Effect of density and thickness of flexible polyurethane foam on the performance of triboelectric nanogenerators

Abstract

Triboelectric nanogenerators (TENGs) offer an attractive approach for energy harvesting for self-powered devices. Improving the output performance of TENGs depends on many factors, including the density and thickness of the materials used. In this study, flexible polyurethane foam (FPU) with different densities of 17, 22, 26, and 33 kg m⁻³ was fabricated by altering the isocyanate index and water content during preparation and the effect on the TENG's output voltage was investigated. Additionally, the effect of changing the thickness of FPU (namely, 4, 6, 8, and 10 mm) for each density on the TENG's output voltage was also examined. The chemical structure and pore morphology of the FPU foams were investigated using FTIR and FESEM. The findings of the study indicate that increasing the isocyanate index and water content led to the formation of larger cavities and pores, resulting in reduced densities and increased porosity. In addition, the compression test results demonstrated that the compressive strength of FPU foam increased as the isocyanate index and water content decreased. The results obtained from the TENG device showed that increasing the applied frequency and the FPU density caused an increase in the output voltage, while increasing the thickness resulted in a drop in the output voltage. Therefore, FPUs with a higher density (33 kg m⁻³) and a smaller thickness (4 mm) produce a higher output voltage. In addition, the FPU-based TENG achieved a maximum power density of 0.025 mW cm⁻² under the conditions of a 5 Hz frequency, 20 MΩ resistance, and 4.8 N force. The TENG device effectively charged a 10 μF capacitor to 15.4 V in approximately 60 seconds, storing 1185.8 μJ of energy. This energy was utilized to illuminate four white commercial LEDs connected in series. Hence, the FPU-based TENG has promising prospects for applications involving the powering of electronics and energy storage.