Vibrational Entropy and Phase Transition Engineering: A Synergistic Approach to Enhancing n-type Thermogalvanic Cells

Thermogalvanic cells (TGCs) convert thermal energy into electrical energy by utilizing the entropy change during redox reactions to generate thermopower (Se). While the role of solvation entropy change is well-established, the influence of other entropic contributions remains largely unexplored. This study reports the unprecedented discovery that the intrinsic vibrational entropy change (ΔSint) of aliphatic chains can significantly enhance the thermopower of TGCs. Furthermore, entropy changes associated with phase transition are harnessed to maximize Se. To realize this concept, the copolymer poly(N-isopropylacrylamide-co-4-(acryloyloxy)butyl ferrocenecarboxylate) P(NIPAM-co-ABFC) is designed and synthesized, which synergistically integrates vibrational and phase-transition-driven entropy effects. In this design, ABFC provides a substantial intrinsic vibrational entropy change, while PNIPAM functions as a thermoresponsive component, generating a large entropic change upon its phase transition. These findings are supported by density functional theory (DFT) and molecular dynamic (MD) simulation. The resulting n-type TGCs achieve a record-high thermopower of 3.64 mV K-1, surpassing other previously reported aqueous n-type TGCs. This work not only introduces a new strategy for boosting thermopower but also provides a deeper understanding of the entropic contributions beyond solvation entropy.