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 (S_e). 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 (ΔS_int) of aliphatic chains can significantly enhance the thermopower of TGCs. Furthermore, entropy changes associated with phase transition are harnessed to maximize S_e. 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.