Regulating spin state of Fe(III) by the Mo single atom anchored in the (001) crystal face of α-Fe2O3 to achieve efficient electrocatalytic nitrate to synthesize ammonia

Ammonia (NH 3 ) plays an important role in agricultural production and is also an ideal zero-carbon energy source in sustainable hydrogen economy. Electrocatalytic nitrate (NO 3 - ) reduction reaction can simultaneously consume nitrogen pollutants in water during the synthesis of NH 3 , which is the most promising and gentle alternative process to the Haber-Bosch. However, due to the interference of hydrogen evolution reaction and high overpotential, the development of efficient directional ammonia conversion catalysts has become the key. In this study, Mo-Fe 2 O 3 material were fabricated by crystal face engineering and orbital manipulation strategies. The (001) face of α-Fe 2 O 3 with the best electrochemical performance was exposed by thermodynamic control, and the in-situ substitution of Mo single atoms for near-surface Fe atoms was further used to achieve excellent ammonia synthesis activity. NH 3 yield of 493.67   μg/h/mg cat and Faraday efficiency of 95.0% were achieved at -0.5   V vs. RHE (pH=7, 0.1   M PBS+500 ppm NO 3 - ). The mechanistic analysis showed that the highly electronegative Mo atoms induced strong interaction by Fe-O-Mo bond, which prompted Fe(III) to preferentially fill the lower t2g orbital and form a low-spin state. The weaker anti-bonding state enhances the interaction between Fe(III) and the coordinating O atoms in NO 3 - , thereby strengthening electron transfer. In summary, the targeted regulation of the crystal facet and electronic orbitals of catalysts presents a promising strategy for enhancing the conversion of NO 3 - to NH 3 .