Research Progress and Perspectives on Active Sites of Photo- and Electrocatalytic Nitrogen Reduction

Ammonia is closely relevant to human production and life. Although the widely used conventional Haber-Bosch process has a relatively high ammonia yield, it has obvious disadvantages of high energy consumption, serious pollution, and harsh reaction conditions. Compared with the Haber-Bosch process, photo-and electrocatalytic N2 fixation has been demonstrated to be energy-saving, environmentally friendly, and economical because the ammonia can be generated under mild conditions. During the photo/electrocatalytic ammonia-production processes, sunlight or electricity is used as the renewable energy input, the atmosphere is used as the nitrogen source, and water is used as the proton source. However, the ammonia yields of the photo-and electrocatalytic nitrogen fixation are commonly low, which is mainly resulted by the lack of active sites to adsorb N2 molecules and active N-N triple bonds. On the basis of the discussion about the importance of active sites for ammonia synthesis by summarizing the reaction mechanism of photo-and electrocatalytic methods, we outline the common methods of producing abundant active sites of N-2 adsorption and activation on the surface of catalysts, including vacancy introduction, heteroatom doping, cocatalyst support, and frustrated Lewis pairs construction. We also summarize the detection methods of ammonia, as well as other problems existing during the photo-and electrocatalytic nitrogen-fixation processes.

Automated summary

Ammonia is closely related to human production and life. The traditional Haber-Bosch process has drawbacks of high energy consumption, pollution, and harsh reaction conditions. Photo-electrocatalytic N2 fixation has been shown to be energy-saving, environmentally friendly, and economical, but it often suffers from low ammonia yields. This is mainly due to the lack of active sites. The importance of active sites and various methods to increase them on catalyst surfaces have been discussed.