Recent Advanced Materials for Electrochemical and Photoelectrochemical Synthesis of Ammonia from Dinitrogen: One Step Closer to a Sustainable Energy Future

Ammonia (NH3), an important raw material for chemical industry and agriculture, is also considered to be an intriguing energy storage and transportation media for chemical conversion schemes. The world's primary NH3 supply is based on the natural nitrogen fixation by diazotrophs through an enzymatic nitrogenase process and the industrial nitrogen fixation through a traditional Haber-Bosch process. The natural synthesis of NH3 can hardly meet the rapidly growing global demand. Meanwhile, the industrial NH3 production is still dominated by the high-temperature and high-pressure reaction between nitrogen and hydrogen (N-2 + 3H(2) -> 2NH(3)), requiring intensive energy input and generating massive CO2. Therefore, seeking a breakthrough in the development of catalysts toward efficient ammonia synthesis has become the frontier of energy and chemical conversion schemes. This review summarizes and discusses the recent progress on developing new strategies to optimize the efficiency of NH3 production coupled with renewable energy sources, with a specific focus on electrocatalytic and photoelectrocatalytic conversion of N-2 to NH3. The most recent advances in the development of catalytic materials, the design of the reaction systems, and the computational insights for electrochemical and photoelectrochemical ammonia synthesis are covered.