Researchers construct nanochannels from graphene oxide nanosheets to harvest osmotic energy from the ocean

Journal of the American Chemical Society (2022). DOI: 10.1021/jacs.2c04663″ width=”650″ height=”346″/>

Graphic abstract. Credit: Journal of the American Chemical Society (2022). DOI: 10.1021/jacs.2c04663

When we think of renewables, the first thing we often think of is the sun or the wind, but what about ocean energy?

The ocean covers more than 70% of the Earth’s surface, which offers enormous potential for renewable and clean energy. Researchers at the Institute for Frontier Materials (IFM) hope to unlock this potential.

In an article published in the Journal of the American Chemical Society, IFM researchers have demonstrated how new advanced two-dimensional (2D) nanomaterial membrane technology can improve blue energy harvesting processes. Harvesting blue energy is a renewable energy that uses the difference in salinity between river water and sea water to generate electricity.

“Ocean energy comes in five forms: tidal energy, water waves, ocean currents, temperature gradients and salinity gradient energy, and offers a potential alternative, boundless source of energy,” said Associate Professor Weiwei Lei, who leads the renewable energy generation project at IFM.

“Therefore, harvesting ocean energy through artificial devices has attracted enormous interest. Energy with a salinity gradient, also known as ‘osmotic energy’ or ‘blue energy’, in particular, holds significant promise for renewable energy development.

“It has a potential of 1 TW of energy (8500 TW h in a year), which is more than the sum of hydraulic, nuclear, wind and solar energy in 2015.

“With the development of nanotechnology and 2D nanomaterials, new 2D nanomaterial membranes with nanopores and nanochannels were designed for blue energy harvesting.

“However, the energy harvesting efficiency of these membranes is still too low to meet the demands of practical applications due to their high internal resistance and low ion selectivity.

“New advanced 2D nanomaterial membranes with novel and robust properties will solve this problem that is now in high demand.”

associate prof. Lei and his team members introduced a strategy to optimize the nanochannels within the 2D nanomaterial membranes to harvest more energy through higher amounts of water.

To do this, researchers constructed nanochannels from graphene oxide nanosheets. The sheets are chemically exfoliated, shaking loose reactive nanosheet fragments called oxidative fragments that are charged under alkaline conditions. The negatively charged channels attract positive ions in seawater. The osmotic pressure can then “push” the ions through the channels to create a net current that can be harvested.

This approach allows the membrane to overcome the trade-off between permeability (how easily the ions can move through the channels) and selectivity (encouraging only positive ions to move through the channels). This gives Assoc. prof. Lei’s membrane a boost in energy generation compared to graphene oxide membranes not treated to accommodate negatively charged nanosheet fragments.

This strategy increased power generation to a level that could power a small electronic device.

“This means we can harvest more energy through large amounts of water. This increased energy generation is due to the enlarged nanochannels along with the enhanced local charge density of the detached oxidative fragments.”

The new strategy of membrane design using these oxidative fragments to decorate the nanochannels offers an alternative and facile approach for many applications that can exploit the ionic charges, such as ion exchange.

associate prof. Lei says this research is currently still limited to lab-sized equipment, but they plan to acquire a large facility to fabricate large membranes and devices for large-scale applications.

“In the real world, we think membranes could be installed in estuaries or at industrial wastewater outlets,” Assoc. says Prof. Lei.

“The wastewater from factories or industry has different surface charge ions with a higher concentration than plain water. If we can put our membrane at the end of their process before the wastewater reaches natural waterways, we can harvest the energy and treat that water as well.

“We are now looking for industry partners interested in developing new membrane technology for renewable energy generation.”

More information:
Yijun Qian et al, Stimulating osmotic energy conversion of graphene oxide membranes via self-exfoliation behavior in nano-confinement spaces, Journal of the American Chemical Society (2022). DOI: 10.1021/jacs.2c04663

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Quote: Researchers construct nanochannels from graphene oxide nanosheets to harvest osmotic energy from the ocean (2022, Nov. 28) Retrieved Nov. 28, 2022 from harvest.html

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