Flexible Thermoelectric Paper and Its Thermoelectric Generator from Bacterial Cellulose/Ag₂Se Nanocomposites

Abstract

In this research, a flexible thermoelectric (TE) paper was fabricated from bacterial cellulose/silver selenide (BC/Ag2Se) nanocomposites. Ag2Se particles were in situ synthesized in the network of BC nanofibers. Several synthesis parameters that crucially affect the formation of Ag2Se particles in the BC structure were investigated to understand the phase formation mechanism. Under the optimized conditions, the BC/Ag2Se paper with a large proportion of Ag2Se up to 75 wt % was successfully obtained. The in situ synthesis limits the Ag2Se formation within the nanopores of the BC structure. As a result, the submicrosize Ag2Se particles with a narrow size distribution were homogeneously dispersed in the BC nanofiber network. The microstructure was further improved by hot-pressing, which increases the density of the BC/Ag2Se paper and makes the BC layered structure more compact. These contributed to a significant enhancement of the TE properties, with the electrical conductivity of 23,000 S/m and the Seebeck coefficient of −167 μV/K at 400 K. The power factor was 642 μW/mK2 at 400 K, a very high value compared to other flexible TE research. The measurement of thermal conductivity yielded the κ value of 0.36 W/mK at 400 K, which led to the maximum ZT of 0.70 at 400 K. To demonstrate the TE conversion, five BC/Ag2Se paper pieces were connected in series to construct a TE module. The module is very flexible and can be curved to attach to any arbitrary shape of the hot/cold surfaces. In addition, the process for fabricating the BC/Ag2Se paper is scalable without any use of advanced or expensive instruments. This makes it a very attractive choice as a flexible TE generator.

Robust, Flexible Thermoelectric Film for Energy Harvesting by a Simple and Eco-Friendly Method

“…However, the pure Ag 2 Te NWs films cannot be selfsupporting very well, and their mechanical properties are not as good as expected. Given that the BC shows impressive mechanical properties and dispersibility, 14 it was incorporated into the Ag 2 Te film to form a flexible film. The SEM image of the composites film in Figure 1m reveals that the nanocomposites with the SINN structure have been fabricated successfully.…”

“…A low κ value of 0.075 W m –1 K –1 was obtained for the hot-pressed Ag 2.2 Te–14BC film, and the κ value of the pure BC film was 0.048 W m –1 K –1 . Such a low κ in the composite film can be explained as that the multiple interfaces and the microporous structure inhibit phonon transmission and increase phonon scattering. , Although the in-plane and overall κ could be different due to the material anisotropy and geometrical constraint, the value can give an idea for approximation . Namely, the ZT of the hot-pressed Ag 2.2 Te–14BC was estimated to be 0.19 at RT.…”

“…By contrast, the approaches of hybrid design process are well able to realize both good TE performances and flexibility. 12,13 Zhao et al 14 fabricated the bacterial cellulose (BC)/Bi 2 Te 3 self-supporting composite films with excellent flexibility generated from the bonding of BC nanofibers (NFs). After 1000 bending cycles, the σ/σ o value is still about 92%.…”

“…The structural design and material selection of the co-blending process affects the performance of the materials. Palaporn et al prepared a flexible freestanding BC/Ag 2 Se film in which Ag 2 Se particles were in situ synthesized in the BC NF network. Finally, the film achieved a ZT of 0.70 at 400 K. Zhou et al fabricated a flexible self-supporting PVDF/Ag 2 Se TE film with a high filler content (90.5 wt %) by a biomimetic approach, displaying a high PF of 189.02 μW m –1 K –2 at 300 K. Recently, Yang et al prepared Ag 2 Se/nylon freestanding films with excellent flexibility by sequential chemical silver plating and selenization reaction on commercial nylon mesh as the backbone, followed by the vacuum hot-pressing process, the PF of the prepared 90 Ag 2 Se/10 nylon-h reached 1825.1 μW m –1 K –2 , which is even comparable to the PF of pure Ag 2 Se.…”

“…BC is a low-cost, inexhaustible, and eco-friendly biomaterial, which possesses a 3D network of intertwined NFs. Because of its impressive optical, mechanical, and thermal properties, the BC has aroused great interest in a flexible TE device field. , Thanks to the advantages of the SINN structure, the Ag 2.2 Te/BC films display a high tensile strength of ∼78.4 MPa, with a PF value of 48.9 μW m –1 K –2 at RT, when the mass amount of BC reaches 14 wt %. Finally, inspired by the bracelet structure based on Ag x Te/BC nanocomposites, a TE device on a polydimethylsiloxane (PDMS) substrate was designed and assembled to efficiently harvest body heat energy.…”