Exceptional n‐Type Ionic Thermoelectric Hydrogels by Synergistic Hydrophobic and Coordination Interactions

Abstract Ionic thermoelectric (i‐TE) materials show promise for flexible energy harvesting and self‐powered sensing due to their high ionic Seebeck coefficients ( S _i ). However, achieving both high thermoelectric performance and mechanical stretchability, especially in n‐type systems, remains a critical challenge. Herein, a poly(vinyl alcohol) (PVA)‐based n‐type i‐TE hydrogel is presented that exhibits both large negative S _i (−38.6 mV K ⁻¹ ) and excellent stretchability (382.5%) through synergistic effect of coordination and hydrophobic interactions. Leveraging the amphiphilic nature of PVA, its hydrophilic hydroxyl groups form coordination bonds with Cu ²⁺ ions from copper chloride (CuCl ₂ ), while its hydrophobic backbone interacts with water‐soluble conjugated polymer (poly(3‐(3′‐N,N,N‐triethylammonium‐1′‐propy‐loxy)‐4‐methyl‐2,5‐thiophene chloride (PMNT). Meanwhile, hydrophobic associations also occur among PMNT chains due to strong π‐π stacking and backbone hydrophobicity. This dual‐interaction strategy approach enhances the thermophoretic difference between chloride anions (from both CuCl ₂ and PMNT) and cations, enabling the giant ionic thermopower. Besides, the long‐range hydrophobic interactions contribute to the overall mechanical robustness. The developed hydrogels are successfully implemented in self‐powered temperature sensors and low‐grade heat harvesting systems, such as powering a cooling fan by utilizing the waste heat from a working tablet. This work offers an alternative pathway toward developing high‐performance i‐TE materials for wearable electronics and low‐grade heat harvesting applications.