Electrochemical technology for environmental treatment and clean energy conversion

The applications of electrochemical technology in environmental treatment, materials recycling, and clean synthesis are briefly reviewed. The diversity of these applications is shown by the number of industrial sectors involved. The scale of operation ranges from microclectrodes to large industrial cell rooms. The features of electrochemical processes are summarized. Available and developing electrode designs are considered and illustrated by examples including the regeneration of chromic acid electroplating baths, metal ion removal by porous, 3-dimensional cathodes, rotating cylinder electrodes (RCEs), and a reticulated vitreous carbon (RVC) RCE. The use of performance indicators based on mass transport, electrode area, and power consumption is emphasized. Electrochemical reactors for energy conversion are considered, with an emphasis on load-leveling and proton-exchange membrane (PEM) (hydrogen-oxygen) fuel cells. Ion-exchange membranes play an essential role in such reactors, and the variation of electrical resistance vs. membrane thickness is described for a series of extruded, Nafion(R) 1100 EW materials. The characterization of high-surface-area, platinized Nafion surfaces is also considered. The development of modular, filter-press cells as redox flow cells in electrical load-leveling applications is concisely described. Trends in electrode, membrane, and reactor design are highlighted, and the challenges for the development of improved reactors for environmental treatment are noted.