Boosting Electrocatalytic Ammonia Synthesis of Bio-Inspired Porous Mo-Doped Hematite via Nitrogen Activation.

Electrochemical N reduction reaction (NRR) emerges as a highly attractive alternative to the Haber-Bosch process for producing ammonia (NH) under ambient circumstances. Currently, this technology still faces tremendous challenges due to the low ammonia production rate and low Faradaic efficiency, urgently prompting researchers to explore highly efficient electrocatalysts. Inspired by the Fe-Mo cofactor in nitrogenase, we report Mo-doped hematite (FeO) porous nanospheres containing Fe-O-Mo subunits for enhanced activity and selectivity in the electrochemical reduction from N to NH. Mo-doping induces the morphology change from a solid sphere to a porous sphere and enriches lattice defects, creating more active sites. It also regulates the electronic structures of FeO to accelerate charge transfer and enhance the intrinsic activity. As a consequence, Mo-doped FeO achieves effective N fixation with a high ammonia production rate of 21.3 ± 1.1 μg h mg as well as a prominent Faradaic efficiency (FE) of 11.2 ± 0.6%, superior to the undoped FeO and other iron oxide catalysts. Density functional theory (DFT) calculations further unravel that the Mo-doping in FeO (110) narrows the band gap, promotes the N activation on the Mo site with an elongated N≡N bond length of 1.132 Å in the end-on configuration, and optimizes an associative distal pathway with a decreased energy barrier. Our results may pave the way toward enhancing the electrocatalytic NRR performance of iron-based materials by atomic-scale heteroatom doping.