The technological promise of soft devices—wearable electronics, implantables, soft robotics, sensors—has accelerated the demand for deformable energy sources. Devices that can convert mechanical energy to electrical energy can enable self‐powered, tetherless, and sustainable devices. This work presents a completely soft and stretchable (>400% strain) energy harvester based on variable‐area electrical‐double‐layer (EDL) capacitors (≈40 µF cm−2). Mechanically varying the EDL area, and thus the capacitance, disrupts equilibrium and generates a driving force for charge movement through an external circuit. Prior EDL capacitors varied the contact area by depressing water droplets between rigid electrodes. In contrast, here, the harvester consists of liquid‐metal electrodes encased in a hydrogel. Deforming the device by ≈25% strain generates a power density ≈0.5 mW m−2. This unconventional approach is attractive because: (1) it does not need an external voltage supply to provide charge; (2) the electrodes themselves deform; and (3) it can work under various modes of deformation such as pressing, stretching, bending, and twisting. The unique ability of the harvester to operate underwater shows promising applications in wearables that contact sweat, underwater sensing, and blue energy harvesting.

Soft pneumatic actuators—such as those used for soft robotics—achieve actuation by inflation of pneumatic chambers. Here, we report the use of electrochemical reduction of water to generate gaseous products that...

Capacitors are great tools to store electrostatic energy and can discharge current almost instantly when needed. Thus, they are widely used in electrical circuits and have become a crucial part of everyday life. Besides, variable capacitors are a vital component of electrostatic energy harvesters that can harvest mechanical energy. However, traditional rigid capacitors exhibit low capacitance due to a thick dielectric layer in between the electrodes limiting the charge storing capacity. Due to their rigid nature, harvesting mechanical energy by varying capacitance is limited to sliding or oscillating the electrodes up and down in a systematic way. Thus, they cannot convert all kinds of mechanical energy into electricity constraining the conversion efficiency. Here we create soft electrical double layer capacitors, which innately offer higher capacitance due to the small distance between the charged layers. Being deformable in nature, they can convert all kinds of mechanical input (slide, stretch, squish, twist, bend) into electrical energy. These devices generate around 0.23 mW m-2 by harnessing energy from mechanical motion without the need for an external power source unlike the traditional electrostatic energy harvesters. We have characterized the behavior of these devices as a function of several parameters including material properties and physical deformation. The devices behave as expected and the response of the devices to deformation match a physics-based model. The soft device generates an electrical signal when deformed, 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.