A Multifunctional MXene/PVA Hydrogel as a Continuous Ionic Thermoelectric Generator and a Strain/Temperature Sensor

Abstract This research reports a continuous output ionic thermoelectric ( i ‐TE) system based on MXene/PVA (polyvinyl alcohol) hydrogel, by utilizing thermo‐diffusion of Cu 2+ and Cl − ions and the redox reaction involving Cu/Cu 2+ at the electrode interfaces. The thermopower of the i ‐TE system can be independently tuned to a value of −3.13 mVK −1 by adjusting the ion diffusivity via MXene (Ti 3 C 2 T x ). The i ‐TE system demonstrates a rapid response time of less than 100 s, outperforming any other polyelectrolyte‐based system. Crucially, the i ‐TE system achieves continuous current output when equipped with copper electrodes, facilitated by the redox reaction involving Cu/Cu 2+ , and maintains stable long‐term outputs across a range of resistances from 1 kΩ to 1 MΩ. A three‐serial‐connected i ‐TE module demonstrates an output voltage of 26 mV with 6 °C temperature difference, confirming the feasibility of creating an array of i ‐TE devices for substantial energy output. Beyond energy harvesting, the MXene/PVA hydrogel serves as multifunctional strain/temperature sensors, capable of detecting mechanical strains via the piezoresistive effect and locating finger contact points via the ionic thermoelectric effect.