Dennis Butcher_Final Defense_072512

© K. S. Suslick, 2008
Investigation of the Surface-Electrolyte
Interface of Semiconductors and Metals
I. Photoelectrochemical Analysis of Metal-Oxide
Composites for Photocatalytic Water Splitting
II. DFT Investigation of K+ adsorption on Au(100)
III. Small Molecule Adsorption and Reactivity on Metal Single
Crystals Study Utililizing Shell Isolated Nanoparticle
Enhanced Raman Spectroscopy (SHINERS)
1
Dennis P. Butcher Jr.
University of Illinois
Advisor: Dr. Andrew Gewirth
July 25, 2012

Outline
2
• Background:
-Raman Spectroscopy
-Surface Enhanced Raman Spectroscopy (SERS)
-Shell Isolated Nanoparticle Enhanced Raman
Spectroscopy (SHINERS)
• Face-dependent SHINERS of 2,2’-bipyridine on Au(100)
and Au(111)
• Investigation of reaction intermediates of nitrate reduction
on Cu(100), Cu(111), and Cu(110)

Raman Spectroscopy
for Surface Characterization
27
Pros:
• Highly specific chemical fingerprint
• Low attenuation from solvent (water)
• Minimal interference from water
vibrations
• No tags or markers required
• Highly versatile for all phases
Cons:
• Low Raman scattering cross-section
• Poor surface selectivity
http://en.wikipedia.org/wiki/File/Raman_energy_levels.svg

Surface Enhance Raman Spectroscopy
(SERS) Overcomes Raman Sensitivity Problem
28
• Incident light excites surface plasmons
(collective oscillations of electrons)
when in resonance; amplifies EM fields
at interface
• Plasmons typically parallel to surface;
Need features much smaller than
wavelength of light to excite dipole
oscillations (perpindicular to surface)
• Achieve enhancement of incident and
scattered light (E4 enhancement); 104-
108 intensity boost
• Metals with localized surface plasmon
resonance in visible region are Au, Ag,
Cu
Huang, Y. F.; Li, C. Y.; Broadwell, I.; Li, J. F.; Wu, D. Y.; Ren, B.; Tian, Z. Q., Electrochimica Acta 2011, 56, 10652.
Anema, J. R.; Li, J. F.; Yang, Z. L.; Ren, B.; Tian, Z. Q., Annual Review of Analytical Chemistry, Vol 4, Cooks, R. G.; Yeung, E. S., Eds. Annual Reviews: Palo
Alto, 2011; Vol. 4, pp 129.
SERS substrate

Variations of SERS Attempt to Expand
Substrates Available for Study
29
Tip Enhanced Raman Spectroscopy (TERS)
SERS with probe nanoparticles
coated in non-enhancing metal
Can we achieve better reliability and signal to noise while expanding to non-
enhancing and single crystal substrates?
Anema, J. R.; Li, J. F.; Yang, Z. L.; Ren, B.; Tian, Z. Q., Annual Review of Analytical Chemistry, Vol 4, Cooks, R. G.; Yeung, E. S., Eds. Annual Reviews: Palo
Alto, 2011; Vol. 4, pp 129.

Shell-Isolated Nanoparticle Enhanced
Raman Spectroscopy (SHINERS)
Li, J. F.; Huang, Y. F.; Ding, Y.; Yang, Z. L.; Li, S. B.; Zhou, X. S.; Fan, F. R.; Zhang, W.; Zhou, Z. Y.; WuDe, Y.; Ren, B.; Wang, Z. L.; Tian, Z. Q., Nature 2010,
464, 392.
Li, J.-F.; Ding, S.-Y.; Yang, Z.-L.; Bai, M.-L.; Anema, J. R.; Wang, X.; Wang, A.; Wu, D.-Y.; Ren, B.; Hou, S.-M.; Wandlowski, T.; Tian, Z.-Q., Journal of the
American Chemical Society 2011, ASAP
30

Outline
35
• Background:
-Raman Spectroscopy
and Au(111)
on Cu(100), Cu(111), and Cu(110)

2,2’-bipyridine on Au surfaces
36Hoon-Khosla, M.; Fawcett, W. R.; Goddard, J. D.; Tian, W. Q.; Lipkowski, J., Langmuir 2000, 16, 2356.
Dretschkow, T.; Wandlowski, T., Electrochimica Acta 1999, 45, 731.
-800 mV -200 mV 400 mV
STM Bpy on Au(111)
300 mV vs. SCE
0.05 M KClO4
3mM bpy
Differential Capacitance bpy on Au(111)
0.1 M KClO4; 1mM bpy
Can SHINERS expand our understanding of 2,2’-bipyridine
on Au single crystal surfaces?
• Corrosion inhibition
• Molecular electronics
• Electrocatalysis
• Metal-bpy systems for solar cells
and electroluminescent devices

Previous examples of 2,2’-bipyridine SERS
37
300 mV
-700 mV
Brolo, A. G.; Jiang, Z.; Irish, D. E., J. Electroanal. Chem. 2003, 547, 163.
Limited by lack of relative intensity, lack of single crystal specificity,
and inconsistent surface preparation techniques
ν(Cl-O)

SHINERS of 2,2’-bipyridine
on Au(100) and Au(111)
38
Anodic Scan
Cathodic Scan
0.1 M KClO4
1 mM 22Bpy

SHINERS of 2,2’-bipyridine
on Au(100)
39
Peak Wavenumber
(cm-1)
Assignment
Au(111) Au(100) Ring Breathing
X 996 996 trans solution
I 1006 1006 cis π-flat
J 1010 1010 physisorbed N-
bound
Y 1019 1019 cisoid
K 1024 1024 cis N-bound
L 1034 1034 cis N-bound
C-C Inter-Ring
Q 1304 1304 trans solution
Α 1307 1307 cisoid
Z 1318 1318 cis N-bound
R 1320 1320 cis N-bound
X

Primer on Correlation Analysis Methods
40
Perturbation Correlation
Moving Window Two
Dimensional Spectroscopy
(PCMW2D)
Two Dimensional Correlation
Spectroscopy
(2DCOS)
• Spectra plotted in 2D map between
Raman Shift and Potential
• Synchronous correlation spectra
proportional to spectral gradient
(velocity of peak change)
• Visualizes regions of strong potential
dependent peak changes
• Used to determine ranges to further
investigate by 2DCOS
• Compares changes at every spectral
variable to changes at all other
variables (Raman Shift × Raman
Shift)
• Synchronous plots symmetric wrt
diagonal; positive cross peaks
indicate peaks changes occur in
same direction
• Asynchronous plots asymmetric with
diagonal; cross peaks develop if
peaks change out of phase with
each other (delayed or accelerated)Collaboration with Renato Canha-Ambrosio

Adsorption Dynamics Revealed by
PCMW2D during Anodic Polarization
41
Read bottom to top
Physisorbed
cis-bpy
Chemisorbed
cis-bpy
Cisoid bpy

Schematic of 2,2’-bipyridine on Au(111)
and Au(100) under anodic polarization
45
• Compact adsorption layer at negative potentials along with an extended
adsorption layer
• Followed by continued formation of a compact layer as potential is
scanned positive.
• Desorption through a torsional intermediate occurs at the positive
potential extreme.

Adsorption Dynamics Revealed by
PCMW2D during Cathodic Polarization
46
Read top to bottomCisoid bpy
Physisorbed
cis-bpy
Chemisorbed
cis-bpy

Schematic of 2,2’-bipyridine on Au(111)
and Au(100) under cathodic polarization
51
• Adsorption through a torsional state occurs at positive potentials.
• This state is consumed to form the compact layer as potential is scanned
negatively.
• Despite spectral sequence difference, the adsorption characteristics are
broadly similar.

Conclusions:
Face Dependent SHINERS of 2,2’-bipyridine
on Au(100) and Au(111)
52
• SHINERS produced strong signal for 2,2’-bipyridine adsorption on polished
single crystal Au(100) and Au(111)
• Spectral analysis reveals a compact adsorption layer as well as an extended
adsorption layer during polarization containing π-flat and vertical N-bound
2,2’-bipyridine; previous studies featured ambiguous results, particularly at
the negative potential extreme
• This work demonstrates the utility of PCMW2D and 2DCOS to deconvolute
complicated spectral transitions
• SHINERS paired with correlation analysis has extraordinary potential for
studying adsoption dynamics of organic films on single crystals
• These methods are being applied to study small molecule reactivity on single
crystal metal surfaces (e.g. nitrate reduction on Cu, oxygen reduction on Au)

Outline
53
• Background:
-Raman Spectroscopy
and Au(111)
on Cu(100), Cu(111), and Cu(110)

Vulnerability of Groundwater to
Nitrate Contamination
54Nolan, B. T.; Hitt, K. J.; Ruddy, B. C., Environmental Science & Technology 2002, 36, 2138.
10 mg/L exposure limit
Risks:
Methemoglobinemia
“Blue Baby Syndrome”
Increased risk of cancer

Electrocatalytic Nitrate Reduction
55Bae, S. E.; Stewart, K. L.; Gewirth, A. A., J Am Chem Soc 2007, 129, 10171
Bae, S. E.; Gewirth, A. A., Faraday Discuss 2008, 140, 113.
NO3
- + 8e- + 9H+ → 3H2O + NH3
Gabriela Elena, B., Electrochimica Acta 2009, 54, 996
Acidic Media:
NO3
- + 2e- + 2H+ → H2O + NO2
-
RDS
Can SHINERS provide new information regarding intermediates of nitrate reduction?
• Cu, Pt, Pd, and bimetallics are commonly used nitrate electrocatalysts
• Cu is the most promising; different faces exhibit different activity
• Nature of the intermediates is not fully known
NO2
- + 6e- + 7H+ → 2H2O + NH3
NO + e- + H+ ↔ HNO
HNO + H+ + e- → H2NO
NO2
- + e- + 2H+ → NO + H2O
H2NO + 3H+ + 3e- → NH3 + H2O

Previous Attempts to Investigate
Nitrate Reduction on Cu Using SERS
56
0.1 M HClO4, 0.5 mM HNO3
0.1 M HF, 10 mM NaNO2
• Poor resolution between nitrate
and nitrite peaks
• No single crystal investigation
• Difficult to reproduce because of
roughening procedure
• Use SHINERS to achieve better
peak definition and to study
reaction on single crystals
Bae, S. E.; Stewart, K. L.; Gewirth, A. A., J Am Chem Soc 2007, 129, 10171

Possible Orientations of NO2
- on Copper
57
Nitro Nitrito
Chelating Nitrito
Bridging NitritoBridging Nitro

Cyclic Voltammetry Indicates
Differential Reduction of Nitrate
58Bae, S. E.; Stewart, K. L.; Gewirth, A. A., J Am Chem Soc 2007, 129, 10171
0.1 M HClO4, 0.05 M HNO3
Paidar, M.; Roušar, I.; Bouzek, K., J. Appl. Electrochem. 1999, 29, 611.
• Scan from 50 mV to -800 mV
• Cu(110) and Cu(111) exhibit
reduction at 0 V;
autocatalytic reduction of
nitrate to nitrite
• Cu(100) is offset by -200 mV
• Hypothesize that prevalence
of Cu2O on Cu(111) and
Cu(110) facilitates nitrate
reduction

SHINERS of Nitrate Reduction on Cu(100)
60
-400 mV
-300 mV
νs(NO2 of NO3
-)
and νa(NO2 of
NO3
-)
νs(NO2
-) and
νa(NO2
-)
0 mV
-800 mV
ν(N-O) and
ν(N=O)
NO2
- Bending

61
0 mV
-800 mV
-400 mV
-300 mV
ν(N=O)
bridging nitro
ν(N=O) and HNO
bend from HNO

62
NO2
- Bending
-300 mV
-250 mV
νs(NO2
-) and
νa(NO2
-)
ν(N-O) and
ν(N=O)
νs(NO2 of NO3
-)
and νa(NO2 of
NO3
-)
0 mV
-800 mV

63
-300 mV
-250 mV
ν(N=O)
bridging nitro
0 mV
-800 mV
ν(N=O) and HNO
bend from HNO

64
-250 mV
-200 mV
NO2
- Bending
νs(NO2
-) and
νa(NO2
-)
ν(N-O) and
ν(N=O)
νs(NO2 of NO3
-)
and νa(NO2 of
NO3
-)
0 mV
-800 mV

65
-250 mV
-200 mV
ν(N=O)
bridging nitro
0 mV
-800 mV
ν(N=O) and HNO
bend from HNO

Adsorption Energy of NO3
- and NO2
- to Cu
Does Not Determine Reduction Activity
67
Does a particular surface stabilize NO3
- or NO2
- adsorption to a greater degree?
Surface Conformation
Adsorption Energy (eV)
Surface
Cu(100) Cu(111) Cu(110)
Nitrate -2.69 -2.28 -2.80
Nitrito -1.42 -1.21 -1.47
Chelating Nitrito -1.97 -1.65 -2.12
If adsorption of NO3
- nor NO2
- to bare Cu surfaces doesn’t
determine relative activity, then what does?

Higher Activity of Cu(110) and Cu(111)
Determined by Surface Oxide
68
Surface
Conformation
Adsorption Energy (eV)
Surface
Cu2O(100) Cu2O(111) Cu2O(110)
Nitrate -0.24 -9.65 -4.22
Chelating Nitrito -0.48 -9.08 -3.50
Cu(110) • Cu(110) exhibits strong SHINERS intensity for
Cu2O; Cu(111) spectra are inconclusive for Cu2O
• However, literature suggests the Cu(111) and
Cu(110) surface oxidizes at a higher rate relative to
Cu(100)
• Cu2O(111) and Cu2O(110) stabilize both NO3
- and
NO2
- more effectively than Cu2O(100), providing a
strong driving force for nitrate autocatalysis
Zhou, G.; Yang, J. C., Journal of Materials Research 2005, 20, 1684.

Delayed Onset of Nitrate Reduction
in Presence of Cl-
69
• Onset potential of
reduction shifted ~300
mV in negative direction
• No autocatalytic priming
reaction is observed as
with the bare Cu(111)
and Cu(110) surfaces
• Nitrate reduction only
occurs as the Cl- starts
to desorb and expose
bare Cu

SHINERS of Nitrate Reduction on Cu
in the Presence of Cl-
70
Cu(100) Cu(111) Cu(110)
Q ρr(NH3) rocking; S and T δs(HNH) of NH3; V δa(HNH) of NH3
U ν(T4) antisymmetric NH2 of NH4
+; V δ(E) antisymmetric NH2 of NH4
+

Tafel Plots Illustrate Different Reaction
Pathways on Bare and Cl- Coated Cu
71
Bare Surface Cl- Decorated Surface
Stepwise Reduction of NOx Delayed Onset, Direct Reduction

Different Reaction Pathways Based
upon Availability of Oxide Formation
72
Bare Cu Cl- Protected Cu
NO3
- + Cu(111) → NO2
- + Cu2O(111)
NO3
- + Cu(110) → NO2
- + Cu2O(110)
NO3
- + Cu(100) → NR
Autocatalysis
Stepwise NOx Reactions
NO + e- + H+ ↔ HNO
HNO + H+ + e- → H2NO
NO2
- + e- + 2H+ → NO + H2O
H2NO + 3H+ + 3e- → NH3 + H2O
NH3 + H+ → NH4
+
No Autocatalysis
NO3
- + 8e- + 9H+ → 3H2O + NH3
NH3 + H+ → NH4
+
NO3
- + 2e- + 2H+ → H2O + NO2
- On Cu(100)

Conclusions and Outlook
73
• Primary intermediate for nitrate reduction on bare Cu is adsorbed nitrite;
presence of a protonated NO species is also observed; no intermediates formed
for nitrate reduction on Cl- decorated surface; direct reduction to NH3 followed by
protonation to NH4
+
• NO2
- exists in at least 3 different orientations on bare Cu; STM and DFT studies
had previously indicated only the chelating nitrito conformation; the orientations
do not appear to determine reaction mechanism or activity
• DFT calculations using VASP show that Cu2O(111) and Cu2O(110) stabilize NO2
-
and NO3
- more effectively than Cu2O(100), providing a driving force for
autocatalysis on Cu(111) and Cu(110)
• SHINERS data complements previous studies of nitrate reduction on Cu single
crystal surfaces; data indicate an critical role for Cu2O in the higher activity
toward nitrate reduction on Cu(111) and Cu(110) relative to Cu(100)
• This work proves the concept that SHINERS can monitor surface reactions and
identify intermediates and products as they are generated

Acknowledgements
74
Special Thanks
Prof. Andrew Gewirth
Matt Thorseth
Rich Helmich
Scott Dunkle
Prof. Catherine Murphy
Renato Canha-Ambrosio
Stefano Boulos
Brandon Long
Nicole Honesty
Mike Hallock
Mauro Sardela
Julio Soares
Funding
Department of Energy
National Science Foundation

Dennis Butcher_Final Defense_072512

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