Energy-efficient electrochemical ammonia removal enabled by replacing hydrogen evolution with four-electron oxygen...

The development of efficient, low-energy technologies for nitrogen-containing wastewater treatment remains a critical challenge in water pollution control. Conventional electrochemical denitrification systems, which rely on the hydrogen evolution reaction (HER) as the cathodic half-reaction, face critical limitations in safety, energy efficiency, and mass transfer performance. To address these challenges, a paradigm-shifting chlorine evolution reaction coupled with four-electron oxygen reduction reaction (CER-4eORR) system is proposed, which fundamentally replaces the conventional cathodic HER (E^θ = 0 V vs. RHE) with the 4eORR (E^θ = 1.23 V vs. RHE). The system features a sulfur-doped iron-nitrogen-carbon single-atom catalyst on nickel foam (Fe-NS-C/NF), where sulfur-mediated modulation of FeN₄ site electronic structures significantly enhances 4eORR activity and stability. Coupled with a Ru-Ir/TF anode for efficient chlorine evolution reaction (CER), the optimized system achieves a cell voltage of 1.12-1.19 V lower than traditional HER-based systems-and approaches the thermodynamic limit of 1.23 V. This breakthrough reduces NH₃N degradation energy consumption from 20.85 to 10.18 kWh/kg (a 51.15% decrease) while maintaining stable operation at 1.2-1.3 V for 100 h without chemical cleaning. When applied to complex real wastewaters of varying compositions, the system consistently reduced cell voltage by approximately 1 V and achieved energy savings of 23.47%-29.04%. This work establishes a green, energy-efficient, and inherently safe electrochemical framework for nitrogenous wastewater treatment, offering a scalable solution aligned with carbon neutrality goals and advancing sustainable water management technologies.