Built–in Electric Field Boosted Tandem Catalysis for Rapid Electrochemical Nitrate Reduction to Nitrogen

Nitrate pollution in water bodies urgently necessitates sustainable electrocatalytic nitrate reduction (NO3RR) technologies, yet achieving high–efficiency catalysis for NO3RR with optimized interfacial charge distribution on electrocatalyst remains challenging. Herein, we report a built–in electric field (BIEF) construction strategy using mesoporous carbon–supported Co/Co3O4 heterojunction catalyst (Co/Co3O4–meso–C), which delivered exceptional NO3RR performance with 90.77% nitrate removal, 99% N2 selectivity (−1.4 V vs SCE), and robust stability (80% activity retention after 30 cycles). Density functional theory (DFT) calculations confirmed that the Co/Co3O4 heterostructure exhibited excellent NO3RR catalytic performance, which was attributed to the charge redistribution induced by the BIEF at the Co/Co3O4 interface (electron–rich Co and electron–deficient Co3O4), creating thermodynamic driving forces for optimized tandem catalysis. Mechanistic studies and theory simulations reveal that the synergy between Co3O4–mediated nitrate capture and Co–driven hydrogenation, enhanced by the mesoporous carbon architecture, underpins the catalytic activity. In a customized cross–flow electrofiltration system, the engineered membrane electrode achieves 80.57% nitrate removal within 6 h (3.0–fold faster than conventional single–cell configurations) and 99% N2 selectivity, enabled by hierarchical pore–enhanced nitrate flux and maximized active site accessibility. This work elucidates BIEF–driven interfacial charge modulation and offers a scalable membrane–electrode design for industrial NO3RR in low–concentration wastewater.