Local Spin‐State Tuning of Iron Single‐Atom Electrocatalyst by S‐Coordinated Doping for Kinetics‐Boosted Ammonia Synthesis

Abstract The electrochemical nitrogen reduction reaction (e‐NRR) is envisaged as alternative technique to the Haber–Bosch process for NH 3 synthesis. However, how to develop highly active e‐NRR catalysts faces daunting challenges. Herein, a viable strategy to manipulate local spin state of isolated iron sites through S‐coordinated doping (Fe SA ‐NSC) is reported. Incorporation of S in the coordination of Fe SA ‐NSC can induce the transition of spin‐polarization configuration with the formation of a medium‐spin‐state of Fe (t 2g 6 e g 1), which is beneficial for facilitating e g electrons to penetrate the antibonding π‐orbital of nitrogen. As a consequence, a record‐high current density up to 10 mA cm −2 can be achieved, together with a high NH 3 selectivity of ≈10% in a flow cell reactor. Both experimental and theoretical analyses indicate that the monovalent Fe(I) atomic center in the Fe SA ‐NSC after the S doping accelerates the N 2 activation and protonation in the rate‐determining step of *N 2 to *NNH.