Omnidirectional energy harvesting fleeces

Abstract

Underwater mechanical energy harvesters are of rising interestdue to their potential for various applications, such as self-powered ocean energyharvesters, monitoring devices, and wave sensors. Pressure-responsive films andstretch-responsive fibers, which provide high electrical power in electrolytes andhave simple structures that do not require packing systems, are promising asharvesters in the ocean environment. One drawback of underwater mechanicalenergy harvesters is that they are highly dependent on the direction of receivingexternal forces, which is unfavorable in environments where the direction of thesupplied force is constantly changing. Here, we report spherical fleece,consisting of wool fibers and single-walled carbon nanotubes (SWCNTs),which exhibit repetitive electrical currents in all directions. No matter whichdirection the fleece is deformed, it changes the surface area available for ions toaccess SWCNTs electrochemically, causing a piezoionic phenomenon. Thecurrent per input mechanical stress of the fabricated SWCNT/wool energy harvester is up to 33.476 mA/MPa, which is the highestamong underwater mechanical energy harvesters reported to date. In particular, it is suitable for low-frequency (<1 Hz)environments, making it ideal for utilizing natural forces such as wind and waves as harvesting sources. The operating mechanism inthe nanoscale region of the proposed fleece harvester has been theoretically elucidated through all-atom molecular dynamicssimulations.