Their proton-conduction values arehigh even at ambient temperatures

Researchers from Pune’s Indian Institute of Science Education and Research (IISER) and National Chemical Laboratory (NCL) have come one step closer to making fuel cells that are cheaper and more efficient. Two novel porous and crystalline hydrogen-bonded organic frameworks (HOFs) that they synthesised could potentially be used as a proton exchange membrane in fuel cells.

Nafion, the proton exchange membrane in use currently, has major drawbacks in terms of applicability at a high temperature range or low humidity, high production costs and gas leakage issues.

The proton-conducting materials synthesised by the researchers address one critical issue — achieving a high proton conduction value even at ambient conditions (low humidity of around 60 per cent and moderate temperature). The proton conduction value is greater at higher humidity. The results were published recently in the journal Angewandte Chemie.

“Among all known porous materials, this is the highest proton conduction value that has been reported at ambient conditions,” says Avishek Karmakar, a research scholar from IISER and the first author of the paper.

“Our materials have the potential to be used as a proton exchange membrane to improve the efficiency of fuel cells. The cost of fuel cells will become cheaper as it is easy to make the membrane,” says Dr. Sujit K. Ghosh of IISER, the corresponding author of the paper .

The HOFs are promising materials for gas separation and storage applications. However, they have not been used for fuel cell applications.

The team synthesised two organic compounds, and each compound has a proton donor site and a proton acceptor site. "The donor-acceptor complementarity is distributed throughout the hydrogen-bonded framework,” says Karmakar.

“The hydrogen bonding serves as a pathway for proton transfer from the donor site to the acceptor site. Water acts as a carrier and plays an important role. When humidity is more the proton transfer becomes easy,” says Dr. Ghosh. “At ambient conditions, the proton conductivity is much higher than other related materials. And at high humidity (95 per cent) the proton conductivity is comparable to the best materials.”

The compounds are made of salt-like ionic materials and improving on the water stability is a challenge. “Using crystal engineering we improved the water stability by increasing the hydrophobic nature of the compounds for real time applications in fuel cell industries,” says Dr. Ghosh. Though the two compounds have different hydrophobic characteristics, proton conductivity was high in both the compounds even at low humidity.

Additionally, the HOF compounds have the potential to remove greenhouse gases such as carbon dioxide. “Although the compounds reported by us separate carbon dioxide from other gases like nitrogen, oxygen and hydrogen at low temperatures, we believe that such materials, if designed systemically, can be used in industries to remove greenhouse gases,” Dr. Ghosh says.