Anode Boundary Layer Extraction Strategy for H⁺–OH^– Separation in Undivided Electrolytic Cell: Modeling, Electrochemical Analysis, and Water Softening Application

Abstract

To promote the application of the electrolysis process for in situ pH adjustment of wastewaters with complex matrices, a robust, industrially scalable, and undivided electrolytic cell featuring the abstraction of H + from the anode boundary layer was developed in this study, where a tubular Ti porous membrane was used as the anode. Modeling, electrochemical analysis, and COMSOL simulation results show that abstracting H + from the anode boundary layer could effectively inhibit the transfer of H + into the bulk solution with the decrease in the anode double-layer thickness and electric double-layer capacitance. Increasing the current density from 6 to 22 mA cm −2 and the influent rate from 330 to 11,100 mL min −1 deteriorated the H + −OH − separation performance, owing to the enhanced electro-migration of H + into the bulk solution and turbulence state near the anode surface, respectively. The H + −OH − separation performance showed a volcanic type change trend with the acid extraction rate with the optimal value at 50 mL min −1 , specifically the separation efficiency of 10%−72% and 16%−94% for H + and OH − in the acidic and alkaline effluents, respectively, at an influent rate of 500 mL min −1 and a current density of 6−22 mA cm −2 . Importantly, the present undivided electrolytic cell showed better H + −OH − separation performance than that of the widely studied membrane-based divided system. The feasibility of this undivided electrolytic cell was also validated by water softening experiments, where the Ca hardness removal efficiency was 42%−92% with energy consumption of 1.2−4.6 kWh (kgCaCO 3 ) −1 at a current density of 6−22 mA cm −2 . In general, this new undivided electrolytic cell opened a new pathway for in situ electrochemically regulating wastewater pH.

An Anti-Scaling Strategy for Electrochemical Wastewater Treatment: Leveraging Tip-Enhanced Electric Fields

“…Electrochemical wastewater treatment, powered by renewable energies such as solar and wind power, has gained significant attention in recent years due to its effectiveness in removing various pollutants and its potential for resource recovery from wastewater. − However, one major issue hindering its large-scale and long-term application is the continuous scaling of electrodes. This scaling issue is primarily caused by the precipitation of inorganic scale (i.e., Mg­(OH) 2 and CaCO 3 ) on the cathode surface. − The precipitation occurs due to the gradual increase in OH – concentration, a consequence of the hydrogen evolution reaction (HER) taking place on the cathode. Figure S1 provides a visual representation of the problem, showing the formation of a thick layer of precipitation on the cathodes of a large-scale electrochemical reactor, which was utilized by our industry partners for the electrochemical treatment of landfill leachate.…”