Recent Advances in Noble-Metal-Free Catalysts for Electrocatalytic Synthesis of Ammonia under Ambient Conditions.

Ammonia is an essential chemical for producing fertilizers and energy carriers. However, the industrial Haber-Bosch process causes huge CO emissions and energy waste. As a promising alternative for Haber-Bosch process, electrochemical synthesis of ammonia has drawn much attention. Catalysts, as a vital part of electrochemical nitrogen reduction reaction (NRR), have developed rapidly in recent years. Compared to noble-metal catalysts, noble-metal-free catalysts possess a low-cost advantage. In this review, noble-metal-free catalysts, including metal-based materials, metal organic frameworks (MOFs), MXenes, and metal-free materials, are summarized. In addition, effective design strategies are discussed, along with the main problems and some potential directions of noble-metal-free NRR catalysts.