Hydrogels Based Triboelectric Nanogenerators (TENGs) for Energy Harvesting and Self-Powered Tactile Sensors

New low power technologies, as the one largely developed for the internet of Things (IoT), wearable and portable electronics, require only few tens of microwatts up to few mW of power supply to operate. This makes it possible their sustainable integration with energy harvesters that can scavenge the environmental wasted energy. In addition to provide the required electrical power to low power electronics, mechanical and thermal energy harvester can also be designed as self-powered sensors. This aspect hugely widens their potential impact in a variety of application fields including soft-robotics, artificial skin, and haptics.<br/>Between mechanical energy harvesters, triboelectric nanogenerators (TENGs) have gained increasing attention as novel low-cost energy solution. Furthermore, they can be fabricated with low environmental impact materials and scalable printing processing. Recent developments in TENGs technology show that they can be used in different applications going from wearable and self-powered sensors to wind and sea wave energy harvesting (blue energy). [1] Differently from other mechanical energy harvesters, as piezoelectric and electromagnetic generators, TENGs can be fabricated from non-toxic, biodegradable and recyclable materials and can efficiently operate also in the low frequency range. [2]<br/>TENGs energy conversion mechanism relies on the charge transfer which occur between two materials placed under friction forces and that own different electron affinities. Strategies to increase the charging of triboelectric materials (tribomaterials) through chemical modification or surface patterning have been proposed. We recently demonstrated that the electrode work function as well as electrode capacitance must be considered to improve TENGs power output, a main aspect which has been often disregarded in previous work. [3,4]<br/>Here, we highlight the fundamental role played by the interface between the tribomaterial and the electrode in contributing to the increase of energy harvesting and tactile sensing of novel TENGs based on hydrogels. The specific role of composition, structure and electrolytic capacitance of hydrogel based on polyvinyl alchool derivatives, will be highlighted, and clarified. This work intends to provide useful guidelines for the future design of new materials and device structure design leading to improved TENGs performances, fostering their sooner integration into novel low power electronics.<br/><b>References:</b><br/>C. Wu, A. C. Wang, W. Ding, H. Guo and Z. L. Wang, <i>Adv. Energy Mater.</i>, 2019, <b>9</b>, 1–25.<br/>Y. Zi, H. Guo, Z. Wen, M. H. Yeh, C. Hu and Z. L. Wang, <i>ACS Nano</i>, 2016, <b>10</b>, 4797–4805.<br/>G. *Pace, F. Bonaccorso, <i>Nano Energy</i>, 2020, <b>76</b>, 104989.<br/>G. *Pace, F. Bonaccorso <i>Nano Energy</i>, 2021, <b>87</b>, 106173.