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Electrochemical Capacitors For Water Desalination

January 22, 2009

Recent advances in electrochemical capacitors for energy storage open new opportunities for water desalination devices with high energy efficiency.

Existing technologies for hard, brackish and sea water desalination are highly energy consuming even in the case of the best available technology nowadays, Reverse Osmosis. In addition to this problem, the construction of desalination plants requires intensive capital expenditures.

Capacitive Deionization is a technological alternative to Reverse Osmosis provided it is a non-membrane and low-pressure process, which are possibly the two main drawbacks of the Reverse Osmosis technology. The Capacitive Deionization concept is schematically represented in the Figure. During the deionization cycle, an external electrical charge is applied on a pair of electrodes introduced in the feed water, this makes the ions dissolved in the water to migrate towards the electrode of opposite charge, where they are adsorbed. In the regeneration cycle, the electrical load of the electrodes is switched off, therefore adsorbed ions are released. If an electrical circuit is connected at this stage, an electrical current will be produced, just like in the discharge of a capacitor.

Early studies almost 40 years ago showed that Capacitive Deionization could be a feasible technology for low-cost water desalination, but by that time appropriate materials were not available yet. However, nowadays with the most recent advances in electrochemical capacitors, there are improved electrodes with performances good enough to bring the Capacitive Deionization systems from research laboratories to real life applications.

With this aim the company PROINGESA and the foundations IMDEA Energy and IMDEA Water have launched a research project to design a low-cost Capacitive Deionization device based on nanomaterials that have been developed for last generation electrochemical capacitors. This project is funded by the Spanish Ministry of Industry Tourism and Commerce with the Strategic Action on Energy and Climate Change of the National Plan of Research, Development and Innovation.

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