High-efficiency heater

A substantial portion of carbon dioxide emissions arises from activities such as heating air and water. With the aim of decarbonising heat generation, a team from the Indian Institute of Technology (IIT) Bombay has designed a nanomaterial that converts sunlight into heat with high efficiency. "We wanted to cover the entire spectrum of the sunlight," says Chandramouli Subramaniam, an author of the study published in ACS Applied Materials & Interfaces (bit.ly/nanoflorets). Commercially available solar cells fail to capture the infrared and ultraviolet parts of the spectrum, which account for much of the solar radiation. Scientists developed nanostructured hard-carbon florets (NCF) that absorb more than 95% of the solar energy and convert 87% of the absorbed light into thermal energy.

The efficiency of the material lies in its shape and structure. The NCF nanoparticles look like marigolds, and have lots of pores and microcavities that allow light to enter. Smaller wavelengths of the solar spectrum get trapped in these microcavities, increasing the absorption efficiency significantly. NCFs efficiently transform a significant portion of the incoming light packets or photons into heat through a process known as photon thermalisation. Subsequently, they preserve this heat without any loss due to thermal conductivity and radiation. The study showcased that NCFs elevate the air temperature from room-level to 60^°Celsius, offering effective, smoke-free space-heating solutions. "This would be a great solution to heat rooms in cold areas," mentions Subramaniam.

The team found that one metre square of the NCF coating converts five litres of water into vapour in one hour. Solar vapour conversion, a technique employed for water purification, is where NCF has eclipsed all competition in efficiently harnessing solar energy with its record-breaking 186% efficiency. The researchers also proved that hollow copper tubes, coated with NCFs, can superheat air flowing through them to temperatures exceeding 72^° Celsius.

Subramaniam collaborated with his colleague Sandip Saha, a Professor in the Department of Mechanical Engineering, to develop a start-up to bring the science to the market and has secured funding for the work. The team has initiated commercialisation of the product by establishing its start-up at the Society for Innovation and Entrepreneurship at IIT Bombay. It will focus on expanding NCF manufacturing and creating NCF-based devices essential for water and space heating.

"If NCF is employed for room heating and water heating, it could potentially reduce carbon dioxide emissions by a remarkable 11 million tonnes per year," claims Subramaniam.