Method for selective separation of monovalent ionic species using electrodes functionalized with sulfonic groups

A method for selective separation of monovalent ionic species from an ionic solution, the method comprising:

• (a) passing the ionic solution comprising a positively charged monovalent ion and a positively charged polyvalent ion, through an electrode capacitor assembly comprising:
• a first electrode and a second electrode, said electrodes comprising nanoporous carbon, wherein the first electrode is modified with sulfonate surface groups;
• and at least one flow channel for the passage of the solution;
• and
• (b) charging the electrode capacitor assembly:
• (1) at a voltage of at least about 1.5 V;
• and/or
• (2) for a scaled charging time of less than about 2,
• thereby providing enhanced adsorption of the positively charged monovalent ion in the first electrode as compared to the adsorption of the positively charged polyvalent ion.