Piezo as energy donor, tribo as catalyst: The true mechanism of flow-activated polyvinylidene fluoride-activated carbon-sodium chloride catalyst

Abstract

Piezoelectric materials offer self-powered redox platforms in water, but their mechanisms remain unclear. We demonstrate that synergy between the piezoelectric effect and triboelectrification via solid–liquid contact electrification (SL-CE) reduces effective Gibbs free energy (ΔG*) and promotes high-energy reactive oxygen species (ROS) pathways thermodynamically favorable. We fabricated a bucket-shaped poly(vinylidene fluoride)/activated carbon/NaCl composite that converts hydrodynamic stress into an open-circuit potential up to 4.10 V (vs NHE). By integrating CFD-resolved pressure fields, electrochemical measurements, radical scavenging, and thermodynamic analysis, we interpreted the coexisting electrification modes. SL‑CE emerges as a thermodynamic catalyst: a streaming voltage that scales with interfacial zeta potential and pressure drop lowers effective free-energy barriers by as much as 174 kJ∙mol−1 and contributes up to 44% of the total thermodynamic enhancement at high flow. Piezoelectric polarization acts as an energy donor that supplies the remaining potential required to activate the high-energy H2O→·OH route, pushing all major ROS pathways into the strongly exergonic regime (ΔG* down to −125.4 kJ∙mol−1). These conditions enabled oxidative degradation, achieving 0.997 (C/C0) degradation of 30 mg∙L−1 tetracycline within 60 min at 0.640 m∙s−1. This work reframes flow-driven piezocatalysts as piezo-enhanced SL‑CE catalysts, offering quantitative design principles for self-powered oxidative remediation.