Flexible cellulose nanofiber/Bi2Te3 composite film for wearable thermoelectric devices

Cellulose nanofiber (CNF) is obtained from cellulose resources (e.g., natural cellulose, bacterial cellulose, etc.) and is considered to be a low-cost, green and inexhaustible material. The impressive optical, mechanical, and thermal properties of this material have aroused great interest in fabricating of flexible electronic devices based on CNF. Hereby, the CNF/Bi2Te3 thermoelectric composite films are fabricated using a facile vacuum filtration method. Subsequently, n-type and p-type films composed of this composite materials are used as legs to assemble thermoelectric generator (TEG) prototype. Besides, these composite films exhibit excellent mechanical flexibility and the electrical conductivity of the CNF/Bi2Te3 film only decreases by 8% after 1000 bending cycles. And the contact angle of the polytetrafluoroethylene (PTFE) solution and alkylketene dimmer (AKD) emulsion co-treated film is as high as 150.7°, which has superhydrophobic properties. The TEG prototype consists of five p-n legs. At a temperature gradient of 60 K, the output voltage of the TEG prototype is 22.34 mV and the output power is 561 nW. This work not only proves the great potential of CNF application in flexible thermoelectric (TE) materials, but also promotes robust development of cellulose-based electronics.