Technologies to harvest electrical energy from wind have vast potentials because wind is one of the cleanest and most sustainable energy sources that nature provides. Here we propose a flutter-driven triboelectric generator that uses contact electrification caused by the selfsustained oscillation of flags. We study the coupled interaction between a fluttering flexible flag and a rigid plate. In doing so, we find three distinct contact modes: single, double and chaotic. The flutter-driven triboelectric generator having small dimensions of 7.5 Â 5 cm at wind speed of 15 ms À 1 exhibits high-electrical performances: an instantaneous output voltage of 200 V and a current of 60 mA with a high frequency of 158 Hz, giving an average power density of approximately 0.86 mW. The flutter-driven triboelectric generation is a promising technology to drive electric devices in the outdoor environments in a sustainable manner.

Relatively low electron mobility has been thought to be a key factor that limits the overall photocatalytic performance of BiVO4, but the behavior of electrons has not been fully elucidated. We examine electron localization and transport in BiVO4 using hybrid density functional theory calculations. An excess electron is found to remain largely localized on one V atom. The predicted hopping barrier for the small polaron is 0.35 eV (with inclusion of 15% Hartree-Fock exchange), and tends to increase almost linearly with lattice constant associated with pressure and/or temperature changes. We also examine the interaction between polarons, and discuss the possible concentration-dependence of electron mobility in BiVO4.

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In recent years, smart light-emitting-type electronic devices for wearable applications have been required to have flexibility and miniaturization, which limits the use of conventional bulk batteries. Therefore, it is important to develop a self-powered light-emitting system. Our study demonstrates the potential of a new self-powered luminescent textile system that emits light driven by random motions. The device is a ZnS:Cu-based textile motion-driven electroluminescent device (TDEL) fabricated onto the woven fibers of a ZnS:Cuembedded PDMS (polydimethylsiloxane) composite. Triboelectrification, which raises a discontinuous electric field, is generated by the contact separation movement of the friction material. Therefore, light can be generated via triboelectrification by the mechanical deformation of the ZnS:Cu-embedded PDMS composite. This study showed that the TDEL emitted light from the internal triboelectric field during contact and from the external triboelectric field during separation. Light was then emitted twice in a cycle, suggesting that continuous light can be emitted by various movements, which is a key step in developing self-powered systems for wearable applications. Therefore, this technology is a textile motiondriven electroluminescence system based on composite fibers (ZnS:Cu + PDMS) and PTFE fibers, and the proposed selfemitting textile system can be easily fabricated and applied to smart clothes.