Subtle introduction of membrane polarization-catalyzed H₂O dissociation actuates highly efficient electrocoagulation...

Electrocoagulation represents a promising process for hardness removal from cooling water. Nevertheless, the slow hydrolysis reaction severely restricted the floc formation, inhibiting the hardness co-precipitation and simultaneously causing secondary pollution from dissolved Al³⁺. Inspired by the detrimental membrane fouling phenomenon in conventional electrodialysis, we reported a rational strategy to substantially enhance the hardness removal efficiency in electrocoagulation by introducing a special membrane polarization-catalyzed H₂O dissociation herein. Leveraging the electron transfer between functional groups (-SO₃^- and -N(CH₃)₃⁺) of ion exchange membrane (IEM) and surface-adsorbed H₂O under the electric field-induced ion depletion scenario, H₂O dissociation could be effectively catalyzed, with this catalytic activity more intensive in -SO₃^- than in -N(CH₃)₃⁺. Such a special H₂O dissociation beneficially created a widely distributed and well-simulated alkalinity zone around the anodic region of IEM, which promoted the conversion of dissolved Al³⁺ to floc Al, thereby enhancing floc formation and circumventing secondary pollution. All these features enabled the resulting membrane-enhanced electrocoagulation (MEEC) to achieve a super-prominent hardness removal rate of 318.9 g h^-1 m^-2 with an ultra-low specific energy consumption of 3.8 kWh kg^-1 CaCO₃, considerably outperforming those of other conventional hardness removal processes reported to date. Additionally, in conjunction with a facile air-scoured washing method, MEEC exhibited excellent stability and universal applicability in various reaction conditions.