Reverse Electrodialysis (RED)
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An electrochemical device capable of converting chemical energy into electric energy using the salinity gradient contained in feed waters, such as seawater, river water, etc. A reverse electrodialysis (RED) stack is comprised of ion exchange membranes (IEMs) that are selective for cations (CEMs) or anions (AEMs), which are responsible for driving the salinity gradient over each ion exchange membrane to generate a voltage difference. When the voltage difference accumulates, an external load is connected to the reverse electrodyalisis stack, creating a flux of ions through the membranes. This, in turn, with the help of electrodes and redox couples in contact with the ends of all membranes, allows the RED stack to transform ionic flux into electrical current.
This technology is currently used in desalination plants to achieve more sustainable and clean water, but recent research points out that RED is also an efficient renewable technology, able to directly produce hydrogen from waste heat generated through water electrolysis. Even if promising, this technology consumes considerable energy to perform desalination, however, this energy could also come from renewable energy sources.