Metal oxide nanomaterials and their application in solar photoelectrolysis of water

Kler, Rantej Singh (2014) Metal oxide nanomaterials and their application in solar photoelectrolysis of water. Doctoral thesis (PhD), University of Sussex.

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Solar generated hydrogen as an energy source is green, sustainable, with a high
energy density. One day the majority of current fossil fuel based technology could
be replaced with hydrogen technology reducing CO2 emission drastically. The goal
in this research is to explore hybrid metal oxide photocatalysts in the pursuit of
achieving highly efficient photoanodes for use in photoelectrochemical cells (PEC).
Achieving high efficiencies of hydrogen production in photoelectrochemical cells is
the key challenge for the commercialisation of PEC technology as a viable, sustainable,
hydrogen source; limited only by the lifetime of the sun and the resources of
the metal oxide materials.
In this research TiO2, Fe-Ti-O, ZnO, and Zn2TiO4 are the photocatalysts explored.
Alloys of Ti-Fe-O showed improvement over TiO2, whilst a hybrid heterostructure
of ZnO/Zn2TiO4/TiO2 enhanced photocurrent densities significantly. A
barrier layer in the photoanode achieved localised exciton separation and reduction
of recombination rates by inhibiting back flow of electrons after injection into the
TiO2 layer.
Nanotubes are created by the simple electrochemical process of anodisation. The
nanotube composition depends on the anode material. To control the composition ofthe anode, iron and titanium are co-deposited onto a substrate using electron beam
evaporation. The introduction of iron into titania nanotubes engineered the band
gap, lowering the band gap energy to that of iron oxide whilst the positions of the
conduction and valence bands with respect to the oxidation and reduction potentials
of water remained favourable. Fe-Ti-O nanotubes showed remarkable photocurrent
density improvement compared to TiO2 nanotubes.
ZnO nanostructures deposited by vapour transport mechanisms showed variability
in the morphology of the structures, as governed by the growth dynamics.
Herein, it is shown that an electronically favourable situation arises by the formation
of a ZnO-Zn2TiO4-TiO2 heterostructure and a high photocatalytic activity is
reported. The structure is composed of a large surface area ZnO nanorod photoabsorber
formed on a Ti foil which forms a Zn2TiO4 barrier layer between ZnO and
TiO2. The Zn2TiO4 layer inhibits electron transport toward the surface of the photoanode
whilst encouraging charge transport to the hydrogenation electrode. The
heterostructure interfacial surface area is extended through the utilisation of TiO2
nanotubes, which demonstrated a 20.22 % photoelectrochemical efficiency under UV
Surface modification of ZnO nanorods with aerosol assisted chemical vapour
deposited TiO2 nanoparticles enhanced photocurrent densities of the ZnO rods,
improving charge separation of excitons created within the TiO2 nanoparticles.
ZnO nanotubes formed via a novel route using chemical bath deposition of ZnO
is investigated, an annulus ZnO seed layer facilitated the site specific growth of ZnO
nanotubes whilst a uniform seed layer formed ZnO nanorods.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Biochemistry
Subjects: Q Science > QD Chemistry > QD0241 Organic chemistry
Q Science > QD Chemistry > QD0241 Organic chemistry > QD0415 Biochemistry
Depositing User: Library Cataloguing
Date Deposited: 12 Jun 2014 14:43
Last Modified: 12 Jun 2014 14:43

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