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.