Molecular Mechanism of Ionic Conductivity Enhancement by Heterogeneous Interface in Composite Hydrogel Electrolytes

Nanoparticle interactions enhance the performance of hydrogel electrolytes via two primary mechanisms: 1) by localizing a high concentration of water molecules at the polymer–nanoparticle interface, effectively forming continuous water channels that facilitate ion mobility, and 2) by perturbing the structural symmetry of hydration shells around mobile ions, thereby weakening the ion-water binding.

Enhancing ion transport in polymer hydrogels is essential for the development of hydrogel-based electrochemical devices. Herein, this study investigates the molecular mechanisms by which embedded SiO₂ nanoparticles enhance the ionic conductivity of poly(acrylic acid) (PAA) hydrogels. Upon hydration, the deprotonated PAA chains expand the intermolecular space through electrostatic repulsion. Concurrently, the strong surface energy of SiO₂ drives the formation of solvent-enriched interfacial water channels. These interfacial structures facilitate ion transport via two synergistic effects: 1) Zn²⁺ ions near the nanoparticle interface experience reduced structural constraints from the polymer network, and 2) the hydration shells of interfacial Zn²⁺ ions are partially disturbed and asymmetric, weakening the ion-water binding. These nanoscale alterations reduce both steric hindrance and solvation energy barriers, resulting in enhanced Zn²⁺ mobility within the hydrogel domains. This work provides a mechanistic framework for understanding nanoparticle–hydrogel interactions and offers insights into the design of composite hydrogel electrolytes with enhanced ion-transport performance.

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