In Situ Fragmented Bismuth Nanoparticles for Electrocatalytic Nitrogen Reduction

The electrochemical nitrogen reduction reaction (NRR) is a promising alternative to the energy‐intensive Haber–Bosch process for ammonia synthesis. Among the possible electrocatalysts, bismuth‐based materials have shown unique NRR properties due to their electronic structures and poor hydrogen evolution activity. However, identification of the active sites and reaction mechanism is still difficult due to structural and chemical changes under reaction potentials. Herein, in situ Raman spectroscopy, complemented by electron microscopy, is employed to investigate the structural and chemical transformation of the Bi species during the NRR. Nanorod‐like bismuth‐based metal–organic frameworks are reduced in situ and fragment into densely contacted Bi0 nanoparticles under the applied potentials. The fragmented Bi0 nanoparticles exhibit excellent NRR performance in both neutral and acidic electrolytes, with an ammonia yield of 3.25 ± 0 .08 µg cm−2 h−1 at −0.7 V versus reversible hydrogen electrode and a Faradaic efficiency of 12.11 ± 0.84% at −0.6 V in 0.10 m Na2SO4. Online differential electrochemical mass spectrometry detects the production of NH3 and N2H2 during NRR, suggesting a possible pathway through two‐step reduction and decomposition. This work highlights the importance of monitoring and optimizing the electronic and geometric structures of the electrocatalysts under NRR conditions. In situ reduced and fragmented Bi nanoparticles are reported to be promising electrocatalysts for the electrochemical nitrogen reduction reaction (NRR). The structural reconstruction and chemical transformation of Bi species during the NRR is investigated by in situ Raman spectrum for the first time. Online differential electrochemical mass spectrometry is employed to detect intermediates and products for pathway determination.