From Body Heat to Boosted Charge: Multiwalled Carbon Nanotube-Based Screen-Printed Textiles for Flexible Energy Harvesting and Storage

The rapid expansion of wearable electronics demands energy solutions that are lightweight, flexible, and sustainable. In this work, a multifunctional textile-based thermally-chargeable supercapacitor (T-TCSC) was fabricated via a scalable screen-printing method using multiwalled carbon nanotube (MWCNT)-based inks and a solid-gel electrolyte of polyvinyl alcohol/orthophosphoric acid (PVA/H3PO4). Five water-based ink formulations were optimized by adjusting the MWCNT concentration (17.5−52.6 g L−1) to achieve optimal printability and electrical conductivity on cotton fabrics. The devices were fabricated by screen-printing the electrode material inks on cotton substrates with an interdigital pattern, followed by coating with the solid-gel electrolyte, resulting in in-plane configurations that eliminate the need for separators and enhance ionic accessibility. Comprehensive electrochemical characterization revealed that the device fabricated with 43.9 g L−1 MWCNT ink (T-TCSC_4) exhibited the best performance, achieving a specific capacitance of 576.2 μF cm−2 (scan rate of 1 mV s−1), low equivalent series resistance (7.1 kΩ), impressive areal energy and power densities (4318.5 nWh cm−2 and 120.6 μW cm−2, respectively), and excellent long-term cycling stability (>100% retention for 10,000 cycles). The thermal energy harvesting capability was also evaluated (13−32 K), demonstrating a maximum Soret coefficient of 420 μV K−1, confirming the suitability of the device for thermionic energy harvesting. While most reported systems address energy storage and thermal energy harvesting separately or in nontextile configurations, this work integrates both functionalities within a planar textile-based architecture, providing a scalable route toward multifunctional wearable energy systems.