August 13, 2020

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IIT Madras faculty working on osmotic power tech

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Researchers at the Indian Institute of Technology Madras (IIT-M) are working on an alternative source of energy called osmotic power.

Assistant Professor Dr Vishal Nandigana and his team of researchers at the IIT Madras Laboratory are developing technology that generates electricity from estuaries by using a semipermeable membrane to separate salt and freshwater to produce power from the resultant pressure.

The team, along with a Switzerland-based technology institution, has created a semipermeable membrane out of molybdenum sulphide compound to generate more power compared to other existing membranes through osmotic power generation.

Dr Vishal Nandigana Image credit: iitmadras; Twitter

Osmotic power, or blue energy, is the extraction of power from mixing salt solutions of different concentrations. It can provide an efficient power source for both nanoscale and industrial-level applications. Power is generated using ion-selective channels or pores of nanometric dimensions in synthetic membrane materials.

A recent review article written by the team describes the superiority of a membrane developed by them. It has been published in the international journal Nature Review Materials in August 2019.

As the name suggests, osmotic power generation is based on the osmotic pressure that is generated when a semipermeable membrane separates saltwater from freshwater. This pressure can be converted into electricity, Dr Nandigana said.

The benefit of it is that estuaries in which seawater and the freshwater rivers meet can be used to generate power. The first osmotic power plant built in Norway, back in 2009, could produce only 4 kilowatts of power (about as much electricity it would take to power a clothes dryer), which is inefficient for large-scale uses.

A breakthrough in the study in 2016 was the discovery that membranes made of an extremely thin layer of molybdenum di-sulphide were able to generate osmotic power of 1 megawatt per square metre. Based on this, Dr Nandigana took the research further and presented a detailed discussion of the membrane’s potential with comparisons and pointers to go forward in this year’s review.

He noted the membrane he has developed could help generate more electricity than other membranes studied so far.

He said that the team’s molybdenum sulphide membrane produces higher power density than other membranes and is much better than its nearest competitor boron nitride nanotubes, which have been shown to produce power density of only 1 kW/m2. The increase in power generation compared to earlier studies is because of the use of a single atomic layer of molybdenum di-sulphide, which is ion-selective, and the osmotic pressure generated voltage is augmented by the ionic current produced.

The 2019 review in Nature Review Materials also covers the opportunities and the challenges associated with osmotic power. One of the challenges is the scalability of the technology. The laboratory is making efforts to grow larger samples of MoS2. The current technology produces MoS2 at micrometer scale, Dr Nandigana said.

The team is trying to produce membranes in the scale of square centimetres rather than square micrometres currently available. This is based on the calculation that a single membrane roughly one square metre wide would generate enough power to light up 50,000 energy-saving bulbs.

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