Dual roles of graphitic carbon nitride in the electrosynthesis of ammonia under ambient conditions

As a metal-free photocatalyst and electrocatalyst, graphitic carbon nitride (g-C3N4) has been intensively researched for a variety of applications ranging from energy storage/conversion to environmental remediation. Herein, we report that g-C3N4 can play dual roles in the electrosynthesis of ammonia under ambient conditions, acting as an electrocatalyst and nitrogen source, and which role dominates depends on the availability of nitrogen gas. It is evident from electrochemical operations, N-15 isotope labeling, and DFT calculations that the g-C3N4 catalyzed ammonia synthesis obeys a Mars-van Krevelen-like mechanism. This is the first clear demonstration of Mars-van Krevelen cycling in a nitrogen-carbon system involving no metal. The understanding of how g-C3N4 works in electrocatalyzing nitrogen fixation is expected to provide inspiration for designing more efficient and competitive catalysts for the synthesis of valuable nitrogenous compounds directly from the air, water, and renewable energies at ambient conditions.