Extremely large Seebeck coefficient of gelatin methacryloyl (GelMA)-based thermogalvanic cells by the dual effect of ion-induced crystallization and nanochannel control

The quasi-solid state thermogalvanic cells (TGCs) have been extensively investigated due to their high Seebeck coefficient (S) and suitability for wearable power generation. However, the influence of hydrogel nanostructure on Seebeck coefficient remains underexplored. In this study, biocompatible TGCs based on gelatin methacryloyl (GelMA) are fabricated via a fast-photocrosslinking process. Moreover, guanidium chloride (GdmCl) salts are directly introduced into the TGCs to enhance the Seebeck coefficient via ion-induced crystallization in the p-type FeCN₆³⁻/FeCN₆⁴⁻ redox system. Small angle X-ray scattering reveals controlled GelMA hydrogel mesh size adjusting the amount of GdmCl, leading to improved intermolecular interactions between the guanidium cations and GelMA polymer. The optimized p-type Seebeck coefficient reaches an unprecedented 21.6 mV K⁻¹, which is the highest thus far reported in the context of the TGC system. Furthermore, a prototype wearable thermoelectric generator (TEG) with an output voltage of 1.6 V under a temperature difference (ΔT) of 9 °C is able to power an LED directly without requiring an additional voltage booster. In brief, the dual effect of ion-induced crystallization and nanochannel control substantially enhances the Seebeck coefficient of the TGC, thereby offering a promising strategy for enhancing the performance of low-grade thermal energy harvesting wearable TEGs.