Graphene based deionization on board the EU Flagship

The billion-euro Graphene Flagship project of the European Commission doubled in size this June. The expansion brought Spain to the second place by the number of Flagship partners, just below Germany and Italy which share the first place as countries with most project participants. Among the freshly accepted projects is GRAPHESALT, “Graphene based capacitive deionization for an energy efficient desalination system”. GRAPHESALT was proposed by the Spanish research organization Tecnalia and the French membrane maker SME Polymem.

GRAPHESALT is one of 21 projects selected from a total of 218 proposals submitted. It focuses on the development of a water desalination system based on a technique called capacitive deionization (CDI).

Image: Sketch of capacitive deionization (CDI). Courtesy of Azonano.

During CDI salt is separated from water by passing seawater between two electrically charged electrodes (anode and cathode), so that the salts are adsorbed on the surface of the electrodes, thereby obtaining drinking water. By reversing the electric charge of the electrodes, the salt is washed out, recovering part of the electric energy used in the process. Although the technology is not new, its performance can be increased dramatically by using metal oxide-graphene electrodes, achieving higher efficiency than that of reverse osmosis desalination. Reverse osmosis is the predominant method in desalination plants today, although it consumes much energy. Metal oxide in contact with graphene is also, not incidentally, the main ingredient of our recently reported efficient organic light emitting diodes (OLEDs). In GRAPHESALT, the graphene will form part of the porous material component of the filter.

Graphene water desalination and filtering is a hot research topic. Back in February, MIT researchers demonstrated a graphene film drilled with closely packed nanopores. The nanoporous graphene is a membrane material that has earlier shown, in calculation, to be ideally suited for water desalination, as salt molecules are too large to pass through the sieve. Following up on that, research that came out of the Oak Ridge National Lab demonstrated a real graphene desalination filter, with performance 100 times better than currently used technology. In that case, the approach was based on graphene oxide, or more precisely graphene oxide frameworks (GOFs). Graphene desalination filters warranted a technology review in a popular desalination online magazine.

GRAPHESALT will play on the excellent performance of metal oxide-graphene electrodes to enhance the performance of the available CDI technology. The method is expected to compete with nanoporous graphene and GOFs on the way to the desalination marketplace.