Wood Skeleton Supported Anisotropic Ionic Thermoelectric Hydrogels for Efficient Low‐Grade Heat Harvesting

Abstract

ABSTRACT Ionic thermoelectric hydrogels show great potential for wearable electronics and low‐power energy harvesting. Achieving high ionic conductivity, large Seebeck effect, mechanical robustness, and environmental stability simultaneously remains challenging. Inspired by natural wood mass transport, we fabricated a wood‐based ionic thermoelectric hydrogel (WPCH) retaining its skeleton structure. The vertically aligned anisotropic wood channels offer mechanical stability and oriented ion transport pathways. The rigid skeleton overcomes the low compression resistance of cellulose‐based counterparts, well balancing thermoelectric performance, mechanics, and environmental stability. Benefiting from oriented, continuous ion transport channels formed by the wood–poly(vinyl alcohol) network, WPCH exhibits a high ionic conductivity of 39.94 mS cm −1 . Strong solvation/coordination interactions between Li + ions and the hydroxyl‐rich cellulose/PVA network retard cation thermodiffusion relative to Cl − , as revealed by molecular dynamics simulations, producing a high n‐type ionic Seebeck coefficient of −2.06 mV K −1 . WPCH also delivers a compressive strength of 890 kPa, enabling applications that require rigid, compressive‐supporting materials. High‐concentration electrolyte impregnation further improves water retention and environmental stability, ensuring durability under practical conditions. Demonstrations in LED powering, fire‐warning systems, and ambient thermal energy harvesting highlight wood‐skeleton engineering as a sustainable route to mechanically robust and environmentally stable ionic thermoelectric devices.