Researchers develop seawater-based energy harvester

The research team was led by principal researcher Seungmin Hyun and senior researcher Hye-Mi So of the Department of Nano-devices and Displays at the Korea Institute of Machinery and Materials (KIMM), and Professor Soo-Hwan Jeong of the Department of Chemical Engineering at Kyungpook National University.

The energy harvester is said to utilise multi-walled carbon nanotubes and graphene oxide films with different content of oxygen functional groups as the cathode and anode and uses seawater as the electrolyte.

During this process, more cations in the electrolyte gather closer to the anode, which has a relatively higher oxygen functional group content, and a potential difference is created because of the rearrangement of ions between the two electrodes.

According to KIMM, conventional water-based energy harvesters have low energy conversion efficiency and require external energy sources to continuously generate the movement of water for reuse, which makes them difficult to be used continuously. Moreover, the utilisation of these harvesters is limited in environments where external sources of energy cannot be supplied.

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The team at KIMM said the new energy harvester can be reused continuously, even after being discharged, through the restoration of its initial open circuit voltage without external energy. Consequently, it can be constantly used as an energy supply device for sensors in environments such as the ocean where the retrieval of devices is challenging.

This new energy harvester has a power density of 24.6mW/cm³, which is approximately 4.2 times higher than that of conventional water-based energy generators made of ionic hydrogel (which have a power density of 5.9mW/cm³), and can provide small devices like calculators, watches, and sensors with sufficient electrical power.

In a statement, Seungmin Hyun said: “The newly developed technology is an eco-friendly energy harvesting technology that allows continuous self-charging and can be used without external energy. 

“It is expected to be used as an energy source to operate sensors and devices in environments where monitoring environmental factors - such as temperature, dissolved oxygen, and inorganic nitrogen in the ocean - is required.”