Electrochemical valorization of HCl for the production of chlorine via a proton-filter functional covalent organic framework

Abstract

Chlorine (Cl₂) is one of the prime building blocks for several industrially important chemicals and engineering materials. HCl electrolysis is a well established technology for the production of Cl₂ at the anode. However, combining it with the hydrogen evolution reaction (HER) at the cathode results in both high energy consumption and safety risks during unexpected shutdowns. Herein, we demonstrated the feasibility of integrating the chlorine evolution reaction (CER) together with the oxygen-depolarized cathode (ODC) by utilizing a nitrogen-rich two-dimensional in situ proton filter functional covalent organic framework (COF, Tta-Dfp) to suppress the HER. The as-synthesized Tta-Dfp COF was explored as a bifunctional catalyst towards the ODC and Cl₂ evolution and exhibited outstanding activity towards Cl₂ evolution with a faradaic efficiency of 92% and demonstrated excellent stability in a corrosive environment even under multiple shut-downs under mimicked industrial conditions. Furthermore, the visualization of the local electrocatalytic activity of the designed COF was analysed by redox competition mode of scanning electrochemical microscopy (RC-SECM) using a Pt ultra-microelectrode and extended to state-of-the-art electrocatalyst, Pt/C (20%). The 3D SECM images demonstrate the excellent stability of the Tta-Dfp catalyst in chlorine rich electrolyte. Therefore, metal-free catalysis for Cl₂ production by integrating the two electrochemical processes with the added advantage of energy saving is a promising cost-effective approach.