ZIF-8 In Situ Modified Flower-like Fe ₃ S ₄ as a Bifunctional Electrocatalyst in Zn-N ₂ and Zn-Nitrate Batteries

Electrocatalytic nitrogen reduction reaction (NRR) and nitrogen oxidation reaction (NOR), as environmentally friendly technologies for nitrogen fixation, can substitute for the traditional industrial Haber–Bosch and Ostwald processes. In this work, we adopt an interface engineering strategy to integrate hydrophobic ZIF-8 into flower-like Fe3S4. The synthesized novel 2-Fe3S4/ZIF-8 catalyst exhibits excellent bifunctional activity through the synergistic effect between Fe3S4 and ZIF-8. In situ Raman spectroscopy reveals the reaction intermediates of the composite during the electrocatalytic nitrogen fixation process and identifies that Fe is the main adsorption site for N2. Furthermore, density functional theory calculations verify that the synthesis of Fe3S4/ZIF-8 heterojunctions enhances interfacial electronic interactions, with electrons transferring from ZIF-8 to Fe3S4, rendering Fe3S4 in an electron-rich state, which reduces the energy barriers of the rate-determining steps for both NRR and NOR. Notably, 2-Fe3S4/ZIF-8 can serve as the cathode of a Zn-N2 battery, achieving an NH3 yield of 11.97 μg h–1 mgcat–1 at a discharge current of 1 mA cm–2. When 2-Fe3S4/ZIF-8 is used as the anode, a Zn-nitrate battery is assembled, which achieves a NO3– yield of 173.68 μg h–1 mgcat–1 at a charge current of 5 mA cm–2. Therefore, this finding provides another pathway for the development of Zn-N2 batteries and Zn-nitrate battery materials.