"Electrochemically Wired Semiconductor Nanoparticles: Toward Vectorial Electron Transport in Hybrid

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"Electrochemically Wired Semiconductor
Nanoparticles Toward Vectorial Electron
Transport in Hybrid Materials and Solar-Assisted
Hydrogen Production
Neal R. Armstrong, Jeffrey Pyun, Dominic McGrath,
Zhiping Zheng, Scott Saavedra Department of
Chemistry, University of Arizona, Tucson, Arizona
85721 nra_at_u.arizona.edu jpyun_at_email.arizona.edu
Preliminary Photoelectrochemistry
NanoMaterials
OUR LONG TERM VISION
Synthesis of Photocatalytic Nanoparticles Objecti
ves Synthesis and functionalization of
semiconductor nanocrystals, organic dendimers and
heterodimeric nanocrytals with electron-rich
conjugated thiophene precursors
Efb - 0.35 V
I. CdSe Semiconductor Nanoparticles

A. Functional Nanocrystals Ligand Exchange
B. Dendritic Ligands for Nanocrystals
Thiophene Functionalized PAMAM Dendrimers
Photo-assisted (filtered 150 W Xe arc lamp)
reduction of methyl viologen (MV, 1mM in
acetonitrile with 0.1 M TBAHFP) on a hybrid
platform. CdSe(ODA, see below) nanoparticles
were spin-cast from toluene solution onto
electrochemically grown PEDOT (e-PEDOT) on ITO.
Electrochemically wired semiconductor
nanoparticles (SC-NP) inclusions in microporous
sol-gel (MPSG) environments
Thiophene Functionalized CdSe Nanocrystals
PAMAM/Thiophene Functionalized CdSe Nanocrystals
Schematic representation of photocatalytic
reduction of MV.
Ligand 4
E (eV)
V vs NHE
THF
PEDOT
0.0
WORK FROM PRIOR DOE SUPPORT WHICH MOTIVATES THIS
EFFORT
CdSe-NP
- 2.95 eV
PAMAM Dendrimer Capped CdSe Nanocrystals
Hexadecylamine (HDA) Capped CdSe Nanocrystals
MV/MV.
Pyridine Capped CdSe Nanocrystals
Thiophene Capped CdSe Nanocrystals
- 3.5 eV
The templated electrochemical growth of
poly(3,4-ethylenedioxythiophene) (PEDOT) into
porous sol-gel films (5050 TEOSMTES) on ITO was
demonstrated, along with PEDOT-mediated electron
transfer to ferrocene modified PAMAM dendrimers
encapsulated within these sol-gel matrices (up to
20 of the ferrocene-decorated PAMAM dendrimers
could be wired to the ITO substrate).

• Heterodimeric Nanostructures
• Introduction of Catalytic Sites
• for H2 Evolution

C. Variation of Nanocrystal Morphology
- 4.15 eV
3-6 nm
Noble Metal Nanoparticle D 7 nm

• 5.05 eV

CdSe Quantum Dot
CdSe Nanorod Length 60 nm Width 7 nm
- 5.5 eV
20 nm
8 nm
Value determined by Eº Eg Value
determined from E º UPS Data (Valence
Band Onset) UPS Data Eg
Au nanotips
CdSe Nanorice
Frontier orbital energies estimated
electrochemically

• Work in progress
• Wiring of SC-NPs to PEDOT/PEDOTCA-like columns.
• Characterization of frontier orbitals in SC-NPs
  wired to conductive substrates (Au, ITO) using
  X-ray and UV photoelectron spectroscopies
• Condutive-tip AFM to measure i/V properties of
  wired SC-NPs on nanometer length scales

60 nm
8 nm
Conducting Polymer Growth in Porous Sol-Gel Thin
Films Formation of Nanoelectrode Arrays and
Mediated Electron Transfer to Sequestered
Macromolecules, Walter J. Doherty III, Neal R.
Armstrong, S. Scott Saavedra, Chemistry of
Materials, 17, 3652-3660 (2005).
CdSe Nanorods
Students/Postdocs supported by this effort
Clayton Shallcross Mike Szalai Yinglan Wu Dr.
In-Bo Shim (postdoc).
Research Support Department of Energy, Office
of Science Hydrogen Fuel Initiative -- Basic
Energy Sciences Solar Hydrogen
Production Leveraging Support DE-FG02-02ER15378
Biomimetic Energy Transduction Artificial
Photosynthesis in a Stabilized Lipid Membrane
Coupled to a Semiconductor (Scott Saavedra, P.I.)