Sustainable and recyclable ionogels for ionic thermoelectric supercapacitor application

Abstract

The conversion of low-grade thermal resources into electricity presents significant potential for advancing a sustainable civilization powered by green energy. Herein, a recyclable ionogel is synthesized comprising α-lipoic acid (LA), hydroxypropyl cellulose (HPC), and acrylic acid (AA) via a one-pot polymerization process, thus resulting in a robust double-network structure. The initial ionogel, designated as LACIG-0% is formulated with 1-butyl-3-methylimidazolium chloride (BMIM:Cl) to enhance the mechanical strain properties and ion mobility. Subsequently, various concentrations (1–5%) of calcium chloride (CaCl₂) are added to obtain LACIG-X% samples with enhanced thermoelectric performance. In particular, the LACIG-3% sample exhibits a substantial thermopower of −30.4 mV K⁻¹ and a ZT_i value of 0.04. Moreover, a prototype stretchable ionic thermoelectric supercapacitor (ITESC) utilizing the LACIG-3% achieves an energy density of 520.78 mJ m⁻² at a resistance of 100 kΩ. Additionally, upon exposure to elevated temperatures, the LACIG-3% transitions to a liquid state, which enables reshaping at room temperature without the use of organic solvents. The recycled ionogel (REC-LACIG-3%) retains a thermopower of −11.0 mV K⁻¹, thus emphasizing its reprocessability and sustainability. The ionogel also supports pattern customization via casting, and demonstrates successful integration into thermoelectric devices. Overall, this work not only provides methods for optimizing the thermopower, but also underscores the material's potential for eco-friendly processing and recycling, thereby contributing to the sustainable conversion of low-grade waste heat into renewable energy.