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Wijewardhana, K. Rohana,Shen, Tian-Zi,Jayaweera, E.N.,Shahzad, Amir,Song, Jang-Kun Elsevier 2018 Nano energy Vol.52 No.-
<P><B>Abstract</B></P> <P>Artificially embedded surface charges can dramatically improve the output energy of water–solid contact electrification devices, but the embedded charges easily escape or are cancelled out by adsorption of opponent ions in ambient conditions. Here, we demonstrate a hybrid energy harvesting nanogenerator by combing water–solid and solid–solid contact electrification schemes. It consists of a water–solid contact electrification device and wind-fluttering ribbons that regularly supplies triboelectric surface charges on the solid surface and hence, the high density of surface charges can remain on the surface. This scheme can enhance the harvesting energy by up to a factor of 30 during rain. Moreover, the fluttering ribbons independently collect electric energy from mild winds without rain. This scheme provides a facile, cost-effective, and robust approach to enhance the energy-harvesting efficiency of a water–solid contact electrification device and to combine the energy harvesting from simultaneous rain and wind.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hybrid nanogenerator combining an EDL device and triboelectric ribbons was demonstrated. </LI> <LI> The hybrid nanogenerator produces electricity in both rainy and windy conditions. </LI> <LI> Wind-driven ribbons provides triboelectric charges, producing 30-times more electricity. </LI> <LI> It provides a solution to enhance the electrification efficiency in water–solid nanogenerators. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Energy harvesting using air bubbles on hydrophobic surfaces containing embedded charges
Wijewardhana, K. Rohana,Shen, Tian-Zi,Song, Jang-Kun Elsevier 2017 APPLIED ENERGY Vol.206 No.-
<P>Technology to harvest electrical power from waste micro-mechanical energy is increasingly in demand. A promising approach lies in manipulating the electrical double layer on hydrophobic surfaces; however, the underlying mechanism is still unclear. Here, we demonstrate that ascending air bubbles in water can produce electrical power in a mode similar to other systems that use descending water droplets. Although the two systems, which are analogous to electrons and holes in semiconductors, are similar in fundamental principle, their detailed electrification mechanisms are significantly different. In the air bubble system, only the pre-existing charges on the surface are involved. However, electrification in the water droplet system is dominated by triboelectric charges accumulated on the surface over time. An air bubble can produce a maximum of nine times more energy than a water droplet due to its advantages in terms of its geometry, hydrodynamics, and electro-circuitry. We also suggest an innovative approach to improve energy-harvesting efficiency using artificially embedded charges.</P>
Wijewardhana, K. Rohana,Shen, Tian-Zi,Vengatesan, M.R.,Kim, Joosung,Lee, Hyoyoung,Song, Jang-Kun Elsevier 2017 Carbon Vol.119 No.-
<P>Transport, relocation, and self-assembly of nano and microparticles in colloidal systems are highly demanded in nanotechnology, photonics, microfluidics, and biotechnology; topological charges can provide an effective means for these purposes. We report that crumpled two-dimensional (2D) graphene oxide (GO) particle sheets in nematic fields can serve as a nest for complicated topological defect loops, which, in turn, provide mobility and inter-adhesiveness to the GO particles. The application of electric fields actuated the GO particles orthogonally, inducing their coalescence into large radial clusters upon absorption of other GO particles. In contrast, in the isotropic phase, where no topological defects existed, the GO particles electrostatically repelled each other owing to the presence of surface charges with equal sign. We also demonstrate that predesigned shallow surface trenches on a substrate can anchor seed GO particles, which attract other GO particles to create a macroscopic structure along the trench. (C) 2017 Elsevier Ltd. All rights reserved.</P>
Shahzad, A.,Wijewardhana, K. R.,Song, J. K. Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.45
<P>Chen et al. suggested a skin- contact type triboelectric energy harvesting device [Chen et al., J. Mater. Chem. A, 2017, 5, 12361], which can give a rise to an electrostatic charge issue adversely affecting a person's physical experience. Here we show that adoption of a higher ranking triboelectric material than skin on the positive electrode and size optimisation of the two electrodes can ensure both high power generation and resolution of the electrostatic charge issue.</P>