High-performance red mud as an electrocatalyst for nitrate reduction toward ammonia synthesis

Red mud (RM) is a solid waste generated in the aluminum industry after the extraction of alumina oxide; its multiple elements and higher pH value likely pose a severe threat to the environment after treatment. However, RM's higher concentrations of metal components, particularly Fe 2 O 3 and rare earth elements (REEs), render RM promising for catalytic application. Hence, this work showed an efficient high-speed RM to catalyze electrocatalytic nitrate-to-ammonia reduction reaction (NARR). RM calcined at 500 °C (RM-500) exhibited excellent catalytic performance. Faradaic efficiency of ammonia ( FE NH 3 ) in an electrolyte solution containing 1 mol·L − 1 NO 3 − achieved a maximum value of 92.3% at −0.8 V ( vs . RHE). Additionally, 24-h cycle testing and post-reaction PXRD and SEM indicated that the RM-500 electrocatalyst is stable during NARR. The RM-500 demonstrated a high FE of NH 3 -to-NO 3 − of 89.7% at 1.85 V ( vs . RHE), showing great potential in the ammonia fuel cells technology and achieving the nitrogen cycle. • Red Mud can be potentially prepared as an electrocatalyst for NARR. • The red mud-derived NARR electrocatalyst has excellent stability and high performance. • FE NH3 achieved as high as 92.6% at −0.8 V (vs. RHE) in 1 M NO 3 − . • FE NO3 (reverse NH 3 -to-NO 3 − ) achieved 89.7% at 1.85 V (vs. RHE).