Solvent Replacement-Driven Ionic Liquid Thermoelectric Gel for Self-Powered Morse Code Communication Assisted by Machine Learning.

The development of ionic liquid gels (IL gels) with both high thermoelectric performance and mechanical flexibility is essential for advancing low-grade heat energy harvesting in next-generation flexible electronics and self-powered systems. Herein, a poly(methacrylic acid) (PMAA)-based IL gel is reported, fabricated via a solvent replacement strategy. By tailoring the synergistic coordination between Fe²⁺/Fe³⁺ redox couples and carboxyl (─COOH) groups in the polymer network, the gel functions as a thermogalvanic electrolyte, and its voltage generation is driven by temperature-dependent redox reactions of Fe²⁺/Fe³⁺. The resulting gel demonstrates excellent thermoelectric stability over a broad temperature range, achieving a high ionic conductivity (σ) of 13.45 S·m^-1 and the Seebeck coefficient (S_i) of -4.67 mV·K^-1. In situ Raman spectroscopy and low-field solid-state nuclear magnetic resonance (NMR) analysis reveal the directional migration behavior of Fe²⁺/Fe³⁺ ions under a thermal gradient and their dynamic coupling with polymer chain motion. Furthermore, a self-powered Morse-code communication system is developed using a machine learning (ML)-assisted framework. A logistic regression model achieved 100% accuracy on an independent test set, indicating a strict monotonic mapping between voltage signals and encoded characters. This work provides new insights into the molecular design and thermoelectric regulation mechanisms of flexible thermoelectric gel, paving the way for their practical application in wearable self-powered communication devices.