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

Abstract

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 −3 .

Energy Harvesting Research: The Road from Single Source to Multisource

“…Tugui et al developed a highly stretchable freestanding electrode, PDMS–carbon black. By integrating such electrodes with a commercial silicone elastomer (Elastosil), an energy density of 1.1 mJ cm −3 was achieved under 200% strain …”

From Amorphous Silicones to Si-Containing Highly Ordered Polymers: Some Romanian Contributions in the Field

“…By properly designing polysiloxanes in terms of structure, molecular weight and crosslinking pattern, it was found that a silicone elastomer based on PDMS ( M w = 80,000 Da) containing 8.4 mol.% vinyl groups crosslinked by thiol-ene addition with a PDMS ( M w = 35,000 Da) containing 16.5 mol.% SH group along the chain, without other additions, incorporated in a DEA developed a lateral actuation of 15% when applying an electric field E = 20 MV/m ( Figure 5 a) [ 53 ]. A DEG built from three circular layers of common silicone with a diameter of 120 mm and coaxial circular stretchable electrodes of 60 mm diameter also based on silicone but embedding 25 wt.% carbon black was able, at 200% strain, to harvest almost 1 mJ ( Figure 5 b) [ 79 ]. An energy harvesting efficiency of η = 8.84% was achieved with a DEG based on silicone filled with 2 wt.% TiO 2 nanotubes and carbon black electrodes ( Figure 5 c) [ 80 ].…”

“…Composites based on silicones and conductive fillers are also being studied as compliant electrodes. Considering that the carbon black particles represent the cheapest powder that can be used as a conductive filler, a rubber electrode was fabricated by incorporating 25 wt.% of carbon black into a high molecular weight PDMS [ 79 , 81 ]. The electrical conductivity was about 0.1 S·cm −1 at 150% strain, remaining almost unchanged even after a few hundred stretching cycles ( Figure 5 d).…”

“… Own performances obtained with dielectric silicone elastomer transducers: ( a ) actuation showed by a DEA with single-layer silicone film based on PDMS (Mw = 80,000 Da) containing 8.4% vinyl groups crosslinked by thiol-ene addition with a PDMS with Mw = 35,000 Da containing 16.5% SH group along the chain [ 53 ]; ( b ) energy harvesting with a DEG based on three layers of silicone elastomer and stretchable electrodes also based on silicone embedding 25 wt% carbon black [ 79 ]; ( c ) energy collected with a DEG based on silicone filled with 2 wt% TiO 2 nanotubes and carbon black electrode [ 80 ]; ( d ) conductivity performances of stretchable electrodes based on PDMS incorporating 25 wt% carbon black within the PDMS matrix [ 81 ]; ( e ) automatic installation for stacked DET manufacturing (block I—stainless steel rigid skeleton, block II—automatic drop of the circular mask, block III—two spray guns that allow the deposition of the electrode solution and the silane, block IV—UV lamp, block V—polymer dispenser, block VI—electronic parts, block VII—left-right mobile rotating disc on stainless steel plate) [ 82 ]. …”

Conductive silicone elastomers electrodes processable by screen printing

“…Cazacu et al . reported a 20 wt% CB/PDMS composite with a moderate conductivity of 0.1 S/cm 26 . Opris et a l. reported the preparation of PDMS/graphite nanocomposites with a conductivity of 0.35 S/cm with graphene nanoplates (GNPs) content of 20 wt.%, while the conductivity below this filler content was unsatisfactory.…”