Emerging artificial nitrogen cycle processes through novel electrochemical and photochemical synthesis

The nitrogen cycle is an important part of the global biogeochemical cycle, while the human activities have already caused a severe imbalance of the global nitrogen cycle. In this review, we proposed a new generation of artificial nitrogen cycle via electrochemical and photocatalytic reactions. In details, the N2 from the air, NO3−/NO2− containing wastewater, nitrogen oxides from vehicle emission are all able to be utilized as a nitrogen source for the synthesis of NH3 under ambient conditions. The oxidation of NH3, N2 and nitrogen oxides can all achieve the aim of obtaining NO3−. Hydrazine can also be synthesized electrochemical and photochemical reactions. Utilizing electrochemical and photocatalytic processes enables to eliminate the hazardous of nitrogen-containing organic chemicals, and some inorganic nitrogen polluted wastewater. More importantly, coupling N-based reaction with other reaction like CO2 reduction enables to synthesize some high-value chemicals such as urea. Then we highlighted some recent achievements in these reactions and proposed some future potential developing directions. The results and funding of this work may help us develop highly efficient catalysts and strategies for the artificial nitrogen cycle, repairing the broken nitrogen cycle balance.