Polyoxometalates as Water Oxidation Catalysts and Their Use in Light-Driven Water Splitting Público
Yin, Qiushi (2010)
Abstract
Abstract
Polyoxometalates as Water Oxidation Catalysts
and Their Use in Light-Driven Water Splitting
By Qiushi Yin
Transition-metal substituted polyoxometalates are used to
construct
molecular analogues of heterogeneous metal-oxide clusters. The
importance of
these ligand-stabilized all-inorganic metal-oxide clusters
originate from both their
functionality and their molecular nature, which provides a system
for mechanistic
studies of metal-oxide water oxidation catalysis. Investigations
were made to
explain two polyoxometalates' ability to oxidize water at low
overpotential with
efficient redox leveling. Chapter I summarizes recent findings on
the chemistry of
a tetra-ruthenium polyoxometalate and includes studies of its rich
redox chemistry.
Chapter II describes discovery of a tetra-cobalt polyoxometalate
water oxidation
catalyst and discusses its possible electronic structure. Chapter
III illustrates that
molecular water oxidation catalysts can be interfaced efficiently
with photo-
driven systems to capture light energy.
Table of Contents
Table of Contents
Abstract
Acknowledgements
List of Figures
List of Tables
Chapter I
Redox Properties of a Polyoxometalate Water Oxidation
Catalyst,
[Ru4O4(OH)2(H2O)4(SiW10O36)2]10-,
and
corresponding Implications in its Oxidation Chemistry
..... 1
Introduction
................................................................................
3
Experimental
..............................................................................
7
Results and Discussion
..............................................................
8
Chapter II
Discovery and Identification of a Carbon-Free
Molecular
Cobalt Oxide Water Oxidation Catalyst and Its
Characterization
.....................................................................
27
Introduction
..............................................................................
29
Experimental
............................................................................
30
Results and Discussion
............................................................
40
Chapter III Coupling of Photosensitizers with Molecular Water
Oxidation
Catalysts for use in Artificial Photosynthesis, and
Light-driven
Water Splitting via Photoelectrochemical Cells
................... 72
Introduction
..............................................................................
74
Experimental
............................................................................
76
Results and Discussion
............................................................
78
List of Figures
Chapter I
Figure 1.1
Energy density diagram
.................................................................
5
Figure 1.2
A chemical scheme for water
splitting............................................ 6
Figure 1.3
UV-Vis spectra of 1 in 0.1 M
H2SO4.............................................
9
Figure 1.4
Voltammogram of 1 in 0.2 M pH 2 lithium sulfate buffer
........... 10
Figure 1.5
E1/2 values of 1(n) as a function of the
redox state ....................... 11
Figure 1.6
Absorption spectra of 1(+2) in 0.1 M
H2SO4 ................................
13
Figure 1.7
Time profile of the absorbance at λ = 445 nm.
............................. 14
Figure 1.8
The UV-visible absorption spectra of reduced 1(-2)
.................... 15
Figure 1.9
The absorbance at 445 nm of a reduced 20 μM 1(-2) at
r.t........... 16
Figure 1.10
The absorbance at 445 nm of a reduced 20 μM 1(-2) at
45°C ...... 17
Chapter II
Figure 2.1
Thermogravimetric Analysis (TGA) of crystalline
Na10-2 ........... 31
Figure 2.2
FT-Infrared spectrum of 2
.............................................................
32
Figure 2.3
UV-Visible spectrum of 1 mM 2 in pH 8
..................................... 33
Figure 2.4
31P NMR of a post catalytic solution containing 2
....................... 39
Figure 2.5
Cyclic voltammogram of 2 at pH 8
............................................... 42
Figure 2.6
X-ray structure of Na10-2.
.............................................................
44
Figure 2.7
Structure of cobalt-containing polytungstate complexes 2-
9........ 46
Figure 2.8
Hyperbolic fit of O2 yield versus catalyst
concentration .............. 48
Figure 2.9
UV-Visible spectra showing cobalt titration using bpy
................ 51
Figure 2.10
31P NMR of 2 at pH 8
...................................................................
53
Figure 2.11
31P NMR of 2 at pH 3.5
................................................................
54
Figure 2.12
31P NMR of 2 at pH 6
...................................................................
55
Figure 2.13
31P NMR of 2 at pH 9
...................................................................
56
Figure 2.14
CV showing catalyst 2 maintaining activity after use
.................. 61
Figure 2.15
CV showing Co(aq.)2+ does not maintaining activity after
use .... 62
Chapter III
Figure 3.1
A scheme for light-driven water oxidation
................................... 75
Figure 3.2
Time-profile of light-driven O2 yield with 2 and
persulfate ......... 80
Figure 3.3
Structure of [Ru(mptpy)2]4+
.......................................................... 80
Figure 3.4
Time-profile of light-driven O2 yield using
[Ru(mptpy)2]4+ ......... 82
Figure 3.5
A scheme for photoelectrochemical splitting of water
................ 83
Figure 3.6
Electronic spectra of a Fe2O3 film with and
without 1 ................. 84
Figure 3.7
Reaction scheme for the functionalization of SMO surface. ........
85
Figure 3.8
Reflectance IR spectrum of functionalized
Fe2O3 surface ............ 85
Figure 3.9
Photocurrent obtained using the photoelectrochemical cell .........
86
Figure 3.10
UV-visible spectrum of Cr-O modified TiO2 surface
................... 88
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