Enhanced nitrate electrosynthesis by in situ growth of CoS2 nanoparticles on poly(zwitterionic liquids) functionalized polypyrrole nanotubes based on accurate nitrate detection

Abstract

The shift from fossil fuels has highlighted electrocatalysis, especially nitrate electrosynthesis via the nitrogen oxidation reaction (NOR), as a sustainable alternative to traditional industrial nitrate production methods. This shift has spurred significant research interest in the design and development of efficient electrocatalysts for the NOR. This study explores the electrosynthesis of nitrate using poly(3-(1-vinylimidazolium-3-yl)propane-1-sulfonate) (PVIPS), a distinctive poly(zwitterionic liquid) with imidazolium and sulfonate groups, as an effective linker. PVIPS facilitates the in situ growth of well-dispersed CoS₂ nanoparticles on the surface of PVIPS functionalized polypyrrole nanotubes (PPyNTs). The resulting CoS₂/PVIPS/PPyNTs demonstrated superior NOR performance compared to CoS₂ and CoS₂/PPyNTs, achieving a maximum nitrate yield of 41.14 μg h⁻¹ mg_act.⁻¹ and a faradaic efficiency (FE) of 1.89% at a low potential of 1.75 V (vs. the reversible hydrogen electrode). This enhancement is attributed to the small size and uniform dispersion of CoS₂ induced by PVIPS. Theoretical calculations revealed that the energy barrier for the potential-determining step (PDS) in the oxidation of adsorbed N₂ to form *NNOH is reduced from 1.75 to 1.69 eV due to the conversion of in situ generated SO₃²⁻ to SO₄²⁻ on CoS₂ during the NOR process, thus accelerating the reaction. Furthermore, the accurate detection of nitrate concentration in the electrolyte post-NOR is critical for evaluating electrocatalyst performance, with findings indicating that the dilution factor and background solution significantly influence NO₃⁻ detection results. This research provides valuable insights for the application of transition metal compounds (TMCs) in the NOR and offers guidance for accurately assessing the performance of NOR electrocatalysts.