This seminar covered various types of nanogenerators including piezoelectric, triboelectric, and pyroelectric nanogenerators. Piezoelectric nanogenerators convert mechanical energy to electricity using materials like ZnO nanowires. Triboelectric nanogenerators use friction-induced static electricity to power devices. Pyroelectric nanogenerators harness temperature fluctuations using materials with electric dipoles that change with temperature. A hybrid generator was also discussed that combines solar cells and piezoelectric nanowires to harvest both light and vibration. More advanced materials like barium titanate and graphene composites were also proposed to improve nanogenerator performance and enable applications like self-powering temperature

1. Seminar on Nanogenerators

Presented by :
Siddhant H Pathak
Roll No. - 20
M.Sc. – 3rd Sem.
Department of :
Materials Science

2. Index

Introduction
3 basic types of nanogenerators
Hybrid Generators
Advance Material for nanogenerators
Nanosized Hydrogen Generator
References

3. Introduction
Renewable energy technologies consists of two distinct processes:

 Energy generation (using sources such as solar, wind, tidal etc.)
 energy storage (batteries, fuel cells).
Accomplishment of these two processes
1) Process converting the original form of energy to electricity.
2) Converting electricity to chemical energy(for storage).
For the first time a device has been made that converts mechanical
energy(any vibration) directly to chemical energy bypassing the
intermediate step of electricity generation. The device hence acts
as a hybrid(generator-battery unit) or in other words, a self-charging
power cell.

4.  For this the researchers started with a coin-type Li-ion
battery and replaced the polyethylene separator that
normally separates the two electrodes with PVDF
(Polyvinylidene difluoride) film
 As a piezoelectric material, PVDF film generates a
charge when under an applied stress.
PVDF film causes positive Li ions to migrate from the
cathode to the anode in order to maintain a charge equilibrium across the battery.
this ion migration process charges the battery without the need for any external voltage source. The
battery is hence SELF-CHARGING

5. Nanogenerators
 Nanogenerator is a device that converts ambient energy(sound, muscle
movement, heat, fluid flow etc) into electricity.
 Nanogenerators are typically of three types -:
1) Piezoelectric nanogenerators
uses mechanical energy
2) Triboelectric nanogenerators
uses frictional energy
3) Pyroelectric nanogenerators
uses fluctuation in temperature

6. Piezoelectric nanogenerator

 Electrode- Typically made of Si coated
with Pt to increase conductivity
 ZnO nanowires have a diameter of 100 to
300 nm and produce 45mV on pulling
back and forth

7. 
Working
 Schottky contact must be formed between the counter electrode and the tip of the
nanowire since the ohmic contact will neutralize the electrical field generated at the
tip. In order to form an effective schottky contact, the electron affinity(Ea) must be
smaller than the work function(φ) of the the counter electrode. For the case
of ZnO nanowire with the electron affinity of 4.5 eV, Pt(φ=6.1eV) is a suitable metal
to construct the schottky contact. By constructing the schottky contact, the electrons
will pass to the counter electrode from the surface of the tip when the counter
electrode is in contact with the regions of the negative potential, whereas no current
will be generated when it is in contact with positive potential [Rectifier]

8. Triboelectric Generator
 A device that takes advantage of static electricity to convert

movement—like a phone bouncing around in your pocket—
into enough power to charge a cell phone battery.
 When thin films of PET plastic and a metal come into contact
with one another, they become charged. And a current flows
between them, which can be harnessed to charge a battery.
When the two surfaces are patterned with nanoscale structures,
their surface area is much greater, and so is the friction
between the materials—and the power they can produce.
 A fingernail-sized square of this triboelectric nanomaterial can
produce eight milliwatts enough to run a pacemaker. A patch
that’s five by five centimeters can light up 600 LEDs at once, or
charge a lithium-ion battery that can then power a commercial
cell phone.

9.  Principle: works on the basis of triboelectric effect. It is a type
of contact electrification in which 
certain materials
become electrically charged after they come into contact with
another different material and are then separated (such as
through rubbing). The polarity and strength of the charges
produced differ according to the materials, surface roughness,
temperature and strain.
Mechanism
1) Vertical
Sliding
Mode

10. 2) Lateral Sliding Mode : By sliding friction, a periodic change in the contact area,
which creates a voltage drop for driving the flow of electrons.
Because of the large difference in the ability to attract electrons, the triboelectrification
will leave one surface with net positive charges and the other with net negative
charges with equal density.
Once the top plate with the positively-charged surface starts to slide outward, the in-plane
charge separation is initiated due to the decrease in contact surface area. The
separated charges will generate an electric field pointing from the right to the left
almost parallel to the plates, inducing a higher potential at the top electrode. This
potential difference will drive a current flow from the top electrode to the bottom
electrode .

11. Pyroelectric Effect
 More than 50 percent of the energy generated by us goes to waste, much of it as heat
released to the environment by everything from computers to cars to long-distance
electric transmission lines. This heat can 
be converted to electricity using something
called the pyroelectric effect
 Harvesting thermoelectric energy relies on the Seebeck effect that utilizes a temp.
difference between two ends of the device for driving the diffusion of charge
carriers. Environment is spatially uniform without a temp. gradient and the Seebeck
effect can not be used to harvest thermal energy.
 The mechanism is based on the
thermally induced random wobbling
of the electric dipole around its
equilibrium axis, the magnitude of
which increases with increasing temp.

12.  When temp. increases the electric dipoles
oscillate within a larger degree of spread
around their respective aligning axes. Total
average spontaneous polarization is decreased
due to the spread of the oscillation angles and
the quantity of induced charges is reduced,
resulting in a flow of electrons.
 If the nanogenerator is cooled instead of heated,
the spontaneous polarization will be enhanced
the amount of induced charges in the electrodes
will increase and the electrons will then flow in
an opposite direction.
 Pyroelectric nanogenerator can be used as an
active temperature sensor, which can work
without a battery i.e utilizing the energy that it
produces [SELF-CHARGING TEMP. SENSOR]

13. Hybrid Nanogenerator

 Now researchers have combined
a nanogenerator with a solar cell to
create an integrated mechanical- and
solar-energy-harvesting device. This
hybrid generator is the first of its
kind and might be used, for instance,
to power airplane sensors by
capturing sunlight as well as engine
vibrations for when solar energy isn’t
available
 The top layer here consists of a thin-film solar cell embedded with dye-coated zinc
oxide nanowires. The large surface area of the nanowires boosts the device’s light
absorption
 The solar cell and the nanogenerator are electrically connected by the silicon
substrate itself, which acts as both the anode of the solar cell and the cathode of the
nanogenerator

14. Advanced material for nanogenerator
So far, efforts to make
nanogenerators have focused on ZnO
nanowires. But barium titanate
(BaTiO3)could lead to better
generators because it shows a
stronger piezoelectric effect, Lab
experiments show that a barium-titanate
nanowire can generate
“16 times” as much electricity as a
ZnO nanowire from the same
amount of mechanical vibrations
High Sensitive accelerometer of BaTiO3
But zinc oxide has its own advantages.
It is nontoxic to biological systems making it better suited than barium titanate for
implantable devices. Also, it is easier to control zinc-oxide growth in order to fabricate
nanowire arrays compared to Barium Titanate

15. Nanosized Hydrogen Generator
 Hydrogen is virtually everywhere on the planet, but is typically
bonded with other elements and must be separated (Like in H2O) to
produce free hydrogen. The process 
available for this right now
consumes too much electricity and releases Co2(A green house gas).
 N.H.G does not extract but make Hydrogen by combining an
electron and a proton
Principle:
It has been long known that some single-celled organisms use a protein
called bacteriorhodopsin (bR) to absorb sunlight and pump protons
through a membrane using the green end of sunlight.
At the same time electrons can be produced by combining these proteins
with titanium dioxide and platinum and then exposing them to
ultraviolet light.
Combining this we can literally manufacture Hydrogen(for fuel)

16. Problem:
Titanium dioxide only reacts in the presence of ultraviolet light, which makes
up a mere 4% of the total solar spectrum
Solution [Materials Science]
For this the researchers looked for a new material. The new material would
need enough surface area to move electrons across quickly and evenly and
boost the overall electron transfer efficiency.
The researchers also needed a platform on which biological components, like
bR, could survive(biologically inert) and connect with the titanium dioxide
catalyst: in short, a material like graphene.
Along with this Graphene is also super strong, super light, transparent and the
best conductor of electricity so far. Its very presence allows the other
components to self-assemble around it, which totally changes how the electrons
move throughout our system.

18. References:

 Phys.orgnews 20th september 2014
 Wikipedia
 Google images
 Nanogenerators for self powered devices and
systems by Zhong Lin Wang, School of Materials
Science and Engineering Georgia Institute of
Technology, Atlanta GA USA(first edition, June
2011)
 Technologyreview.com