Direct electrosynthesis of sodium hydroxide and hydrochloric acid from brine streams


Seawater is an abundant resource across the world, and its purification and by-product recovery methods are crucial for economical, environmentally safe and sustainable utilization. Desalinating seawater generally produces brine as a by-product that cannot be purified economically with current technologies and which is instead released to the environment. In this Perspective, we discuss direct electrosynthesis of sodium hydroxide (NaOH) and hydrochloric acid (HCl) from sea-water desalination brine as an emerging alternative solution. In this direct electrosynthesis (DE) process, the water splitting reaction is used to produce H+ and OH, which combine with the brine stream to produce NaOH and HCl. After introducing the scope of the process, we describe developments in earth-abundant catalysts for water splitting and the competing chlorine evolution reaction (CER), as well as challenges in inefficiency and productivity associated with these processes. Finally, we discuss the economic impact and feasibility of direct electrosynthesis.

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Fig. 1: Schematic drawings of electrodialysis systems.
Fig. 2: Scheme and activity of water splitting catalysts.
Fig. 3: Comparison of oxygen and chlorine selectivities for different ruthenia-based catalysts.
Fig. 4: Schematic illustration of different sources of brine for the DE-BMED process.

Change history

  • 25 February 2019

    In the version of this Perspective originally published, authors Amit Kumar and Katherine R. Phillips should have had a note in the affiliations indicating that they are equally contributing authors; this has now been corrected.


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This work was supported by Cadagua, a Ferrovial subsidiary, through the MIT Energy Initiative. The authors would like to thank G. Han for contributing to Fig. 4, K.G. Nayar for input on the ‘Economic potential’ section, and J. Cai for assistance on the overall research program.

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Correspondence to Amit Kumar or John H. Lienhard V.

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Kumar, A., Phillips, K.R., Thiel, G.P. et al. Direct electrosynthesis of sodium hydroxide and hydrochloric acid from brine streams. Nat Catal 2, 106–113 (2019).

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