Lotus-root-fiber inspired stretchable and self-healing ionic thermoelectric gels with carbon nanotubes for enhanced high-temperature performance

Abstract

Ionic thermoelectric (i-TE) gels have emerged as a promising alternative for converting low-grade heat into electricity, owing to their high ionic thermopower and flexibility. However, integrating high stretchability and self-healing capability with robust high-temperature i-TE performance remains a significant challenge, particularly for wearable applications involving repeated deformation and physical damage. In this study, we developed a stretchable and self-healing i-TE gel, denoted as G-0.1 M FeCN^4−/3−-6 wt% MWCNTs, inspired by the structure of lotus root fibers. Multi-walled carbon nanotubes (MWCNTs) served as both structural connectors and supports, enabling stretchability and self-healing while providing selective ion transport pathways that enhanced the thermodiffusion effect to improve high-temperature performance. A stretchability of 310% was achieved after self-healing, compared to the original value of 350%. At 313 K, the i-TE gel exhibited an ionic thermopower of 11 mV K⁻¹, a maximum output power density (P_max/(ΔT)²) of 1.7 mW m⁻² K⁻², and an energy harvesting density of 0.39 J m⁻² K⁻² over one hour. Furthermore, the i-TE gel device generated a P_max/(ΔT)² of 0.8 mW m⁻² K⁻² (with 4 gel thermocells in series) and an output voltage of 953 mV (under simulated-light exposure, with 25 gel thermocells in series) at 313 K. This bioinspired design strategy offers a viable route to achieve flexibility, self-healing, and high performance in other i-TE systems and energy gels.