Hybrid Liquid Epoxidized Natural Rubber-Based Hydrogel for Freestanding Triboelectric Nanogenerator Applications

The development of multifunctional, flexible materials for triboelectric nanogenerators (TENGs) is essential for advancing next-generation energy harvesting systems. This work presents a highly stretchable and self-healing hydrogel composed of liquid epoxidized natural rubber (LENR), poly(acrylamide-co-acrylic acid) [P(AAm-co-AA)], copper sulfate (CuSO4), and reduced graphene oxide (rGO). The dual cross-linked network, formed through ionic coordination and hydrogen bonding, endows the hydrogel with mechanical resilience, ionic conductivity (6.66 × 103 S/m), and intrinsic self-repairing capability, restoring over 85% of its mechanical integrity within 30 min postdamage. Comprehensive structural and morphological characterizations (FTIR, 1H NMR, DSC, and FESEM) confirm successful component integration and network formation. The optimized formulation (0.1% rGO) exhibited enhanced triboelectric performance in a freestanding TENG configuration, achieving an output voltage of up to 8 V, a peak current of ±45 μA, and a transferred charge of ∼1.2 μC per cycle. The hydrogel-powered device successfully illuminated a 3 V LED with a peak light intensity of ∼750 au and maintained consistent electrical output across varying tapping frequencies (2–15 Hz), demonstrating strong responsiveness and durability. These findings highlight the potential of LENR-based hydrogels as flexible and multifunctional platforms for wearable TENGs and self-powered electronics.