Electroactive self-polymerized dopamine with improved desalination performance for flow- and fixed- electrodes capacitive deionization

[Display omitted] •Dopamine was polymerized onto the surface of activated carbon (PDA@AC).•PDA@AC electrodes provide higher hydrophilicity and suspension stability.•CDI and FCDI desalination performances using PDA@AC are significantly enhanced due to redox-active PDA functionality. Capacitive deionization (CDI) is an emerging desalination technology with several advantages, including a high energy efficiency and a simple process. In particular, flow electrode CDI (FCDI) shows greatly enhanced salt removal performance by supplying slurry electrodes into a cell, resulting in continuous desalination operation. Along with carbon-based electrodes, Faradaic materials have been widely introduced for FCDI desalination to realize a higher salt removal capacitance. Organic redox-active materials have received significant attention for replacing conventional inorganic electrodes due to their superior characteristics such as cost-effective and eco-friendly properties, light weight, and high theoretical capacity. In this study, dopamine was self-polymerized onto carbon surfaces to provide polydopamine (PDA) grown activated carbons (AC). Strong adhesion property of PDA prevented their dissolution in electrolytes during electrochemical reactions. In addition, it provided a much improved surface wettability and suspension stability. Results showed that the salt adsorption capacity of PDA@AC CDI electrode was significantly enhanced from 6.03 to 10.43 mg/g (a 73% increase). Salt removal rate of an FCDI was also greatly increased from 1.20 to 2.12 mmol/m2s (a 76% increase) for a PDA@AC slurry electrode. The demonstrated approach is expected to open a new door for realizing desalination of a highly saline solution including seawater.