Module 5-2

APPLICATIONS OF NANOMATERIALS IN ENERGY SECTOR:
The following table gives the use of nanomaterials in all fields - energy production,
transformation and storage.
Nanomaterials for sustainable energy.
The main recent advances in the use of nanomaterials for alternate energy solutions
are in 1) solar cells 2) hydrogen storage and 3) sustainable electricity storage in
rechargeable batteries and supercapacitors.
Solar cells:
PV solar cells are devices which produce electricity from the sun radiation by means of the
photoelectric effect, i.e., the photons from light are converted into electrical current.
Currently, the PV market is based on silicon wafer-based solar cells (thick cells of around
150–300 nm made of crystalline silicon). This technology, classified as the first-generation of
photovoltaic cells, accounts for more than 86% of the global solar cell market. The second
generation of photovoltaic materials is based on the introduction of thin film layers (1–2 nm)
of semiconductor materials. Unfortunately, although a lower manufacturing cost is achieved
through nanofabrication methods, it also involves low conversion efficiencies.
The inclusion of nanoscale components in PV cells can help control the energy bandgap of
the solar cell. Secondly, nanostructured materials enhance the effective optical path and
significantly decrease the probability of charge recombination. The use of nanocrystal
quantum dots enhances the efficiency of solar cells because they emit multiple electrons per
solar photon. Another alternative offered by nanotechnology to conventional silicon-based
solar cells is the use of dye-sensitised solar cells. These along with quantum dot technology
represents the third generation of photovoltaics.
Solar energy can also be directly used to produce hydrogen using photocatalytic water
splitting (artificial photosynthesis).
Hydrogen storage
Most available hydrogen storage systems are quite inefficient. For example, pressure
vessels for its storage as pressurised gas are bulky and heavy, and hydrogen storage as
liquid fuel requires very low temperatures. Consequently, a great part of the energy
produced is lost due to these shortcomings.
For these reasons, a great effort is being carried out on increasing the capacity of existing
hydrogen storage systems as well as to develop in parallel good hydrogen transport devices.
Currently, hydrogen adsorption, either chemisorption or physisorption, is considered to be
one of the most efficient ways to store this light gas.
Novel alternatives to efficiently store hydrogen include nanostructures such as carbon
nanotubes, graphite nanofibers and zeolites, just to cite a few.
Hydrogen conversion
Hydrogen fuel cells can directly convert hydrogen feed to electricity through electrochemical
processes. The main barriers to overcome are the high manufacturing costs due to the
expensive materials used for the fabrication of electrodes, electrolytes, membranes and
catalysts. Nanodiamonds, carbon nanorods etc have been used to make the components of
fuel cells and to overcome these barriers.
Sustainable electricity storage

Many of the sustainable energy alternatives herein described produce (e.g. PV solar cells) or
require (e.g. water splitting) electricity. Therefore novel more efficient ways to store electricity
are very much needed in the way to a more sustainable production, transformation and use
of energy. Some of the most important energy storage systems are batteries and capacitors.
The contribution of nanotechnology to hydrogen storage has been explored in the previous
section.
Most of the active research in this field is currently focused on rechargeable lithium batteries.
Lithium-ion batteries have the disadvantages of being expensive, prone to explosion and
have low energy density. The aforesaid shortcomings can be reduced (or are being reduced)
by the application of nanotechnology to the field of rechargeable batteries. Actively research
in nanobatteries points out the use of nanomaterials for both the electrodes and the
non-aqueous electrolyte.
Electrochemical capacitors (ECs), also named supercapacitors and ultracapacitors, store
electrical energy, like batteries, but using a different mechanism. While batteries do it
chemically, ultracapacitors store electricity physically, by separating the positive and negative
charges. The main factor that determines the energy density of EC is the surface area of the
electrodes. The use of nanostructured materials dramatically increases this surface area.
Conclusion
To transit from a carbon-based energy economy to others more sustainable, many
technological breakthroughs are needed, not only in the energy production (we tend to focus
too much on the energy source) but also in the transportation, transformation, storage, and
final use of the energy. In all these steps we face significant scientific and engineering
challenges.Thanks to the unprecedented control over the size, structure, and organisation of
matter that many nanotechnologists around the World are getting, novel materials with
unique properties are already contributing to overcome some of these challenges. This is an
excellent example of how better material science can contribute to the well-being of present
and future generations.
Nanomaterials as catalysts
A catalyst works by lowering the activation energy barrier of a chemical reaction so that the
reaction proceeds faster. Catalysts function by providing an alternative route to complete the
reaction that proceeds either via a different transition state or by lowering the activation
energy barrier. Nanotechnology has a profound impact on increasing the catalytic activity on
account of its high surface area to volume ratio, which helps the catalysts at the nanoscale
to interact better with the reactants due to the availability of a large number of atoms on
surfaces. It is not only the size that makes nanomaterials attractive candidates for catalysis,
but it has also been found that exposure to selective planes on crystals is effective in
particular catalytic applications. Applications of nanotechnology in the area of clean energies
are as follows:
1. Hydrogen is much in demand as a clean source of energy because of its high
storage energy content and non-polluting nature. Carbon nanotubes (CNTs) that are
cylindrical shaped molecules of carbon have been explored as sources for hydrogen
storage as they are porous, lightweight and inexpensive.
2. Water purification: Nanofiltration is an effective method for the removal of ions or
metal contaminants. Magnetic nanoparticles have the potential to eliminate heavy
metal contaminants from wastewater. The efficiency of nanoparticles to absorb the
contaminants is very high and comparatively inexpensive compared to usual filtration
techniques.
3. Pollution control: Nanocatalysts and nanostructured membranes are highly useful in
reducing air pollution. They can be used to trap harmful gases in emissions from
automobiles/industry, like CO and methane. For example carbon nanotube
membranes have the potential to separate large amounts of greenhouse gases from
other gases, and thus offer huge potential to reverse climate change. CNT
membranes can also help trap methane during coal mining and separate it before
extracting the coal.

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APPLICATIONS OF NANOMATERIALS IN ENERGY SECTOR:

Nanomaterials for sustainable energy.

Sustainable electricity storage

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