Research Progress on Ni-Based Electrocatalysts for the Electrochemical Reduction of Nitrogen to Ammonia

The electrochemical nitrogen reduction reaction (NRR) to synthesize ammonia (NH₃) is considered as a promising method due to its approvable advantages of zero-pollution emission, feasible reaction proceedings, good safety and easy management. The multiple efforts have been devoted to the exploration of earth-abundant-element-based nanomaterials as high-efficiency electrocatalysts for realizing their industrial applications. Among these, the Ni-based nanomaterials is prioritized as an attractive non-noble-metal electrocatalysts for catalyzing NRR because they are earth-abundance and exceedingly easy to synthesize as well as also delivers the potential of high electrocatalytic activity and durability. In this review, after briefly elucidating the underlying mechanisms of NRR during the electrochemical process, we systematically sum up the recent research progress in representative Ni-based electrocatalysts, including monometallic Ni-based nanomaterials, bimetallic Ni-based nanomaterials, polymetallic Ni-based nanomaterials, etc. In particular, we discuss the effects of physicochemical properties, such as phases, crystallinity, morphology, composition, defects, heteroatom doping, and strain engineering, on the comprehensive performance of the abovementioned electrocatalysts, with the aim of establishing the nanostructure-function relationships of the electrocatalysts. In addition, the promising directions of Ni-based electrocatalysts for NRR are also pointed out and highlighted. The generic approach in this review may expand the frontiers of NRR and provides the inspiration for developing high-efficiently Ni-based electrocatalysts.