“One-stone-two-birds”: engineering a 2D layered heterojunction of terbium tungstate incorporated on molybdenum disulfide nanosheets for a battery-free self-charging power system via the integration of a wearable piezoelectric nanogenerator and an asymmetric supercapacitor

Piezoelectric-driven self-charging power systems play a crucial role nowadays, as they can simultaneously harvest, convert, store, and deliver energy to portable electronic devices. Researchers are focused on two major objectives: (1) understanding the primary mechanisms of energy harvest from environmentally sustainable sources using wearable flexible piezoelectric nanogenerators and (2) improving the energy storage and delivery processes, such as supercapacitors, respectively. Herein, we developed self-charging power systems integrated with a piezoelectric nanogenerator and an asymmetric supercapacitor device. We utilized finger-tapping and acoustic motions to generate the voltages from the nanogenerator and stored them in the supercapacitor device to power portable electronic devices. The piezoelectric performance showed that the nanogenerator can generate a peak-to-peak voltage of 2.81 V (~ 4.2 times better than pure molybdenum disulfide) due to the incorporation of terbium and molybdenum disulfide, which allows for flexible orientation of terbium–oxygen, tungsten–oxygen, and molybdenum–sulfur bonds under external force. The fabricated nanogenerator exhibited a power density of 7.3 µW m⁻², which is higher than previously reported results. Next, electrochemical supercapacitor studies showed a higher capacity (62.6 mAh cm⁻²) for the proposed composite than that of molybdenum disulfide (58.8 mAh cm⁻²) and pure terbium tungstate (21.4 mAh cm⁻²). Finally, studies on self-charging power systems showed that it can self-charge to 1.6 V within 237 s and self-discharge very slowly at 11,763 s (~ 3.26 h) until 57 mV, powering various electronics and demonstrating its practicability. These excellent results of the piezoelectric-driven energy transfer process in self-charging power systems demonstrate its potential capability as a sustainable power source for portable electronic devices.