Nitrogenase-Inspired Vs-MoS₂/Vo-Fe₂O₃ Heterojunction with Fixed Molar Ratio Promotes Bifunctional Nitrogen Fixation

The development of efficient heterojunction catalysts for electrochemical bifunctional nitrogen reduction reaction (NRR) and nitrate reduction reaction (NO3RR) as a replacement for the Haber–Bosch (H–B) process is on the stage, yet the controlled synthesis of heterojunction catalysts with fixed composition ratios remains a formidable challenge. Herein, we employed oxygen-rich polyoxometalates (POMs) as precursors to form a metal sulfide/metal-oxide heterojunction catalyst via the one-pot method, specifically nanoflower-like MoS2/Fe2O3 heterojunctions enriched with vacancies (Vs-MoS2/Vo-Fe2O3). Notably, the composition ratio of the heterojunction precisely mirrors the proportion of metal components in the POMs. This catalyst has demonstrated efficient all-pH nitrogen reduction activity, with the highest performance observed in acidic electrolytes (NH3 yield rate = 73.14 ± 1.35 μg h–1 mg–1cat., Faraday efficiency = 42.68 ± 2.12%). Simultaneously, it exhibits superior nitrate reduction activity in neutral electrolytes (Selectivity = 97.50 ± 0.75%, Faraday efficiency = 80.39 ± 3.71%). In situ Raman spectroscopy, extended X-ray absorption fine structure spectroscopy (EXAFS) combined with Density functional theory (DFT) calculations have verified that superior catalytic activity of Vs-MoS2/Vo-Fe2O3 can be primarily attributed to facile N2 adsorption at S vacancies, an electronic coupling between Fe and Mo, enhanced conductivity at heterojunctions, and a reduced Gibbs free energy for NH* hydrogenation to NH2* at O vacancies.