Washable and Eco-Friendly PEDOT:PSS Coated Silk Yarn Based-Transpiration-Driven Electrokinetic Power Generator with Tremendous Energy Generation

Since the importance of eco-friendly technologies and environmental consideration has been increased gradually, energy harvesting technologies that generate electricity from ambient has been gained attentions, including a solar cell, a piezoelectric, a triboelectric, and a thermoelectric device. However, since the relative low energy generation efficiency has been considered as the obstacle, the research on a novel energy harvesting technology is necessary. A transpiration driven-electrokinetic power generator (TEPG), one of the hydro-electric nanogenerators, has been developed recently and researched due to the abundant energy resource (water), the ability to generate energy continuously, no sensitivity to ambient condition, etc. The basic concept is based on the transpiration process where the water flows from roots to leaves by water gradient in the plants. The water gradient in TEPG system is formed with dropping water at one side of the device. There are two main components, including a conductive material and a hydrophilic substrate. The conductive materials with high surface area capture the cations in solution to decrease a surface energy, leading to formation of the electrical double layer. The hydrophilic substrate promotes the flow of solution along the substrate, leading to the transfer of electrons in the conductive material. Herein, we utilize the PEDOT:PSS as conductive material and silk yarn as hydrophilic material. A silk yarn is a natural and biodegradable material with the high mechanical properties, lightweight, and biocompatibility. PEDOT:PSS is promising candidate for TEPG device because its negative charged PSS groups attract the cations selectively via electrostatic interaction, leading to the increase of potential difference between wet/dry region. However, the low washing resistance of PEDOT:PSS is the limitation for practical wearable devices since the cleanness is essential. During the cleaning process, the PEDOT:PSS is easily detached from the substrate. Therefore, the research on the PEDOT:PSS with sufficient water resistance is essential for its wider utilization. In general, an ethylene glycol (EG) is commonly used for improving water resistance of PEDOT:PSS through hydrogen bonding with PSS parts. However, it is also known as the agent to enhance electrical conductivity via removal of excess PSS. Thus, we introduce the divinyl sulfone (DVS) as a covalently cross-linker for enhancing washing resistance of PEDOT:PSS. In this