High-Performance Graphene/PVA Spray-Coated Electrode for Wearable Triboelectric Nanogenerators

Wearable mechanical energy-generating and harvesting devices have emerged in the past decade as potential power sources. [1, 2] As a new energy harvesting strategy, textile-based triboelectric nanogenerators (TENGs) have received enormous attention due to their high flexibility, low cost, and lightweight. [3, 4] TENG works on the combined principle of triboelectrification and electrostatic induction, which can convert low-frequent mechanical energy to electrical energy with high conversion efficiency. Two-dimensional (2D) materials are attractive for fabricating textile-based and lightweight wearable TENG devices. [5, 6] As a monolayer of atomic carbon of crystal, graphene offers remarkable electrical properties due to its linear dispersed band structure near the Dirac point.[7] Moreover, graphene has a high Young’s modulus of 1 TPa and an inherent tensile strength of 130 GPa. [8, 9] Such high stiffness and robustness make graphene a good candidate for fabricating wearable e-devices. [10, 11] Graphene is commonly deposited on wearable substrates with various methods, serving as the electrode and triboelectric materials in TENGs. [12, 13] Emphasizing the need for careful consideration during fabrication, we stress the importance of ensuring strong adhesion and uniformity of the graphene layer on wearable TENGs. In our work, we proposed a cost-effective, large-scalable, and simple spray-coating technique to deposit graphene flakes on commercial cotton textiles, enabling the fabrication of 2x2 cm²-sized wearable electrodes. The ultrasonication-assisted liquid phase exfoliation (LPE) is employed for the synthesis of graphene inks thanks to its high compatibility and scalability. Low-boiling-point 2-propanol (IPA) and biocompatible PVP were introduced as solvents and stabilizers for the graphene, respectively. The polyvinyl alcohol (PVA) solution was simply sprayed on the cotton textiles before spraying graphene ink. This process facilitates the establishment of hydrogen bonds between the chemical chains of PVA and PVP. It was demonstrated that a graphene/PVA composite layer on the textiles exhibits significant electrical conductivity and stability compared to a pure graphene layer, especially under conditions involving multiple bendings at different angles. As the electrode and the triboelectric part in a wearable TENG, this electrode effectively harvested mechanical energy from various human motions and powered daily tiny electronics.<br/>References:<br/>[1] T. Carey, S. Cacovich, G. Divitini, J. Ren, A. Mansouri, J.M. Kim, C. Wang, C. Ducati, R. Sordan, F. Torrisi, Nat. Commun., 8 (2017) 1202.<br/>[2] F. Yi, Z. Zhang, Z. Kang, Q. Liao, Y. Zhang, Adv. Funct. Mater., 29 (2019) 1808849.<br/>[3] W. Li, L. Lu, A.G.P. Kottapalli, Y. Pei, Nano Energy, 95 (2022) 107018.<br/>[4] Y. Gao, Z. Li, B. Xu, M. Li, C. Jiang, X. Guan, Y. Yang, Nano Energy, 91 (2022).<br/>[5] S. Bayan, D. Bhattacharya, R.K. Mitra, S.K. Ray, Nanoscale, 12 (2020) 21334-21343.<br/>[6] S. Bayan, S. Pal, S.K. Ray, Nano Energy, 94 (2022).<br/>[7] C. Soldano, A. Mahmood, E. Dujardin, Carbon, 48 (2010) 2127-2150.<br/>[8] A.K. Geim, K.S. Novoselov, Nat. Mater., 6 (2007) 183-191.<br/>[9] D.G. Papageorgiou, I.A. Kinloch, R.J. Young, Progress in Materials Science, 90 (2017) 75-127.<br/>[10] X. Ji, W. Liu, Y. Yin, C. Wang, F. Torrisi, J Mater Chem C, 8 (2020) 15788-15794.<br/>[11] J. Ren, C. Wang, X. Zhang, T. Carey, K. Chen, Y. Yin, F. Torrisi, Carbon, 111 (2017) 622-630.<br/>[12] I.J. Chung, W. Kim, W. Jang, H.-W. Park, A. Sohn, K.-B. Chung, D.-W. Kim, D. Choi, Y.T. Park, Journal of Materials Chemistry A, 6 (2018) 3108-3115.<br/>[13] S.A. Han, W. Seung, J.H. Kim, S.-W. Kim, ACS Energy Letters, 6 (2021) 1189-1197.