Soft and elastic hygroelectric fiber for wearable human monitoring textiles

Hygroelectric energy harvesting that uses ambient humidity change to produce electricity is considered important technology in wearable energy sources and self-powered sensors. However, most of these generators are 2-dimensional structures (e.g., film type) and have a low softness with limited elasticity, limiting their wider application, especially in the field of wearable devices. To address the issue, we developed here a soft and highly elastic hygroelectric fiber that consists of hetero-chemically treated carbon nanotube buckles: highly oxidized zone, and non-oxidized pristine carbon nanotubes. By the proton generation in response to ambient humidity change and consequent diffusion from the oxidized carbon nanotube buckle to the pristine one, our hygroelectric fiber generates a high open-circuit voltage (80 mV), a short-circuit current (6 mA/m2), and a peak power density (2.5 mW/m2). The present fiber generator also shows a high elasticity up to 100 % strain and an average Young's modulus of less than 0.47 MPa, which are much elastic and softer than previously reported hygroelectric generators. Textile type hygroelectric energy harvester is also demonstrated by weaving fiber generators into the commercialized textile, which enables non-invasive measurement of humidity in respiration corresponding to body activity and real-time tracking of breath of the human.