Researchers have synthesized novel porous and crystalline hydrogen-bonded organic frameworks that could potentially be used as proton-exchange membranes in fuel cells1. These compounds may also find application in energy-storage devices.

Nafion polymer is widely used for making proton-exchange membranes of fuel cells, but it is expensive and leaks gas during fuel cell operation. To devise an efficient membrane, the researchers produced two hydrogen-bonded organic frameworks by separately reacting napthalenesulfonic acid and biphenylsulfonic acid with guanidine hydrochloride at room temperature.

Since both organic compounds donate and accept protons, their proton-conducting efficiencies were probed at low humidity. The proton conduction of both compounds increased when the relative humidity (RH) was gradually increased, reaching a maximum at 95% RH and 30 degrees Celsius.

The high proton conductions of the compounds at low humidity are encouraging because unhindered proton transport is desirable for fuel cells and energy-storage devices.

In addition, the compounds could separate carbon dioxide from a mixture of gases such as nitrogen, oxygen and hydrogen at low temperatures, suggesting that such compounds could potentially be used for removing greenhouse gases in industry.

“Besides their utility in fuel cells, the compounds are being tested for potential applications in gas storage, molecular separation and sensing,” says lead researcher Sujit Kumar Ghosh from the Indian Institute of Science Education and Research, Pune.