A Humidity-Resistance, Super-Durable Triboelectric Nanogenerator from a fluorinated Polymer Sponge for Efficiently Harvesting Biomechanical Energy

Wearable electronics are becoming increasingly significant owing to their widespread and farreaching applications in the forthcoming Internet of Things (IoTs) era, including but not limited to health monitoring, motion tracking, and interactive entertainment. The rapid development and potential market of wearable technologies make it urgent to strategically re-aligning currently predominant power supplies, i.e. batteries, considering the limitations in terms of regular recharging and replacing, size and weight, as well as environmental pollution. In this regard, alternative energy supplying technology with the merits of sustainable, maintenance-free, and eco-friendly is highly desired. Triboelectric nanogenerators (TENGs) are proven to be efficient, simple, and environmentally friendly to generate power by daily human motion. Nevertheless, it remains a challenge to improve its unsatisfactory performance under the humid condition that obstructs the practical wearable applications, e.g. being integrated into clothes or shoes, since sweating is inevitable for the body to release excessive heat routinely.

In this work, we report a fluorinated polymer sponge-based TENG (FPS-TENG), which is capable of addressing the moisture-sensing issue benefiting from intrinsic hydrophobicity of the sponge structure and chemical introduction of hydrophobic terminated functional groups, achieving a relatively stable output performance over a wide range of ambient humidity. Concurrently, the FPS-TENG is super durable even under heavy abrasion (simulated via wearing away 1mm-thickness surface layer), indicating the capability in longterm operation under harsh conditions. Specifically, the FPS-TENG is primarily assembled with electropositive copper electrodes and a critical electronegative component, i.e. polydimethylsiloxane (PDMS) based functionalized polymer sponge (FPS), which is suitable for wearable applications for its excellent shock absorption and comfortability due to the elastic property. Under a relative humidity of 40%, the open-circuit (OC) voltage, volume current density, and transfer volume charge density can reach 181 V, 0.55 A/m , and 17.5 mC/m by the FPS-TENG treated at 95°C for 60min during the fluorinated process, respectively, corresponding to a volume power density of 60 W/m , providing up to 364 % increase compared with those of pristine PDMS sponge-based TENGs (PPS-TENGs) and pristine PDMS film-based TENGs (PPF-TENGs). With the remarkable humidity resistance of FPS-TENGs, 60% electrical output is reserved from 20% RH to 85% RH, comparing to only 10% for PPF-TENGs, demonstrating the feasibility of FPS-TENGs to be applied in potential wearable applications. Last but not least, quasi-bulk-phase
functionalization brings about dramatic improvement in working stability and durability than surface functionalization, by which the improvement would vanish once the functionalized surface is worn away. Herein, the enhanced performance of FPSs from functionalization is certified to degrade by only 10% after wearing away 1mm-thickness surface layer. Additionally, the FPS-TENG charges a 50μF capacitor from zero to 5 V within 10min and successfully lights up a LED panel through tapping by hands.