Dual-Scale Hydration-Induced Electrical and Mechanical Torsional Energy Harvesting in Heterophilically Designed CNT Yarns

Abstract

Water holds vast potential for a useful energy source, yet traditional approaches capture only a fraction of it. This study introduces a heterophilically designed carbon nanotube (CNT) yarn with an asymmetric configuration. This yarn is capable of both electrical and mechanical torsional energy harvesting through dual-scale hydration. Fabricated via half-electrochemical oxidation, the yarn contains a hydrophilic region enriched with oxygen-containing functional groups and a hydrophobic pristine CNT region. Molecular-scale hydration triggers proton release in the hydrophilic region. Consequently, a concentration gradient is established that generates a peak open-circuit voltage of 106.0 mV and a short-circuit current of 20.6 mA cm⁻². Simultaneously, microscale hydration induces water absorption into inter-bundle microchannels, resulting in considerable yarn volume expansion. This process leads to hydro-driven actuation with a torsional stroke of 78.8° mm⁻¹ and a maximum rotational speed of 1012 RPM. The presented simultaneous harvesting results in electrical and mechanical power densities of 3.5 mW m⁻² and 34.3 W kg⁻¹, respectively, during a hydration cycle. By integrating molecular and microscale hydrations, the proposed heterophilic CNT yarns establish an unprecedented platform for simultaneous electrical and mechanical energy harvesting from water, representing a groundbreaking development for sustainable applications.