Ferromagnetic Fe-TiO spin catalysts for enhanced ammonia electrosynthesis.

Magnetic field effects (MFE) of ferromagnetic spin electrocatalysts have attracted significant attention due to their potential to enhance catalytic activity under an external magnetic field. However, no ferromagnetic spin catalysts have demonstrated MFE in the electrocatalytic reduction of nitrate for ammonia (NORR), a pioneering approach towards NH production involving the conversion from diamagnetic NO to paramagnetic NO. Here, we report the ferromagnetic Fe-TiO to investigate MFE on NORR. Fe-TiO possesses a high density of atomically dispersed Fe sites and exhibits an intermediate-spin state, resulting in magnetic ordering through ferromagnetism. Assisted by a magnetic field, Fe-TiO achieves a Faradaic efficiency (FE) of up to 97% and an NH yield of 24.69 mg mg at -0.5 V versus reversible hydrogen electrode. Compared to conditions without an external magnetic field, the FE and NH yield for Fe-TiO under an external magnetic field is increased by ~21.8% and ~ 3.1 times, respectively. In-situ characterization and theoretical calculations show that spin polarization enhances the critical step of NO hydrogenation to NOH by optimizing electron transfer pathways between Fe and NO, significantly boosting NORR activity.