Electrocatalytic Reduction of Nitrogen: From Haber-Bosch to Ammonia Artificial Leaf

The electrocatalytic nitrogen reduction reaction (eN2RR) is an emerging route complementing one of the pillars of the chemical industry, the Haber-Bosch (HB) process. Its flexibility expands suitable operating conditions from highly pure nitrogen and hydrogen streams and high temperature to very mild ones, such as air and water at ambient conditions, which can expand the ammonia synthesis toward the on-site production of carbon-neutral fertilizers when powered, for instance, by sunlight (ammonia artificial leaf). This review uses performance maps to (1) provide a bird's-eye view of the gap separating it from practical implementation and (2) identify sources of inefficiency, mostly associated with the reduced ability of available catalysts to operate with high energy efficiency. In addition, we discuss basic aspects influencing the design of an ammonia artificial leaf and comment on future directions.