Recent advances in transition metal electrocatalysts for effective nitrogen reduction reaction under ambient conditions

As one of the world's largest chemical products, ammonia (NH₃) plays a vital role in the industry, agricultural production, and national defense. In modern industry, NH₃ is produced primarily through the high-temperature high-pressure Haber–Bosch process, which consumes large amounts of energy and releases large amounts of greenhouse gases. Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions has been widely considered among many nitrogen fixation methods, which can be produced using renewable energy. However, the main challenge is to achieve both high NH₃ yield and Faraday efficiency, which is attributed to the strong N ≡ N bond and serious hydrogen evolution reaction. Based on the key problems, this review discussed the transition metal (TM) catalysts, including alloys, TM oxides, TM sulfides, TM carbides, and strategies for tuning the electronic structure, regulating the morphology, and bimetallic synergistic effect on improving the NRR performance. Moreover, this review also summarized the NH₃ detection methods and the reliable control experimental parameters in the NRR process to obtain accurate experimental results. Finally, the challenges and future directions of TM catalysts for NRR are considered, emphasizing the available opportunities by following the giving principles.