mechanistic understanding

Debajeet K. BoraLaboratory for High Performance Ceramics,

Empa. Swiss Federal Laboratories for Materials Science and Technology, CH – 8600, Dubendorf,

Switzerland

Acknowledgement

Swiss Federal Office of Energy (project no: 153613/102809) Prof. Andreas Luzzi Dr. Stefan Oberholzer, BfE Prof. Edwin C. Constable, Thesis Advisor, University of Basel Dr. Artur Braun, Supervisor, EMPA Dübendorf Prof. Thomas Graule, EMPA Dübendorf

Collaborators Dr. Kevin Sivula, EPFL, Switzerland Dr. Elena Rozhkova, Argonne National Laboratory, USA Dr. Jinghua Guo, Advanced Light Source, Lawrence Berkeley National Laboratory, USA Dr. Rolf Erni, Electron Microscopy Center, EMPA Dübendorf, Switzerland Dr. G. Fortunato, abt272, EMPA St. Gallen, Switzerland Dr. F. La Mattina, abt 173, EMPA Dübendorf, Switzerland Dr. Stefan Hug, Eawag, Switzerland Dr. Max Doebli, ETH Zürich, Switzerland

OutlineIntroductionAcknowledgement MotivationSynthesis and properties of hematite thin film

as photoanodeSynthesis of hematite thin film doped with

siliconHematite nanoflowersHematite-Phycocyanin nanobio PEC electrodeNiO-Hematite electrodeConclusion and outlook

What will be alternative source of energy after 100 years ?

Answer will be solar energy

“Due to the increased demand of clean energy in near future, research on the development of alternative energy source is gaining momentum from last decade”

Upto what extent fossil fuel will serve the increasing global energy demand?

Question rises how the civilization will continue if oil reserve deplete fully ?

In 1972, motivated the scientist to develop the photo electrochemistry concept although it was also demonstrated by Becquerel in 1839.

Hydrogen is considered as eco- friendly green fuel

www.anl.gov

6

First photoelectrochemical cell developed by Fujishima and Honda in 1972

Plants and cyanobacteria produce this hydrogen gas by utilizing the water splitting machinery of photosynthetic process.

Photosynthesis

Ref: Prof. D. Nocera, MIT

Comparison of photoanode function with natural oxygen evolving complexArtificial: Hematite as oxygen evolution catalyst

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Semiconductor-Electrolyte Interface A space- charge layer is build up in

a semiconductor upon contact and in equilibrium with another phase unless the chemical potential gradient for electrons is different.

The chemical potential is normally given by the Fermi level in the semiconductor.

When initial Fermi level in an n- type semiconductor overcome the Fermi level of electrolyte, equilibrium is obtained by the transfer of electrons from semiconductor to electrolyte.

A positive space charge layer is formed called as depletiion layer.

A new potential barrier is established which prevents further electron transfer into electrolyte.

It formed as a result of bending of conduction band and valence band edges.Ref: Nozik, A. J. Ann. Rev. phy. Chem. 1978, 29, 189-222.

Figure: Energy level diagram of semiconductor – electrolyte junction

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Material screening for the photoanode development

Why Hematite as materials of choice?

Why Hematite? Semiconducting Behavior

Suitable band gap (Eg`= 1.9 -2.2 eV)for visible light absorption

Earth abundant

Environmental Friendly

Well matched valence band edge position with water oxidation potential

Main purpose is to generate oxygen

http://en.wikipedia.org/wiki/File:Hematite.jpg#file

Motivation Efficiency of pure or „unmodified“ hematite is relatively low

Optimization through doping or morphological modification

Si doping makes dendritic nanostructures → huge performance improvement

Hierarchical nano-architectures have been constructed → increased efficiency

To improve the performance of hematite by integrating with light harvesting protein ( Realization of Artificial Photosynthesis)

To study the effect of NiO electrocatalyst on hematite performance

Hematite electronic structure study in both ex-situ and in-situ PEC condition with NEXAFS spectroscopy ( not the major focus of PhD thesis. Carried out as a part of group activity)

Synthesis of Pristine Hematite Film

Fe2(NO3)3•9 H2O+

Oleic Acid

125° C Viscous Mass THFSuspension

Supernatant Solution

CentrifugeFTO Substrate

Dip coating, 25° CIron Oleate Film

500° C, 2 Hours

Hematite Film (-Fe2O3)

Nanoparticle Size = 80 nm

20 30 40 50 60 70 80

0

200

400

600

800

1000

(321

),SnO

2(202

),SnO

2

(301

),SnO

2

(300

),-F

e 2O3

(310

),SnO

2

(211

),-F

e 2O3

(220

),SnO

2

(211

),SnO

2

(202

),-F

e 2O3

(210

),SnO

2

(113

),-F

e 2O3

(024

),-F

e 2O3

(200

),SnO

2

(110

),-F

e 2O3

(101

),SnO

2

(104

),\g

-Fe 2O

3

(110

),SnO

2(0

12),

-Fe 2O

3

Hematite film from Iron oleate precursor

Inte

nsity

(a.u

.)

20

500 nm

800 1000 1200 1400 16000

50

100

150

200

250

300

350

Cur

rent

Den

sity

(A

/cm

2 )

Potential vs. RHE (mV)

Dark Current Light Current