Pressure-Defined Self-Powered Ammonia Sensing Using a 3D Piezoelectric Sponge Architecture

Reliable gas monitoring in wearable and confined environments demands sensors that operate continuously under mechanical activity without batteries or external amplification. Here, we report a self-powered ammonia-sensing platform built around a three-dimensional chitosan–DWNT-coated polyurethane sponge sandwiched between electrospun PVDF nanofiber layers. The sponge scaffold (40 ppi, 620–860 μm cell size) provides a gas-permeable 3D conductive network with a high density of amine-rich adsorption sites, while the electrospun PVDF layers (15 wt %, DMF/acetone) generate a stable piezoelectric baseline under cyclic compression through preferential β-phase crystallization. This pressure-defined baseline is continuously modulated by ammonia-induced resistance changes at the chitosan–DWNT interface and can be acquired directly at the microcontroller level without external amplification, which distinguishes this platform from prior self-powered ammonia sensors that rely on external signal conditioning. Ammonia detection yields a near-linear concentration dependence ( R 2 > 0.99) over 0–69 ppm, with a limit of detection of 3.33 ppm, a response time of ∼9 s, and recovery within ∼50 s. The platform is further extended to a threshold-triggered ventilation response, in which the self-powered sensing output automatically activates a miniature fan to accelerate ammonia removal and restore the signal baseline, demonstrating a minimal closed-loop sensing-to-action capability. This work bridges the gap between material-level self-powered sensing and actionable system integration, offering a practical blueprint for autonomous gas monitoring in mechanically active, power-limited environments.