Enhanced Stability for Nitrate Electrosynthesis by Heterogeneous FeOOH–TiO2 Anchored on 2-Methylimidazolium Functionalized Polypyrrole/Graphene Oxide

Abstract

The electrocatalytic nitrogen oxidation reaction (NOR) technology offers an environmentally friendly, cost-efficient, and controllable method for nitrate production under mild conditions. Advances in NOR heavily rely on the discovery of effective and affordable electrocatalysts. This study unveils a novel approach by meticulously integrating FeOOH–TiO₂ heterostructures onto a sophisticated substrate of 2-methylimidazolium functionalized polypyrrole/graphene oxide (2-MeIm/PPy/GO), through in situ growth processes involving ion-exchange and coordination between the 2-MeIm groups and metal precursors. The resulting FeOOH–TiO₂@2-MeIm/PPy/GO exhibits remarkable resilience during the NOR process, which achieves a notable NO₃^– yield of 83.24 μg h^–1 mg_act.^–1, accompanied by a peak Faradaic efficiency (FE) of 5.47% at 1.94 V (vs reversible hydrogen electrode). Nitrogen oxidation primarily occurs at iron sites, where the doped Fe²⁺ in TiO₂ can all gradually convert to Fe³⁺ during the process; meanwhile, titanium sites within FeOOH–TiO₂@2-MeIm/PPy/GO maintain stable chemical states, ensuring sufficient electroactivity for oxygen evolution reactions (OER) to produce *O necessary for nonelectrochemical steps in NOR. This synergistic interplay between iron and titanium contributes significantly to both the stability and durability of FeOOH–TiO₂@2-MeIm/PPy/GO, positioning it as a promising candidate for real-world NOR applications. This work provides valuable insights into the design and fabrication of next-generation electrocatalysts for sustainable nitrate production.