Multi-scale modified PVDF/Ag@C layer based on dielectric doping and plasma treatment for high-performance triboelectric nanogenerators and self-powered water sterilization

Abstract

The limitations of dielectric properties and surface electron affinity and the harsh environment including high humidity, high salt content, and biological fouling restricted the efficient ocean energy harvesting of triboelectric nanogenerators (TENGs). Here, Ag@C dielectric doping and two-step O2+CF4 plasma treatment are applied to achieve multi-scale modification of triboelectric materials. The coating of C shell avoided the agglomeration of Ag NPs. Besides, the amorphous C shell inhibited the formation of electron transport pathways, and the mechanism of suppressing dielectric loss of triboelectric layers were clarified via DFT calculations at the particle (Ag@C)-polymer (polyvinylidene difluoride, PVDF) interface. The surface charge density of plasma treated polyvinyl alcohol (PVA)-PVDF/Ag@C-based TENG (PT-TENG) increased from 64.26 µC/m2 to 216.60 µC/m2, representing a significant breakthrough in energy harvesting efficiency. The mechanism of enhanced triboelectric properties was investigated based on modified Overlapped Electron Cloud model. Besides, DFT was applied to analyze the reaction mechanism in depth and predict the products of chemically-surface modification process. The oxygen-containing functional groups introduced by O2 plasma treatment likely serve as a "bridge" for the second-step grafting, which helps to build a more convincing reaction mechanism. The superhydrophobic PVDF/Ag@C exhibited excellent moisture-resistance, salt-resistance, and anti-bioadhensive properties, with outstanding charge density (321.45 µC/m2) at 95% RH, making it very suitable for energy harvesting in harsh marine environments. Moreover, the water sterilization system based on PT-TENG demonstrated a high sterilization rate of 98.74%, which was significantly higher than conventional AC power (89.96%).