Catalysis Fundamental and Applied Research Advances for Green Ammonia Synthesis and Recovery

The nitrogen (N2) gas reduction reaction (NRR) offers a sustainable alternative to the energy-intensive Haber–Bosch process for the large-scale synthesis of ammonia (NH3) under ambient conditions while mitigating the dramatic environmental and health impacts of fossil-fuel-based economies worldwide. However, the competing hydrogen evolution reaction (HER) remains a significant issue in NRR systems and devices. To comprehend and overcome such a challenge, we summarized and discussed in this status update the latest strategies consisting of leveraging the specific characteristics of Earth-abundant materials for the design of purpose-built electrocatalysts with optimal performance for the green electrochemical synthesis of NH3 by suppressing the competing HER and facilitating the hydrogen spillover process by lowering the energy barrier of proton transfer and hydrogenation reactions through advanced experimental and theoretical design and surface engineering, such as single-atom doping, built-in electric field, and defect and crystal-facet engineering. In addition, a detailed description of the recent advances of operando synchrotron-based spectroscopic and imaging techniques to probe and elucidate the complete electrochemical reaction mechanism at the atomic scale in real time and in operational conditions is presented. Practical recommendations for further experimental studies are also proposed. Finally, a brief summary of the current methods for ammonia recovery from natural waste into valuable resources is also presented to facilitate the necessary transition from a fossil-fuel-based economy to green decarbonized hydrogen/ammonia economies and societies for a safe, clean, and sustainable energy-, transportation-, and food-secure future.