Enhancing the Performance of a Stretchable and Transparent Triboelectric Nanogenerator by Optimizing the Hydrogel Ionic Electrode Property

Triboelectric nanogenerators (TENGs) with high transparency and stretchability are desired for invisible and adaptable energy harvesting and sensing. Hydrogel-based TENGs (H-TENG) have shown promising attributes toward flexible and transparent devices. However, the effect of hydrogel property on the triboelectric performance of H-TENG is rarely investigated. Herein, dual-network hydrogels composed of dual-cross-linked poly(vinyl alcohol) (PVA) and sodium alginate (SA) were synthesized and used as ionic electrodes in H-TENGs. The elasticity of the hydrogel was controlled by varying the concentration of SA, and the distinct influence of hydrogel viscoelastic property on H-TENG performance was verified for the first time. By tuning the conductivity and viscoelasticity of PVA/SA hydrogel, the optimum H-TENG exhibited high transparency (over 90%) and stretchability (over 250%) and peak output voltage and current of 203.4 V and 17.6 μA, respectively. A specially designed polydimethylsiloxane (PDMS) bag effectively prevents hydrogel dehydration and maintains a stable output in continuous operation. The H-TENG achieved a power density of 0.98 W/m2 on a 4.7 MΩ external resistor. The H-TENG could easily light 240 green and blue LEDs simultaneously and demonstrated capability to power small electronics, such as a digital timer and pedometer. This study provides insights into the influence of hydrogel property on H-TENG performance and gives guidance for designing and fabricating highly stretchable and transparent TENGs.