Reverse Electrodialysis using capacitive electrodes

Reverse Electrodialysis using capacitive electrodes

In Reverse Electrodialysis (RED) electricity is produced using the transport of ions. At the electrodes, the ionic flow is converted in a transport of electrons in order to power an electrical device (for example a lamp). Traditionally, the ion transport generates electron transport through a reduction/oxidation reaction at metal electrodes. However, these reduction/oxidation reactions cause practical problems. For most reactions, overpotential is required, which reduces the power output of RED. Furthermore, the electrolyte solution can leak to the feed flow compartments, polluting the effluent or diluting the electrolyte.

A new way of converting ion transport into electron transport is by using capacitive electrodes, made from active carbon. Active carbon has many micropores, which give space to adsorb many ions. At the cathode side, an excess of positive ions will adsorb to the carbon; at the anode an excess of negative ions will be adsorbed. The carbon acts as a capacitor: when the anode and cathode are connected through an electrical circuit, electrons will be forced to flow from the anode to the cathode. After some time, the active carbon will get saturated and the feed flow needs to be switched (which will also switch the current direction). In this way, an electrical current can be generated without any chemical reactions.

The capacitive electrodes are recently in use at Wetsus (in Leeuwarden) for other projects: capacitive de-ionization (CDI/mCDI) and the reverse technique (RmCDI). By applying these capacitive electrodes on Reverse Electrodialysis (RED), one of the bottlenecks of this sustainable energy source can be tackled. The aim of this project is to build a RED stack with capacitive electrodes, compare the efficiency with a standard RED stack and determine the optimal conditions (switch interval, current density, stack potential, etc).

Preferable background: Chemical Engineering, Environmental Technology

Use of project: MSc-thesis or MSc-internship