A triboelectric generator based on self-poled Nylon-11 nanowires fabricated by gas-flow assisted template wetting

Abstract

Triboelectric generators have emerged as potential candidates for mechanical energy harvesting, relying on motion-generated surface charge transfer between materials with different electron affinities. In this regard, synthetic organic materials with strong electron-donating tendencies are far less common than their electron-accepting counterparts. Nylons are notable exceptions, with odd-numbered Nylons such as Nylon-11, exhibiting electric polarisation that could further enhance the surface charge density crucial to triboelectric generator performance. However, the fabrication of Nylon-11 in the required polarised d 0 -phase typically requires extremely rapid crystallisation, such as melt-quenching, as well as ''poling'' via mechanical stretching and/or large electric fields for dipolar alignment. Here, we propose an alternative one-step, near room-temperature fabrication method, namely gas-flow assisted nano-template (GANT) infiltration, by which highly crystalline ''self-poled'' d 0 -phase Nylon-11 nanowires are grown from solution within nanoporous anodised aluminium oxide (AAO) templates. Our gas-flow assisted method allows for controlled crystallisation of the d 0 -phase of Nylon-11 through rapid solvent evaporation and an artificially generated extreme temperature gradient within the nanopores of the AAO template, as accurately predicted by finite-element simulations. Furthermore, preferential crystal orientation originating from template-induced nano-confinement effects leads to self-poled d 0 -phase Nylon-11 nanowires with higher surface charge distribution than melt-quenched Nylon-11 films, as observed by Kelvin probe force microscopy (KPFM). Correspondingly, a triboelectric nanogenerator (TENG) device based on as-grown templated Nylon-11 nanowires fabricated via GANT infiltration showed a ten-fold increase in output power density as compared to an aluminium-based triboelectric generator, when subjected to identical mechanical excitations. Broader contextEnergy harvesting from ubiquitous ambient vibrations represents a viable energy solution for the rapidly increasing number of low-power autonomous, wireless, portable and wearable electronic devices. Triboelectric generators have recently generated tremendous interest in this regard as they are capable of converting mechanical energy from the relative motion of two dissimilar materials into useful electricity, based on contact electrification and electrostatic induction arising from the materials having different electron affinities. In order to achieve high levels of energy harvesting performance, materials with electron-donating tendencies must be paired with those with electron-accepting tendencies. The bulk of the literature focuses on the latter, as these typically include materials that are easier to synthesise. Nylon-11 belongs to the less-explored family of synthetic and organic electron-donating materials, although the crystalline phase required for superior triboelectric performance has remained elusive in the bulk due to the typically harsh p...

Nanostructured polymer-based piezoelectric and triboelectric materials and devices for energy harvesting applications

“…In this section, we review a recent work by Choi et al where self-poled nylon-11 NWs have been employed in triboelectric NGs [51]. The enhancement of surface charge density resulting from the polarization of the nylon-11 NWs led to a dramatically improved triboelectric energy harvesting performance.…”

“…Such modifications have been mostly conducted on or in tribo-negative polymers, such as PVDF, poly tetrafluoroethylene (PTFE, or teflon), polyurethane (PU), with far less focus on polymers from the tribo-positive side of the series. Although tribo-positive polymeric candidates are limited, nylon, particularly in the form of odd-numbered ferroelectric nylon NWs, is a notable exception that has been reported to result in enhanced triboelectric energy harvesting performance [51], as will be reviewed in the following sections.…”

“…Figure 6(b) illustrates a template being placed floating above the heated polymer solution, where capillary force pulls the polymer up along the pores [31,38]. Although NWs synthesised by these methods have been reported to show certain polarization preference [19,20], the crystallization during infiltration, however, can be further adjusted by applying gas flow on top of the template to control the temperature distribution, namely, gas-flow assisted nano-template (GANT) nanowire growth method [51] (figure 6(c)). Some examples of polymer-ceramic nanocomposite NGs using polymeric templates are also included in figures 6(d) and (e), where the piezoelectric active material is ZnO NWs.…”

“…In contrast with the aligned nylon-11 nanowire-based triboelectric NG described above, a separate nanowire-based NG was fabricated in the same study using nylon-11 NWs that were freed from the template and which formed a randomly aligned nanowire mat lying on a substrate [51]. The triboelectric energy harvesting performance obtained from these randomly aligned NWs was substantially lower due to random orientation of polarization even though the mat had a smaller thickness and a rougher surface, which were believed to be the main beneficial factors for triboelectric NG output.…”

Mechanical Energy Harvesting Performance of Ferroelectric Polymer Nanowires Grown via Template‐Wetting

“…While there have been recent reports of ferroelectric polymers, such as polyamides (odd‐numbered nylons), having found applications in mechanical energy harvesting, polyvinylidine fluoride (PVDF) and its co‐polymers have received by far the most interest for ferroelectric polymer nanogenerator applications due to their superior electromechanical properties. PVDF is a fluoro‐polymer known to exhibit piezoelectricity since 1969 and ferroelectricity since 1981 .…”