Charge-Spin-Orbit Modulated Carbon-Encapsulated FeP/Fe3O4 Heterojunctions for Ultrafast and Stable Conversion of Low-Concentration Nitrate to Ammonia.

Electrocatalytic nitrate reduction reaction offers an effective route for ammonia synthesis and actual wastewater treatment. Despite some important achievements, the progress is still low than expected, especially in low-concentration nitrate, mostly because of slow hydrogenation kinetics and interfering substances. In this work, we presented that, by engineering spin orbital orientation, a carbon-encapsulated FeP/Fe3O4 heterojunctions (FeP/Fe3O4@C) enabled ultrafast and stable NH3 electrosynthesis from low-concentration nitrate. In-situ characterization and theoretical calculation confirmed that FeP/Fe3O4 heterojunctions induced spin orbit splitting of Fe, resulting in electron transition from low spin to high spin. The resulted non-degenerate orbitals caused the energy levels shift up and guided the electron migration from FeP to Fe3O4, which thus activated additional 3d orbital electron states. This spin orbital orientation further optimized the chemisorption properties of nitrogen-oxygen intermediates and H* spillover, thus accelerating hydrogenation kinetics for ultrafast NH3 electrosynthesis. Meanwhile, FeP/Fe3O4@C electrocatalyst alleviated the phosphate poisoning of active metal sites during industrial wastewater treatment, demonstrating excellent anti-interference capability and environmental sustainability for real application. This work by modulating the "charge-spin-orbit" structure of active sites provided a new strategy for rational design of high-performance electrocatalysts for various electrocatalytic reactions.