posted on 2023-11-20, 14:35authored byChia-Yu Lee, Yen-Ting Lin, Shao-Huan Hong, Chia-Hsin Wang, U-Ser Jeng, Shih-Huang Tung, Cheng-Liang Liu
Mixed
ionic–electronic conducting (MIEC) thermoelectric
(TE) materials offer higher ionic conductivity and ionic Seebeck coefficient
compared to those of purely ionic-conducting TE materials. These characteristics
make them suitable for direct use in thermoelectric generators (TEGs)
as the charge carriers can be effectively transported from one electrode
to the other via the external circuit. In the present study, MIEC
hydrogels are fabricated via the chemical cross-linking of polyacrylamide
(PAAM) and polydopamine (PDA) to form a double network. In addition,
electrically conducting carboxylated carbon nanotubes (CNT-COOH) are
dispersed evenly within the hydrogel via sonication and interaction
with the PDA. Moreover, the electrical properties of the hydrogel
are further improved via the in situ polymerization of polyaniline
(PANI). The presence of CNT-COOH facilitates the ionic conductivity
and enhances the ionic Seebeck coefficient via ionic–electronic
interactions between sodium ions and carboxyl groups on CNT-COOH,
which can be observed in X-ray photoelectron spectroscopy results,
thereby promoting the charge transport properties. As a result, the
optimum device exhibits a remarkable ionic conductivity of 175.3 mS
cm–1 and a high ionic Seebeck coefficient of 18.6
mV K–1, giving an ionic power factor (PFi) of 6.06 mW m–1 K–2 with a correspondingly impressive ionic figure of merit (ZTi) of 2.65. These values represent significant
achievements within the field of gel-state organic TE materials. Finally,
a wearable module is fabricated by embedding the PAAM/PDA/CNT-COOH/PANI
hydrogel into a poly(dimethylsiloxane) mold. This configuration yields
a high power density of 171.4 mW m–2, thus highlighting
the considerable potential for manufacturing TEGs for wearable devices
capable of harnessing waste heat.