Abstract
Thermoelectric (TE) generators consisting of flexible and lightweight p- and n-type single-walled carbon nanotube (SWCNT)-based composites have potential applications in powering wearable electronics using the temperature difference between the human body and the environment. Tuning the TE properties of SWCNTs, particularly p- versus n-type control, is currently of significant interest. Herein, the TE properties of SWCNT-based flexible films consisting of SWCNTs doped with polyethyleneimine (PEI) were evaluated. The carrier type of the SWCNT/PEI composites was modulated by regulating the proportion of SWCNTs and PEI using simple mixing techniques. The as-prepared SWCNT/PEI composite films were switched from p- to n-type by the addition of a high amount of PEI (>13.0 wt.%). Moreover, interconnected SWCNTs networks were formed due to the excellent SWNT dispersion and film formation. These parameters were improved by the addition of PEI and Nafion, which facilitated effective carrier transport. A TE generator with three thermocouples of p- and n-type SWCNT/PEI flexible composite films delivered an open circuit voltage of 17 mV and a maximum output power of 224 nW at the temperature gradient of 50 K. These promising results showed that the flexible SWCNT/PEI composites have potential applications in wearable and autonomous devices.
Highlights
Thermoelectric (TE) energy-harvesting generators, composed of multiple p- and n-type TE materials that are electrically and thermally connected in series and in parallel, respectively, can directly convert heat energy into electric energy and vice versa under a temperature gradient without moving parts
The single-walled carbon nanotube (SWCNT)/PEI composite film was prepared via vacuum filtration of the SWCNT-PEI dispersion onto a poly(vinylidene fluoride) (PVDF) membrane (0.22 μm) and subsequent drying at 55 ◦ C overnight in a vacuum oven (Shanghai Soxpec Instrument„ Shanghai, China)
Our work demonstrates for the first time the feasibility of fabricating both p- and n-type SWCNT/PEI composites with enhanced thermoelectrical properties by modulating carrier type via simple mixing techniques
Summary
Thermoelectric (TE) energy-harvesting generators, composed of multiple p- and n-type TE materials that are electrically and thermally connected in series and in parallel, respectively, can directly convert heat energy into electric energy and vice versa under a temperature gradient without moving parts These generators are quiet, exhibit long lifetimes, and are environmentally friendly which gives them wide applicability in power generation for frontier electronic devices [1,2,3]. Yu et al reported that treatment with the strong reducing agent NaBH4 followed by lamination improved the air stability of n-type PEI-doped CNT composites, yielding Seebeck coefficients as large as −80 μV/K [23]. Through controlling the carrier type of SWCNT/PEI composites, the prepared composites exhibited maximum Seebeck coefficients of 49 and −40 μV/K with electrical conductivities of 210 and 170 S/cm for p- and n-type legs, respectively. A flexible TE generator comprising p- and n-type SWCNT/PEI composites has been assembled to demonstrate the TE energy conversion ability of these composites
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