Stability and Selective Anion Removal of High-Performance Carbon Electrodes Modified with Polyaniline in Capacitive Deionization

• Polyaniline coatings prepared electrochemically onto porous carbon electrodes. • Resulting hybrid electrode applied in capacitive deionization (CDI) • Stable CDI electrodes at + 0.35 V ( vs. Ag/AgCl) • Chloride removal capacity as high as 65 mg Cl /g Anode at high efficiencies. • Highly chloride selective in binary ion solutions with monovalent phosphate or sulfate. Capacitive deionization (CDI) is a technology used for water desalination and ion recovery based on the use of capacitive electrodes. Typically, the porous carbon electrodes used for CDI display limited ion storage capacity and selectivity due to the mechanism of ion storage in the electric double layer, but impressive improvements have been achieved using alternative, redox-based electrode materials, including conducting polymers like polyaniline (PAni). PAni is capable of capturing anions based on redox chemistry, but it degrades at anodic potentials typically used in CDI. In this work, we employed a multi-channel membrane CDI cell to map the stability window of a porous carbon electrode modified with PAni by controlling the anodic potential. We demonstrated for the first time that applying a potential as low as + 0.35 V ( vs. Ag/AgCl) yields a stable and high chloride removal capacity (65 mg Cl /g Anode ) with charge and coulombic efficiencies close to 100% for CDI. Furthermore, this is first work to explore the selectivity of the PAni-modified CDI electrodes towards chloride in binary solutions, evidencing that chloride is preferred regardless the valence of the competing anions. We believe that this work provides an important contribution for a larger figure, one in which CDI can be used for both high-performance water desalination, and efficient anion-selective removal and recovery.