Percolating Carboxylated Carbon Nanotube Networks Regulated Piezoionic Hydrogels for Wearable Sensing

Piezoionic hydrogels exhibit promising application potential for self-powered sensing as they realize mechanical–electrical conversion through strain-driven ionic migration, which is independent of the dipole polarization of traditional piezoelectric materials. However, significant challenges remain in terms of mechanical stability, low output, and so on. To address these limitations, a piezoionic hydrogel based on a quaternized gelatin (EPTAC-Gel) and poly(acrylic acid) (PAA) double network was designed in this work and synergistically reinforced via the Hofmeister effect and nanofilling with carboxylated carbon nanotubes (C-CNTs). The oppositely charged quaternary ammonium and carboxyl groups were verified as the preferred structural motifs to control the migration rate of ions and establish concentration gradients to induce the piezoionic effect, and multiple hydrogen bonds between the two polymer networks were confirmed to reinforce the hydrogel network. By using C-CNTs to regulate the EPTAC-Gel/PAA double network, the mechanical properties were dramatically improved, and meanwhile, additional transport channels were built up for movable ions to enhance the piezoionic output. This synergistic design enables highly efficient mechanical–electrical conversion and the critical synergistic matching of mechanical properties, piezoionic effect, and ionic conduction, thus fulfilling high-performance self-powered sensing. The as-fabricated hydrogel-based self-powered sensor features a rapid response time of 82 ms, demonstrating an excellent capability for accurate human motion monitoring. Moreover, the method of using penetrating nanofillers to regulate ionic transportation in hydrogel networks provides a novel perspective for the development of high-performance piezoionic sensing electronics.