Iron-Based Metal-Nitrogen-Carbon Catalyst for Electrochemical Nitrogen Reduction Reaction

Abstract

Ammonia is a key industrial chemical with diverse applications. However, the traditional Haber-Bosch process is energy-intensive and environmentally taxing. Electrochemical nitrate reduction reaction presents a sustainable alternative for NH3 synthesis, leveraging nitrate's high solubility and abundant availability. This study evaluates carbon nanotube-supported metal phthalocyanine catalysts, focusing on FePc, CoPc, NiPc, CuPc, and MnPc. CuPc/CNT exhibits the highest Faradaic efficiency and catalytic activity in alkaline conditions, but its performance significantly drops in neutral environments due to competition with the hydrogen evolution reaction. It requires precise pH control, limiting its applicability in diverse conditions. CoPc/CNT and NiPc/CNT show balanced performance in both alkaline and neutral environments, with moderate NH3 selectivity and catalytic activity. They are suitable for a wide range of applications but do not achieve the highest efficiency. MnPc/CNT demonstrates the lowest NH3 selectivity, primarily stabilizing early intermediates like NO2-. It is less effective for deep reduction to NH3 but may be useful in applications requiring selective intermediate generation. In contrast, while not the most active catalyst, FePc/CNT shows remarkable stability and adaptability in both alkaline and neutral conditions. Its strong binding with intermediates like NO2 and NO ensures consistent NH3 selectivity, making it a promising candidate for industrial applications where stability is prioritized. The study highlighted that the stable performance of FePc/CNT under different conditions highlights its potential for practical applications. Future research directions include tuning CNT oxygen surface groups and MPc side groups to enhance catalytic activity and selectivity and exploring magnetization strategies to regulate metal center electronic structures. This work provides insights for advancing NO3RR catalysts toward sustainable ammonia production.