Piezoelectric-Like Response and Energy Harvesting Potential of a Moldable PVA/PANi Composite Prepared via Frozen-Gel Polymerization

Introduction:
Soft, mechanically compliant materials capable of converting mechanical energy into electrical output are essential for the next generation of wearable electronics and self-powered sensors. While piezoelectricity is typically associated with crystalline ceramics or ferroelectric polymers, recent efforts have focused on organic mixed ionic–electronic conductors (OMIECs) as functional alternatives. Here, we report a moldable, water-processable PVA/PANi composite exhibiting strain-sensitive electrical response and piezoelectric-like energy conversion, synthesized through a straightforward frozen-gel polymerization method.

Methods:
Poly(vinyl alcohol) and glycerol were dissolved in water to form a hydrogel precursor, followed by in situ polymerization of aniline under frozen conditions. The composite was subjected to mechanical compression and stretching cycles, and its electrical output was evaluated via open-circuit voltage (VOC), short-circuit current (ISC), and power output across various load resistances. The structure was characterized via scanning electron microscopy (SEM), revealing platelet-like nanoparticle PANi domains embedded in the soft matrix.

Results:
The composite exhibited a reproducible piezoelectric-like response under compressive strain, with VOC reaching 0.08 mV/mm and ISC exceeding 8 µA/mm² at ~4.6% strain. Maximum power density of ~7 nW/cm³ was obtained at an optimal load of 1 kΩ. Theoretical Pmax estimates based on VOC × ISC closely matched experimental results. SEM revealed granular and fibrillar self-assembled nanoparticle PANi domains, likely templated by ice grains during polymerization, suggesting an interface-driven morphological control.

Conclusions:
The PVA/PANi composite exhibits mechano-electrical conversion in the absence of conventional piezoelectric phases, enabled by a unique morphology arising from frozen-gel polymerization. Its moldability, conductivity, and scalability highlight its potential for low-cost, flexible energy harvesting and sensing applications.