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Among the alternative energy sources harvesting energy directly from the environment, our abundant water resources are usually one of the top options pursued. Most water-based solutions harvest energy directly from the motion of water. However, conventional water-based energy harvesters have low energy conversion efficiency and depend on external energy sources to continuously produce sufficient wave generation for harvesting reuse.
Now, an energy harvester developed by the Korea Institute of Machinery and Materials (KIMM) features advances in nano-microelectronics to develop energy generators that capitalize on the motion of water while being self-charging, eliminating the need for external energy. As a result, the generator can be used continuously as an energy supply device for sensors—even in the ocean, where charging devices is an ongoing challenge. This blog will look at the science behind harvesting energy from water and explore what makes KIMM’s approach a breakthrough.
Electricity generated by waves has shown great potential as an alternative energy source, but its viability has faced challenges in terms of reliability. Movement-based water energy harvesters suffer from low-energy conversion efficiency and need an external energy source to generate water movement, making continuous use problematic. Instead of relying on movement, this innovative self-charging generator harnesses the power of salt water to tackle these challenges, offering superior energy conversion efficiency and eliminating the need for constant external energy sources to drive water flow for reuse. By comparison, salt water is a reliable and sustainable option for several environments, including where external energy sources are limited.
While attempts have been made to use seawater-based energy harvesting, the solution is sensitive to environmental conditions, which, so far, has limited sustainability. However, a team from KIMM’s Nano-convergence Manufacturing Research Division, led by Principal Researcher Seungmin Hyun and Senior Researcher Hye-Mi So, has developed a self-charging energy harvester that generates electricity from the movement of ions in seawater. By altering the movement this form of energy harvesting relies on, KIMM’s harvester can function independently without relying on external energy sources, making it a safer option for the environment.
KIMM's cutting-edge energy harvesting technology delivers a constant, self-sustaining form of electricity, making it an ideal solution for applications requiring continuous use without reliance on external energy. Its power density of 24.6mW/cm³ outshines previous water-based generators. Additionally, by linking several harvesters or expanding the collection area, the research team found that the system’s energy output can be amplified, unlocking even greater potential for renewable energy production and enhancing the technology’s scalability.[1]
KIMM's saltwater-based electricity generator (SWEG) makes several notable advancements compared to traditional water-based energy harvesters. This continuous energy generation is based on ion redistribution between the surface of electrodes and the saltwater electrolytes (Figure 1). The SWEG system uses multi-walled carbon nanotubes (MWNT) and graphene oxide (GO) films to maximize energy output and achieve the necessary resilience against environmental factors that can curtail performance.
Figure 1: A saltwater-based electricity generator (SWEG) can repeatedly discharge and self-recharge without external energy sources due to the ion redistribution between the surface of electrodes and saltwater. (Source: Chemical Engineering Journal)[2]
By functioning independently of external energy sources, a SWEG system can support continuous, long-term applications in a variety of aqueous environments. As the ions move, they create an electrical current, and ion redistribution between electrodes enables continuous self-charging. These self-sustaining features mean the harvester could continuously power such small devices as sensors, calculators, and even watches in remote or hard-to-reach locations where retrieving or maintaining equipment via outside intervention is impractical.
The harvester's power density is approximately 4.2 times higher than conventional water-based generators made from ionic hydrogels.[3] This technology not only provides more power but greater reliability and longevity. According to the research, once fully discharged at a high current density (0.5 µA cm−2), the voltage can be recovered in two hours, and at a moderate discharge current density, considerable voltage is maintained for 24 hours. Reuse is key in energy harvesting, and KIMM’s SWEG system maintains a steady voltage output even after repeated use.
Seungmin Hyun explained the process: “The system can be reused even after being discharged by restoring its initial open circuit without external energy. There's an inherent oxygen functional group difference between two electrodes—carbon nanotube (CNT) electrode and graphene oxide (GO) electrode. When the circuit is opened, ions start rearranging following the electrostatic force between the ion and electrode. Since the GO electrode possesses much more oxygen functional group than the CNT electrode, more cations are attracted to the GO electrode than the CNT electrode. By that rearrangement of ions, surface energy difference between two electrodes is recovered, which means voltage is recovered.”[4]
The applications for this technology include powering sensors and devices to the monitoring of environmental factors like temperature, dissolved oxygen, and inorganic nitrogen, supporting low-power electronic devices in remote areas and providing valuable data for conservation and research initiatives. The harvester's abilities can also support new applications ranging from maritime security to offshore energy production. Its compact size and high power density encourage use in devices where traditional power sources are impractical or impossible.
“Calculators, watches, and sensors are just examples of those small devices that our generator can be used to power,” said Hyun. “We expect that since the saltwater-based electricity generator we developed can be used continuously without external energy input, perhaps [it can be used] as an electrical power source for sensors for monitoring the marine environment.”
Harnessing the natural properties of seawater may create new possibilities for powering our world. Potential use cases can make great strides in providing not just sustainable energy but energy that is easily integrated into our future.
Sources
[1] https://www.sciencedirect.com/science/article/abs/pii/S1385894724025415?via%3Dihub [2] DOI: 10.1016/j.cej.2024.151054 [3] https://techxplore.com/news/2024-09-energy-harvester-generates-electricity-seawater.html [4] Personal communication with the author.
Carolyn Mathas is a freelance writer/site editor for United Business Media’s EDN and EE Times, IHS 360, and AspenCore, as well as individual companies. Mathas was Director of Marketing for Securealink and Micrium, Inc., and provided public relations, marketing and writing services to Philips, Altera, Boulder Creek Engineering and Lucent Technologies. She holds an MBA from New York Institute of Technology and a BS in Marketing from University of Phoenix.
