Identification of M-NH₂ -NH₂ Intermediate and Rate Determining Step for Nitrogen Reduction with Bioinspired Sulfur-Bonded FeW Catalyst

The multimetallic sulfur-framework catalytic site of biological nitrogenases allows the efficient conversion of dinitrogen (N₂ ) to ammonia (NH₃ ) under ambient conditions. Inspired by biological nitrogenases, a bimetallic sulfide material (FeWS_x @FeWO₄ ) was synthesized as a highly efficient N₂ reduction (NRR) catalyst by sulfur substitution of the surface of FeWO₄ nanoparticles. Thus prepared FeWS_x @FeWO₄ catalysts exhibit a relatively high NH₃ production rate of 30.2 ug h^-1 mg^-1_cat and a Faraday efficiency of 16.4 % at -0.45 V versus a reversible hydrogen electrode in a flow cell; these results have been confirmed via purified ¹⁵ N₂ -isotopic labeling experiments. In situ Raman spectra and hydrazine reduction kinetics analysis revealed that the reduction of undissociated hydrazine intermediates (M-NH₂ -NH₂ ) on the surface of the bimetallic sulfide catalyst is the rate-determing step for the NRR process. Therefore, this work can provide guidance for elucidating the structure-activity relationship of NRR catalysts.