Energy-efficient chlorine-mediated paired electrocatalysis for simultaneous H₂O₂ production and coal chemical...

Energy-efficient treatment of chloride-containing coal chemical wastewater remains challenging, primarily due to high electricity demand, limited current utilization, and concerns over by-product control. Herein, a chlorine-mediated paired electrocatalysis was established, coupling a mixed metal oxide (MMO) anode with a natural air-diffusion cathode (NADE) in a membrane-separated dual-chamber reactor. In the anode chamber, phenol and ammonia nitrogen (NH₃-N) were proved to be oxidized via a free-radical pathway (^•ClO) and a non-radical pathway (HClO), while hydrogen peroxide (H₂O₂) was produced through the aeration-free oxygen reduction reaction in the cathode chamber. Key parameters of the process and membrane materials were investigated and optimized. Proton exchange membrane (PEM), cation exchange membrane (CEM), and bipolar membrane (BPM) were compared, and PEM exhibited the highest current efficiency (93.48 %) and lowest specific energy consumption for H₂O₂ generation (3.79 kWh/kg). Under the optimal conditions, the process achieved removal efficiencies of 95.25 % for phenol, 75.43 % for chemical oxygen demand (COD), 70.79 % for NH₃-N, and 65.17 % for total nitrogen within 90 min. The cumulative concentration of H₂O₂ reached 761.21 mg/L, and the associated economic benefit completely offset the energy consumption of the integrated electrocatalytic system. Overall electricity costs of the paired electrocatalysis were reduced by ∼59 % versus anodic oxidation alone and by ∼45 % versus single-pollutant operation. The chlorine-mediated paired electrocatalysis enables simultaneous degradation of phenolic and nitrogenous pollutants and in-situ H₂O₂ generation, providing an energy-efficient and economically favorable strategy for advanced treatment of coal-chemical wastewater.