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Hybrid Molecular, Materials, and Biology Approaches to Solar-to-
Chemical Conversion
Christopher J. Chang
Departments of Chemistry and Molecular and Cell Biology and the Howard
Hughes Medical Institute, University of California, Berkeley
Chemical Sciences Division, Lawrence Berkeley National Laboratory
Rising global energy demands and climate change motivate the invention of
new technologies for solar-to-chemical conversions for sustainable use of
limited carbon resources. In this context, we are inspired by natural
photosynthesis, which takes light, water, and carbon dioxide to make the
value-added products that form biomass to sustain life. We seek to create
artificial photosynthesis systems that take light, water, and carbon dioxide to
make value-added products for societal benefit. As such, we have initiated a
program aimed at creating new molecular, materials, and biological catalysts
for generating hydrogen from water and carbon dioxide fixation, with
particular interest in developing earth-abundant metal systems that operate in
green aqueous media and do not generate organic byproducts during catalysis.
This talk will present our latest results on electrocatalytic and photocatalytic
generation of hydrogen and reduction of carbon dioxide by merging concepts
from chemistry with allied fields of materials science and biology.
Solving Structures of Energy Materials
Mark A. Green
School of Physical Sciences,
University of Kent
Critical to the development of energy related materials is a detailed
understanding of their atomic level composition, structure and dynamics.
Neutron and X-ray diffraction are commonly used techniques to obtain
nuclear and magnetic structures. However, energy materials provide additional
complex challenges as their structures often possess dynamical components.
For example, the functionality of solid oxide fuel cells, batteries, and gas
absorption systems is reliant on mobility of parts of their structure. We will
discuss alternative approaches to traditional structure refinement to obtain a
more complete structural description in a number of examples, including
perovskite photovoltaics, oxide ion conductors, batteries, and metal - organic
frameworks.
References:
Yajima, T. et al. Nature Chemistry,
7, 1017 (2015).
Jun et al, Nature Materials, 7, 953
(2008).
Kuang et al, Nature Materials, 7,
498 (2008).
Nakatsuji et al, Science, 336, 559
(2012).
Zajdel et al, JACS, 132, 13000
(2010)
Bao et al, PRL, 102, 247001 (2009)
Huang et al, PRL, 101, 257003 (2008).
Organo-Lead Trihalide Hybrid Perovskites Solar Cell Powered Devices
Hong Jin Fan
School of Physical & Mathematical Sciences,
Nanyang Technological University
Organic-inorganic lead halide perovskites are currently being investigated
as materials for next-generation photovoltaic cells due to their high power
conversion efficiency and solution processability, and other applications such
as lasing, photodetection and light emission. I will present our recent research
on organo-lead trihalide perovskites in energy conversion applications,
including photolysis water splitting, electrochromic batteries, and photo-
supercapacitors. We combine printable perovskite solar cells with other
components either in tandem or integration to realize multifunctionalities. For
the particular example of electrochromic batteries, the tandem device exhibit
functions of solar energy harvesting, electrochromics (optical modulation),
and electrochemical energy storage and reutilization. Another example is to
achieve simultaneous energy storage by integrating supercapacitive electrode
material into perovskite solar cells.
Application of Redox Targeting Principles to the Design of Rechargeable
Li-S Flow Batteries
Jingfa Li, Liuqing Yang, Shiliu Yang and Jim Yang Lee*
Department of Chemical and Biomolecular Engineering,
National University of Singapore
Redox flow batteries (RFBs) are a scalable technology platform for the large-
scale storage of electrical energy. Their most salient feature is the decoupling
of energy and power. RFBs are however constrained by the solubility of the
redox-active species in the electrolyte to usually exhibit a low energy density.
The ‘redox-targeting” approach developed of late (Angew. Chem. Int. Ed.
2006, 45, 8197–8200) addresses this limitation by using the dissolved redox
species only for charge transfer with a solid-state energy storage compound
stored in an “energy tank”. In principle the “redox-targeting” can effectively
combine the flow battery technology with any advanced battery chemistry to
form hybrid chemical/electrochemical rechargeable systems. This has been
demonstrated for the lithium-ion batteries as the “redox-flow lithium ion
batteries” (Adv. Energy Mater. 2014, 4, 1400567).
We applied the redox targeting concept to address some key challenge in the
operation of rechargeable Li-S batteries. The lure of rechargeable Li-S
batteries is their very high theoretical energy density (≈ 6 times of lithium-ion
batteries). The Li-S batteries are however operationally handicapped by a
number of technical issues: the low electronic conductivity of sulfur (thereby
requiring the presence of a conductivity agent in large excess), volume
changes in the S electrode during battery discharge and charge, and sulfur
dissolution as polysulfides. We demonstrate how these problems may be
solved by the “redox-targeting” approach. Specifically a pair of facile redox
couples, bis-(pentamethyl-cyclopentadienyl) chromium (CrCp*2) and bis-
(pentamethyl-cyclopentadienyl) nickel (NiCp*2), which straddle the S/Li2S
battery reactions, were used to inject/extract charges into/from solid sulfur
stored in an energy tank. The redox mediators, which were oxidized/reduced
in due course, were regenerated in a separate electrochemical reactor. The
capacity of the battery constructed as such could be easily augmented
(“mechanically recharged”) any time as and when need arises. It is not our
intent to provide an optimized cell design, but rather to demonstrate the
application of the redox targeting principles to overcome the major challenges
in rechargeable Li-S batteries.
Improving Electron Transport in Nanostructured TiO2 Electrode
Liu Bin
School of Chemical and Biomedical Engineering,
Nanyang Technological University
Titanium dioxide (TiO2) is one of the most widely used semiconductors in
photovoltaics and photocatalysis because it is nontoxic, abundant, stable and
photoactive. However, the wide bandgap, low electron mobility and short
minority carrier diffusion length of TiO2 limit its quantum efficiency in these
applications. In this work, we present a solution chemical approach for making
TiO2 nanostructures for improving the electron transport in nanostructured
TiO2 electrodes.
Natural Gas Storage in Metal-Organic Frameworks
Jeffrey R. Long
Departments of Chemistry and Chemical & Biomolecular Engineering,
University of California, Berkeley and
Materials Sciences Division, Lawrence Berkeley National Laboratory
As a cleaner and more evenly distributed fuel, natural gas has significant
advantages over petroleum as a source of energy for the transportation sector,
but its low volumetric energy density presents substantial challenges,
particularly for light-duty passenger vehicles with limited space. Adsorbed
natural gas systems have the potential to eliminate these issues by storing high
densities of methane within a porous material at ambient temperature and
reduced pressures. Although activated carbons, zeolites, and metal-organic
frameworks have been investigated extensively for this application, there are
still no commercially available adsorbed natural gas vehicles, owing to the
challenges involved in designing a practical system with a high capacity of
usable CH4 and sufficient thermal management. Here, a new concept in gas
storage will be introduced, wherein a reversible phase transition is used to
maximize the deliverable capacity of a gas while also providing internal heat
management during adsorption and desorption. In particular, the flexible
metal-organic frameworks Co(bdp) and Fe(bdp) (bdp2–
= 1,4-
benzenedipyrazolate) are shown to undergo a structural phase transition in
response to specific CH4 pressures, resulting in adsorption and desorption
isotherms that feature a sharp step. Such behavior enables storage capacities
that push beyond the limits of classical adsorbents, while also reducing the
amount of heat released during CH4 adsorption and the impact of cooling
during desorption. Significantly, the pressure and energy associated with the
phase transition can be tuned either chemically or by application of
mechanical pressure.
Integrated Optoplasmonics for Solid-State All-Optical Computing
Hongkun Park
Department of Chemistry and Chemical Biology & Department of Physics,
Harvard University
All-optical integrated circuits, which consist of photonic transistors and logic
circuits complete with on-chip light sources and detectors, have long been a
major goal for scientists and engineers because they may allow ultra-fast
computing with ultra-low power consumption. The actual realization of this
dream has been very difficult, however, because photons rarely interact with
each other and, even with the aid of nonlinear optical materials, interact very
weakly. My group leverages recent advances in photonics, plasmonics,
optoelectronics, and quantum optics to develop new material and technology
platforms for solid-state all-optical information processing. Specifically, we
combine recently developed material and technology platforms – two-
dimensional plasmonic crystals and metasurfaces, silicon-vacancy centers in
nanostructured diamond, and two-dimensional transition metal
dichalcogenides – and realize integrated all-optical devices and logic circuits
that work all the way down to the single-photon level. In this presentation, I
will discuss some recent examples of these research efforts.
Artificial Photosynthesis by Light Absorption, Hydrogen Evolution, and
Biomass Valorization
Soo Han Sen
School of Physical and Mathematical Sciences,
Nanyang Technological University
Artificial photosynthesis has been recognized as a sustainable approach to
utilize solar energy for chemical reactions and energy storage. Some of the
critical functions of artificial photosynthetic systems include light absorption,
charge separation, and multi-electron catalysis. In this presentation, I will
summarize my team’s early contributions to each of these elementary
components. I will describe our efforts in the preparation of Cu(I) and In
photosensitizers supported by bis(arylimino)acenaphthene ligands. The In
complexes have been prepared through solvent-free, mechanochemical
methods. The diamagnetic, homoleptic Cu(I) complexes exhibit panchromatic
light absorption extending to the near infrared region. The transient absorption
spectroscopic and photoluminescence measurements of some of the new Cu(I)
complexes will be reported. For the multi-electron reductive half-reaction, my
team has recently reported new salicylaldimine nickel complexes bearing ether
pendant arms that perform as hydrogen evolution electrocatalysts, even in
seawater. Regarding the multi-electron oxidative half-reaction, I will describe
my team’s discovery of a new selective, photoredox C-C activation reaction,
which occurs under ambient, atmospheric conditions using visible light as the
energy source.
Halide Perovskites: The New Wonder Photovoltaic Material
Sum Tze Chien
School of Physical & Mathematical Sciences,
Nanyang Technological University
Organic-Inorganic halide perovskite solar cells are presently the forerunner
amongst the solution-processed photovoltaic technologies – with efficiencies
exceeding 22%. In this talk, I will review the photophysical mechanisms of
the workhorse CH3NH3PbI3 system. In addition, I will highlight some of our
latest findings in perovskite single crystals and low-dimensional perovskites
(i.e., core-shell perovskite nanocrystals and nanoplatelets). Other novel
properties of this amazing family of materials beyond the CH3NH3PbI3
system will also be featured.
Molecular Analogs of MoS2 Edges for Hydrogen-Evolution
Electrocatalysis and their Applications in Dye-Sensitized Solar Fuels
Wu Yiying
Ohio State University
MoS2 edges have been identified as the active sites for hydrogen evolution
reaction (HER) electrocatalysis. Designing molecular mimics of MoS2 edge
sites is an attractive strategy to understand the underlying catalytic mechanism
of different edge sites and improve their activities. Herein I will discuss our
recent progress in this aspect and their applications in dye-sensitized
photocatalytic water reduction. The first example is a dimeric molecular
analog [Mo2S12]2-
, as the smallest unit possessing both the terminal and
bridging disulfide ligands. The second example is a group of compounds with
the general formular of MoO(S2)2bpy. By varying substitution on the bpy
ligand, we demonstrate the induction effect on the S—S ligand, thereby tuning
the rate constants for HER and overpotentials. At the end, I will present the
use of MoS2 molecular analogs coupled with our design of anorganic
donor−acceptor dye for dye sensitized photocatalytic water reduction. The dye
prevents both dye desorption andsemiconductor degradation by mimicking
the hydrophobic/hydrophilicproperties of lipid bilayer membranes. The
protection afforded by this membrane-mimicking dye gives this
systemexcellent stability in extremely acidic (pH 0) conditions. The result is
of interest to tandem dye-sensitized photoelectrochemical cells (DSPECs) for
total water splitting.
Cutting Edge Photon-converted Rare-earth Nanostructures for Precise
Regulation of Cellular Functions and Localized Thernaostics
Xiangzhao AI, Jing MU, Bengang XING 1, 2
*
1School of Physical and Mathematical Sciences;
Nanyang Technological University 2Institute of Materials Research and Engineering (IMRE),
Agency for Science, Technology and Research (A*STAR)
Currently, nanotechnology has been a multidisciplinary scientific field
undergoing explosive development on the basis of the unique physical
properties (e.g., optical, structural, magnetic, etc) of various types of
nanomaterials. Among these promising nanostructures, lanthanide-doped
upconversion nanocrystals (UCs) have attracted much attention owing to their
exceptionally photon-converted properties which can exchange low energy
NIR light (e.g., 980 nm) irradiation into high energy UV or visible light
emission through the non-linear multiphoton processes. Moreover, the NIR
light responsive UCs could be easily functionalized with therapeutic reagents
or biomolecules on their multifunctional surface, which can therefore greatly
benefit the photo-mediated therapeutic platforms for the controlled drug
delivery and bioimaging upon NIR light irradiation in diversely biomedical
applications. Herein, we demonstrate some unique strategies by combining
versatile “photocaged” moieties or environmental responsive groups with the
Rare-earth doped nanoparticles for precise regulation of cellular functions and
localized thernaostics.
Reference:
[1] X. Z. Ai, C. Ho, J. Aw, A. Attia, J. Mu, Y. Wang, X. Wang, X. Liu, H.
Chen, M. Gao, X. Chen, K. Yeow, G. Liu, M. Olivo, B. Xing. Nat. Commun.,
2016, 7, 10432;
[2] J. Mu, F. liu, L. Lu, Q. Xu, B. Liu, L. Ng, B. Xing. Angew. Chem. Intl.
Ed, 2014, 53, 14357;
[3] Y. M. Yang, Q. Shao, R. Deng, C. Wang, X. Teng, Z. Cheng, L. Huang, Z.
Liu, X. G. and B. G. Xing. Angew. Chem. Int. Ed. 2012, 51, 3125, and “Hot
Article” and “Inside Cover” in “Angew. Chem”.
[4] Y. Z. Min, J. M. Li, F. Liu, E. Yeow and B. G. Xing. Angew. Chem. Int.
Ed. 2014, 53, 1012.
Metal-Organic-Framework Derived Photo/electro-catalysts for Energy
Conversion
Tianhua Zhou,1,2
Jianyu Han,1 Danping Wang,
3 Rong Xu
1,2*
1School of Chemical and Biomedical Engineering,
Nanyang Technological University, Singapore;
2SinBeRISE CREATE, National Research Foundation, Singapore;
3School of Materials Science & Engineering,
Nanyang Technological University, Singapore
Construction of photocatalysts and electrocatalysts with well defined solid
structures allows control of the cataltyic centers and understanding of
structure-activity relationship toward designing more advanced and robust
solid systems. We have employed metal organic frameworks (MOFs) to
embed various types of molecular and nanoclustered catalysts to facilitate
photocatalytic water reduction and oxidation processes.1-4
Furthermore, MOFs
have been demonstrated as effective precursors to generate low-cost, highly
efficient and stable oxygen evolution and reduction electrocatalysts.5-6
By
detailed structural analyses before and after reaction, we are able to reveal the
critical factors that control the catalytic activities, such as metal-metal
interaction, metal coordination environment, metal-ligand distance. This talk
will present our recent works on different types of MOF and MOF derived
catalyst systems which are expected to open up promising avenues into the
exploration of highly active and stable catalysts towards replacing noble
metals for energy conversion applications.
References
1) Zhou, T. H., Du, Y. H., Borgna, A, Hong, J. D., Wang, Y. B., Han, J. Y.,
Zhang, W., Xu, R., Post-Synthesis Modification of Metal-Organic
Frameworks to Construct a Bifunctional Photocatalyst for Hydrogen
Production, Energy Environ. Sci, 6, 3229 - 3234, 2013.
2) Zhou, T. H., Wang, D. P., Goh, S. C. K., Hong, J. D., Han, J. Y., Mao, J.
G., Xu, R., Bio-inspired organic cobalt(II) phosphonates toward water
oxidation, Energy Environ. Sci., 8, 526-534, 2015.
3) Han, J. Y., Wang, D. P., Du, Y. H., Xi, S. B., Hong, J. D., Yin, S. M.,
Chen, Z., Zhou, T. H., Xu, R., Metal-Organic Framework Immobilized
Cobalt Oxide Nanoparticles for Efficient Photocatalytic Water OxidationJ.
Mater. Chem. A, 3, 20607-20613, 2015.
4) Han, J. Y., Wang, D. P., Du, Y. H., Xi, S. B., Chen, Z., Yin, S. M., Zhou,
T. H., Xu, R., Immobilized in MIL-101(Cr) as an Efficient Catalyst for
Water Oxidation, Appl. Cat. A-Gen., 2016, in press.
5) Zhou, T. H., et al., Unraveling the High Activity of Co-P-C
Electrocatalysts for Oxygen Evolution Reaction: Cobalt Phosphate
Boosting the Activity, submitted.
6) Zhou, T. H., et al., Nitrogen-Doped Cobalt Phosphate as Advanced
Electrocatalysts for the Oxygen Reduction Reaction, submitted.
Steering Self-Propelled Active Micro-Swimmers and Insights into
Biological Locomotion
Haw Yang
Department of Chemistry, Princeton University
Biological locomotion is invariably subjected to random fluctuations from the
environment. This occurs on all scales, ranging from as large as the biggest
mammal on Earth to as small as individual protein molecules. Over the
millennia, biology has evolved to be able to utilize such nuisances to its
advantage. Take as an example the single-celled bacteria which are capable of
effectively foraging food using a simple “tumble-and-swim” strategy to
overcome a highly viscous environment amid incessant thermal fluctuations.
The biological and molecular machineries that enable a bacterium to
accomplish such a feast are by no means simplistic. Yet, could man-made
artificial micro-swimmers using an analogous strategy behave similarly albeit
the detailed algorithm—which can be taken as the molecular mechanism in
living organisms—is completely different? This presentation attempts to look
at this problem both experimentally and theoretically.
CO2 + H2O + Sunlight Chemical Fuels + O2
Peidong Yang
Department of Chemistry and Department of Materials Science Engineering,
University of California, Berkeley; Materials Science Division, Lawrence
Berkeley National Lab, Berkeley
Solar-to-chemical (STC) production using a fully integrated system is an
attractive goal, but to-date there has yet to be a system that can demonstrate
the required efficiency, durability, or be manufactured at a reasonable cost.
One can learn a great deal from the natural photosynthesis where the
conversion of carbon dioxide and water to carbohydrates is routinely carried
out at a highly coordinated system level. There are several key features worth
mentioning in these systems: spatial and directional arrangement of the light-
harvesting components, charge separation and transport, as well as the desired
chemical conversion at catalytic sites in compartmentalized spaces. In order to
design an efficient artificial photosynthetic materials system, at the level of the
individual components: better catalysts need to be developed, new light-
absorbing semiconductor materials will need to be discovered, architectures
will need to be designed for effective capture and conversion of sunlight, and
more importantly, processes need to be developed for the efficient coupling
and integration of the components into a complete artificial photosynthetic
system. In this talk I will discuss our latest efforts in this direction.
Electrochemical and Molecular Approaches for Artificial Photosynthesis
Kyung Byung Yoon
Korea Center for Artificial Photosynthesis, Sogang University
The ultimate goal of artificial photosynthesis is to produce liquid fuels such as
methanol from carbon dioxide and water using solar light as the energy source.
The fastest approach would be coupling the electrochemical water splitting
and thermal catalytic reduction of carbon dioxide with the electrochemically
produced hydrogen. For this, to be economically feasible, the over potential of
the water oxidation electrode should be low and the platinum electrode for
hydrogen production should be replaced with cheap yet efficient electrodes.
Our recent effort to address this issue will be presented.
Eventually, to be able to commercialize artificial photosynthesis, the artificial
photosynthesis process should be very simple, not requiring sophisticated
devices like solar panels. For this, the artificial photosynthesis should be
carried out by simply adding proper catalysts into the pool of water. To make
this feasible the water oxidation and CO2 reduction should be carried out by
molecular catalysts in water. Our recent effort to address this issue will also be
presented.
New Preparation Methods for Integrated Nanocatalysts
Hua Chun Zeng
Department of Chemical and Biomolecular Engineering,
National University of Singapore
Integrated nanocatalysts (INCs) with multicomponent and hierarchically
complex structures have recently drawn extensive research attention in terms
of their fundamental sciences and industrial applications, and many innovative
strategies have been established. In this presentation, we will highlight the
state-of-the-art of INCs with different porous materials for catalyst technology
and heterogeneous catalysis. We will briefly introduce catalytic active
components (mainly metal, metal oxide, and hybrid nanoparticles) that are
commonly used in INCs. Combining such active components with various
porous materials provides us a huge array of architectural designs for INCs
that can be used in chemical reactions. In choosing host materials for INCs,
in particular, we will focus on the mesoporous siliceous materials (e.g., silica
and metal silicates) and microporous metal-organic frameworks (e.g., MOFs),
since they represent the two important classes of porous materials known
today. Recent developments of INCs which comprise these mesoporous and
microporous solids will be reported with special emphasis on their roles as
supports, encapsulating shells, and metal sources, and future research
directions in this field will also be discussed.
Targeted Synthesis of Porous Aromatic Frameworks: From Structure
Design to Advanced Application
Guangshan Zhu*
Northeast Normal University, Changchun, China
Porous organic frameworks (POFs) have been developed greatly as new
family of porous materials owing to their high stability, high surface area,
tuning pore size, and adjustable skeletons, etc. Nowadays, POFs have been
attracted great attentions in the field of gas storage and separation, sensors,
and catalysis[1,2]
. To obtain POFs with pre-determined structures and tunable
property, it is important to select the suitable building blocks and effective
reaction. With the aid of computational design, we have successfully
synthesized a series of porous aromatic framework (PAF) materials. Because
of the flexibility of building blocks, the functional groups are decorated into
PAF skeletons, and then their corresponding post-modified products are
obtained. We focus our research on gas (CH4, CO2, H2, C2H4, C2H6, C3H6, I2,
etc.) adsorption and separation.[3-7]
References
[1] X. Q. Zou, H. Ren, G. S. Zhu, Chem. Commun., 2013, 49, 3925.
[2] G. S. Zhu, H. Ren, Springer, 2015, ISBN, 978-3-662-45455-8.
[3] H. P. Ma, H. Ren, X. Q. Zou, F. X. Sun, Z. J. Yan, K. Cai, D. Y. Wang, G.
S. Zhu, J. Mater. Chem. A, 2013, 1, 752.
[4] H. P. Ma, H. Ren, X. Q. Zou, F. X. Sun, G. S. Zhu, Polym. Chem., 2014, 5,
144.
[5] Y. Yuan, F. X. Sun, F. Zhang, H. Ren, M. Y. Guo, K. Cai, X. F. Jing, X.
Gao, G. S. Zhu, Adv. Mater. 2013, 25, 6619.
[6] Y. Yuan, F. X. Sun, L. N. Li, P. Cui, G. S. Zhu, Nat. Commun., 2014, 5,
4260.
[7] Z. J. Yan, Y. Yuan, Y. Y. Tian, D. M. Zhang, G. S. Zhu, Angew. Chem.
Int. Ed. 2015, 127, 12924.
Development of durable rechargeable zinc-air batteries
Xiaoming Ge, Bing Li, Afriyanti Sumboja, Tao An, Zhaolin Liu and
Yun Zong*
Institute of Materials Research and Engineering,
Agency for Science, Technology and Research (A*STAR)
[email protected]; [email protected]
Though being the most competitive product in market, Li-ion batteries are
facing challenges in large volume applications, e.g. in grid energy storage,
which are known as high cost, insufficient battery life and unsatisfactory
safety. There is a clear need to search for alternative technologies that offer
safer and more durable batteries with high energy density at low cost.
A promising option is Zn-air technology which uses earth-abundant yet easily-
recyclable zinc as anode, aqueous electrolyte and oxygen in ambient air as
cathode materials. Despite its success in primary batteries, their secondary
counterparts are still under development. In this presentation I will talk about
some major technical hurdles in the development of durable rechargeable Zn-
air batteries, and share our journey in the research of such batteries, including
some hybrid-, metal-free and carbon-free air-electrodes, as well as a near-
neutral electrolyte which is less vulnerable to the carbonation under the
ambient air conditions.
POSTERS
POSTER NO: 1
Nanoporous Gold Nanoframes with Minimalistic Architectures: Lower
Porosity Generates Stronger Surface-Enhanced Raman Scattering
Capabilities
Chew Wee Shern
School of Physical and Mathematical Sciences,
Nanyang Technological University
Current synthesis of gold nanoframes has only demonstrated morphological
control over wall thickness and wall length. Here, we demonstrate the ability
to control the nanoscale porosity of these nanoframes, using a template seed-
mediated approach. The porosity on these nanoporous gold nanoframes
(NGNs) is tuned by controlling the crystallite size of Au nanoparticles
deposited on the AgCl templates. The yield of the NGNs approaches 100%.
Despite its minimalist architectural construction, the NGNs are mechanically
robust, retaining its morphology even after multiple centrifugation and
sonication rounds. We further highlight that decreasing the porosity on the
NGN leads to improved surface-enhanced Raman scattering (SERS)
enhancement. Increasing the constituent Au crystallite size decreases the
porosity, but increases the surface roughness of NGN, hence leading to greater
SERS enhancement. The introduction of porosity in a gold nanoframe
structure through our synthesis method is novel and generic, suggesting the
extendibility of our method to other types of templates.
POSTER NO: 2
Ultrafast Auger-Mediated Hole Trapping and Coherent Phonon
Dynamics in CdSe/CdS Core/Shell Colloidal Semiconductor
Nanoplatelets
Shuo Dong,1,*
Jie Lian, 2 Yinthai Chan,
2,3 and Zhi-Heng Loh
1
1 School of Physical and Mathematical Sciences,
Nanyang Technological University 2 Institute of Materials Research & Engineering (IMRE) Agency for Science,
Technology and Research (A*STAR) 3 Department of Chemistry, National University of Singapore
Atomically flat, quasi-two-dimensional, colloidal semiconductor nanoplatelets
(NPLs) that comprise only a few monolayers have recently emerged as a new
class of materials.1 Their narrow absorption and photoluminescence emission
spectra, which originate from the atomically precise, well-defined thickness,
have motivated increasing efforts to study them.2 Here, we report the use of
ultrafast transient absorption (TA) spectroscopy to study the early-time carrier
dynamics of CdSe/CdS core/shell NPLs following their band-gap heavy-hole
(HH) to conduction band (CB) photoexcitation. The electron and hole
dynamics can be interrogated separately by monitoring the HH-CB and light-
hole (LH)-CB transitions. Fluence-dependent measurements reveal a fast
population decay and concomitant spectral blue shifts that are attributed to
Auger-mediated hole trapping (Fig. 1a), characterized by a second-order rate
constant of 3.5 ± 0.1 cm2/s. Oscillatory features observed in the first-moment
time traces (Fig. 1b) can be assigned to the coherent longitudinal optical
phonon (208 cm-1
) and low-frequency acoustic phonons (5 and 20 cm–1
). The
latter are analogous to the classical vibrational modes of thin plates, albeit on
the nanoscale. The elementary carrier and phonon dynamics of colloidal
semiconductor NPLs observed herein could potentially influence their
optoelectronic properties.
Fig. 1(a) Fluence-dependent zeroth-moment time traces obtained for the HH-CB transition. Fig. 1(b) Oscillatory part of first-moment time trace of HH-CB, displaying low frequency vibrational modes beyond the LO phonon.
References 1 S. Ithurria, M. D. Tessier, B. Mahler, R. P. S. M. Lobo, B. Dubertret, and Al
L. Efros, Nat. Mater. 10, 936 (2011). 2 Lucas T. Kunneman, Juleon M. Schins, Silvia Pedetti, Hadrien Heuclin,
Ferdinand C. Grozema, Arjan J. Houtepen, Benoit Dubertret, and Laurens D.
A. Siebbeles, Nano Lett. 14, 7039 (2014).
POSTER NO: 3
Household Items as Replacement of Carbon Cloth in Microbial Fuel Cells
Joyce Fu Si Qi and Naomi Kong-Vega
National Junior College
[email protected]; [email protected]
Microbial fuel cells (MFCs) are devices that harness electricity from
microorganisms, and hold a promising future for renewable energy. It is
possible that it will gain popularity and open up the option of widespread
usage in households. However, MFCs are expensive, due to a key component -
the carbon cloth, which is the most costly component of the MFC. This paper
aims to propose affordable household materials, namely aluminum foil and
graphite, to replace the carbon cloth, and still allow the MFC to function
optimally. MFCs with the carbon cloth replaced by each of these materials
were connected to a voltage sensor connected to a data logger. The voltage
produced over a period of 5 hours were recorded and compared. From our
results, we have found that the MFC with graphite produces a higher average
voltage as compared to the one with aluminum. Hence, graphite would be a
more appropriate material to replace the carbon cloth in a MFC we conclude
that.
POSTER NO: 4
Identification of enclosed Molecular Grafting Reaction using Laser
induced SERS in Plasmonic Liquid Marble
Han Xuemei
School of Physical and Mathematical Sciences
Nanyang Technological University
Revealing interaction between light and material and achieving highest
conversion efficiency of light energy to chemical, biochemical, and electric
energy is a significant fundamental study for further development of
prominent material as well as electrical devices, such as solar cell. Here, we
demonstrate Ag nanocube-functionalized plasmonic liquid marble (PLM) as a
microreactor, and its application for molecular-level identification of reaction
dynamic by isolating microliter-sized reaction droplet within the Ag shell.
Utilizing the ultrasensitive laser induced surface-enhanced Raman scattering
(SERS) capability imparted by the plasmonic shell, we unravel the mechanism
and kinetics of aryl-diazonium surface grafting reaction in-situ, using just a 2
µL reaction droplet. This reaction is a robust approach to generate covalently-
functionalized metallic surfaces, yet its kinetics remain unknown. Experiments
and simulations jointly uncover an unprecedented two-step sequential grafting
process. An initial Langmuir chemisorption of sulfonicbenzene diazonium
(dSB) salt onto Ag surfaces forms an intermediate sulfonicbenzene monolayer
(Ag-SB), followed by subsequent autocatalytic multilayer growth of Ag-SB3.
Kinetic rate constants reveal 19-fold faster chemisorption than multilayer
growth. Our ability to precisely decipher molecular-level reaction dynamics
creates tremendous opportunities to develop more efficient processes in
synthetic chemistry and nanotechnology.
POSTER NO: 5
Photo(electro)catalytic hydrogen evolution from seawater using earth-
abundant metal complex as catalyst
Haiyan Shao,1,2,3
Xianliang Ho
*1,2 and Han Sen Soo
1,2,3
1School of Physical and Mathematical Sciences,
Nanyang Technological University 2Singapore-Berkeley Research Initiative for Sustainable Energy (SinBeRISE)
3Solar Fuels Laboratory, Nanyang Technological University
Converting solar energy to chemical fuels, such as hydrogen, for storage and
transport is an attractive solution to address increasing energy demands and
the associated climate change.1 Efficient and low cost hydrogen evolution
catalysts will be essential for the large-scale utilization of such solar-powered
systems.2
A new salicylaldimine nickel complex, comprising solely of Earth-abundant
elements, has been developed for hydrogen evolution catalysis. A proton relay
system in the form of second-sphere ether functionalities is incorporated into
the ligand design to facilitate the catalytic process. The peripheral ether arms
are reported to be able to enhance hydrogen production in the presence of
alkali metal cations.3 The complex has been studied with cyclic voltammetry
and UV-Vis spectroscopy. The activity of the catalyst in the presence of alkali
metal cations and its application in the production of hydrogen from seawater
will be presented. Preliminary results in using visible light as the energy
source through photosensitizers will also be discussed.
References
(1) Tran, P. D.; Wong, L. H.; Loo, J. S. C. Energy Environ. Sci., 2012, 5,
5902
(2) Teets, T. S.; Nocera, D. G. Chem. Commun., 2011, 47, 9268–9274.
(3) Shao, H.; Muduli, S. K.; Tran, P. D.; Soo, H. S. Chem. Commun. 2016, 52,
2948–295
POSTER NO: 6
Confining microliter-scale electrochemical reaction in a bifunctional
SERS- and electro-active Ag shell for molecular-level reaction
investigation
Koh Sher Lin Charlynn
School of Physical and Mathematical Sciences,
Nanyang Technological University
Due to its ability to isolate small volumes of liquid, liquid marbles are often
exploited as micro reactors. In the final year project, we investigate the use of
iquid marbles (PLM) as microliter scale electrochemical cell with additional
ability to perform in-situ surface-enhanced Raman spectroscopy (SERS). The
bifunctional Ag nanocubes shell not only as a serves working electrode, but
also a substrate-less SERS-active sensing platform. We have demonstrated the
feasibility of performing an electrochemical reaction within a PLM at the
microliter scale by studying the electrochemical behavior of methylene blue
(MB) via cyclic voltammetry. The electrochemical results have shown that
MB is reduced in two one-electron step process. The reversible change in
intensity of the C=N ring stretch observed in the SERS spectra as the potential
is varied correlates well with the cyclic voltammogram and mechanism,
indicating the capability of the PLM to function as a SERS-active
electrochemical micro reactor. The ability of liquid marbles to enable charge
transfer expands the potential applications of liquid marbles as
electrochemical micro reactors. This is particularly desirable in the biological
field since most biochemical reactions are driven by electric potential or
current.
POSTER NO: 7
Optimising consistency of voltage output using 3D printed MFC
Koh Jing Xuan, Mosammat Nazman Nahar and Ng Seow Teng
National Junior College
[email protected]; [email protected]; [email protected]
A microbial fuel cell (MFC) exhibiting a higher peak voltage and more
consistent voltage output has been cheaply constructed using 3D printing.
MFCs are renewable sources of energy. Although they have a high voltage
output, it is inconsistent. The orientation of the cell and interaction between
electrodes and solution prevent high energy output from Bennetto’s cell (Kim,
Chang, & Gadd, 2007) and the aim of this research is therefore to optimise the
consistency of voltage output from MFCs by changing its size and orientation.
MFCs with different dimensions allowing more interaction between the
electrodes and solutions have been designed. The volume of solution the MFC
can hold was increased and the cell was placed horizontally instead of
vertically to reduce density differences within the solutions. The redesigned
cells were 3D printed and the voltage for both redesigned and Bennetto’s cells
were recorded by dataloggers. Runs were conducted to compare voltage
output of an original Bennetto cell and a printed Bennetto cell, a printed cell
with same volume but different dimensions and a printed cell with maximised
volume. The runs show that the voltage of the maximised cell indeed exceeded
the Bennetto cell by 5.35%.
POSTER NO: 8
ransformative Two-Dimensional Array Configurations by Geometrical
Shape-shifting Protein Microstructures
Chee Leng Lay1,2
, Mian Rong Lee1, Hiang Kwee Lee
1,2, In Yee Phang
2,
and Xing Yi Ling1,*
1 School of Physical and Mathematical Sciences,
Nanyang Technological University 2 Institute of Materials Research and Engineering (IMRE), Agency for Science,
Technology and Research (A*STAR)
Two-dimensional (2D) geometrical shape-shifting is prevalent in nature, but
remains challenging in man-made “smart” materials and are limited to single-
direction responses. Here, we fabricate geometrical shape-shifting bovine
serum albumin (BSA) microstructures, achieving circle-to-polygon and
polygon-to-circle shape-shifting behaviors. By fabricating our shape-shifting
microstructures in periodic arrays, we construct reversibly transformative 2D
patterned arrays. Such versatile array configuration transformations give rise
to new structure-to-physical properties, including array porosity and pore
shape, which are crucial for the development of on-demand multi-functional
“smart” materials, especially in the field of photonics, microfluidics and cell
micropatterning.
POSTER NO: 9
Nanoscale Surface Chemistry Directs the Tunable Assembly of Silver
Octahedra into Three Two-Dimensional Plasmonic Superlattices
Lee Yih Hong
School of Physical and Mathematical Sciences,
Nanyang Technological University
Abstract: A major challenge in nanoparticle self-assembly is programming the
large-area organization of a single type of anisotropic nanoparticle into
distinct superlattices with tunable packing efficiencies. Here, we utilize
nanoscale surface chemistry to direct the self-assembly of silver (Ag)
octahedra into three distinct two-dimensional plasmonic superlattices at a
liquid/liquid interface. Systematically tuning the surface wettability of Ag
octahedra leads to a continuous superlattice structural evolution, from close-
packed to progressively open structures. Notably, Ag octahedra standing on
vertices arranged in a square lattice is observed using hydrophobic particles.
Simulations reveal that this structural evolution arises from competing
interfacial forces between the particles and both liquid phases. Structure-to-
function characterizations reveal that the standing octahedra array generates
plasmonic ‘hotstrips’, leading to nearly 10-fold more efficient surface-
enhanced Raman scattering (SERS) compared to the other more densely
packed configurations. The ability to assemble these superlattices on the
wafer-scale over various platforms further widens their potential applications.
POSTER NO: 10
Al2O3 Surface Complexation for Photocatalytic Organic
Transformations
Leow Wan Ru, Ng Kwok Hung, Tze Chien Sum, Hajime Hirao,
Xiaodong Chen
School of Materials Science and Engineering
Nanyang Technological University
The use of sunlight to drive organic reactions constitutes a green and
sustainable strategy for organic synthesis. Herein, we discovered that the
earth-abundant and commercially-available aluminum oxide (Al2O3), though
paradigmatically known to be an insulator, could elicit an immense increase in
the selective photo-oxidation of different benzyl alcohols in the presence of
different dyes and O2. This unique phenomenon is based on the surface
complexation of benzyl alcohol (BnOH) with the Brønsted base sites on
Al2O3, which reduces its oxidation potential and causes an upshift in its
HOMO for electron abstraction by the dye. The surface complexation of O2
with Al2O3 also activates the adsorbed O2 for receiving electrons from the
photoexcited dyes. This discovery brings forth the potential of utilizing
surface complexation mechanisms between the reactants and earth abundant
materials to effectively achieve a wider range of photoredox reactions.
POSTER NO: 11
Femtosecond time-resolved photoemission electron microscopy
Lin Wang, Shu-Zee Alencious Lo
and Zhi-Heng Loh*
School of Physical and Mathematical Sciences,
Nanyang Technological University
Observation of the dynamic process of material with high spatial and temporal
resolution is quite fascinating for physical and chemical scientists. The
conventional optical pump-probe microscope experiments have demonstrated
its application on Nano-material1-3
. But due to the probe and pump light’s
diffraction limitation, the spatial resolution is usually around µm range. In
addition, the images taken by this mothed are based on the difference of
dielectric constant or the surface plasmons, which are not the real electron
density mapping.
Photoemission electron microscopy (PEEM) using photoemission electron to
form the image has much higher spatial resolution (~10 nm) benefiting from
much smaller diffraction angle. Time resolved PEEM (TR-PEEM) 4, 5
is an
apparatus by combining the conventional pump-probe femtosecond scale
temporal resolution with PEEM nanometer scale spatial resolution, which is a
very powerful tool to trace different dynamics in material science.
In our lab, we utilize the 1030nm, 300 fs pulse width fiber-laser with tunable
repetition as the laser source. Firstly the pulse spectrum is broadened through
a Xe gas filled hollow-core fiber, and then the pulse is compressed to 77 fs
cross-correlation FWHM (Fig.1 (a)). In order to visualize the dynamics of
photo generated electrons in various materials, several different type of BBO
crystals are using for harmonic generation. These harmonics have relative
broadband spectrum, which can support 50 fs or even down to 25 fs pulse
width. For now we can get ~90 nm lateral resolution (Fig.1 (b)) when using
our 4th harmonic pulse, with further optimization we should obtain better
resolution. Taking advantage of temporal and spatial resolutions, it makes us
possible to observe the electron dynamics on sub-micrometer region by
monitoring the image intensity’s change. We have utilized our setup to
observe some 2D materials recently; Fig.1(c) depicts the electron dynamics
process of WSe2. At -5 ps delay time, we can see a shallow outline at the edge
of WSe2 triangle. Then at 0 ps, the signal from central part of the WSe2 sample
becomes strongest, which means that most excited electrons are concentrated
in this region. But within 1 ps, the signal shifts from the central to the fringe
part of Sample. What happened here in such short period is quite different
from what have reported by using the traditional optical pump-probe result.
So in this poster, we will briefly introduce our setup and demonstrate some
preliminary results.
1. Hong, X.; Kim, J.; Shi, S.-F.; Zhang, Y.;
Jin, C.; Sun, Y.; Tongay, S.; Wu, J.; Zhang, Y.;
Wang, F., Ultrafast charge transfer in atomically
thin MoS2/WS2 heterostructures. Nat Nano 2014,
9, 682-686.
2. He, J. Q.; He, D. W.; Wang, Y. S.; Cui,
Q. N.; Ceballos, F.; Zhao, H., Spatiotemporal
dynamics of excitons in monolayer and bulk
WS2. Nanoscale 2015, 7, 9526-9531.
3. Vega-Mayoral, V.; Vella, D.; Borzda, T.;
Prijatelj, M.; Tempra, I.; Pogna, E. A. A.; Dal
Conte, S.; Topolovsek, P.; Vujicic, N.; Cerullo,
G.; Mihailovic, D.; Gadermaier, C., Exciton and
charge carrier dynamics in few-layer WS2.
Nanoscale 2016, 8, 5428-5434.
4. Bauer, E., A brief history of PEEM. Journal of Electron Spectroscopy
and Related Phenomena 2012, 185, 314-322.
5. Fukumoto, K.; Onda, K.; Yamada, Y.; Matsuki, T.; Mukuta, T.;
Tanaka, S.-i.; Koshihara, S.-y., Femtosecond time-resolved photoemission
electron microscopy for spatiotemporal imaging of photogenerated carrier
dynamics in semiconductors. Review of Scientific Instruments 2014, 85,
083705.
Fig.1 (a) Fundamental pulse width after a pair
of prisms is measured by single-shot FROG.
(b) The lateral resolution measured by our
PEEM. (c) The WSe2 time-resolved PEEM
images
POSTER NO: 12
Precision Synthesis: Designing Hot Spots over Hot Spots via Selective
Gold Deposition on Silver Octahedra Edges for More Efficient SERS
Yejing Liu,1 Srikanth Pedireddy,
1 Yih Hong Lee,
1 Ravi Hegde,
2
Weng Weei Tjiu,3 Yan Cui,
1 Xing Yi Ling
1
1 School of Physical and Mathematical Sciences,
Nanyang Technological University
2 Institute of High Performance Computing (IHPC),
Agency for Science, Technology and Research (A*STAR)
3 Institute of Materials Research and Engineering (IMRE),
Agency for Science, Technology and Research (A*STAR)
Plasmonic hot spots are typically confined to highly localized regions on metal
nanoparticles. A major challenge is to be capable of efficiently increasing the
hot spot volumes on single metal nanoparticles for stronger signals in
plasmon-enhanced applications. In this work, we demonstrate an efficient
enhancement of the plasmonic hot spot volumes on single metal nanoparticles
by selective edge gold-deposited Ag octahedra (SEGSO) using a two-step
seed-mediated protocol. Such “hot spots over hot spots” strategy is attributed
to our precise synthesis of plasmonic-active nanodots onto the edge and tip hot
spots regions of nanoparticles. We probe the localized surface plasmon
responses of the selective gold-deposited octahedra using
cathodoluminescence hyperspectral imaging at the single-particle level with a
spatial resolution of ~10 nm. The hot spot areas on the Ag octahedra are
clearly enlarged after Au deposition, with an increase in emission intensities
observed across the visible wavelengths. Single-particle surface-enhanced
Raman scattering (SERS) measurements demonstrate an order of magnitude
increase in the SERS enhancement factor of the SEGSO as compared to pure
Ag octahedra, and a 3-fold increase as compared with non-selective gold-
deposited Ag octahedra (NSEGSO). The practicality of designing hot spots
selectively over hot areas is also demonstrated using theoretical simulations,
where the local electromagnetic field enhancement of our edge-deposited
particles is 15 times and 1.3-fold times stronger than pure Ag octahedra and
facet-deposited particles, respectively. The synthetic mechanisms underlying
the growth of such designer nanoparticles are also discussed together with a
demonstration of the versatility of this synthetic protocol to create a library of
selective gold-deposited Ag-based nanoparticles, which can be subsequently
etched to cages as well as frames.
POSTER NO: 13
Development of bis(arylimino)acenaphthene (BIAN) copper complexes as
visible light harvesters
Ng Yik Yie; Kee Jun Wei; Lisa Tan Jiaying; Chai Yoke Tin; Soo Han Sen
School of Physical and Mathematical Sciences,
Nanyang Technological University
Dye-sensitized solar cells have utilized to harvest sunlight to produce
electricity and ‘solar chemicals’. One of the remaining unsolved challenges is
the development of an affordable, robust dye with panchromatic light
absorption and efficiently provides separated charges for the desired
photochemistry. Currently, the most commonly employed molecular
photosensitizers include the noble metal-based ruthenium and iridium
complexes, synthetically challenging porphyrin derivatives, and expensive,
functionalized polypyridine compounds.[1-3]
In this poster, we describe the development of Cu(I) dyes supported by
bis(arylimino)acenaphthene (Ar-BIAN) ligands, which can be synthesized in
three steps (or less) from affordable, commercially available reagents. The
diamagnetic, homoleptic complexes have been characterized by a suite of
steady-state and transient absorption spectroscopic and electrochemical
methods, and exhibit panchromatic light absorption extending to the near
infrared (NIR) region. The spectroscopic studies also revealed that one of the
synthesized Cu(I) complexes is photoluminescent. On the other hand, another
Cu(I) complex previously reported by our team possesses an unusual, almost
planar-rhomboid crystal structure.[4]
References
[1] Mishra, A.; Fischer, M. K. R.; Bäuerle, P. Angew. Chem., Int. Ed. 2009,
48, 2474.
[2] Li, L.-L.; Diau, E. W.-G. Chem. Soc. Rev. 2013, 42, 291.
[3]Bozic-Weber, B.; Constable, E. C.; Housecroft, C. E. Coord. Chem. Rev.
2013, 257, 3089.
[4] Kee, J. W.; Ng, Y. Y.; Kulkarni, S. A.; Muduli, S. K.; Xu, K.; Ganguly, R.;
Lu, Y.; Hirao, H.; Soo, H. S. Inorg. Chem. Front. 2016, Advance Article
(DOI: 10.1039/C5QI00221D).
POSTER NO: 14
Scale-down Chemistry to the Picoscale: Ultralow-volume Reactions in
Functional Droplets
G.C. Phan-Quang1, H.K. Lee
2, W. Gao, I.Y. Phang
2, X.Y. Ling
1
1 School of Physical and Mathematical Sciences,
Nanyang Technological University
2 Institute of Materials Research and Engineering (IMRE),
Agency for Science, Technology and Research (A*STAR)
Small scale chemistry features multiple advantages in green chemistry and
energy conservation due to their low sample volume used. However, current
miniaturized reactors are unable to provide in-situ reaction monitoring, and
lack the ability to manipulate reaction temperature and extent. Here, we
fabricate functional liquid marbles such as plasmonic liquid marbles (PLM)
that can provide ultrasensitive multiphase sensing ability, or graphene liquid
marble (GLM) that is capable of temperature manipulation. We further
advance to isolate liquids in picoliter colloidosomes to perform parallel
interfacial reaction monitoring. These micro/pico-capsules feature multiple
advantages as miniaturized platforms for small-scale study of interfacial
phenomena commonly encounter in the areas of food chemistry, clinical
analysis and drug treatment, which ultimately leads to the minimization and
conservation of energy and materials.
POSTER NO: 15
Enhanced Performance of Electrical CO2 Reduction on Cu Electrode:
Role of Zn Doping
Yuanmiao Sun*, Shuzhou Li
School of Material Science and Engineering,
Nanyang Technological University
The reduction of CO2 is of vital importance to a sustainable energy scenario as
it converts CO2 into fuels and useful chemicals. The products of CO2 eletro-
reduction (ER) are dependent on the electrode catalyst, where CO2 can
combine with hydrogen and electron pairs to form unsaturated carbides. Of all
the studied metal electrodes, Cu attracts the most interests as it is the only one
displaying the potential to produce hydrocarbons. However, Cu’s catalytic
property on CO2 ER suffers from the low faradaic efficiency (FE) and high
overpotential. The former is caused by the competitive hydrogen evolution
reaction (HER) and the latter is resulted from the inappropriate adsorption
energies of key reaction intermediates. In this work, we propose that the CO2
ER ability of copper electrode can be improved by doping Zn atom into the
surface of Cu. In our ab inito calculations, the Zn-doped Cu electrode can
dramatically suppress the HER performance while shows positive shift in
lowering the free energy barrier for hydrocarbon production. We thus predict
that this Zn-doped Cu electrode should display higher FE and require lower
overpotential than pure Cu electrode.
POSTER NO: 16
In-Operando Identification of Geometrical-Site-Dependent Water
Oxidation Activity of Spinel Co3O4
Hsin-Yi Wang,1 Sung-Fu
Hung,
2 Han-Yi Chen,
3 Ting-Shan Chan,
4 Hao
Ming Chen,2* and Bin Liu
1*
1School of Chemical and Biomedical Engineering,
Nanyang Technological University 2Department of Chemistry, National Taiwan University
3TUM CREATE
4National Synchrotron Radiation Research Center
[email protected], [email protected]
Introduction
Spinel Co3O4, comprising one Co2+
in the tetrahedral site (Co2+
Td) and the
other two Co3+
in the octahedral site (Co3+
Oh), has been widely explored as
promising oxygen evoltuion reaction (OER) catalyst. Here, we investigated
the geometrical-site-dependent OER activity of Co3O4 catalyst by substituting
Co2+
Td and Co3+
Oh with inactive Zn2+
and Al3+
, respectively. Following a
thorough in-operando analysis by electrochemical impedance spectroscopy
and X-ray absorption spectroscopy, it is revealed that Co2+
Td site is responsible
for the formation of cobalt oxyhydroxide (CoOOH), which acts as the active
site for water oxidation.
Results and Discussion
Bode phase plots generalized from in-operando EIS reveals Co3+
Oh in Co3O4 is
responsible for surface double layer capacitance (DLC), while Co2+
Td is
responsible for water oxidation reaction as an non-homogeneous charge
distribution caused by surface oxidized species (e.g., Co3+
→Co4+
) is observed
on the low frequency range. In-operando XAS reveals Co2+
Td with initially
low oxidation state is able to release electrons under applied bias, which
facilitates the interaction with oxygen intermediates on the catalyst surface.
This electron-releasing and oxygen-adopting process suggests the formation of
CoOOH on the catalyst surface, which acts as the main active sites for water
oxidation on Co3O4.
Figure 1. (a) Bode phase plots generalized form in-operando electrochemical
impedance spectroscopy revealing two featured frequency region for different
active sites. In-operando EXAFS spectra and the corresponding variation of
Co-O bonding distance under applied voltage in (b) Co3O4, (c) ZnCo2O4, and
(d) CoAl2O4, respectively.
Conclusions
Our work highlights the vital role of Co2+
Td for Co3O4 toward water oxidation
especially under applied bias, and emphasizes the importance of in-operando
investigations on electrocatalysis for instantaneously probing the real-time
electrochemical kinetics and surface reactions.
POSTER NO: 17
Synergistically Engineering Pt Catalytic Activity via Nanoporous Gold
Bowls Co-catalyst Platform
Yang Zhe
School of Physical and Mathematical Sciences,
Nanyang Technological University
Nanoporous gold (NPG), a nanomaterial with unique bicontinuous porosity, is
highly promising for catalytic and optical applications. Although NPG
exhibits high surface area, there is still plenty room for improving its
applicability. Incorporating secondary metal with inherently strong catalytic
properties to form bimetallic catalysts based on NPG is anticipated to exhibit
unprecedented catalytic performance due to synergistic effects arising from
the bimetals. Herein, we apply zero-dimensional nanoporous gold bowls
(NPGBs) as co-catalyst platform for the design of Pt-NPGB bimetallic catalyst.
To study the synergistic effects brought about by the interaction between
NPGB and Pt, surface electronic structures of Pt-NPGB bimetallic catalysts
are studied using X-ray photoelectron spectroscopy. Downshift of d-band
center is achieved in presence of NPGB co-catalyst platform, resulting in
weakened binding strength with poisoning intermediate species, therefore
enhancing catalytic performance of Pt. Pt-NPGB bimetallic catalysts exhibit
excellent current response and stability for methanol oxidation reaction, with
over 11-fold increase in mass current, 5-fold increase in specific current and
227-fold increase in durability compared to commercial Pt products. Our
results demonstrate the relationship between surface electronic structures and
synergistic effects-enhanced catalytic activity. We envisage the promising
potential of NPGB in the design of novel high-performance bimetallic
catalysts.
POSTER NO: 18
A Chemical Approach to Break the Planar Configuration of Ag
Nanocubes into Tunable Two-dimensional Metasurfaces
Yang Yijie
School of Physical and Mathematical Sciences,
Nanyang Technological University
Current plasmonic metasurfaces of nanocubes are limited to planar
configurations, restricting the ability to create tailored local electromagnetic
fields. Here, we report a new chemical strategy to achieve tunable
metasurfaces with non-planar nanocube orientations, creating novel lattice-
dependent field localization patterns. We manipulate the interfacial behaviors
of Ag nanocubes by controlling the ratio of hydrophilic/hydrophobic
molecules added in a binary thiol mixture during the surface functionalization
step. The nanocube orientation at an oil/water interface can consequently be
continuously tuned from planar to tilted and standing configurations, leading
to the organization of Ag nanocubes into three unique large-area metacrystals,
including square close-packed, linear, and hexagonal lattices. In particular, the
linear and hexagonal metacrystals are unusual open lattices comprising non-
planar nanocubes, creating unique local electromagnetic field distribution
patterns. Large-area ‘hot hexagons’ with significant delocalization of hot spots
forms in the hexagonal metacrystal. With a lowest packing density of 24 %,
the hexagonal metacrystal generates nearly 350-fold stronger surface-
enhanced Raman scattering as compared to the other denser-packing
metacrystals, demonstrating the importance of achieving control over the
geometrical and spatial orientation of the nanocubes in the metacrystals.
POSTER NO: 19
The Confinement Effect in Doped Graphene for Cathode Oxygen
Reduction Reaction
Lixin Zhang
School of Physics, Nankai University
First principles calculations reveal that in N-doped graphene, the N atoms
should form clusters with the number of N atoms no less than three in order to
adsorb oxygen molecules properly for oxygen reduction reaction [1, 2]. For S-
doped graphene, similar results can be obtained [3]. This indicates that on the
graphene sheet, confinement of the dopants may be crucial to the various
applications of graphene.
References:
[1] Yexin Feng, Feifei Li, Zhenpeng Hu, Xiaoguang Luo, Lixin Zhang*,
Xiang-Feng Zhou, Hui-Tian Wang, Jing-Jun Xu, and E. G. Wang, “Tuning the
Catalytic Property of Nitrogen Doped Graphene for Cathode Oxygen
Reduction Reaction”, Phys. Rev. B 85, 155454 (2012).
[2] Yexin Feng, Xiaolong Yao, Mei Wang, Zhenpeng Hu, Xiaoguang Luo,
Hui-Tian Wang, and Lixin Zhang*, “The atomic structures of carbon nitride
sheets for cathode oxygen reduction catalysis”, J. Chem. Phys. 138, 164706
(2013).
[3] Yang Li and Lixin Zhang*, “Hunting for the Active Sites for Oxygen
Reduction Reaction in Sulfur Doped Graphene”, to be published.
