Stretchable Energy Harvesting Devices: Attempts To Produce High-Performance Electrodes

Dielectric elastomer transducers (DETs), essentially consisting of highly deformable insulating films sandwiched between electrodes, are able to convert mechanical work in electrical energy and vice versa. Although still immature, these represent a simple and low-cost alternative to already known technologies for harvesting energy from renewable sources, in this case converting environmental mechanical energies (e.g., wave energy, human body movement) to an electrical one. However, the development of this new technology raises several challenges in terms of finding more efficient materials. For high conversion efficiencies, a dielectric film should meet certain properties such high breakdown strength and small mechanical hysteresis, while the electrodes should be compliant and able to keep conductivity along repeated large deformations. Regarding these aspects, two types of electrodes were successfully achieved, an ultrathin silver electrode of about 40 nm thickness and a PDMS-carbon black composite rubber electrode of about 30 μm thickness. Both electrodes were analyzed in terms of morphology and electrical and mechanical behaviors, as well as actuation response. The results indicate that the rubber electrode is more appropriate because it has proved to work perfectly in hundreds of cycles at large deformations (150%) without losing conductivity. On this basis, three types of capacitors with 120 mm diameters with coaxial electrodes of 60 mm diameters having one (DEG I), two (DEG II), and three (DEG III) active layers were built by a simple and efficient method using a commercial silicone (Elastosil) as the dielectric. The achieved arrays were tested in an energy-harvesting setup. At 200% strain and a bias voltage of 3 V μm^–1, DEG I produced 0.07 mJ, DEG II produced 0.2 mJ, and DEG III produced almost 1 mJ with an energy density of 1.1 kJ m<sup>–3