1. Introduction
Nanotechnology has been receiving significant
exposure regarding its potential to offer evolutionary
advancements in a wide breadth of applications. It could turn
out to be the most important technological development for
advancing energy technologies, which might someday allow for far
more powerful, more efficient and less expensive energy
production and storage technologies.
The main areas that the focus group would like
to investigate are,
- Solar energy
- Li-ion Batteries
- Hydrogen Production & Storage
- Fuel Cells
Topics such as thermoelectrics, supercapacitors,
biomass, coal & natural gas conversion etc are also within the
research scope.
2. Research Plans & Focus
A) New Prototypes of High Performance Quantum
Dot Excitonic Solar Cells
Increasing demand for energy has always
forced us to seek environmentally clean alternative
energy
resources. The projected demand has been shown to meet using
renewable energy sources such
as solar radiation. This requires
new initiatives to harvest incident photons with higher
efficiency. In
the Shockley and Queisser calculation, the result
of which set a theoretical limit of solar-to-
electrical conversion efficiency of ~32%, the difference between the
absorbed energy and the semi-
conductor bandgap was assumed to be
lost as heat through phonon relaxation. If photons having
energies greater than the bandgap of the absorbing material did
not dissipate their excess energy as
heat, instead produce more
voltage or generate multiple, low-energy, thermalized electrons
from the energy
of a single absorbed photon, theoretical
efficiencies in excess of 60% would, in principle, be
attainable. Absorbers having a highly quantized band structure,
such as quantum wells and quantum dots,
can produce the desired
effects through a processes which is inverse of Augur process
called
multi-exciton generation (MEG) or impact ionization.
Recent experimental observations on PbSe quantum
dots have
demonstrated the multi exciton generation from a single absorbed
photon; thereby establishing
an existence proof for the process
of interest.
The objective of this research proposal is to
use quantum dots in excitonic solar cells and to
develop
new prototypes of quantum dot excitonic solar cells by
studying thoroughly the factors that control
the exciton
generation, splitting, carrier transport, rejuvenation of the
oxidized quantum dots.
A
cartoon showing a typical problem of a quantum dot and electrode
are interfaced through a linker. The
linker is expected to play
a vital role in excitonic solar cells employing quantum dots.
The goals are:
i. To develop high quality chalcogenide-based quantum dots of:-
-
high degree of crystallinity;
- stability;
and
-
multi-exciton
generation capacity such that they can be used in excitonic
solar cells for over several years without degradation.
ii. To achieve incident-photon-to conversion efficiency (IPCE)
>100% by:-
- optimizing the relative band positions of the
quantum dots and photoelectrodes and
- optimizing proper
surface ligands for quantum dots such that the ligand neither
quench fluorescence by
itself nor cool the excited electrons.
iii. To reduce the power loss by charge recombination by fine
tuning the local electrical potential at the interfaces of light
absorber and charge collectors.
iv. To improve the charge collection efficiency of photocells by
(i) proper selection of electrodes and electrolytes and (ii)
examination of new architectures such as linear alignment of
quantum dots on aligned nanofiber electrodes.
B) Materials Development for Hydrogen Energy
Hydrogen fuel cells provide an ideal solution to the present
energy crisis. It is an efficient, combustion-
less, virtually
pollution-free power source.
There are strong pushes towards the so-called hydrogen
economy
from Governments and Industries.
The technical challenges in the implementation of
hydrogen-based energy are:
i.
New polymer electrolyte membranes for fuel cells.
ii.
Highly active and low cost catalyst for electrochemical
reactions.
iii.
Efficient hydrogen storage materials.
iv.
Large-scale hydrogen Production from renewable energy
sources.
From materials development point of view, items I-III have
attracted great attention worldwide.
I.
New polymer electrolyte membranes for fuel cells
Fuel cells convert fuel and air directly to electricity, heat
and water in an electrochemical process. In
polymer electrolyte
membrane (PEM) fuel cells, the synthesis and characterization of
new high
temperature membrane polymers with improved performance
which combine the beneficial physical,
chemical and mechanical
properties, are the focal areas of research. Research topics
include:
i. Synthesis of heat resistant polymers with sulfonic acid
groups directly bonded to the polymer backbone
and those with
the sulfonic acid groups attached to the side chain.
ii. Synthesis of phosphonated polymers which show a higher
hydrolytic and thermal stability than
sulfonated polymers.
iii. Mixing Nafion (membrane material) with nano-sized
inorganic proton conductors, which lead to
the enhancement of
water retention and therefore, extends the operation temperature
range.
The targets
of the material are set by
the US Department of Energy, i. e., operating temperature is
120
°C while the relative humidity is 50%.
II.
Highly active and low cost catalyst for electrochemical
reactions
The slow rate of oxygen-reduction catalysis on the cathode has been a
primary factor hindering develop-
ment of the PEM fuel cells. The
state-of-the-art catalysts are mainly Pt-based materials, which
are
expensive
and hence
constitute a higher barrier to commercialization of fuel cell.
Intensive research
activities are in line with the reduction of
Pt loading in the electrodes and development of non-precious,
highly effective nanoporous catalysts. Nanosized alloys as main
catalysts and nanomaterials as supports
are potential solutions.
The ultimate
goal is to reduce the use of platinum in fuel cell cathodes by
at least a factor of 20 or eliminate it altogether to decrease
the cost of fuel cells to consumers.
III.
Efficient hydrogen storage materials
Materials that
could meet the requirements of practical applications, such as,
high hydrogen capacity,
near ambient operating temperature, low
cost and environmentally benign, are imperative to a success-
ful
hydrogen economy. This involves the research and development of
novel materials and identification of
new chemical processes for
hydrogen storage. There are three main research directions,
which are:
i. Conventional metal hydrides.
ii. Complex & chemical hydrides.
iii. High surface area sorbents.
Substantial attention has been given to the complex hydrides and
high surface area sorbents. Complex
and chemical hydrides
normally have high hydrogen content, therefore, show significant
potential in
meeting the practical requirements. Hot materials
include borohydrides and their composites, such as
Mg(BH4)2,
LiBH4-MgH2, amide-hydrides combinations,
amine borane
etc. Metal Organic Frameworks (MOFs)
and nanocarbon etc. are
high surface area materials under intensive investigations.
Solid-state
reactions normally encounter kinetic problem. It has
been reported that nano-size transition metals or
alloys exhibit
remarkable catalytic effect in reducing reaction temperatures.
The objectives
of the research lie in the development of condensed material,
which have,
i. Storage capacity of 6.0 wt% or higher.
ii. Lower operation temperature (<100°C).
iii. Fast kinetics in charging and discharging.
C) Novel Electrode Materials for Next Generation Lithium-ion Batteries
Recent
developments in mobile electronic devices as well as emerging
hybrid electric vehicle (HEV) market demands affordable,
long-lasting, safe and environmentally benign power supplies.
High power lithium-ion
(Li-ion) batteries, the most successful
electrochemical devices, offer the promise of higher efficiency,
longer life, and easier state-of-charge control at lower weight,
volume and cost. Intensive research activities are
in progress
currently on both cathode and anode materials for high
energy/power density Li-ion batteries.
One of the key factors
affecting storage performances of Li-ion batteries operated at
room temperature is
the kinetics associated with the transport
of Li+ ions and e- in the electrode
materials. Nano-size materials
can overcome such kinetic issues
due to reduced transport lengths for Li+ ions and e-.
Thus current progress on novel Nanomaterials and
Nanotechnologies can lead to next generation Li-ion batteries.
Current
research focuses include:
i.
Novel nanostructured cathode materials with high capacity
and rate performances: Olivine phosphates such as LiMPO4
(M = Fe, Mn, Co, Ni) and Li2MSiO4 (M = Fe,
Mn). Controlling morphology is a key factor here
to achieve
enhanced storage performances.
ii. Novel anode materials:
a. Nanocomposites of transition metals with Li2O/LiF/Li2S
which exhibit enhanced storage capacity with
nearly 4 times
higher than conventional graphite and high cyclic performances.
b. Alloy reactions of Sn, Si, etc., with Li for enhanced
lithium storage
iii.
Novel concepts: Extra lithium storage at low potential
due to interfacial lithium storage, where Li+ and
e-
are stored at the interfaces of nano-composites of transition
metals and Li2O/LiF/Li2S. This interfacial
storage mechanism bridges the battery performance and
supercapacitor behavior.
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