Moscow | Scientists have developed new ion-exchange synthetic membranes that could be used to make cleaner and more efficient fuel cells.
Fuel cells use a reducing agent (usually hydrogen, methanol or methane) and an oxidising agent, oxygen, to convert energy of chemical reactions into electrical current. They consist of a cathode and an anode, separated by an ion-exchange membrane. Choosing the correct membrane plays an important role in improving fuel cells.
The material that the membrane is made from must be as inexpensive as possible, chemically stable, technologically advanced, and its pores must provide adequate selectivity.
The pore size is directly related to the efficiency of the fuel cell. These pores determine how efficiently ions are screened and energy is converted in a fuel cell.
Scientists, including those from Moscow Institute of Physics and Technology and Moscow State University, were able to form pores from certain molecules for membranes of a fuel cell so that the opening is exactly the diameter required for the optimum functioning of the cell.
The molecules called A-Na and Azo-Na are classified as benzenesulfonates, the researchers said.
They are wedge-shaped and can independently assemble themselves into supramolecular structures – complex organised groups of multiple molecules. Depending on the conditions set by the scientists, the molecules form discs which in turn form columns with ion channels inside.
This self-assembly of complex structures of individual molecules is possible due to their electrical properties. At one end of these molecules is a polar chemical group, ie a group with an electric charge, and in a solution it naturally turns towards charged water molecules.
At the other end of these molecules there are non-polar hydrocarbon tails that again due to their electrical properties try to stay as far away from water molecules as possible.
Scientists were able to predict the formation of these discs with pores and cylinders based on information on the structure, geometry, physical and chemical properties of the benzenesulfonates being studied.
Using this information, the scientists first made a mathematical model based on the properties of complex supramolecular structures formed by A-Na and Azo-Na.
During experiments, they obtained various different forms of ion channels maintaining the substances at a certain humidity and temperature, and then irradiating them with UV light for polymerisation.
The polymers created with this method were tested for selective permeability of ions and this enabled the scientists to identify which conditions of the synthesis of polymer membranes are best suited for making potential fuel cells.