(332b) Soft and Stretchable Energy Harvesting Using Metal/Gel Interfaces

Capacitors are widely used in electrical circuits due to their ability to store electrostatic energy and discharge current almost instantly when needed. Variable capacitors are those that can change capacitance – usually via geometric changes—to convert mechanical energy to electrical energy. Despite the headway, harvesting mechanical energy by varying capacitance is limited to sliding or oscillating the electrodes up and down in a systematic way due to their rigid nature. In addition, the relatively large gap between the electrodes in a traditional rigid capacitor results in low capacitance, limiting the charge storing capacity. To address these limitations, we utilize a so-called electric double layer capacitor. Such a capacitor forms at the interface between metal and electrolyte, due to the formation of oppositely charged layers form at the interface. Electrical double layers innately offer higher capacitance than conventional capacitors due to the small distance between the charged layers. We use liquid metal for the electrode, which allows the area of these interfaces to vary in response to mechanical forces. Thus, we were able to create variable area capacitors that can harvest mechanical energy. Since they are soft and deformable, they can convert all modes of mechanical input to electricity including pressing, stretching, bending, and twisting. These devices generate ~1 mW m^-2 by harnessing energy from mechanical motion without the need for an external battery, unlike the conventional electrostatic energy harvesters. We have characterized the behavior of these devices as a function of several parameters including material properties, design architecture, and mechanical deformation. The devices perform as expected and the response of the devices to deformation matches a physics-based model. The liquid metal-based soft device generates an electrical signal when deformed and works underwater, which may be useful for oceanic energy harvesting as well as wind energy harvesting. Besides, these devices can harvest human motion thereby find applications in wearable electronics, healthcare systems like rehabilitation and prosthetics.