High‐Performance Triboelectric Nanogenerators Based on Solid Polymer Electrolytes with Asymmetric Pairing of Ions

Abstract

The power output of TENGs strongly depends on the selection of the contact materials. [16] For high output, the two contact layers of a TENG should preferably be on opposite sides of the triboelectric series. [17] Due to the highest electron affinity, fluoroplastics such as polytetrafluoroethylene (PTFE) are the most suitable for the negative contact layer for TENGs. [18] On the other hand, though some dielectric materials such as nylon are relatively more positive than metals like gold (Au) and aluminum (Al), metals are the best candidates for the positive contact layer as they have sufficient free electrons to transfer during contact electrification. [18] For this reason, metal-polymer pairs, specifically metal-PTFE pairs, are mostly utilized for TENGs. In addition, in order to enhance the output performance of the TENGs, various approaches are proposed. Surface functionalization is carried out in order to enhance the charge transfer ability of the contact layer by treating with materials such as poly-l-lysine, [19] F 13 -RCS silane, [19] or fluorine plasma (CF 4 , C 4 F 8 ). [20] Surface morphology is generally carried out in order to increase the area of triboelectrification by incorporating various micropatterns on the surface. [8] Nevertheless, surface morphology requires extra fabrication steps, [8,21] and both the surface functionalization and the surface morphology control suffer from poor durability. [8] Although importance of controlling workfunction of triboelectric material is already emphasized, [22] there are still lack of material itself improvement. Due to all these reasons, it is necessary to improve the triboelectric property of the material itself in order to have durable, high output TENGs.Here, we investigate the reliable ionic doping effect on the triboelectric property of polymer contact layers for high-performance TENGs for the first time. We successfully demonstrate through KPFM measurements that electrolytes with asymmetric pairing of ions can significantly enhance the triboelectric property of polymers. The addition of CaCl 2 , which has more anions than cations, can make PVA one of the most positive triboelectric materials. Likewise, H 3 PO 4 , which has more cations than anions, can make PVA one of the most negative triboelectric materials. In order to observe the corresponding enhancement in output power, we realized a contact mode TENG with CaCl 2 -PVA-based SPE and PTFE as the contact layers and found that the SPE-based TENG provides dramatically higher output In general, various kinds of surface modifications are utilized to enhance the power output performance of triboelectric nanogenerators (TENGs), but they typically have limited stability. Here, a new strategy of adding electrolytes with asymmetric ion pairing to polymer friction layers of TENGs is introduced in order to enhance their triboelectric property. Indeed, Kelvin probe force microscopy (KPFM) measurements show that an addition of phosphoric acid (H 3 PO 4 ), an electrolyte with more cations than anions, to polyvinyl...

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