Metal-free electrocatalysts for nitrogen reduction reaction

Ammonia is one of the most important chemicals in modern world for food supply, yet its production through nitrogen reduction is mainly relied on the Haber–Bosch process, requiring rigid reaction conditions including high temperature and pressure. Recently, electrocatalytic nitrogen fixation into ammonia has provoked wide attention due to its capability to be performed under mild condition, with the electricity as the only power input. Nevertheless, the conventional metal-based electrocatalysts normally suffers from their difficulty in balancing the competitive reactions of nitrogen adsorption/activation and hydrogen generation, hampering the ammonia production efficiency. Lately, metal-free electrocatalysts have turned up as a promising candidate for such an approach due to their highly controllable surface-structure and relatively sluggish hydrogen generation activity. In this review, we summarize recent progress in electrocatalytic nitrogen reduction reaction using metal-free electrocatalysts, with the particular emphasis on their electronic structure and microstructure modulations for ameliorating N₂ adsorption/activation and electron transfer. Finally, the challenges and future directions of metal-free catalyst for nitrogen reduction reaction are given.