Electronic device components produce e-waste that significantly contributes to increasing environmental pollution. For designing such devices, researchers have carried out a substantial amount of work to explore various eco-friendly materials, such as electromagnetic generators (EMGs), piezoelectric nanogenerators (PENGs), and triboelectric nanogenerators (TENGs) . Among them, electromagnetic generators are based on Faraday’s law of electromagnetic induction, which predicts how a magnetic field interacts with an electric circuit to produce an electromotive force (EMF), suitable for large-scale power generation. As the name suggests, Piezoelectric nanogenerators can convert small physical deformation into electricity for small-scale power devices. Finally, triboelectric nanogenerators are based on the triboelectrification effect, and electrostatic induction is considered a cost-effective, clean, and sustainable way to convert mechanical energy into electricity.
In common words, triboelectrification refers to the process in which two uncharged bodies become charged when brought into contact and then separated. Triboelectric nanogenerators have been used for several human-machine interfacing devices by converting biomechanical energies into sensory information. The existing research  confirms the usage of TENGs for demonstrating the process of Morse code generation but faces several drawbacks such as low stability, decoding, and efficiency. Researchers at the University of Surrey, Loughborough University, and the Free University of Bolzano-Bozen, Piazza Universitá recently developed a recycled material-based triboelectric nanogenerator to power low-power electronic devices. Later, the team used a custom-made triboelectric nanogenerator to generate a Morse code for a wearable device for autonomous communication.
In the paper titled “Wearable Triboelectric Nanogenerator from Waste Materials for Autonomous Information Transmission via Morse Code,” the researchers provide a solution by reusing plastic waste and carbon-coated recycle paper wipes to fabricate the active layers of an eco-friendly triboelectric nanogenerator . The collected plastic from the waste bins is coated with carbon nanoparticles through a cost-effective brush painting method, then by the curing treatment. Carbon-coated paper wipes are used as a positive triboelectric material, while polytetrafluoroethylene is employed as a negative triboelectric material in TENG. Using X-ray diffraction and Raman spectroscopy, the surface morphology, structural information, and crystalline characteristics of the carbon nanoparticles and carbon-coated paper wipes were examined. The sheet resistance of the carbon-coated paper wipes was measured at 10 different areas with a surface area of just 1 cm2 and an average value was noted.
The working mechanism of the triboelectric nanogenerators is initiated when the polytetrafluoroethylene and carbon-coated paper wipes of opposite polarity are brought into contact. When both the layers start to separate, these charges or electrons start to flow between the electrodes resulting in an electric current flow from the top to the bottom electrode. The charge flow between the two electrodes continues until it reaches electrostatic equilibrium. As polytetrafluoroethylene and carbon-coated paper wipes are brought closer to each other, the polarization decreases, and the charges start to flow back again and thus creating current flow from the bottom to the top of the electrodes.
The wearable device uses an area of 30x30 mm2 of which the carbon-coated paper wipes-based triboelectric nanogenerators are packed into the polythene to protect it from the external environmental moisture that influences the output performance of TENG. The custom-built device is used as a Morse code generator by tapping the device in a Morse code generation pattern of dot and dash by touch and release for dot and touch-hold-release for the dash. The experimental plan for Morse code decoding is the use of the LabVIEW module for peak detection, energy harnessing, and converting it to a digital signal. The decoder screen is made using the LabVIEW graphical user interface of which the decoded information is stored in the system and a message can be sent via email.
To further validate the practical applicability of the custom triboelectric nanogenerators, they were used to develop a 9-segment keypad and connected it to the computer screen using an Arduino controller. The keypad can provide input and can be attached to the home-surveillance systems. “This has the potential to be used for self-powered data transmission and for a door lock security system that is wireless in connection with IoTs,” said the team in confidence. Also, to provide extended information on the usability of the carbon-coated paper wipes-based triboelectric nanogenerators, they were used to power low-power electronic hardware devices such as LEDs and LCDs via a commercially available capacitor. “These experiments clearly demonstrate that the proposed C@PWTENG is adequate to significantly be employed for self-powered applications,” the team notes.
“Based on the experimental analysis, our carbon-coated paper wipes-based TENG device is expected to have an impact on future self-powered sensors and internet of things systems,” the researchers conclude.
This research article is published in ACS Applied Materials & Interfaces 2022 under open-access terms for public viewing.
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