Solid-state interrupted chemical reaction-based tri-phase design of the FeMoO4/CuFe2S3/CuSe2 electrocatalyst for enhancing electrochemical nitrogen reduction

Abstract

The electrochemical nitrogen reduction reaction (N₂RR) to ammonia (NH₃) is a sustainable and eco-friendly approach that can help restore the disrupted nitrogen cycle and address environmental challenges. However, achieving selective NH₃ synthesis is challenging due to the complex nitrogen reduction process, competition from the hydrogen evolution reaction (HER), the strong NN triple bond, and the low solubility of N₂ in water. Therefore, the design and development of highly efficient N₂RR catalysts are crucial for industry and the environment. This study presents a tri-phase FeMoO₄/CuFe₂S₃/CuSe₂ system, synthesized via a solid-state interrupted reaction, as a highly efficient electrocatalyst for the N₂RR. The optimized catalyst exhibits an impressive faradaic efficiency of 93.8% and a high ammonia yield of 6.15 mg h⁻¹ cm⁻² at −0.6 V vs. RHE. When implemented in a stack cell with an Fe(MoO₄)/CuFe₂S₃/CuSe₂ cathode and a NiFeV anode, the system achieves an NH₃ yield rate of 2.09 mg h⁻¹ cm⁻² at 2.0 V, with an FE of 50.9%, while maintaining a low energy consumption of 18.58 kWh kg⁻¹. Collectively, these results outperform most reported transition metal-based catalysts, highlighting the effectiveness of rational catalyst design and its strong potential for practical electrochemical ammonia synthesis. A time-dependent ¹⁵N₂-labeling experiment confirmed that the produced NH₃ originated solely from the supplied ¹⁵N₂, excluding contamination. The enhanced performance of the FeMoO₄/CuFe₂S₃/CuSe₂ electrocatalyst is attributed to oxygen vacancies and variable oxidation states, which are induced by incorporating selenium and copper into the catalyst system. The trapping of inert N₂ is enhanced by oxygen vacancy-mediated polarization, metal-site vacancies, and interfacial effects between catalyst phases. This study presents a versatile approach for designing catalysts that enhance electrocatalytic methods for ammonia (NH₃) production through electrochemical nitrogen reduction.