Alternative Strategies Toward Sustainable Ammonia Synthesis

As one of the world's most produced chemicals, ammonia (NH3) is synthesized by Haber-Bosch process. This century-old industry nourishes billions of people and promotes social and economic development. In the meantime, 3%-5% of the world's natural gas and 1%-2% of the world's energy reserves are consumed, releasing millions of tons of carbon dioxide annually to the atmosphere. The urgency of replacing fossil fuels and mitigating climate change motivates us to progress toward more sustainable methods for N-2 reduction reaction based on clean energy. Herein, we overview the emerging advancement for sustainable N-2 fixation under mild conditions, which include electrochemical, photo-, plasma-enabled and homogeneous molecular NH3 productions. We focus on NH3 generation by electrocatalysts and photocatalysts. We clarify the features and progress of each kind of NH3 synthesis process and provide promising strategies to further promote sustainable ammonia production and construct state-of-the-art catalytic systems.