Materiais funcionais de baixo custo como transdutores de energia: triboeletricidade, flexoeletricidade e higroeletricidade

Abstract

The growing energy demand worldwide in recent decades and the limited availability of fossil fuels and global warming have made the search for new sustainable and environmentally friendly energy sources one of society's greatest challenges. Devices developed for energy harvesting show promising features able to supply low-density devices, such as the Internet of things and wearable electronics. The electrostatic phenomena triboelectricity, flexoelectricity and hydroelectricity have been inserted in this context to supply the energetic demand in daily life. The triboelectricity generates electric charges during the friction/contact between surfaces. On the other hand, flexoelectricity is related to the electric polarization induced in a material that undergoes mechanical bending and vice versa. Finally, the most recently discovered phenomenon is hygroelectricity. From this phenomenon, material is able to generate energy from atmospheric humidity in view of the asymmetric partition of ions from the autoionization of water molecules, which adsorb at a solid-vapor/gas interface. Triboelectric, flexoelectric, and hygroelectric generators have been extensively studied and are able to collect considerable energy from anthropic and natural environments. Indeed, the advances in these electrostatic areas suggest that demo units will appear soon, but it will not be possible using devices built from costly materials and process. In this work, low-cost devices were developed to act as energy transducers based on tribo, flexo, and hygroelectric phenomena. The triboelectric device was built from recycled carton packaging and showed voltage and current of 150 V and  0.3 µA, respectively. The flexoelectric device developed from graphite nanostructured and natural rubber showed applicability as a tactile and force sensor. The results obtained from the flexoelectric device demonstrated that it can identify and distinguish tactile stimuli, such as friction, twist, and touch. Finally, the hygroelectric device built from nanostructured graphite, kraft paper, and aluminum showed great efficiency, and one cell of 2.5 x 2.5 cm² reached 1 V and 0.12 A. It was possible to turn on many high brightness LEDs hygroelectric device through series connections. The devices showed in this thesis were made with low-cost materials and simple and scalable processes.