Unraveling the Active Sites on Mesoporous CuFe2O4@N-Carbon Catalysts with Abundant Oxygen Vacancies and M-N-C Content for Boosted Nitrogen Reduction Towards Electrosynthesis of Ammonia

Transition metal centers dispersed over nitrogen-doped carbon (M–NC) supports have been widely explored for electrocatalytic reactions. However, sparsely reported for electrochemical nitrogen reduction reaction (ENRR). Particularly, the single-atom catalysts (SACs) have shown reasonable ammonia yield rate and faradaic efficiency (FE), but their complex synthesis and low durability for long-term electrocatalysis runs restrict their use on a larger scale. Importantly, the catalytic active sites in metal nanostructured-based M-NC catalysts towards enhanced N 2 adsorption and activation are still not clear as they are highly challenging to reveal. A few studies have predicted that the surface oxygen vacancies (O vac ) favor an enhanced ENRR performance. Herein, we devise a strategy to use both tailored M-NC content and O vac in a single catalyst for enhanced electrosynthesis of ammonia. A mesoporous bimetallic spinel oxide (CuFe 2 O 4 ) supported over N-doped carbon (CuFe 2 O 4 @NC) derived from Prussian blue analog (PBA) via controlled pyrolysis possess was found to show boosted ENRR activity. Moreover, operando NH 3 formation over the catalyst was observed using four electrode set up. We demonstrate that this experimental approach enables a rapid and preliminary evaluation of electrocatalytic efficacy and helps in avoiding false positive results. Further, our comprehensive rotating disc electrode voltammetric investigations indicate that mass transport in acidic media and surface adsorption in alkaline media primarily regulate ENRR over CuFe 2 O 4 @NC electrocatalyst.