High Performance Mechanical Energy Harvesting from Ionomer Coated Carbon Nanotube Yarn Twist

Mechanical energy harvesters such as piezoelectric, triboelectric are widely investigated to scavenge electrical energy from body movements to ocean waves. A high-power yarn-type mechanical energy harvester called “twistron” was reported in 2017. When stretching it, the increased twist reduces the effective surface area forming an electrical double layer capacitance (EDLC), and electricity is produced in proportion to the amount of EDLC change. By stretching with a sinusoidal applied strain, 140 mV of maximum open circuit voltage (OCV) and 250 W/kg of maximum peak power was obtained. Here, we increased the generated voltage from twistron by coating potential of zero charge (PZC) shifting materials. The shifted PZC increases the amount of intrinsic bias voltage (|OCV-PZC|) used for harvesting electricity. By coating the PZC shifting materials, the produced maximum OCV and peak power increased 1.63 and 4.06 times. Also, by comprising the yarn pair asymmetrically with pristine CNT and the PZC shifting materials coated CNT, the generated voltage can be the sum of the voltages from each electrode. Since the intrinsic bias voltage becomes negative, the direction of generated voltage becomes reversed for PZC-shifted materials coated CNT twistrons compared to pristine CNTs. These asymmetrically composing twistron yarn pairs were attached to joints such as the elbow, knee, and fingers in a form of textile, and energy harvesting from bending motions in seawater was demonstrated. Improved performance of twistron harvester was achieved by the simple coating of PZC shifting materials. Increased voltage without cell separation for serial connection is beneficial to be utilized in confined spaces.