Making the most of twists and turns: The rise of small-scale, portable electronics and wearable devices has boosted the desire for ways to harvest energy from mechanical motion. Such approaches could be used to provide battery-free power with a small footprint. Kim et al. present an energy harvester made from carbon nanotube yarn that converts mechanical energy into electrical energy from both torsional and tensile motion. Their findings reveal how the extent of yarn twisting and the combination of homochiral and heterochiral coiled yarns can maximize energy generation. Science , this issue p. 773

Predicting and preventing disasters in difficult‐to‐access environments, such as oceans, requires self‐powered monitoring devices. Since the need to periodically charge and replace batteries is an economic and environmental concern, energy harvesting from external stimuli to supply electricity to batteries is increasingly being considered. Especially, in aqueous environments including electrolytes, coiled carbon nanotube (CNT) yarn harvesters have been reported as an emerging approach for converting mechanical energy into electrical energy driven by large and reversible capacitance changes under stretching and releasing. To realize enhanced harvesting performance, experimental and computational approaches to optimize structural homogeneity and electrochemical accessible area in CNT yarns to maximize intrinsic electrochemical capacitance (IEC) and stretch‐induced changes are presented here. Enhanced IEC further enables to decrease matching impedance for more energy efficient circuits with harvesters. In an ocean‐like environment with a frequency from 0.1 to 1 Hz, the proposed harvester demonstrates the highest volumetric power (1.6–10.45 mW cm⁻³) of all mechanical harvesters reported in the literature to the knowledge of the authors. Additionally, a high electrical peak power of 540 W kg⁻¹ and energy conversion efficiency of 2.15% are obtained from torsional and tensile mechanical energy.

Strategies for converting mechanical energy into electrical energy hold significant importance in diverse battery‐free and battery‐supported applications. Recent studies have demonstrated promising approaches involving the twisting of carbon nanotube yarns, which alter the intrinsic electrochemical capacitance during mechanical motion, thereby generating electrical energy in various aqueous environments. However, the fundamental mechanism of chemo–mechanical energy harvesters based on the nanoscale piezoionic effect, as well as the kinetics of both cations and anions within the system, remains to be clarified. In this study, experimental and computational approaches aimed at fundamentally understanding the piezoionic effect in nanoscale chemo–mechanical dynamics are presented. This phenomenon is analyzed using in situ Raman scattering, piezoelectrochemical impedance spectroscopy, and molecular dynamics simulations. The findings elucidate the collective contributions of cations and anions under mechanical energy inputs and demonstrate the impact of piezoionic kinetics on electrical energy outputs. By gaining a comprehensive understanding of the fundamental piezoionic effect in chemo–mechanical energy harvesting systems, significant advancements in energy sustainability across numerous practical applications are anticipated.