IIT Mandi’s novel catalyst offers to make hydrogen more viable as fuel

The carbon-based catalyst reduces the overpotential of the oxygen evolution reaction.

Published - March 31, 2023 10:30 am IST - New Delhi

A bird’s eye view of IIT Mandi.

A bird’s eye view of IIT Mandi. | Photo Credit: IIT Mandi website

Researchers at IIT Mandi have developed a novel carbon-based catalyst to make water electrolysis more efficient, as well as being more stable and more affordable than other catalysts that perform the same function.

Water electrolysis is the process of choice to produce ‘green hydrogen’, so the new compound, and its underlying concepts, are also relevant to the prospect of this element as a fuel of the future.

The findings were published in the journal Carbon Trends in October 2022.

What is water electrolysis?

In water electrolysis, water molecules are split into hydrogen and oxygen using electricity inside a device called an electrolyser. However, this process consumes a lot of electrical energy.

A well-known solution is to use a catalyst to induce the water molecules to split at a much lower energy. The better catalysts are often based on the metals iridium and ruthenium, which are expensive, in great demand in other sectors, and not consistently stable as the reaction progresses.

In a new study, research groups of assistant professor Swati Sharma and associate professor Aditi Halder, both at  IIT Mandi, have reported a porous carbon material containing nitrogen that functions both as a catalyst and as the anode in electrolyser units – and could substitute the metal-based catalysts.

The researchers produced this material, called ‘laser carbon’, by exposing a sheet of a polymer called polyimide to a laser beam, which carbonised the exposed bits, leaving the remainder rich in nitrogen.

How does laser carbon help?

Inside an electrolyser, the nitrogen atoms were found to draw electron clouds towards themselves. This rendered the nearby carbon atoms to want to bond with atoms or molecules containing electron pairs. In effect, the location of these atoms became active sites for the oxygen evolution reaction (OER).

The OER is a stumbling block in electrolysis. Electrolysing water produces hydrogen and oxygen. At the negatively charged cathode of the electrolyser, electrons are transferred to protons to form hydrogen gas. At the positively charged anode, an oxidation reaction occurs that releases oxygen gas and electrons, which move towards the cathode and complete the circuit.

OER is a bottleneck in this ideal reaction process because it proceeds slowly, with many intermediate steps, lowering the total reaction efficiency. Laser carbon offers to fix this problem by reducing the OER overpotential.

Overpotential here is the difference between the voltage at which OER takes place in reality and the minimum voltage at which it can take place. So lowering the OER overpotential means the reaction kicks off sooner and proceeds with more vigour.

What are the advantages of the catalyst?

Laser carbon also presents advantages over other carbon-based catalysts. According to Dr. Sharma, laser carbon is “highly power efficient”, cheaper to produce, has a simpler synthesis technique, and “can be batch-manufactured with a laser”.

Dr. Halder said this manufacturing process is also environment-friendly “as no waste is generated and there are no wet chemicals that would require disposal”.

“Most of the reported catalysts are in powder form and require a loading substrate, such as glassy carbon,” she added. “Our material does not require a substrate as it is self-supported in the form of a film, acting as both electrode and electrocatalyst.”

Dr. Halder also highlighted that while many other catalysts need to be ‘activated’ so that they present more surface area to the electrolysis reaction, laser carbon “does not need this as the production process itself induces porosity and inherent nitrogen surface functionalities required for OER, owing to the chemical structure of polyimide.”

On the flip side, the researchers said that the catalytic activity of laser carbon may not be as high as that of some metals – “but it is comparable. Further improvements in the fabrication process and use of other polymers may address this challenge,” they said.

Sunderarajan Padmanabhan is a Delhi-based freelance science correspondent.

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