Structurally robust cellulosic triboelectric materials under high moisture conditions for self-powered sensing

Eco-friendly cellulosic fibers-based triboelectric nanogenerators (TENGs) are enormously and increasingly demanded for self-powered flexible electronics. However, under high moisture conditions (e.g. sweat, sailing and rain day), the mechanical behaviors of hydrophilic paper were severely reduced due to the weak wet strength and the cellulosic paper-based sensors were easily destroyed under external force, leading to the device failure and invalid signal acquisition. Herein, an industrial-friendly polyethylenimine (PEI)-assisted pulping strategy was developed to produce advanced cellulosic papers, which possessed reinforced wet strength and tribopositive performance. During pulping procedure, the cationic PEI molecules could be quickly in situ bonded onto the surface of fibers under electrostatic interaction and the interfacial interaction between fibers was significantly enhanced through the formation of hydrogen bonds between the amino groups on PEI and the hydroxyl groups on cellulose fibers. The wet strength was significantly enhanced from 1.93 MPa for pristine paper to 8.33 MPa for cellulose/PEI1.5% with an enhancement of 4.32 times. Moreover, originating from the enhanced dielectric behaviors upon the introduction of PEI, the optimized cellulose/PEI1.5% TENG delivered the maximum VOC of 157.3 V, ISC of 3.47 μA, QSC of 42.73 nC and instantaneously maximum power density of 145.93 mW·m-2. Our findings proposed a new perspective for fabricating high-performance tribopositive cellulosic materials that withstand high humid conditions.