Green electricity produced from ion transfer

A nanomaterial membrane has allowed scientists in France to develop a system that generates electricity using the diffusion of salt ions.

Known as osmotic power, this was achieved using seawater, fresh water and a semipermeable membrane three atoms thick made from molybdenum disulphide (MoS2). The membrane separates two fluids with different salt concentrations and salt ions pass through the membrane until the concentrations are equal.

As the ions pass through a tiny hole in the membrane, a nanopore, electrons are transferred to an electrode which generates an electric current. As positively charged ions pass though the membrane, negatively charged membranes are left behind, creating a voltage, allowing for the current generated by the transfer of ions to flow.

Jiandong Feng, lead author from the Ecole Polytechnique Fédérale de Lausanne (EPFL), said: “We had to first fabricate and then investigate the optimal size of the nanopore. If it’s too big, negative ions can pass through and the resulting voltage would be too low. If it’s too small, not enough ions can pass through and the current would be too weak.”

The scientists calculate a 1m2 membrane with 30% of its surface covered with these nanopores should be able to produce 1MW of electricity – enough to power 50,000 standard energy-saving light bulbs. As MoS2 can be easily found in nature or grown via chemical vapour deposition, the system could be ramped up to a larger scale.

Feng said: “From an engineering perspective, a single nanopore system is ideal to further our fundamental understanding of membrane-based processes and provide useful information for industry-level commercialisation.’’

It is hoped, once more developed, these systems will play a major role in the generation of renewable energy. This study was carried out by scientists at EPFL and Illinois University.

The research was published in Nature.