Researchers at Indian Institute of Technology, Madras, have developed a ‘vanadium redox flow battery’ (VRFB) through a project funded by ONGC Energy Centre Trust and the Pudukkottai-based company High Energy Batteries. Redox flow batteries (RFB) promise to become a game-changer for future energy storage systems in the stationary segment.

Dr Kothandaraman Ramanujam of the Department of Chemistry at IIT-Madras notes that “adopting VRFB into the energy distribution chain will ensure continuous power supply from wind and solar farms. Since it utilises an aqueous electrolyte, it is safe and does not get affected by thermal runaway issues. Besides, this can be used as large-scale UPS [uninterrupted power supply] for office buildings”.

Transporting the charged electrolyte to remote locations, just like a tanker carrying petrol, will help generate electricity onsite using a simple pumping mechanism without need for the complicated engines used in power generators.

Ramanujam’s team successfully demonstrated 1kW/10kWh VRFB using solar power charging. More than 300 cycles (each cycle takes about three days) have been completed using solar charging. The developed VRFB can operate at a high current density with 80-85 per cent efficiency.

Currently, an ion-conducting membrane, called ‘Nafion,’ is used in the VRFB stack. This constitutes nearly 25 per cent of the system cost. The research group is looking into developing cost-effective ceramic-hydrocarbon-based porous membranes in place of Nafion, says a statement from IIT-Madras. In order to further reduce the cost of RFB, alternatives to vanadium, based on lead and organic redox materials, are being explored.

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The group is also working on alternative flow battery chemistries that use abundant lead, zinc, iron and organic redox-active materials. This would bring down the cost of energy storage on par with or lower than the cost of energy production from solar photovoltaics. Currently available energy storage options are more expensive than the cost involved in generating electricity.

Novel material for energy harvesting

Scientists at Bengaluru’s Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) have discovered a novel material called single-crystalline scandium nitride (ScN) that can emit, detect, and modulate infrared light with high efficiency, making it useful for solar and thermal energy harvesting, as also optical communication devices.

Electromagnetic waves are a renewable energy source for electricity generation, telecommunication, defence and security technologies, sensors, and healthcare services. Scientists use high-tech methods to manipulate such waves precisely — in dimensions that are many thousand times smaller than human hair — using specialised materials. However, not all wavelengths of light (electromagnetic waves) are easy to utilise, especially infrared light, since it is difficult to detect and modulate.

For infrared light applications, intelligent and cutting-edge materials are required that can enable excitation, modulation, and detection at desired spectral range with high efficiency. Only a few existing materials can serve as hosts for light-matter interactions in the infrared spectral range, albeit with low efficiencies. The operational spectral range of such materials also does not cover industrially important short wavelength infrared (SWIR) spectral range.

KC Maurya of JNCASR and his co-workers have utilised a scientific phenomenon called polariton excitations, which occur in tailored materials when light couples with either the collective free electron oscillations or polar lattice vibrations, to achieve this feat. “They have carefully controlled material properties to excite polaritons (a quasi-particle) and achieve strong light-matter interactions in single-crystalline scandium nitride using infrared light,” says a press release from JNCASR.

These exotic polaritons in scandium nitride can be utilised for solar and thermal energy harvesting. Belonging to the same family of materials such as gallium nitride, scandium nitride is compatible with modern complementary-metal-oxide-semiconductor (CMOS) or Si-chip technology and, therefore, could be easily integrated for on-chip optical communication devices.

“From electronics to healthcare, defence, security and energy technologies, there is a great demand for infrared sources, emitters and sensors. Our work on infrared polaritons in scandium nitride will enable its application in many such devices,” said Dr Bivas Saha, assistant professor at JNCASR. Researchers from the Centre for Nano Science and Engineering at the Indian Institute of Science (IISc) and the University of Sydney also participated in this study, which was published recently in the scientific journal Nano Letters.

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