Powering a piezoelectric nanogenerator with onion skin bio waste
(Nanowerk Spotlight) Nanogenerators are innovative self-powered energy harvesters that convert kinetic energy created from vibrational and mechanical sources into electrical power, removing the need for external circuits or batteries for electronic devices (read more: "Nanotechnology for self-powered systems").
Self-powered nanotechnology based on one type of nanogenerators – piezoelectric nanogenerators (PNGs) – aims at powering nanodevices and nanosystems using the energy harvested from the environment in which these systems are suppose to operate. This offers a completely new approach for harvesting mechanical energy using organic and inorganic materials.
"The development of non-toxic, ultra-sensitive, and flexible bio-inspired piezoelectric nanogenerators has become a great challenge for next generation biomedical applications," Jin Kon Kim, a professor in the Department of Chemical Engineering at Pohang University of Science and Technology, and Director of National Creativity Research Initiative Program for Smart Block Copolymers, tells Nanowerk. "Many high-performance organic/inorganic materials based piezoelectric nanogenerators have some limitations due to their toxicity, non-biodegradable/ non-biocompatibility, brittleness as well as complex synthesis and fabrication steps. For biomedical health monitoring, body attachable and implantable self-powered PNGs device should be non-toxic and biocompatible."
The fabricated onion skin BPNG (OSBPNG) is capable of harvesting several types of mechanical energies, including body movements, wind flow and even machine vibrations, and generated output voltage, current, instantaneous power density and high piezoelectric energy conversion efficiency of ∼18 V, ∼166 nA, ∼1.7 µW/cm2, and ∼61.7%, respectively, and turned on 30 green LEDs by a single device under repeated compressive stress of ∼34 kPa and ∼3.0 Hz frequency.
In addition, the team achieved a maximum output voltage (∼106 V) when they connected 6 units in series, which instantaneously turned on 73 combined LEDs (30 green, 25 blue, and 18 red).
To explore the potential application of OSBPNG in harvesting energy from human body motions, even at resting condition, the researchers carried out experiments by attaching OSBPNG to the human chest.
" Our OSBPNG is highly effective during throat movement such as coughing, drinking and swallowing," notes Kim. "Furthermore, because it works at very low pressure originating from heart pulse or beat, it could be used in pacemakers and health care units. Finally, OSBPNG successfully differentiates speech signals, indicating its potential for speech recognition."
"Even today, the origin of piezoelectricity in biomaterials is not completely understood due to their unusual behavior and they do not follow the classic models of piezoelectric theories based on idealized, crystalline structures," says Kim. "From the literature we know that pure cellulose fibers exhibit shear piezoelectricity due to an uniaxially oriented system of cellulose crystals but cellulose can also show longitudinal piezoelectric sensitivity under vertical compression."
Onion skin consists of α-cellulose, carbonyl, carboxyl, and amino groups, as well as N-containing bio-ligands and quercetin as plant pigment (flavonoid). Being biodegradable, it could be very useful in various in vivo biomedical diagnostic applications compared to other piezoelectric materials.
As onion skin is naturally abundant in huge amounts worldwide, this simple and cost-effective approach could be very helpful for generating electricity especially in rural areas with insufficient energy supply.
"Inexpensive and recyclable onion skin biowaste could be a very promising biopiezoelectric material to fabricate self-powered nanogenerators as alternative green energy resource for powering small electronic devices and would also be applicable in large scale industrial applications," Kim concludes.