High performance flexible triboelectric nanogenerators using bio-derived films made of siloxane-modified castor oil

Triboelectric nanogenerators (TENGs), capable of converting mechanical energy into electricity, are sought to enable self-powered devices reducing reliance on traditional power sources. However, traditional triboelectric materials fall short of meeting the urgent need for sustainable and environmentally friendly energy solutions. Emerging bio-derived triboelectric materials promise a lower environmental footprint than their traditional counterparts, yet predominantly exhibit tribopositive characteristics. This results in a diminished surface potential difference in bio-derived layers, leading to reduced energy output and hindering the development of fully bio-derived TENGs (bio-TENGs). Here we introduce a novel material based on castor oil (CO), synthesized by integrating CO with silane coupling agents through processes like esterification, Michael addition, and free radical polymerization. This synthesis produces a siloxane-CO complex, resulting in bio-derived films with high negative surface potential, ideally suited as a tribonegative layer in bio-TENGs. To estimate their position in the triboelectric series, the CO-based films are paired with a polyimide tribolayer to form a dual-layer TENG. In this configuration, the CO-hybrid film manifests a maximum peak output voltage of approximately 330 V and a power density as high as 450 mW m⁻². Further investigation revealed that increasing the VTES concentration in the CO shifts its position in the triboelectric series downwards, enhancing its tribonegative properties. This adjustment allows for the development of a flexible, entirely CO-based TENG (All-CO TENG) capable of generating voltages up to 55 V and a power density of 18 mW m⁻². Furthermore, the CO-based TENGs are operated in single electrode mode against various surfaces, highlighting their versatility and applicability.