The latest research findings show that membranes can be used for conversion of pressure into electrical energy with high efficiency. In the long term, this could be the key to more efficient and cost-effective energy conversion.

It looks like a very thin piece of plastic, but in reality it is an ion conducting membrane which is currently being used in e.g. fuel cells. What is special about the small piece of plastic lying on the table in the chemistry laboratory at Aarhus University is that it has been extensively studied by a small group of researchers over the last few years. They hope that they now have identified a new method for the conversion of energy with a very low loss of energy.

A detailed examination
With specially designed equipment, the researchers have carried out detailed studies of the membrane’s properties for the conversion of energy. The study includes electrokinetic conversion where pressure is converted directly into electricity through the membrane or vice versa where electricity is converted into pressure.

A number of parameters affect the efficiency of these energy conversion processes, and the research group has now mapped the properties of ion conducting membranes that are important for obtaining high conversion efficiencies.

The first tests show that the membrane can be optimised to an efficiency of up to 20 percent. This exceeds by far the previous maximum measured efficiency of five percent in silicon-based nanopores.

Membrane-based gas compressor for cooling
One of the major advantages of electrokinetic energy conversion is that it requires no moving parts in contrast to e.g. pumps with motors. For this reason, membrane-based energy conversion systems can compete on both price, efficiency and reduced environmental impact, especially in small systems.

The technology is therefore of commercial interest in a number of different applications. This could be as an energy supply for homes where solar panels can be used to heat a liquid and thereby generate pressure that can be converted into electricity. Or it could be used in relation to cooling. The research group is in the process of developing a membrane-based energy conversion system for gas compression as a substitute for mechanical compressors.

Cheap, simple and efficient
Membrane technology may prove to be cheaper, simpler and far more energy efficient when it comes to cooling in smaller systems such as refrigerators. Working with the existing membranes on the market, the researchers have already achieved remarkable results with electrokinetic energy conversion. By optimising the properties of the membranes, they expect to be able to considerably increase the conversion efficiency.

However, it will take some years before the technology has matured for commercial use.