High-entropy switching with 3d metal crossover sites for zinc–nitrite battery and ammonia supply

Abstract

The electrochemical nitrite reduction (eNO2R) reaction advances a green strategy to ammonia (NH3) production, while zinc–nitrite solution batteries enable a “three-in-one” strategy for electricity, NH3 generation, and NO2− removal. However, developing low-cost, selective, and durable electrocatalysts remains a challenge. Herein, a high-entropy Prussian blue analog (HEPBA) was synthesized via coprecipitation of divalent 3d transition metal crossover (Co, Ni, Cu, and Zn) with trivalent Fe species. This then underwent high-entropy interphase switching into a single-phase spinel high-entropy oxide (FeCoNiCuZn-high-entropy oxide [HEO]) via calcination, followed by pulsed laser irradiation in liquids to form a high-entropy alloy (FeCoNiCuZn-high-entropy alloy [HEA]). The HEA electrocatalyst reaches a Faradaic efficiency of 88.9 % for NH4+ production during eNO2R, with a utmost yield rate of 894.3 μg h−1 cm−2 at −1.0 V versus Ag/AgCl, while maintaining stability over multiple cycles. The superior eNO2R performance of FeCoNiCuZn-HEA, compared to HEPBA and HEO, stems from its stable atomic arrangement, along with the combined effects of lattice defects and high-entropy stabilization. In situ and ex situ spectroscopy, validated via density functional theory, confirm the eNO2R pathway on the uniformly distributed active sites on the HEA surface, involving NO2− adsorption, deoxygenation, protonation, and NH4+ formation through *NO and *NOH2 intermediates. Finally, an aqueous Zn–NO2− battery using the HEA cathode exposes a high open circuit voltage of 1.4 V versus Zn/Zn2+ and a power density of 2.14 mW cm−2, along with an impressive NH4+ production. © 2025 Elsevier B.V.