Building a Flexible High-Performance TENG from Waste Polystyrene Through Surface Structuring and Chemical Modifications

Triboelectric nanogenerator (TENG) is a promising route for harvesting green energy from motion and vibrations.[1] TENGs can be made from a wide array of materials and studies show that different surface modifications can increase energy density by almost 300%.[2-3] This study focuses on improving the triboelectric properties of recycled polystyrene (R-PS) films through a combination of physical and chemical surface modifications aimed at enhancing their performance in TENGs for sustainable energy harvesting. Polystyrene, commonly used in packaging, presents a significant environmental challenge due to its long decomposition period.[4] Recycling this material into TENGs provides an innovative pathway for waste management, transforming it into valuable energy-harvesting devices. In this work, R-PS films were subjected to surface modification to increase the triboelectric performance. Physical surface roughness was created using immersion precipitation, while chemical modification involved the introduction of self-assembled monolayers (SAMs), namely (3-aminopropyl)triethoxysilane (APTES), vinyltrimethoxysilane (VTMS), and 3-(trimethoxysilyl)propyl methacrylate (TMSPMA).<br/>The roughness of the R-PS surfaces was confirmed by AFM and SEM, which revealed the formation of highly porous surface structures contributing to increased triboelectric performance. FTIR and XPS were used to validate the chemical surface modifications, by confirming functional group characteristic of the applied SAMs. Water contact angle measurements demonstrated the increased hydrophilicity of the modified surfaces, further supporting the effectiveness of the chemical modifications.<br/>Initial triboelectric tests were conducted in contact-separation mode against indium tin oxide (ITO) electrode, where SAM-modified films demonstrated significantly enhanced performance compared to pristine R-PS. APTES-modified films exhibited a positive surface charge, while films modified with TMSPMA and VTMS displayed a strong negative charge. The optimal combination of surface roughness and SAM modifications resulted in substantial improvements in the triboelectric output of the films. To further understand the underlying mechanisms, calculations were performed to estimate the net group charge for the SAM-modified films after bond scission. [5] Calculations revealed that heterolytic cleavage of Si–C bonds in the SAM molecules leads to the formation of charged species, which directly influence the observed surface charge polarity.<br/>Two TENG prototypes, composed of matched and unmatched R-PS films were fabricated and tested under controlled conditions. The matched TENG, consisting of rough APTES/R-PS and smooth VTMS/R-PS, outperformed the unmatched TENG in terms of short-circuit current and charge density, reaching 23.9 μA and 1.52 nC cm², respectively. Energy and power density calculation also indicated that the matched TENG achieved higher values across the chosen load resistances. Long-term durability tests, conducted over 100,000 contact-separation cycles, showed excellent stability, with minimal performance degradation.<br/>This research highlights the potential for recycled polystyrene to be repurposed into high-value triboelectric devices, addressing both environmental concerns and the growing demand for sustainable energy solutions. By combining surface roughness modifications with tailored SAMs, the study demonstrates a viable approach to enhancing the charge density and overall performance of TENGs made from recycled materials.<br/>References:<br/>[1] <i>Nano Energy</i>, 2012, 1, 328.<br/>[2] <i>Nano Energy</i>, 2015, 15, 523.<br/>[3] <i>J. Mater.Chem. A</i>, 2016, 4, 3728.<br/>[4] <i>Environ. Sci. Technol. Lett.</i>, 2019, 6, 669.<br/>[5] <i>Nat. Commun.</i>, 2024, 15, 1986.<br/>The authors acknowledge funding by the Latvian Council of Science, project “Development of triboelectric laminates for energy harvesting by recycling waste polystyrene packaging,” project no. lzp-2021/1–0603.