Renewable-energy-derived electrochemical nitrogen fixation represents a sustainable way to produce green ammonia (NH

3

)

but the energy efficiency is limited by its sluggish kinetics and complex reaction pathways. Highly active

selective and robust electrocatalysts are strongly needed to promote the efficiency of nitrogen conversion. Here

we provide an overview of the recent progress in understanding the structure–function correlation of single-atomic site catalysts (SASCs) for electrochemical nitrogen fixation

to provide mechanistic insights and guide the future rational design of SASCs. First

we review the fundamental understanding of both N

2

and oxynitride reduction on SASCs

with different hydrogenation pathways. Afterwards

we present the recent progress in the development of well-defined SASCs with various metal centres and the influence from local chemical environments

such as the coordination number

first-shell and second-sphere coordination. At last

we listed some perspectives on future study in this emerging research field.