Normal↔inverse spinel nanocage charge modulation in nickel ferrite/nitrogen–doped carbon composite for efficient ammonia electrosynthesis and energy supply

Abstract

Nickel ferrite (NiFe2O4)-based materials play a crucial role in the electrocatalytic reduction of nitrate (NO3−) to ammonia (NH3). Herein, we report for the first time the facile synthesis of a normal↔inverse spinel NiFe2O4/nitrogen-doped carbon (NC) composite via CO2 laser irradiation, which is subsequently employed as an efficient electrocatalyst for NH3 production. The NiFe2O4/NC composite is derived from a Prussian Blue analog (PBA) precursor. Initially, a NiFe-based PBA (NiFePBA) is synthesized and then subjected to with a CO2 laser irradiation in ambient air, resulting in the formation of the spinel-phase NiFe2O4/NC composite within a short processing time of 5 min. Subsequently, it is used as an electrocatalyst for the NO3− reduction, achieving an NH3 yield rate of 11,138.16 μg h−1 cm−2 with a faradaic efficiency of 95.59 % at a fixed reduction potential of −0.4 V vs. the reversible hydrogen electrode. The reduction mechanism and reaction intermediates are examined using in situ micro-Raman spectroscopy and ex situ Fourier transform infrared spectroscopy. Density functional theory analysis validates the NO3RR pathway facilitated by the NiFe2O4/NC composite during the electrocatalytic conversion of NO3− to ammonia, identifying the hydrogenation of *NO to *NOH via. N-side pathway. Furthermore, a zinc–nitrate battery (ZNB) fabricated using the NiFe2O4/NC composite cathode and a zinc anode delivers a power density of 0.96 mW cm−2 at 6 mA cm−2. The ZNB achieves an open-circuit voltage of 1.35 V and exhibits a long-term cycling stability of 100 h, demonstrating its potential for next-generation energy storage systems.