Enhanced electrocatalytic production of H2O2 at N-doped porous carbon air-diffusion cathodes for water treatment via electro-Fenton.

Efficient cathodic catalysts and low-energy electro-Fenton (EF) systems are crucial for industrial pollutant degradation. This study presents a templating-assisted strategy using azodicarbonamide (nitrogen source/template), glucose (carbon precursor), and sodium bicarbonate (oxygen dopant/activator). The resulting metal-free nitrogen-doped porous carbon (NPC) materials exhibited a honeycomb-like morphology, tunable pore structures, and broad pore size distributions. An air-diffusion electrode was constructed based on NPC, which eliminated the need for external aeration by directly utilizing atmospheric oxygen for the oxygen reduction reaction, thereby significantly enhancing H2O2 production. Compared with the traditional vertical configuration, the air-diffusion mode increased H2O2 yield by 17.5-fold (up to 480.7 mg/L). Unlike the conventional EF process dominated by hydroxyl radicals (•OH), this system enabled bisphenol A (BPA) degradation primarily through singlet oxygen (1O2, 52.6 %), with contributions from superoxide radicals (•O2-, 31.7 %) and •OH (15.4 %), forming a multi-reactive oxygen species (ROS) pathway. Both theoretical calculations and experimental results demonstrated that Graphitic N and Pyridinic N groups facilitated H2O2 production, whereas Pyrrolic N and Pyridinic N promoted ROS activation. In addition, the system showed wide pH adaptability, robust immunity to complex aqueous matrices, and excellent reusability. Notably, even under real industrial wastewater conditions, the degradation performance remained largely unaffected, highlighting the advantages of 1O2 in resisting natural organic matter and inorganic ion interference. This work effectively integrates pore structure optimization, ROS pathway modulation, and reactor design, offering new insights and theoretical guidance for the sustainable and green remediation of industrial wastewater.