Mesoscopic confined ionic thermoelectric materials with excellent ionic conductivity for waste heat harvesting

Harvest energy from ubiquitous low-grade waste heat with thermoelectric (TE) materials is a prospective and crucial strategy in sustainable development. High-performance ionic thermoelectric (ITE) materials with flexible, low-cost, mass productive and biodegradable features are in high demand. Herein, a novel, flexible and high-performance ITE material (carboxyl-functionalized bacterial cellulose-based ionogels, CBCIGs) based on biofriendly 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized bacterial cellulose (TOBC) and "green" solvent (ionic liquid, 1-ethyl-3-methylimidazolium dicyanamide, [EMIm][DCA]) is reported. The as-fabricated CBCIG exhibits a high tensile strength, skin-like stretchability, excellent adhesion and biodegradability. The ionogels were designed to manipulate the confinement of ILs within the functionalized natural biopolymer, aiming to improve the electric conductivity as the ionic TE materials. The proposed CBCIG with 99.52 wt% [EMIm][DCA] exhibits a high ionic conductivity of 79 mS cm−1. The maximum Seebeck coefficient is 11.55 mV K−1 observed on CBCIGs-90 wt%. The employment of the CBCIGs as a flexible ionic thermoelectric capacitor (ITEC) device for thermoelectric conversion is also demonstrated. We expect that the development of the flexible ITE materials will provide an effective solution for utilizing low-grade waste heat for flexible wearable self-powered devices.