Bi-doped directional spin-polarised electron injection modulates MBene surface d–d coupling to promote nitrogen reduction kinetics

Abstract

The electrocatalytic nitrogen reduction reaction (NRR) holds great promise in the field of artificial ammonia synthesis. Nevertheless, the difficulty of N₂ adsorption and dissociation as well as the competitive hydrogen evolution reaction (HER) has presented intractable problems. We provide a unique method to construct a large number of crystalline–amorphous heterostructures by uniformly growing amorphous Bi-doped FeOOH quantum dots (QDs) on MBene, changing the spin state of Fe 3d orbitals, directionally injecting electrons toward Mo atoms on the surface of MBene via d–d hybridised orbitals, and enhancing the synthesis of ammonia. The Bi-FeOOH/MBene composite gave an ammonia yield of 35.96 μg h⁻¹ mg⁻¹ and FE of 38.28% at −0.4 V vs. RHE. Density functional theory (DFT) calculations identified Mo atoms as the main active sites of the NRR. The doping of Bi atoms effectively modulated the d-band center of Mo to change the electronic structure of the active sites at the heterostructures and enhanced the interactions and electron transport capacity between Mo atoms and *N₂, which directly promoted the dissociation and activation HER of N₂. In addition, the introduction of Bi atoms significantly dispersed the Bi-FeOOH QDs and inhibited the HER. In situ Fourier transform infrared (in situ FTIR) spectroscopy reveals that the electrocatalytic NRR process on the surface of the catalyst follows the distal-associative pathway in the associative pathway.