Sodium alginate based energy harvesting fibers: Multiscale structure and moist-electrical properties

Moist-electric generation, a new energy harvesting technology, exhibits unique advantages in sustainable energy collection and compatibility with environment. However, the lack of research on fiber based moist-electric generation materials and multiscale structure-moist electric performance relationship has restrained the extensive development and application of this energy generation method. In this work, sodium alginate (SA)/multi-walled carbon nanotubes (MWCNT) coaxial fibers with radial gradient difference of oxygen-functional group are prepared through wet spinning. Meanwhile, the aggregate structures of SA/MWCNT fibers are regulated by adjusting the spinning and post-drawing process. The relation between moist electric generation performance and multiscale structure of SA/MWCNT fibers, including the effect of oxygenated group distribution and crystalline structure, are investigated for the clarification of moist-electric mechanism. Based on structure design, the coaxial fiber moist-electric generator (CFMEG) shows excellent moist-electric properties, continuous output ability, and environmental adaptability. The maximum output power density of CFMEG with a length of only 1 cm can reach 3.09 ∼ 9.50 μW/cm2 at RH = 90 ∼ 95% from an extreme voltage of 0.35 ∼ 0.38 V and current of 1.64 ∼ 1.74 μA, which exceeds most of the same type of moist-electric research. A long-last output voltage of 0.15 V for more than 36 h can be obtained from this CFMEG, which is able to generate an output voltage of 1.0 to 6.9 V after series and parallel connection to illuminate LEDs directly without additional capacitors. The CFMEG from multiscale structure design provides a way of preparation of flexible power supply devices using green resource with low density and exhibits great opportunity for common purpose application.