Putting stored hydrogen to work without consuming it: A flexible system for energy conversion and water desalination

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We report a flow battery that utilises hydrogen as a charge carrier in both the cathode and anode and makes use of the energy released in acid-base neutralisation to desalinate seawater and generate electricity, based on cheap and relatively safe electrolytes stored externally. We demonstrate desalination of simulated seawater from 0.6 to 0.009 ± 0.005 M NaCl and successful removal of Na+, K+, Mg2+, and Ca2+ from real seawater to potable levels. The battery can also be used for osmotic energy conversion through reverse electrodialysis (RED) if the acid and base are substituted by neutral diluted aqueous solution (e.g., freshwater), reaching power densities similar to state-of-the-art systems while using a much more environmentally friendly redox charge carrier, namely hydrogen, than those common in RED systems. The most important characteristics of the reported system are (i) its flexibility, which allows easy tuning to favour either energy generation or degree of desalination by changing the flow rates and volumes of each individual channel and/or the discharge current and (ii) the possibility of putting hydrogen to work without consuming it while stored for later shipment, thereby producing a profit that can contribute to decreasing the cost of green hydrogen.