Modern energy technology, for example fuel cells which are used commercially in hydrogen fuel–based cars, require good catalysts that are efficient as well as cost-effective. Now, a multi-institutional team from India has developed a selenium-graphene–based catalyst which is more efficient, costs less and also remains stable for longer than the usual platinum based catalysts. The institutes involved in the work are: Tata Institute of Fundamental Research, Hyderabad (TIFR-H), University of Hyderabad and Indian Institute of Science Education and Research (IISER) Thiruvananthapuram. The research has been published in the journal ACS: Applied Energy Materials.
Normally, fuel cells use expensive platinum-like elements. “These expensive metal-based technologies perform excellently for initial few cycles, but then get degraded in performance due to many reasons,” explains T.N. Narayanan of TIFR-H, the corresponding author. As a result, there is a need to change this part of the fuel cell routinely.
The oxygen reduction reaction is a key step in the functioning of the fuel cell. Graphene by itself is a “poor” catalyst of this reaction. In the sense that it involves reduction of oxygen in two steps, each of which consume two electrons. This is not very useful either for fuel cells or metal-air batteries.
Platinum is often used to catalyse this reaction. As a substitute, the group developed the catalyst with selenium and graphene. “Graphene modified with selenium atoms in very low amounts can perform like platinum in a demonstrated reaction,” Dr. Narayanan clarifies.
While neither selenium nor graphene can do the trick by themselves, the combination works efficiently. “When you do the right chemistry together with small amount of selenium with high amount of carbon containing graphene, you end up with a very useful catalyst, which is very cheap too,” he adds.
Poisoning-resistant
Methanol fuel cells, a common form of fuel cell used, suffer from a “poisoning” effect. This is a part of the process where the methanol reaches the negative electrode and coats it, so that the electrode becomes ineffective after some cycles. This is especially problematic when expensive catalysts like platinum are used, as they often are. “We found that the catalyst we have developed has a high tolerance [to poisoning] while platinum got affected,” says Dr Narayanan.
The concept of single-atom catalyst – that category into which this catalyst falls – is not new. But earlier concepts had used heavy metals such as platinum, palladium and gold. Using selenium is a novel idea mooted by this group.
“Such direct water converting oxygen reduction reaction catalyst has enormous applications in other fields too, such as metal-air battery. It is ongoing research for the development of high energy density devices in batteries. This will be far better than the existing lithium ion-based battery,” he says.
Published - June 15, 2019 04:31 pm IST
