Molecular Engineering of Redox‐Induced Conformational Entropy in Polyviologens for Organic Thermogalvanic Cells

Abstract

ABSTRACT Thermogalvanic cells are attractive for harvesting low‐grade thermal energy because of their strong thermoelectrochemical response and simple architecture. Because the redox entropy change directly governs their Seebeck coefficient, engineering redox entropy offers an effective strategy for enhancing thermoelectric performance. Herein, redox‐induced conformational entropy engineering is introduced as a molecular strategy for organic redox‐active polymers. Ortho‐ xylylene‐linked polyviologen ( o‐ PV), meta‐ PV, and para‐ PV ( p‐ PV) are synthesized to modulate steric constraints and conformational reorganization during the viologen redox process. Electrochemical and spectroscopic results indicate that o‐ PV undergoes the most pronounced conformational reorganization upon reduction and exhibits the largest conformational entropy change, consistent with its sterically constrained architecture. Consequently, o‐ PV exhibits the greatest Seebeck‐coefficient magnitude of −1.87 mV K −1 , whereas p‐ PV displays the lowest response. This structure–entropy relationship guides the development and subsequent integration of an end‐capped o‐ PV derivative into a poly(acrylamide) hydrogel thermocell, which achieves a Seebeck coefficient of −2.25 mV K −1 and a normalized maximum power density of 0.88 mW m −2 K −2 . A hydrogel‐based thermoelectric generator demonstrates scalable voltage output, stable operation, and effective low‐grade human body heat harvesting. These findings establish conformational entropy engineering as a strategy for tuning redox thermodynamics and advancing high‐performance organic thermogalvanic materials for sustainable heat‐to‐electricity conversion.