Improved electrode systems for reverse electro-dialysis and electro-dialysis

Reverse Electro-Dialysis, RED, is an electrochemical technique to extract work by mixing aqueous solutions of different salinities. Electro-Dialysis, ED, is an electrochemical technique to extract potable water from seawater. Both RED and ED typically employs noble metal oxide catalysts in the conversion between electronic current and ionic current. By testing several different electrode materials and red-ox salts, this paper demonstrates that these electrochemical reactions are controlled by mass transfer in the electrolyte rather than by the electrocatalytic properties of the electrode material. By comparing two different carbon materials and standard noble metal oxides, we show, for two red-ox salts, that the electrochemical performances of the inexpensive and expensive materials are similar. Relatively inexpensive graphite along with environmentally benign FeCl2 and FeCl3 in moderate concentrations was demonstrated to lower the electrode concentration overpotential.

► We study electrodes suitable for reverse electrodialysis in saline power plants.
► Ferric/ferrous red-ox couples on noble metal oxide electrodes serve as reference.
► The electrode reaction is mass controlled; iron chlorides on carbon function well.
► The electrodes may also be relevant for water production by electro dialysis.