Removal of Na+ and Ca2+ with Prussian blue analogue electrodes for brackish water desalination

• Published in: Desalination Vol. 487; no. C; p. 114479
• Main Authors: Sebti, Elias, Besli, Münir M., Metzger, Michael, Hellstrom, Sondra, Schultz-Neu, Morgan J., Alvarado, Judith, Christensen, Jake, Doeff, Marca, Kuppan, Saravanan, Subban, Chinmayee V.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.08.2020; Elsevier
• Subjects: Brackish water; Ca-ion; Desalination; Intercalation; Na-ion; Prussian blue analogue; Na-ion; Ca-ion; Brackish water; Intercalation; Desalination; Prussian blue analogue
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/j.desal.2020.114479

Desalination of brackish water sources is critical to addressing the growing global freshwater demand. One promising approach is electrically driven desalination using intercalation electrodes. While intercalation electrodes have been widely researched for energy storage applications, only a small subset of those materials is suitable for desalination. Here we report the synthesis, characterization, and in-device testing of three Prussian blue analogue intercalation compounds: copper, manganese, and zinc hexacyanoferrate with formulas KxM[Fe(CN)6]z·nH2O (M = Cu, Mn, Zn). The desalination performance for each of these materials against carbon electrodes is reported for Na+ intercalation and for Ca2+ intercalation using 1000 ppm NaCl and 1000 ppm CaCl2 feed solutions, respectively. While the copper and manganese analogs showed promising performance for Na+ and Ca2+ intercalation, the zinc compound was unstable and underwent rapid dissolution. Manganese hexacyanoferrate showed the best desalination performance in terms of salt removal capacities and salt removal rates with NaCl while copper hexacyanoferrate performed the best with CaCl2. The manganese analog proved to be the most stable intercalation material, retaining 83% and 72% of its salt removal capacity after 280 cycles in NaCl and CaCl2 feed solutions respectively. [Display omitted] •Synthesis of copper, manganese, and zinc hexacyanoferrate for intercalation desalination•Testing of each material in a hybrid cell with a carbon counter electrode•Evaluation of Na+ and Ca2+ intercalation in each system using 1000 ppm feed solutions•Best performance by manganese analog in NaCl and by copper analog in CaCl2•Zinc analog unstable in NaCl and CaCl2