Mass transport in reverse electrodialysis for sustainable energy generation

Reverse electrodialysis (RED) is a promising and potentially attractive technology for the generation of sustainable energy from the mixing of salt and fresh water. It uses the free energy of mixing two solutions of different salinity (e.g. river and sea water) to generate power. In RED, a concentrated salt solution and a less concentrated salt solution are brought into contact through an alternating series of anion exchange membranes (AEM) and cation exchange membranes (CEM). Anion exchange membranes contain fixed positive charges which allow anions to permeate through the AEM towards the anode and cation exchange membranes contain fixed negative charges which allow cations to be transported through the CEM towards the cathode. At the electrodes a redox couple is used to mitigate the transfer of electrons. The ion exchange membranes are one of the key elements in the RED process as they, together with ion transport phenomena and concentration polarization effects occurring at the membrane-solution interface determine to a large extent the net power output of the system. This PhD thesis investigates the design, optimization and practical potential of the reverse electrodialysis process, with a special focus on membrane and spacer properties, mass transfer of the ionic species and concentration polarization phenomena. The results of this work show the high potential of RED as renewable energy source and it also brings RED closer to practical implementation.