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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Roberts, D. A., Johnston, E. L. & Knott, N. A. Impacts of desalination plant discharges on the marine environment: a critical review of published studies. Water Res. 44, 5117–5128 (2010).
Ghaffour, N., Missimer, T. M. & Amy, G. L. Technical review and evaluation of the economics of water desalination: current and future challenges for better water supply sustainability. Desalination 309, 197–207 (2013).
Du, F., Warsinger, D. M., Urmi, T. I., Thiel, G. P., Kumar, A. & Lienhard, J. H. Sodium hydroxide production from seawater desalination brine: process design and energy efficiency. Environ. Sci. Technol. 52, 5949–5958 (2018).
Khedr, M. G. A case study of RO plant failure due to membrane fouling, analysis and diagnosis. Desalination 120, 107–113 (1998).
Rahardianto, A., Gao, J., Gabelich, C. J., Williams, M. D. & Cohen, Y. High recovery membrane desalting of low-salinity brackish water: integration of accelerated precipitation softening with membrane RO. J. Membr. Sci. 289, 123–137 (2007).
Pastor, M. R., Ruiz, A. F., Chillón, M. & Rico, D. P. Influence of pH in the elimination of boron by means of reverse osmosis. Desalination 140, 145–152 (2001).
Milstead, C. E., Riedinger, A. B. & Lonsdale, H. K. Rejection of carbon dioxide and pH effects in reverse osmosis desalination. Desalination 9, 217–223 (1971).
Ning, R. Y. Discussion of silica speciation, fouling, control and maximum reduction. Desalination 151, 67–73 (2003).
Redondo, J. A. & Lomax, I. Experiences with the pretreatment of raw water with high fouling potential for reverse osmosis plant using FILMTEC membranes. Desalination 110, 167–182 (1997).
Hydranautics Technical Service Bulletin. Nitto Denko http://www.lenntech.com/Data-sheets/tsb107-L.pdf (2011).
O’Brien, T. F., Bommaraju, T. V. & Hine, F. Handbook of Chlor-Alkali Technology (Springer US, New York, 2005).
Yang, Y., Gao, X., Fan, A., Fu, L. & Gao, C. An innovative beneficial reuse of seawater concentrate using bipolar membrane electrodialysis. J. Membr. Sci. 449, 119–126 (2014).
Thiel, G. P., Kumar, A., Gómez-González, A. & Lienhard, J. H. Utilization of desalination brine for sodium hydroxide production: technologies, engineering principles, recovery limits, and future directions. ACS Sust. Chem. & Eng. 5, 11147–11162 (2017).
Bagastyo, A. Y. et al. Electrochemical oxidation of reverse osmosis concentrate on boron-doped diamond anodes at circumneutral and acidic pH. Water Res. 46, 6104–6112 (2012).
Bergmann, M. E. H. & Koparal, A. S. Studies on electrochemical disinfectant production using anodes containing RuO2. J. Appl. Electrochem. 35, 1321–1329 (2005).
Reig, M., Casas, S., Valderrama, C., Gibert, O. & Cortina, J. L. Integration of monopolar and bipolar electrodialysis for valorization of seawater reverse osmosis desalination brines: production of strong acid and base. Desalination 398, 87–97 (2016).
Lin, H. W. et al. Direct anodic hydrochloric acid and cathodic caustic production during water electrolysis. Sci. Rep. 6, 20494 (2016).
Lewis, N. S. & Nocera, D. G. Powering the planet: chemical challenges in solar energy utilization. Proc. Natl Acad. Sci. USA 103, 15729–15735 (2006).
Nocera, D. G. Solar fuels and solar chemicals industry. Acc. Chem. Res. 50, 616–619 (2017).
Walter, M. G. et al. Solar water splitting cells. Chem. Rev. 110, 6446–6473 (2010).
Karlsson, R. K. & Cornell, A. Selectivity between oxygen and chlorine Evolution in the chlor-alkali and chlorate processes. Chem. Rev. 116, 2982–3028 (2016).
Cheng, F. & Chen, J. Metal-air batteries: from oxygen reduction electrochemistry to cathode catalysts. Chem. Soc. Rev. 41, 2172–2192 (2012).
Lee, J.-S. et al. Metal-air batteries with high energy density: Li–air versus Zn–air. Adv. Energy Mater 1, 34–50 (2011).
Eftekhari, A. Electrocatalysts for hydrogen evolution reaction. Int. J. Hydrog. Energy 42, 11053–11077 (2017).
Roger, I., Shipman, M. A. & Symes, M. D. Earth-abundant catalysts for electrochemical and photoelectrochemical water splitting. Nature Rev. Chem. 1, 0003 (2017).
Seh, Z. W. et al. Combining theory and experiment in electrocatalysis: insights into materials design. Science 355, eaad4998 (2017).
Trasatti, S. in Advances in Electrochemical Science and Engineering Vol. 2 (eds Gerischer, H. & Tobias, C. W) 1–85 (Wiley-VCH, Weinheim, 2008).
Zeng, M. & Li, Y. Recent advances in heterogeneous electrocatalysts for the hydrogen evolution reaction. J. Mater. Chem. A 3, 14942–14962 (2015).
Suen, N. T. et al. Electrocatalysis for the oxygen evolution reaction: recent development and future perspectives. Chem. Soc. Rev. 46, 337–365 (2017).
Tahir, M. et al. Electrocatalytic oxygen evolution reaction for energy conversion and storage: a comprehensive review. Nano Energy 37, 136–157 (2017).
Mahmood, J. et al. An efficient and pH-universal ruthenium-based catalyst for the hydrogen evolution reaction. Nat. Nanotechnol 12, 441–446 (2017).
Over, H. Surface chemistry of ruthenium dioxide in heterogeneous catalysis and electrocatalysis: from fundamental to applied research. Chem. Rev. 112, 3356–3426 (2012).
Kong, D., Cha, J. J., Wang, H., Lee, H. R. & Cui, Y. First-row transition metal dichalcogenide catalysts for hydrogen evolution reaction. Energy & Environ. Sci. 6, 3553–3558 (2013).
McCrory, C. C. et al. Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices. J. Am. Chem. Soc. 137, 4347–4357 (2015).
Danilovic, N. et al. Using surface segregation to design stable Ru-Ir oxides for the oxygen evolution reaction in acidic environments. Angew. Chem. Int. Ed. 53, 14016–14021 (2014).
Montoya, J. H. et al. Materials for solar fuels and chemicals. Nat. Mater. 16, 70–81 (2016).
Shi, Y. & Zhang, B. Recent advances in transition metal phosphide nanomaterials: synthesis and applications in hydrogen evolution reaction. Chem. Soc. Rev. 45, 1529–1541 (2016).
Wang, H., Yuan, H., Sae Hong, S., Li, Y. & Cui, Y. Physical and chemical tuning of two-dimensional transition metal dichalcogenides. Chem. Soc. Rev. 44, 2664–2680 (2015).
Fan, C. Study of electrodeposited nickel-molybdenum, nickel-tungsten, cobalt-molybdenum, and cobalt-tungsten as hydrogen electrodes in alkaline water electrolysis. J. Electrochem. Soc. 141, 382–387 (1994).
McKone, J. R., Sadtler, B. F., Werlang, C. A., Lewis, N. S. & Gray, H. B. Ni–Mo nanopowders for efficient electrochemical hydrogen evolution. ACS Catal 3, 166–169 (2013).
Raj, I. A. & Vasu, K. I. Transition metal-based hydrogen electrodes in alkaline solution: electrocatalysis on nickel based binary alloy coatings. J. Appl. Electrochem. 20, 32–38 (1990).
Wang, Y. et al. A 3D nanoporous Ni–Mo electrocatalyst with negligible overpotential for alkaline hydrogen evolution. ChemElectroChem 1, 1138–1144 (2014).
Bhowmik, T., Kundu, M. K. & Barman, S. Growth of one-dimensional RuO2 nanowires on g-carbon nitride: an active and stable bifunctional electrocatalyst for hydrogen and oxygen evolution reactions at all pH values. ACS Appl. Mater. Interfaces 8, 28678–28688 (2016).
Greeley, J. Theoretical heterogeneous catalysis: scaling relationships and computational catalyst design. Annu. Rev. Chem. Biomol. Eng. 7, 605–635 (2016).
Meng, Y. et al. Structure−property relationship of bifunctional MnO2 nanostructures: highly efficient, ultra-stable electrochemical water oxidation and oxygen reduction reaction catalysts identified in alkaline media. J. Amer. Chem Soc. 136, 11452–11464 (2014).
Hong, W. T. et al. Toward the rational design of non-precious transition metal oxides for oxygen electrocatalysis. Energy & Environ. Sci. 8, 1404–1427 (2015).
Kanan, M. W., Surendranath, Y. & Nocera, D. G. Cobalt-phosphate oxygen-evolving compound. Chem. Soc. Rev. 38, 109–114 (2009).
Man, I. C. et al. Universality in oxygen evolution electrocatalysis on oxide surfaces. ChemCatChem 3, 1159–1165 (2011).
Subbaraman, R. et al. Trends in activity for the water electrolyser reactions on 3d M(Ni,Co,Fe,Mn) hydr(oxy)oxide catalysts. Nat. Mater. 11, 550–557 (2012).
Vojvodic, A. & Nørskov, J. K. New design paradigm for heterogeneous catalysts. Natl. Sci. Rev. 2, 140–149 (2015).
Zhang, B. et al. Homogeneously dispersed multimetal oxygen-evolving catalysts. Science 352, 333–337 (2016).
Seitz, L. C. et al. A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction. Science 353, 1011–1014 (2016).
Chen, W. et al. In situ electrochemical oxidation tuning of transition metal disulfides to oxides for enhanced water oxidation. ACS Cent. Sci 1, 244–251 (2015).
Wang, H. et al. Bifunctional non-noble metal oxide nanoparticle electrocatalysts through lithium-induced conversion for overall waters. Nat. Commun. 6, 7261 (2015).
Danilovic, N. et al. Activity-stability trends for the oxygen evolution reaction on monometallic oxides in acidic environments. J. Phys. Chem. Lett. 5, 2474–2478 (2014).
DeSario, P. A., Chervin, C. N., Nelson, E. S., Sassin, M. B. & Rolison, D. R. Competitive oxygen evolution in acid electrolyte catalyzed at technologically relevant electrodes painted with nanoscale RuO2. ACS Appl. Mater. Interfaces 9, 2387–2395 (2017).
Chung, C. M., Hong, S. W., Cho, K. & Hoffmann, M. R. Degradation of organic compounds in wastewater matrix by electrochemically generated reactive chlorine species: kinetics and selectivity. Catal. Today 313, 189–195 (2018).
Cho, K. et al. Effects of anodic potential and chloride ion on overall reactivity in electrochemical reactors designed for solar-powered wastewater treatment. Environ. Sci. Technol. 48, 2377–2384 (2014).
Park, H., Vecitis, C. D. & Hoffmann, M. R. Electrochemical water splitting coupled with organic compound oxidation: the role of active chlorine species. J. Phys. Chem. C 113, 7935–7945 (2009).
Dionigi, F., Reier, T., Pawolek, Z., Gliech, M. & Strasser, P. Design criteria, operating conditions, and nickel-iron hydroxide catalyst materials for selective seawater electrolysis. ChemSusChem 9, 962–972 (2016).
Fujimura, K. et al. Anodically deposited manganese-molybdenum oxide anodes with high selectivity for evolving oxygen in electrolysis of seawater. J. Appl. Electrochem 29, 769–775 (1999).
Kato, Z. et al. Electrochemical characterization of degradation of oxygen evolution anode for Seawater Electrolysis. Electrochim. Acta 116, 15–157 (2014).
Trasatti, S. Electrocatalysis in the anodic evolution of oxygen and chlorine. Electrochim. Acta 29, 1503–1512 (1984).
Nikolić, B. Ž. & Panić, V. in Encyclopedia of Applied Electrochemistry (eds Kreysa, G., Ota, K. -i. & Savinell, R. F) 411–417 (Springer-Verlag, New York, 2014).
Hansen, H. A. et al. Electrochemical chlorine evolution at rutile oxide (110) surfaces. Phys. Chem. Chem. Phys. 12, 283–290 (2010).
Barmashenko, V. & Jörissen, J. Recovery of chlorine from dilute hydrochloric acid by electrolysis using a chlorine resistant anion exchange membrane. J. Appl. Electrochem. 35, 1311–1319 (2005).
Kuznetsova, E., Petrykin, V., Sunde, S. & Krtil, P. Selectivity of nanocrystalline IrO2-based catalysts in parallel chlorine and oxygen Evolution. Electrocatalysis 6, 198–210 (2014).
Petrykin, V., Macounová, K., Okube, M., Mukerjee, S. & Krtil, P. Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolution. Catal. Today 202, 63–69 (2013).
Mavrov, V., Chmiel, H., Heitele, B. & Rögener, F. Desalination of surface water to industrial water with lower impact on the environment. Desalination 124, 205–216 (1999).
Petrykin, V., Macounova, K., Shlyakhtin, O. A. & Krtil, P. Tailoring the selectivity for electrocatalytic oxygen evolution on ruthenium oxides by zinc substitution. Angew. Chem. Int. Ed. 49, 4813–4815 (2010).
Rodell, M. et al. Emerging trends in global freshwater availability. Nature 557, 651–659 (2018).
IDA Desalination Yearbook (The International Desalination Association, 2015).
Chung, H. W., Nayar, K. G., Swaminathan, J., Chehayeb, K. M. & Lienhard, J. H. Thermodynamic analysis of brine management methods: zero-discharge desalination and salinity-gradient power production. Desalination 404, 291–303 (2017).
Global chlor-alkali market: trends analysis & forecasts to 2021. Business Wire https://www.researchandmarkets.com/research/lwwgnn/global (2017).
Sedivy, V. M. (ed.) Economy of Salt in Chloralkali Manufacture (National Salt Conference, 2008).
El-Manharawy, S. & Hafez, A. Study of seawater alkalization as a promising RO pretreatment method. Desalination 153, 109–120 (2003).
Barron, O. et al. Feasibility assessment of desalination application in australian traditional agriculture. Desalination 364, 33–45 (2015).
Burn, S. et al. Desalination techniques—a review of the opportunities for desalination in agriculture. Desalination 364, 2–16 (2015).
Yermiyahu, U. et al. Environmental science: rethinking desalinated water quality and agriculture. Science 318, 920–921 (2007).
Zarzo, D., Campos, E. & Terrero, P. Spanish experience in desalination for agriculture. Desalin. Water Treat 51, 53–66 (2013).
Nable, R. O., Bañuelos, G. S. & Paull, J. G. Boron toxicity. Plant and Soil 193, 181–198 (1997).
Bartlett, R. W. Solution Mining: Leaching and Fluid Recovery of Materials 2nd edn (Gordon and Breach Science Publishers, Philidephia, 1998).
Turek, M. Electrodialytic desalination and concentration of coal-mine brine. Desalination 162, 355–359 (2004).
Thiel, G. P., Tow, E. W., Banchik, L. D., Chung, H. W. & Lienhard, J. H. Energy consumption in desalinating produced water from shale oil and gas extraction. Desalination 366, 94–112 (2015).
Mohsen, M. S. Treatment and reuse of industrial effluents: case study of a thermal power plant. Desalination 167, 75–86 (2004).
Rau, G. H. et al. Direct electrolytic dissolution of silicate minerals for air CO2 mitigation and carbon-negative H2 production. Proc. Natl Acad. Sci. USA 110, 10095–10100 (2013).
Badruzzaman, M., Oppenheimer, J., Adham, S. & Kumar, M. Innovative beneficial reuse of reverse osmosis concentrate using bipolar membrane electrodialysis and electrochlorination processes. J. Membr. Sci. 326, 392–399 (2009).
Ibáñez, R., Pérez-González, A., Gómez, P., Urtiaga, A. M. & Ortiz, I. Acid and base recovery from softened reverse osmosis (RO) brines. Experimental assessment using model concentrates. Desalination 309, 165–170 (2013).
Wang, M., Wang, K.-K., Jia, Y.-X. & Ren, Q.-C. The reclamation of brine generated from desalination process by bipolar membrane electrodialysis. J. Membr. Sci. 452, 54–61 (2014).
Davis, J. R., Chen, Y., Baygents, J. C. & Farrell, J. Production of acids and bases for ion exchange regeneration from dilute salt solutions using bipolar membrane electrodialysis. ACS Sustain. Chem. Eng. 3, 2337–2342 (2015).
Reig, M. et al. Integration of nanofiltration and bipolar electrodialysis for valorization of seawater desalination brines: production of drinking and waste water treatment chemicals. Desalination. 382, 13–20 (2016).
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.
The authors declare no competing interests.
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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). https://doi.org/10.1038/s41929-018-0218-y
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