Asymmetric Mechano-Electrochemical Energy Harvesting System with Surface Charge-Modified Carbon Nanotube Yarn for Wearable Devices

Abstract

Mechano-electrochemical harvesters are being explored for various applications, including wearable and implantable devices. However, their application in practical devices still requires the development of a structurally optimized two-electrode system to avoid mutual voltage cancellation. Herein, the two-electrode system is improved by enhancing individual electrode performance and resolving voltage cancellation through polarity-controlled electrode design via asymmetric surface charge modification. When negatively charged poly(sodium-4-styrenesulfonate) and positively charged (vinylbenzyl)trimethylammonium chloride are coated on the carbon nanotube (CNTs), the potential of zero charge (PZC) shifted toward the positive and negative directions, respectively. This shift in PZC alteres the configuration of the electric double layer and reverses the direction of the voltage generated at each electrode. Thus, when the two electrodes are stretched simultaneously, the maximum open-circuit voltage reaches 294.4 mV, which is significantly higher than that of the symmetric configuration, which yieldes only 4.7 mV owing to the voltage cancellation. This enhancement originates from both the increased intrinsic bias voltage, which amplifies voltage generation at each electrode, and the summation of the voltages generated by the two electrodes. For practical applications, an asymmetric harvester is fabricated as a one-body structure that can be woven into textiles, providing a compact and efficient solution for energy harvesting.