Recent trends in 2D materials and their polymer composites for effectively harnessing mechanical energy

Self-powered wearable devices, with the energy harvester as a source of energy that can scavenge the energy from ambient sources present in our surroundings to cater to the energy needs of portable wearable electronics, are becoming more widespread because of their miniaturization and multifunctional characteristics. Triboelectric and piezoelectric nanogenerators are being explored to harvest electrical energy from the mechanical vibrations. Integration of these two effects to fabricate a hybrid nanogenerator can further enhance the output efficiency of the nanogenerator. Here, we have discussed the importance of 2D materials which plays an important role in the fabrication of nanogenerators because of their distinct characteristics, such as, flexibility, mechanical stability, nontoxicity, and biodegradability. This review mainly emphasizes the piezoelectric, triboelectric, and hybrid nanogenerator based on the 2D materials and their van der Waals heterostructure, as well as the effect of polymer-2D composite on the output performance of the nanogenerator.