Electrocatalytically active and charged natural chalcopyrite for nitrate-contaminated wastewater purification extended to energy storage Zn-NO₃⁻ battery

Charged natural chalcopyrite (CuFeS₂, Ncpy) was developed for a three-dimensional electrochemical nitrate reduction (3D ENO₃⁻RR) system with carbon fiber cloth cathode and Ti/IrO₂ anode and Zn-NO₃⁻ battery. The 3D ENO₃⁻RR system with Ncpy particle electrodes (PEs) possessed superior nitrate removal of 95.6 % and N₂ selectivity of 76 % with excellent reusability under a broad pH range of 2–13 involving heterogeneous and homogeneous radical mechanisms. The Zn-NO₃⁻ battery with Ncpy cathode delivered an open-circuit voltage of 1.03 V and a cycling stability over 210 h. It was found that Ncpy PEs functioned through self-oxidation, surface dynamic reconstruction (Cu_1.02Fe_1.0S_1.72O_1.66 to Cu_0.61Fe_1.0S_0.27O_2.98), intrinsic micro-electric field (Cu^I, S²⁻ anodic and Fe^III cathodic poles), and reactive species (^•OH, SO₄^•−, ¹O₂, ^•O₂⁻ and ^•H) generation. Computational analyses reveal that CuFeS₂(112) surface with the lowest surface energy preferentially exposes Fe and Cu atoms. Cu site is beneficial for reducing NO₃⁻ to NO₂⁻, Fe and Fe−Cu dual sites are conducive to N₂ selectivity, lowering the overall reaction barriers. It paves the way for selective NO₃⁻ reduction in wastewater treatment and can be further extended to energy storage devices by utilizing low-cost Ncpy.