Amine-functionalized lignin hydrogels for high-performance N-type ionic thermoelectric materials†

Abstract

Over the past decade, the escalating global energy crisis has necessitated innovative solutions for sustainable development. This study explores a novel approach to address this challenge by harnessing abundant and ubiquitous low-grade thermal energy for electricity generation. Here, we report an efficient method utilizing lignin, a byproduct of the paper and pulp industry, to develop high-performance ionic thermoelectric (i-TE) materials. This research demonstrates the transformation of lignin-based hydrogels from p-type to n-type materials through a green synthesis approach involving cross-linking and amine functionalization. The optimized functionalized lignin-based hydrogel when infiltrated with a 1 M KCl electrolyte, exhibits a negative ionic thermopower (−7.48 mV K⁻¹) and high ionic conductivity (39.9 mS cm⁻¹). These properties result in an exceptional power factor (223.52 μW m⁻¹ K⁻²) and a figure of merit (iZT) of (0.145), surpassing many existing state-of-the-art materials in sustainable n-type ionic thermoelectric performance. Our findings highlight the potential of functionalized hydrogels (n-type material) for low-grade waste energy harvesting. This work advances the performance of n-type i-TE materials and opens avenues for further practical applications in n–p type connected devices. These novel materials offer a promising pathway for self-powered flexible wearable electronics, marking a significant step towards sustainable energy solutions and energy storage devices for efficient utilization of low-grade thermal energy.