Removal of chloride ions using bismuth electrode in capacitive deionization (CDI)

Abstract

Non-carbon material in capacitive deionization (CDI) can help to enhance the capacity of removed ions. Here we firstly report the removal of chloride ions (Cl−) by bismuth (Bi) anode when coupled with activated carbon (AC) cathode in CDI. The effect of carbon black in Bi electrode, the applied voltage, the electrode mass loading and the initial concentration on Cl− removal are investigated. Moreover, the cycle performance is also tested. Results show that addition of carbon black in Bi electrode (Bi@CB) significantly improves Cl− removal. The decline trend of Cl− concentration and appearance of peaks assigned to products of bismuth oxychloride (BiOCl) in XRD patterns confirm Cl− storage by Bi electrode, which is enhanced as increase in voltage. When coupled with AC in a fixed mass, increasing in Bi mass does not contribute to more Cl− removal. Although the cycle performance is not excellent (the attenuation rate is 74% after 10 cycles), chloride removal capacity is ~2-3 times the value of AC (e.g. 0.95 vs. 0.32 at 1.2 V in 500 mg L−1 NaCl solution). Besides, Bi-AC electrode pair in CDI is more suitable to remove Cl− from solution with Cl− concentration below 600 mg L−1.