Cebo. Ndlangamandla

Synthesis of Iron Oxides nanorods for water splitting application

Energy Postgraduate Conference 2013

iThemba LABS/ UniZulu

OUTLINE

• Introduction

•What has been done

•Why Iron Oxide?

•Experimental Approach

•Results Discussion

•Conclusion

Energy Crisis: The world’s economy depend on fossil fuel and countries without fossil fuel depend to those with it.

Very Expensive so renewable Energy (cheap) is a need.

Non-Renewable Resources for the Production of Energy are limited.

Global warming: is due to the continuous emission of green house gases. so environmental friendly energy production systems are needed. The Fossil fuel need to be substituted

INTRODUCTION

Nanosystems for water Nanosystems for water splittingsplitting

Photo catalysis of water first reported by Honda and co-worker in 1970 and now has received interest since it offers a renewable nonpolluting approach of hydrogen production. US DEO’s target for photo electrochemical hydrogen production for solar hydrogen conversion efficiency is (8% by 2010 and 10% by 2015).

Solar Hydrogen at Tungsten Trioxide, Vaysseries et al (2001)Solar Hydrogen at Titanium Dioxide, Honda et al (1970)Solar Hydrogen at nano-composite semiconductors, Yoshihiro et al (2006)Hydrogen System nanodevices, Vaysseries et al (2005)Hydrogen System on ZnO, Levey-Clement et al (2003)

In all systems, the efficiency is still less than 6%

Pt Counter electrode e-

Ag/AgCL reference electrode

e-

h+

H2O

H2 O2

300W Xe-Lamp or Solar Simulator

Photoelectrode

Potentiostat

Principle of water splitting

M. Gratzel et al, ChemSusChem (2011)

ChallengesCarrier transportValence Band EdgeWater Oxidation KineticsLow optical absorption

PromiseBand gaps ~ 2.2 eV (it absorb up to 40% of solar light).Abundant and inexpensiveHigh Stability in electrolytes Thermodynamically stable.

Iron Oxide is a commonly-found material with band gap well-suited for the direct solar water splitting of water but its performance has been severely limited by opto-electronic properties. This material is promising because of Photo Oxidation of water for hydrogen production, transparent electronics applications.

PEC increaseGrowth of crystalline OxideDirect growth along the preferred electron conduction paths (orientation)High surface area material

Shift of Band Position

Quantum size effect Transition metal doping

Iron Oxide

-4

-5

-6

-7

-8

-1

0

1

2

3

2.2 eV 3.0 eV 2.8 eV 3.2 eV

E/eV

Fe2O3

TiO2

rutileWO3

ZnO

H2/H+

H2O/O2

BACK CONTACT IN DEFERENT MORPHOLOGY

eee e

SUN

EXPERIMENTAL APPROACHEXPERIMENTAL APPROACH

ACG uses simple equipments, low temperature deposition and the reaction is less hazardous, Template-less, Surfactant-free and there is no need to use the metal catalysts.

The size, shape and the orientation of the nanostructure can be easily being tailored. The coverage and the growth of the nanostructures on the substrate can be monitored.

An aqueous solution of FeCl3 and NaNO3 is used and parameters such as Time, pH can be controlled. 95oC was used for deposition.

Synthesis (Aqueous Chemical growth)Synthesis (Aqueous Chemical growth)

Vaysseries et al (2001)

SEM images of doped and undoped Fe2O3 nanorods grown onto FTO.

0.006 g

0.030 g

0.018 g

Pure

X-RAY POWDER DIFFRACTION (XRD).

Hematite has a trigonal/rhombohedra structure with approximately hexagonal close-packed array of oxygen. Fe3+ ions occupy two thirds of octahedral sites between oxygen’s each FeO6 octahedron shares a face with another in the layer above or below. Iron atoms lie on planes spaced approximately one third and two-thirds the distance between oxygen layers. Belong to the space

group R-3C.

Vayssieres et al, Adv. Mater.,Vol 17, 2320-2323

RAMAN MEASUREMENTS

Raman Study on Hematite samples

modes

Beattie et al 1970 (cm-1)

Massey et al 1990 (cm-1)

Shim et al 2001 (cm-

1)

This Study (cm-1)

A1g(1) 226 228 224 219

A1g(1) 245 246 243 243

A1g(1) 293 294 290 293

A1g(1) 298 300 297 388

A1g(1) 413 412 408 408

A1g(2) 500 496 496 496

A1g(1) 612 614 609 608

Eu 659 658

2Eu 1320 1316 1312

Optical measurements of Fe2O3 thin film deposited on FTO.

CONCLUSIONCONCLUSION

Randomly perpendicular oriented nanorods were obtained by adjusting the solution pH. This orientation is preferred to avoid recombination.

Spherical may not provide a good electrical pathway for the photo-generated electron to travel to the FTO back contact.

The band gap of hematite can be tailored by growth parameters such doping.