Humidity-Resistant Wearable Triboelectric Nanogenerator Utilizing a Bound-Water-Rich Zwitterionic Hydrogel With Microphase-Separated Domains

Abstract

Triboelectric nanogenerators (TENGs) represent an effective approach for transforming mechanical energy into electrical power, making them suitable for wearable electronic applications. Hydrogels as TENGs electrodes are common, but their use as direct triboelectric layers remains insufficiently explored. Here, a novel zwitterionic monomer 3-{1-[6-(hydroxymethyl)-2-methyl-3,8-dioxo-9-aza-4,7-dioxadodec-1-en-12-yl]imidazol-3-ium-3-yl}propane-1-sulfonate (VNIPS) is synthesized in combination with acrylic acid (AA) and zwitterionic sulfobetaine methacrylate (SBMA) to create a double-network zwitterionic hydrogel. The hydrogel is developed using a solvent-exchange process that facilitated the creation of microphase-separated domains, notablely increasing its mechanical strength (211.9 kPa, 472.3%), conductivity (0.6 mS cm⁻¹), and anti-freezing capability (−18.3 °C). In addition, the hydrogel's hydrophilic groups interacted with water molecules, reducing charge loss in humid conditions. When employed as the triboelectric positive layer, the hydrogel-based TENGs achieved a substantial charge density of 456 µC m⁻² and an output power density of 464 mW m⁻², while maintaining a steady open-circuit voltage (V_oc) of 97 V, with 92% retention under 80% relative humidity. Moreover, the hydrogel's strong adhesion and biocompatibility make it suitable for wearable applications, such as motion sensing and Morse code communication. This work demonstrates the feasibility of zwitterionic hydrogels as triboelectric materials, providing a new strategy for creating efficient, humidity-resistant energy harvesters.