Nanogenerators

NANOTECHNOLOGY

HARVESTING

KINETIC/THERMAL

ENERGY

NANOGENERATOR

GENERATING ELECTRICITY

Body movement

Heart beating

Blood flow

Wind

Temperature fluctuations

Waves

nanowires

Nano scale components

Small scale

Large scale

Types of nanogenerators

Type (effect) Energy harvested

Piezoelectric Mechanical

Triboelectric Mechanical

Pyroelectric Thermal

Piezoelectric nanogenerators

• Harvesting external energy using nanostructured piezoelectric material.

• First introduced by Zhong Lin Wang in 2006

Wang, Z. L.; Song, J. (June 2006). Science 312 (5771): 242–246.

Prof. Zhong Lin Wang at Georgia Institute of Technology, Georgia state, USA.

Piezoelectric effect

Definition: The linear electromechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry.

Force

Force

- +

Electric field Charge accumulation

Mechanism

• Two cases:

• Force exerted ⊥ to nanowire

• Force exerted || to nanowire

Force ⊥

(a) A tip is swept through the tip of the nanowire. Only the negatively charged portion will allow the current to flow through the interface. (b) The nanowire is integrated with the counter electrode by using a tip-like grating. As of (a), the electrons are transported from the compressed portion of nanowire to the counter electrode because of Schottky contact.

Schottky barrier: (A) Before contact. (B) After contact (C) Reverse bias, (positively charged section of NW) (D) Forward bias (negatively charged section of NW)

Force ||

Geometrical configuration

• Three types:

• VING - Vertical nanowire Integrated Nanogenerator

• LING - Lateral nanowire Integrated Nanogenerator

• NEG - Nanocomposite Electrical Generators

VING

• 3D configuration

• Consists of an electrode, a NW array and a counter electrode.

• Partial contact – Geometry of counter electrode important.

– DC

• Full contact – Good for || force

– AC

LING

• 2D configuration

• Consists of a base electrode, a laterally grown piezoelectric nanostructure and a metal electrode for schottky contact.

• LING is an expansion of the single wire generator (SWG)

NEG

• 3D configuration

• Consists of a metal plate electrodes and a vertically grown NW array in a polymer matrix.

• Flexibility, large area and small thickness.

Materials

Material Structure Geometry Output Voltage

Output Power

Synthesis

ZnO (n-type) Wurtzite D: 100 nm L: 200-500 nm

Vp = 9 mV R = 500 MΩ

0.5 pW per cycle

CVD, hydrothermal process

ZnO (p-type) Wurtzite D: 50 nm L: 600 nm

Vp = 50-90mV R = 500 MΩ

5-16.2 pW per cycle

CVD

ZnO-ZnS Wurtzite - Vp = 6 mV R = 500 MΩ

0.1 pW per cycle

Thermal evaporation and etching

GaN Wurtzite D: 25-70 nm L: 10-20 μm

Vavg = 20 mV Vmax =0.35mV R = 500 MΩ

0.8 pW per cycle

CVD

CdS Wurtzite D: 100 nm L: 1 μm

Vp = 3 mV

0.3 aJ per cycle

PVD, hydrothermal process

BaTiO3 Perovskite D: 280 nm L: 15 μm

Vp = 25 mV R = 100 MΩ

2.5-90 pW per cycle

High temperature chemical reaction

PVDF Polymer D: 0.5-6.5 μm L: 0.1-0.6 μm

Vp = 5-30mV

Electro spinning

Applications • Self-powered nano/micro devices

• Smart Wearable Systems

• Transparent and Flexible Devices

• Implantable Telemetric Energy Receiver

Wearable nanogenerator attached on an elbow (a), and the voltage produced during folding and releasing of the elbow (b)

implantable generator that can convert heartbeats into energy for a pacemaker.

Prof. Zhong Lin Wang holds a nanogenerator containing 700 rows of nanowire arrays. The generator was used to power nanometer-scale sensors.

Triboelectric nanogenerator

• Triboelectric effect: friction static electricity

• Electrostatic induction: redistribution of electrical charge in an object

• 60% conversion efficiency

• Low cost

• Robust & reliable

• Environmental friendly

First demonstrated in Prof. Zhong Lin Wang's group at Georgia Institute of Technology in 2012. Here he is holding a triboelectric nanogenerator.

Operation modes

• Vertical contact-separation mode

• In-plane sliding mode

• Single-electrode mode

Vertical contact-seperation mode

In-plane sliding mode

Single-electrode mode

Materials and surface

• Almost all materials

• Gaining/losing electron depends on material polarity.

• Surface morphology important

• Surface functionalization

• Composite materials

• Huge amount of choices

Image shows pyramid patterns created in a polymer sheet to increase current production in the triboelectric generator.

A flexible and transparent triboelectric nanogenerator produced from transparent polymer materials.

Applications

• Harvesting energy:

– Vibration energy

– Human body motion

• Self-powered devices:

– Self-powered active strain/force sensors

– Self-powered active chemical sensors

Triboelectric nanogenerator built inside shoe insole for harvesting walking energy

Pyroelectric nanogenerators

• Convert external thermal energy into an electrical energy.

• (used) Pyroelectric effect: ability of certain materials to generate a temporary voltage when they are heated or cooled.

• (not used) Seebeck effect: a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances.

Mechanism

• Primary pyroelectric effect

– Ferroelectric materials (PZT, BTO)

• Secondary pyroelectric effect

– Wurtzite-type materials (ZnO, CdS)

- +

-

+

Decreasing T less vibration

Increasing T more vibration

- +

Thermal deformation

Piezoelectric response

Applications

• Time-dependent temperature fluctuation

• Self-powered thermal sensor

• Thermal imaging

Video: Zhong Lin Wang

• https://www.youtube.com/watch?v=7jsOerwz4Z8