Heterogeneous electrocatalysts design for nitrogen reduction reaction under ambient conditions

Ammonia, as an important carbon-free energy carrier and also an important chemical for producing fertilisers, is mainly synthesized by a traditional Haber-Bosch process with high energy consumption and large amounts of greenhouse gas emissions. Recently, electrocatalytic nitrogen reduction reaction (NRR) has attracted worldwide research attentions as a promising route for achieving green and sustainable ammonia synthesis at ambient conditions. Although exciting advances have been made in the NRR field, the development of electrochemical nitrogen-to-ammonia conversion is still challenging because of the low ammonia yield and unsatisfactory Faradaic efficiency mainly deriving from the poor catalytic activity of catalysts. Herein, various catalyst design strategies for increasing the exposed active sites or altering the electronic structure aiming at improving the apparent activity or intrinsic activity are summarized in this review article. On the basis of effective design strategies, a range of recently reported NRR electrocatalysts, including noble metal-based materials, non-noble metal-based materials, single-metal-atom catalysts, and metal-free materials, are summarized, and the mechanisms of tuning the catalytic activity by applying the design strategies are emphasized based on the combination of theoretical calculations and experimental investigations. It is anticipated that the established correlation between physicochemical properties of catalysts and NRR performance can provide guidance for designing heterogeneous NRR electrocatalysts with high activity, good selectivity, and high stability.