Pseudocapacitive Charge-Transfer Interface via Polyoxometalate-Functionalized Mesoporous MOF for Highly Reliable and High-Fidelity Bioelectronic Hydrogels.

Abstract

Soft bioelectronics require conductive hydrogels with balanced mechanical-electrical performance for high-fidelity electrophysiological recording, yet conventional ones lack a balance between stretchability and electrochemical stability due to poor interfacial charge transfer. We present a molecularly engineered polyoxometalate-functionalized mesoporous metal-organic framework (meso-MOF@POM) nanoarchitecture that simultaneously reinforces the hydrogel network and enhances interfacial charge kinetics. The meso-MOF serves as a hierarchical scaffold with multiscale channels for polymer anchoring, while the sub-nanometer Keggin-type POM layer creates abundant redox-mediated electron transfer pathways. Upon integration of meso-MOF@POM into a dual-network poly(acrylic acid)/polyacrylamide hydrogel, the composite hydrogel enables high stretchability (>1000% strain), minimal electrical creep (<0.13% s^-1@100% strain), and good cyclic durability (>3000 cycles). Crucially, the engineered organic-inorganic interface endows the hydrogel with excellent pseudocapacitive charge-transfer kinetics, which achieves low skin-electrode impedance (64 kΩ at 1 Hz vs. 287 kΩ at 1 Hz for Ag/AgCl gel). As a result, the skin-interfacing electrode enables high-fidelity recording of on-skin electrophysiological signals, including electrocardiogram, electromyogram, and electrooculogram, with an enhanced signal-to-noise ratio (e.g., 23.8 dB for ECG vs. 21.3 dB for Ag/AgCl gel). This work provides a novel fabrication strategy for highly conductive interfaces, enabling long-term applications in wearable health monitors and human-machine interfaces.