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

The electrochemical nitrogen reduction reaction (e-NRR) is envisaged as alternative technique to the Haber-Bosch process for NH3 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 (FeSA -NSC) is reported. Incorporation of S in the coordination of FeSA -NSC can induce the transition of spin-polarization configuration with the formation of a medium-spin-state of Fe (t2g 6 eg 1), which is beneficial for facilitating eg 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 NH3 selectivity of ≈10% in a flow cell reactor. Both experimental and theoretical analyses indicate that the monovalent Fe(I) atomic center in the FeSA -NSC after the S doping accelerates the N2 activation and protonation in the rate-determining step of *N2 to *NNH.