Triboelectric nanogenerators
(TENGs) can be incorporated into modern
electronic devices requiring sustainable, renewable, and reliable
microscale energy sources. We report the first use of human hair,
which is known to be a highly triboelectric material, for the fabrication
of biobased TENGs. Ethanolic NaOH was used to dissolve hair, and two
simple fabrication techniques, bar- and spin-coating methods, were
used to prepare hair-based films on electrode substrates. The dissolved
hair paste has somewhat different chemical composition from original
hair, but the hair-based film has almost the same level as the untreated
human hair in the triboelectric series. The spin-coated film is thinner
and has more even surface compared with the bar-coated one, and exhibits
better performance in triboelectric generation. The TENG using a spin-coated
hair film produced the maximum peak-to-peak voltage of 103 V and the
power density of 60 mW m–2 across a 1.2 MΩ
resistor; using the TENG device, an array of LEDs was in situ lighted
without the aid of energy-collecting capacitors. A biowaste human
hair offers the advantage of easy accessibility and processability
into a highly tribopositive material for TENGs, and our work thus
broadens the choice of positive tribo-materials and offers a novel
approach for fabricating cost-effective, high efficiency, and biobased
TENGs.
Liquid-solid contact electrification is a useful mechanism to harvest wasted micromechanical energy. In this study, we investigate how the surface properties of a solid substrate affect contact electrification efficiency. Substrate surfaces were modified from hydrophilic to hydrophobic by changing the density of self-assembled monolayers (SAMs) on a SiO2 surface. A substrate with a partially-covered SAM exhibited superior performance. The partially-covered SAM substrate is hydrophobic enough to induce quick dewetting of water from the surface and sufficiently electronegative to induce a high charge density on the surface. The quick dewetting results from the aliphatic tail groups of the SAM and -OH groups make the SiO2 surface electronegative; these two competing properties can be simultaneously obtained by optimizing the SAM density. Our findings contribute to the understanding of contact electrification in liquid-solid-type energy-harvesting devices and advance the strategies to maximize the electrification efficiency by optimizing surface geometries and properties.
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