Recent progress on cobalt-based electrocatalysts for nitrate reduction to ammonia

Ammonia serves as a cornerstone in modern chemical and fertilizer sectors, and has emerged as a highly promising novel zero-carbon energy carrier. The conventional Haber-Bosch route, with intensive energy expenditure and significant carbon emissions, serves as the primary strategy for mass ammonia production. Meanwhile, nitrate pollution caused by agricultural and industrial activities has become a global environmental crisis, seriously disrupting the nitrogen cycle balance and posing a risk to ecosystems and public health. Utilizing renewable electricity to drive nitrate electroreduction offers a viable solution to mitigate its environmental contamination and achieve green ammonia generation. For environmentally benign ammonia generation, it is essential to construct electrocatalysts that exhibit high selectivity. This review showcases the cobalt-based electrodes developed in recent years for electrochemical nitrate-to-ammonia reduction, including monometallic cobalt, cobalt-based alloys, cobalt oxides, cobalt sulfides, and cobalt phosphides, alongside cobalt-based metal-organic frameworks (MOFs) and their derivatives. The fundamental reaction mechanisms involving various nitrogen-containing intermediates are elucidated. Particular emphasis is placed on the structure-activity relationships, analyzing how the intrinsic electronic structure and geometric coordination of cobalt species influence the reaction kinetics. The design principles and electrochemical performance are comprehensively reviewed. In addition, effective strategies for improving the catalyst activity are outlined, and a perspective on future developments is provided.