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 (NO 3 RR) technologies, yet achieving high–efficiency catalysis for NO 3 RR 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/Co 3 O 4 heterojunction catalyst (Co/Co 3 O 4 –meso–C), which delivered exceptional NO 3 RR performance with 90.77% nitrate removal, 99% N 2 selectivity (−1.4 V vs SCE), and robust stability (80% activity retention after 30 cycles). Density functional theory (DFT) calculations confirmed that the Co/Co 3 O 4 heterostructure exhibited excellent NO 3 RR catalytic performance, which was attributed to the charge redistribution induced by the BIEF at the Co/Co 3 O 4 interface (electron–rich Co and electron–deficient Co 3 O 4 ), creating thermodynamic driving forces for optimized tandem catalysis. Mechanistic studies and theory simulations reveal that the synergy between Co 3 O 4 –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% N 2 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 NO 3 RR in low–concentration wastewater.