Nitrogen Reduction to Ammonia on Atomic‐Scale Active Sites under Mild Conditions

Abstract

Ammonia is one of the most important chemicals and energy carriers. Currently, ammonia is industrially produced through the Haber–Bosch process under harsh conditions of high pressure and high temperature, which are energy consuming and environmentally unfriendly. Recently, nitrogen reduction to ammonia under ambient conditions has attracted intensive research interest, in which highly efficient catalysts are of great importance. In this review, recent theoretical and experimental progresses on novel heterogeneous catalysts with low atomicity for the nitrogen reduction reaction (NRR) under ambient conditions are highlighted. Reaction mechanisms for the NRR are first introduced. Then, advances in the synthesis and characterization of catalysts with single atom features are summarized, with a particular focus on the rational design of atomic catalysts for the NRR. Lastly, the critical challenges, possible solutions, and future perspectives in the research on NRR catalysis are presented. This review systematically presents the readers with the latest advances in this field, and more importantly, sheds light on the future development of NRR catalysis with the single atomic feature.

Heterogeneous Single Atom Electrocatalysis, Where “Singles” Are “Married”

“…As a key feedstock of the main fertilizers in farming, NH 3 is critically important for the entire eco‐chain of plants, animals, and humans on the earth. Considering the high abundance of nitrogen N 2 existing in nature, fixation of N 2 into NH 3 is of great importance, but it is energetically challenging, since high energies are needed to overcome the high triple bond energy of NN (941 KJ mol −1 ) in N 2 as well as the high first bond cleavage energy (410 KJ mol −1 ) . Currently, the industrial production of NH 3 commonly relies on the Haber–Bosch process requiring a combination of high temperature and pressure (400–600 °C, 20–40 MPa), and therefore consuming a large amount of energy .…”

“…Hence, the investigation of NRR to generate NH 3 under ambient conditions is regarded as a key pathway to replace the energy‐intensive industrial process. Although the electrochemical NRR catalyzed by a range of single atom metals under ambient conditions has been studied by DFT calculations, there are only a few of experimental studies that have successfully been applied to the NRR . The main problem with the electrocatalytic NRR is the poor overall productivity with low NH 3 yield rate and poor FE .…”

“…Considering the high abundance of nitrogen N 2 existing in nature, fixation of N 2 into NH 3 is of great importance, but it is energetically challenging, since high energies are needed to overcome the high triple bond energy of NN (941 KJ mol −1 ) in N 2 as well as the high first bond cleavage energy (410 KJ mol −1 ). [116] Currently, the industrial production of NH 3 commonly relies on the Haber-Bosch process requiring a combination of high temperature and pressure (400-600 °C, 20-40 MPa), and therefore consuming a large amount of energy. [49,[117][118][119] Hence, the investigation of NRR to generate NH 3 under ambient conditions is regarded as a key pathway to replace the energy-intensive industrial process.…”

Nitrogen‐Doped Porous Carbon Supported Nonprecious Metal Single‐Atom Electrocatalysts: from Synthesis to Application

“…The single atoms (such as Fe and Mo) doped in the carbon nanostructures have been testified as the active sites and played a vital role in the N 2 ‐to‐NH 3 conversion, which reveals that the single atom stabilized on 2D carbon materials can be a novel candidate catalyst for N 2 ‐fixation. Besides Fe and Mo, Cu anchored on CN, Mn anchored on C 2 N were proved to be efficient catalysts for N 2 RR, Mn 2 ‐C 2 N with dual‐Mn atom cluster exhibited better performance for electrochemical N 2 RR than Mn 2 ‐C 2 N due to the stronger adsorption energy for N 2 …”

“…Besides Fe and Mo, Cu anchored on CN, Mn anchored on C 2 N were proved to be efficient catalysts for N 2 RR, Mn 2 -C 2 N with dual-Mn atom cluster exhibited better performance for electrochemical N 2 RR than Mn 2 -C 2 N due to the stronger adsorption energy for N 2 . [151]…”