Chalcogen‐Bond‐Driven Electrochemical Bromide Sequestration in Benzothiazole‐Functionalized Covalent Organic Frameworks

Bromide contamination in water sources is a growing health concern because it can generate carcinogenic disinfection byproducts during conventional water treatment. However, the selective removal of bromide from reverse osmosis (RO) permeate remains challenging. Herein, we report a benzothiazole‐functionalized covalent organic framework (COF) designed as a chalcogen‐bond donor, where σ‐holes along the C─S bond axes preferentially interact with the softer, more polarizable Br − over Cl − . Two COFs, mesoporous BTzTp (∼2.45 nm) and microporous TTzTp (∼1.13 nm), were investigated to assess the role of pore accessibility while preserving identical recognition sites. The BTzTp@rGO composite exhibited a specific capacitance of 47 F g − 1 and a maximum bromide adsorption capacity of 36.7 mg‐Br − g − 1 at pH 4. Notably, it maintained ∼99% capacitance retention after 50 cycles, representing the highest cycling stability reported for a bromide‐selective HCDI electrode, together with excellent selectivity (α Br/Cl = 10). Density functional theory calculations reveal that selectivity originates from strong chalcogen bonding, evidenced by near‐linear C─S···Br − geometries (178°–179°), normalized contacts of 0.84, HOMO delocalization across the S···Br − interface, and greater charge transfer to Br − (0.222 e) than Cl − (0.154 e). This work demonstrates a viable strategy for highly selective and stable bromide removal in energy‐efficient water purification systems.