Study on electrochemical water softening mechanism of high-efficient multi-layer mesh coupled cathode

•Electrochemical mechanism of multi-layer mesh coupled cathodes was elucidated.•External and internal layers synergically enhance performance of coupled cathodes.•Scales grow and shed alternately on external layers, prolonging deactivation time.•Internal layers accelerate scale deposition, reducing cathode area requirements. High cathode area requirement limits industrial applications of electrochemical water softening technology. Based on previous works, the electrochemical water softening mechanism of high-efficient multi-layer mesh coupled cathode which consists of multilayers of stainless steel woven nets with different mesh sizes was studied systematically in this paper. Results reveal that the external and internal layers synergically enhance the performance of the coupled cathode. Calcium carbonate deposition reaction preferentially occurs on the external layers of the coupled cathode, due to the shielding effect caused large differences in current density and potential among the layers of the coupled cathode. Meanwhile, hydrogen bubbles can not only serve as soft templates, allowing nucleation sites to be transferred from the substrate surface to the formed calcium carbonate crystals, but also easily bring scale films with low coverage and adhesion force away from the substrate surface by mechanical stripping, prolonging the cathode deactivation time and making the cathode self-cleaning. Besides, the internal layers provide an alkaline environment through the stable hydrogen evolution process, further accelerating the deposition of hardness ions and reducing the cathode area required for water softening.