Fig. 8: Energy harvesting driven by moisture and steam through thermos-osmotic and thermoelectrokinetic processes.

a Schematic illustration of an ionic thermoelectric supercapacitor device of PEO doped with NaOH, equipped with an Au/CNT electrode. Reproduced with permission from ref. ²⁵³ Copyright 2016, Royal Society of Chemistry. b Molecular structures and fabrication process of PAA-PEO-NaCl ionic hydrogels. c Thermopower of PAA-PEO-NaCl hydrogels with varying salt concentration under different temperature gradients. d Ionic conductivity and Seebeck coefficient of the PAA-PEO-NaCl ionic hydrogels with different NaCl content. Inset: schematic diagram illustrating the setup for measuring ionic thermovoltage. b–d Reproduced with permission from ref. ²⁵⁴. Copyright 2023, Wiley. e Schematic of charging and discharging cycle of the Ionic Thermoelectric Supercapacitor (ITESC). (i) establishing the temperature gradient(16 K) to induce thermovoltage, (ii)charging an electrochemical capacitor through an external load, (iii)removing the gradient and isolating the device, and (iv)discharging (both with R_load = 100 kΩ). Reproduced with permission from ref. ²⁵³. Copyright 2016, Royal Society of Chemistry. f Seebeck coefficient of PVA-based materials with different concentration (PVA 10% (gray), PVA 15% (red) and PVA 25% (blue)) at different humidity. Reproduced with permission from ref. ²⁵⁵. Copyright 2024, Elsevier. g Design and synthesis of the moist thermoelectric generator (MTEG): polyelectrolyte membrane was prepared via copolymerization of AMPS and SSS under UV light, then encapsulated between carbon cloths coated with carbon nanotubes and assembled into the MTEG, electricity generated by the dislocation and diffusion of Na⁺ and H⁺ ions under hygrothermal synergistic system.(top), and the voltage output of the MTEG remain stable for 118 h under 60% ΔRH and 15 K temperature difference (Environment temperature at 70 °C) and the image of the LED bulb light up by using waste steam(bottom). Reproduced with permission from ref. ²⁹. Copyright 2023, Wiley. h Schematic illustration of the energy harvesting using asymmetric SPEEK/PES blend membrane subjected to temperature gradient(top), and the output power densities of the membrane under different concentration gradient ranging from 5 to 1000, with top side facing the low concentration (LiBr) solution (0.01 M) and output power densities of the asymmetric SPEEK/PES blend membrane with a 50-fold concentration difference under various ΔT from −30 to 30 °C (bottom). Reproduced with permission from ref. ²⁵⁶. Copyright 2021, Springer Nature.