Exciting Breakthrough in Energy Harvesting Inspired by Electric Rays!
Researchers are continually searching for innovative and sustainable energy sources, particularly for use in distributed electronics and wearable technology. The need for energy harvesters that are reliable, scalable, and require little to no maintenance is more pressing than ever. However, many current solutions depend on mechanical changes, environmental variations, or specially designed gradients, which can lead to inconsistent power outputs and shorter device lifespans.
But here's where it gets groundbreaking: a team has unveiled a bioinspired ionic heterojunction energy harvester that produces direct current solely from spontaneous ion migration at interfaces—without needing any external energy input. This revolutionary device features an asymmetric bilayer structure crafted from ionic liquids and charged polymers within a thermoplastic polyurethane matrix. This configuration generates a built-in potential that facilitates the movement of ions in a specific direction when the layers come into contact. A single unit, measuring just 0.2 mm thick, can deliver approximately 0.71 V along with a volumetric power density of 66.8 µW/cm³. Remarkably, this device maintains stable operation for over 60 hours and shows impressive resilience to mechanical strain (up to 50%) and humidity (up to 90% relative humidity). Furthermore, by stacking these units, researchers can achieve linear voltage scaling, allowing them to directly power everyday devices like a 6 W light bulb, a calculator, or a watch without the need for rectification.
This innovative solid-state platform offers a sustainable, scalable pathway toward creating self-powered wearables and distributed electronic systems. Inspired by electric rays, which generate significant voltages through layered electrocytes, the researchers at UNIST have developed a unique energy harvesting technology that replicates this natural mechanism. In contrast to electric rays that necessitate mechanical stimulation, this new technology works autonomously, producing power independently of external influences.
Under the guidance of Professor Hyunhyub Ko from the School of Energy and Chemical Engineering, the research team has successfully constructed a bioinspired bilayer ionic asymmetric stack (or BIAS) that is only 0.2 millimeters thick. When multiple BIAS cells are stacked together, they can generate voltages exceeding 100 volts, which can enable the direct operation of electronic devices, such as LED lights, calculators, and digital watches—eliminating the need for rectification.
To put things into perspective, while a single electrocyte from an electric ray produces around 0.1 volts, connecting these cells in series allows for a high-voltage output akin to that of traditional batteries. The key innovation in this technology lies in its unique cell structure: an asymmetric bilayer made up of cationic and anionic polymer films. This design creates an internal electric field that propels ion migration, generating voltages similar to the membrane potential found in biological cells.
Figure 1 illustrates the all-polymer bilayer ionic heterojunction generator, which operates independently of any external energy sources. Unlike conventional ionic devices that require external stimuli—such as mechanical force or environmental shifts—the BIAS generates electricity naturally through internal ion movement. Reports indicate that a single cell can yield roughly 0.71 V, more than 30 times higher than symmetric structures, and stacking multiple cells effectively powers practical electronic gadgets.
The durability and environmental resilience of this device are equally impressive. It sustained its voltage output even after undergoing more than 3,000 mechanical stretching cycles and could stretch up to 1.5 times its original length without losing performance. Furthermore, it functioned reliably across a wide range of humidity conditions—from dry environments to 90% humidity—with minimal fluctuations in power output. These capabilities indicate a strong potential for applications in wearable electronics, where constant movement and varying environmental factors are common.
Led by first authors Seungjae Lee, Youngoh Lee, and Cheolhong Park from the School of Energy and Chemical Engineering, the team expressed that by mimicking the ion-selective membrane potentials observed in biological entities, they developed the BIAS—a unit cell capable of generating significant voltage autonomously when stacked together.
Professor Ko emphasized the significance of their work, stating, "This technology harnesses internal ion migration within the bilayer structure to generate high voltage without relying on any external energy source. In contrast to traditional energy harvesting methods that depend on wind, sunlight, pressure, or temperature variations, our approach is free from external stimuli, which could potentially reduce maintenance needs for wearable power sources."
The results of this fascinating research were published online in Advanced Energy Materials, a leading international journal focused on energy materials, on December 8, 2025. The study received support from the National Research Foundation of Korea (NRF) and the Ministry of Science and ICT (MSIT) through initiatives aimed at advancing nanotechnology and energy materials.
