Desalination of sea water to potable levels without external energy input by electrochemical acid-base neutralisation

Abstract

We report a flow battery that uses hydrogen as a charge carrier and makes use of the energy released in acid-base neutralisation to desalinate seawater and generate electricity, based on cheap and relatively safe electrolytes which are stored externally for scalable capacity. We demonstrate desalination of simulated seawater from 0.6 to 0.009 ± 0.005 M NaCl and successful desalination of sodium, potassium, magnesium, and calcium from real seawater to potable levels. The battery can also operate as a Reverse Electrodialysis (RED) system if the acid and base are substituted by neutral diluted aqueous solutions (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. Probably the most important characteristics of the reported system are, though (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..